Cover. A member of the American Museum of Natural History 1896 expedition enter- ing the badlands of the Willwood Formation on Dorsey Creek, Wyoming, near what is now US. Geological Survey fossil vertebrate locality D1691 (Wardel Reservoir quadran- gle). View to the southwest. Photograph by Walter Granger, courtesy of the Department of Library Services, American Museum of Natural History, New York, negative no. 35957. DISTRIBUTION AND STRATIGRAPHIC CORRELATION OF UPPER PALEOCENE AND LOWER EOCENE FOSSIL MAMMAL AND PLANT LOCALITIES OF THE FORT UNION, WILLWOOD, AND TATMAN FORMATIONS, SOUTHERN BIGHORN BASIN, WYOMING Upper part of the Willwood Formation on East Ridge, Middle Fork of Fifteenmile Creek, southern Bighorn Basin, Wyomino. The Kirwin intrusive complex of the Absaroka Range is in the background. View to the west. Distribution and Stratigraphic Correlation of Upper Paleocene and Lower Eocene Fossil Mammal and Plant Localities of the Fort Union, Willwood, and Tatman Formations, Southern Bighorn Basin, Wyoming By Thomas M. Bown, Kenneth D. Rose, Elwyn L. Simons, and Scott L. Wing U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1540 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994 US. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Robert M. Hirsch, Acting Director For sale by US. Geological Survey, Map Distribution Box 25286, MS 306, Federal Center Denver, CO 80225 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the US Government Library of Congress Cataloging-in-Publication Data Distribution and stratigraphic correlation of Upper Paleocene and Lower Eocene fossil mammal and plant localities of the Fort Union, Willwood, and Tatman Formations, Southcm Bighorn Basin, Wyoming /by Thomas M. Bown [et al.]. p. cm. — (US. Geological Survey professional paper; 1540) Includes bibliographical references. Supt. of Docs. no.: I 19—16: 1540 l. Mammals, Fossil—Wyoming. 2. Plants, Fossil—— Wyoming. 3. Paleobiogeography—Wyoming. 4. Paleontology, Stratigraphic. 5. Paleontology—Wyoming. 6. Paleontology—Paleocene. 7. Paleontology— Eocene. 8. Bighom Basin (Mont. and Wyo.) 1. Series. QE881.D57 1993 93-2l 628 569’.09787—dc20 CIP CONTENTS Abstract ................................................................................................................................. 1 Introduction ........................................................................................................................... 1 Fossil Vertebrate Localities .................................................................................................. 9 Geographic Localities ................................................................................................. 9 Stratigraphic Localities ............................................................................................... 9 Sedimentologic Localities .......................................................................................... 15 Average and Noteworthy Localities ........................................................................... 17 Faunal Composition .................................................................................................... 17 Stratigraphic Sections ........................................................................................................... 19 Meyer-Radinsky Section (1965) ................................................................................. 19 Neasham-Vondra Section (1966—69) ......................................................................... 19 Sand Creek-No Water Creek (Bown) Sections (1974—75) ......................................... 27 Schankler-Wing Section (1976—78) ........................................................................... 35 Fifteenmile Creek (Bown) Sections (1980—92) .......................................................... 37 General Considerations ......................................................................................... 37 Fort Union-Willwood Contact ...................................................................... 37 Cut-and-Fill Sequences ................................................................................. 38 Pedofacies Section Measurement ................................................................. 40 Unresolved Aggradational Biostratigraphy .................................................. 41 Section Correlations .................................................................................................... 42 Correlation with the Schankler-Wing Section ............................................................ 43 Correlation with the Clarks Fork Basin Sections ....................................................... 47 Fossil Plant Localities ........................................................................................................... 54 Paleobotanical Sampling ............................................................................................ 54 Depositional Settings of Plant Fossils ........................................................................ 59 Exceptional Localities ................................................................................................ 60 References Cited ................................................................................................................... 60 PLATES [Plates are in pocket] 1. Fossil vertebrate and plant localities and lines of measured sections of the Willwood Formation, south-central Bighorn Basin, Wyoming. 2. Fossil vertebrate localities and lines of measured sections of the Willwood Formation, southeast Bighorn Basin. FIGURES 1. Map showing location of study area in the Bighorn Basin of northwest Wyoming ............................................... 2 2—10. Photographs showing: 2. Surface localities for fossil vertebrates, Willwood Formation ....................................................................... 10 3. Quarry sites for fossil vertebrates, Willwood Formation ............................................................................... 11 4. Operations at Rose quarry, Willwood Formation ........................................................................................... 12 5. Sediment-washing operations at Teakettle Hill, Willwood Formation ........................................................... 13 6. Calcified holes of fossil trees, Fort Union and Willwood Formations ........................................................... 14 7. Mandible of Coryphodon (Mammalia, Pantodonta) in place, Willwood Formation ..................................... 15 8. Stratigraphic fossil vertebrate localities, Willwood Formation ...................................................................... 16 9. Sedimentologic fossil vertebrate locality, Willwood Formation .................................................................... 18 10. Depositional and erosional cuts, Willwood Formation .................................................................................. 39 V VI 11. 12. l3. 14. 15. 16. 17. 18. 19. 10. 11. 12. 13. 14. 15. 16. 17. 18. CONTENTS Diagrams showing effects of erosional scours on temporal correlations, Willwood Formation ................................ 41 Block diagram showing pedofacies model, Willwood Formation ............................................................................. 42 Diagram showing constraints of avulsion mechanism on Willwood Formation biostratigraphy .............................. 43 Plot of area of second lower molar in omomyid primates, Willwood Formation, unrevised section ........................ 53 Plot of area of second lower molar in omomyid primates, Willwood Formation, revised section ............................ 54 Diagram showing relative correlation of Willwood sedimentary rocks and time between the study area and Clarks Fork area of the northern Bighorn Basin ........................................................................................................ 55 Photograph showing lenticular carbonaceous shale unit, lower part of Willwood Formation ................................... 57 Photograph showing tabular carbonaceous shale unit, upper part of Willwood Formation ....................................... 57 Photograph showing quarry site for fossil plants, lower part of Willwood Formation .............................................. 58 TABLES Provisional list of fossil mammals from the Willwood Formation of the south-central and southeastern Bighorn Basin ............................................................................................................................................................. 4 US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and southern Bighorn Basin ................................................................................................................. 68 Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and southern Bighorn Basin ................................................................................................................. 88 Duke University Primate Center fossil vertebrate localities in the Willwood Formation of the central and southern Bighorn Basin .............................................................................................................................................. 99 University of Michigan fossil vertebrate localities in the Willwood Formation of the central and southern Bighorn Basin ............................................................................................................................................................. 100 University of Wyoming fossil vertebrate localities in the Willwood Formation of the central and southern Bighorn Basin ............................................................................................................................................................. 101 The most significant fossil vertebrate localities in the Willwood Formation of the southern Bighorn Basin and synopsis of stratigraphic position, paleosol maturation stage (if known), and vertebrate remains ............................ 20 Provisional faunal list and fossil mammal composition, US. Geological Survey locality D1162 (includes locality Y40), 48l‘m level of the Willwood Formation, southern Bighorn Basin ..................................... 24 Provisional faunal list and fossil mammal composition, US. Geological Survey locality D1177 (includes localities D1315, D1316, Y253, UMRB], and UMRB2), 481-m level of the Willwood Formation, southern Bighorn Basin .............................................................................................................................................. 26 Provisional faunal list and fossil mammal composition, US. Geological Survey locality D1198 (includes localities D1160, D1160N, D1244, D1314, Y45, and Y45S), 470-m level of the Willwood Formation, southern Bighorn Basin ........................................................................................................................... 28 Provisional faunal list and fossil mammal composition, US. Geological Survey locality D1204 (includes localities D1203, D1208, and Y338), 438—444—m levels of the Willwood Formation, southern Bighorn Basin .............................................................................................................................................. 30 Provisional faunal list and fossil mammal composition, US. Geological Survey locality D1256 (includes localities D1463, D1583, Y192, Y193, and Y315), 546-m level of the Willwood Formation, southern Bighorn Basin .............................................................................................................................................. 32 Provisional faunal list and fossil mammal composition, US. Geological Survey locality D1326, 425-m level of the Willwood Formation, southern Bighorn Basin ................................................................................................ 34 Provisional faunal list and fossil mammal composition, US. Geological Survey locality D1454 (includes locality D1460 but not D1460Q), 409-m level of the Willwood Formation, southern Bighorn Basin ...................... 36 Diversity indices for mammalian faunal assemblages listed in tables 8—14, southern Bighorn Basin ...................... 38 Names and locations of measured spur stratigraphic sections of the Fifteenmile Creek master section of the Willwood Formation, south-central and southeast Bighorn Basin .................................................................. 44 Fossil vertebrate localities related to measured sections of the Willwood Formation in the southern Bighorn Basin with respect to institutions housing the fossils ................................................................................... 47 Stratigraphic distribution of fossil vertebrate and plant localities in the Fort Union, Willwood, and Tatman Formations of the southern Bighorn Basin ................................................................................................... 48 19. 20. 21. CONTENTS VII Mammalian taxa of potential biostratigraphic significance for correlating Willwood Formation measured sections of the southern Bighorn Basin and the Clarks Fork area in the northern Bighorn Basin ............................. 56 US. National Museum fossil plant localities in the Fort Union and Willwood Formations of the south-central Bighorn Basin ............................................................................................................................................................. 61 Provisional megafloral taxa of the Willwood Formation, southern Bighorn Basin ................................................... 62 Distribution and Stratigraphic Correlation of Upper Paleocene and Lower Eocene Fossil Mammal and Plant Localities of the Fort Union, Willwood, and Tatman Formations, Southern Bighorn Basin, Wyoming By Thomas M. Bown, Kenneth D. Rosel, Elwyn L. Simonsz, and Scott L. Wing3 ABSTRACT The fossil mammals of the lower Eocene part of the Willwood Formation in the southern Bighorn Basin of north- west Wyoming constitute by far the largest sample of strati- graphically documented fossil mammals of any age from anywhere in the world. For this reason, the southern Bighorn Basin Willwood sample of fossil vertebrates has become the most important for empirically derived paleontological stud- ies of tempo and mode of evolution in Mammalia. Locality data for 1,472 Willwood fossil mammal sites (about 1,146 hitherto unpublished) and the detailed stratigraphic correla- tion of 941 of them into measured stratigraphic sections (700 newly correlated) afford a framework for the biostrati- graphic integration of nearly 80,000 catalogued and at least 30,000 uncatalogued specimens. Earlier published and unpublished measured sections of the Willwood Formation of the central and southern Bighorn Basin that related fossil mammal localities to one another are partly revised; all are tied to a new master section. Revisions to earlier sections do not materially affect published accounts of the principally gradual nature of evolution of Willwood mammals. A pre- liminary list of the Willwood mammal fauna of the south- central and southeast Bighorn Basin and mammalian compo- sitions for some of the most important sites are presented. Locality and stratigraphic correlations are also provided for 37 fossil plant localities in the Fort Union, Willwood, and Tatman Formations, data that offer considerable potential for correlation of late Paleocene and early Eocene plant and mammal biostratigraphies. Fossil pollen also permits direct correlation of Willwood rocks with standard marine zonations. 1Johns Hopkins University School of Medicine, Baltimore, Md. 2Duke University Primate Center, Durham, N.C. 3Smithsonian Institution, Washington, DC. INTRODUCTION The first fossil vertebrates from the lower Eocene part of the Willwood Formation of the Bighorn Basin, northwest Wyoming, were collected within the study area (fig. 1) by J .L. Wortman in 1880 (Cope, 1882a, 1882b). Since that time, perhaps as many as 120,000 catalogued museum specimens have been recovered from Willwood rocks, the results of more than 75 major expeditions spanning more than a cen- tury. The bulk of these specimens are upper and lower jaw fragments; however, many' more complete specimens are also represented. The principal recent sustained field endeavors, by the Yale Peabody Museum (1961—66, 1968—72, 1974—78), the University of Wyoming (1973—76); the US. Geological Survey-Johns Hopkins University School of Medicine (US. Geological Survey, 1977—79; with the Johns Hopkins University School of Medicine, 1980—present), and the University of Michigan Museum of Paleontology (1974—present), account for more than 100,000 specimens recovered on 45 expeditions in the last 31 years. Important collections of Willwood mammals, including some very fine specimens, also are catalogued at many other institutions, among them the American Museum of Natural History (New York, NY), the Carnegie Museum of Natural History (Pittsburgh, Pa), the Duke University Primate Facil- ity (Durham, N.C.), the Los Angeles County Museum (Los Angeles, Calif), the Museum of Comparative Zoology (Cambridge, Mass), the National Museum of Natural His- tory (Washington, DC), the Pratt Museum (Amherst, Mass), the Princeton University Museum (specimens now at the Yale Peabody Museum), the Raymond M. Alf Museum (Claremont, Calif), the Royal Ontario Museum (Toronto, Canada), the University of California Museum of Paleontol- ogy (Berkeley, Calif), the University of Colorado Museum (Boulder, Colo), the University of Kansas Museum of 1 2 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING 108° BIGHORN T51N Basin xSheep M untain X Red Butte H97 W‘ 44° agaw R95W n94w H93W 47 " " *Worland N ""3131" BASIN i I I 1 20 l 4U KILUMETEHS | EXPLANATION - Tatman Formation I: Willwood Formation Fort Union Formation ,l‘ Cretaceous and older rocks Figure 1. Map showing location of study area in the Bighorn Basin of northwest Wyoming. Geology by T.M. Bown (1975 and unpub. data) and Love and Christiansen (1985). Natural History (Lawrence, Kans.), and the University of Nebraska State Museum (Lincoln, Neb.). This report is concerned with what is known of fossil mammal and plant localities and their stratigraphic correla- tion in the south-central and southeast parts of the Bighorn Basin (south of the Greybull River). Similar contributions to these subjects have been presented for the mammals of the Clarks Fork area of the northern Bighorn Basin by Rose (1981a) and Gingerich and Klitz (1985). Gingerich (1980a) reviewed the history of vertebrate fossil collecting in Ter- tiary deposits of the Bighorn Basin. Between World War I and about 1960, there were no sustained vertebrate paleonto- logical collecting efforts in the vast badland area between the Greybull River on the north and Gooseberry Creek on the south. E.L. Simons (then at Yale University) initiated the first sustained expeditions to the region in 1961. The Simons expeditions established 477 fossil vertebrate localities in the Willwood Formation and explored paleontologically INTRODUCTION 3 virtually all of this region between Meeteetse and Worland, Wyo. From 1979 through 1992, Simons has made significant collections from the Willwood Formation under the auspices of the Duke University Primate Facility. From 1973 to 1976, T.M. Bown (then at the University of Wyoming) led expeditions in search of Willwood mam- mals in the Sand Creek-No Water Creek area, southeast of Worland, and in the more extensive badlands northwest of Worland as far as Red Butte and the Elk Creek Rim (pls. 1 and 2). These expeditions continued uninterrupted, first with the US. Geological Survey (1977—79), and then with the joint US. Geological Survey-Johns Hopkins University School of Medicine field efforts (l980—present). A small but important group of localities was established in the region of Red Butte in 1976 and on the east margin of Sheep Mountain in 1981 by University of Michigan field parties under the direction of PD. Gingerich. The first plant fossils recovered from Willwood strata were reported by Hewett (1926) from the Oregon Basin near Cody, Wyo., approximately 10 in (meters) above the base of the formation. Brown (1962) reported several fossil plant localities of probable Wasatchian age from the upper part of the Fort Union Formation west of Greybull, Wyo., and Erling Dorf made several small collections of Willwood plants for Princeton University during the 1950’s and 1960’s in the area south of Burlington. Dorf also collected plants from tuffaceous shales immediately overlying the Willwood Formation west of Meeteetse, but more recently Bown (1982) correlated those deposits with the Tatman Formation. Dorf’s collections of these Eocene plants now reside at the US. National Museum. Systematic investigations of early Eocene fossil plants were begun by SE Wing at Yale in 1978 and have continued through 1992, now under the aus- pices of the Smithsonian Institution. Resulting field work has established more than 100 localities, dispersed in the upper part of the Fort Union Formation and in the Willwood and Tatman Formations of the central and southern Bighorn Basin. The collection consists of more than 15,000 speci- mens, most of which are held at the US National Museum. A small collection is housed at the Yale Peabody Museum. Willwood fossil mammals are important because they include many representatives of archaic groups, more char- acteristic of Paleocene faunas, coexisting with some of the earliest known members of extant higher taxa (table 1). Research on these fossils, perhaps more so than studies of mammals from any other single formation, has contributed substantially to almost every aspect of paleobiological inquiry for the Paleogene. The fossils constitute a very important source of information about: (1) mammalian taphonomy on a formation-wide scale (Bown and Kraus, 1981b; Bown, 1987; Bown and Beard, 1990); (2) compara- tive and functional anatomy (for example, Osborn, 1898, 1900; Matthew, 1915, 1918; Rose, 1982, 1985, 1987, 1990 and references therein; Rose and Walker, 1985); (3) tempo and mode of mammalian evolution (for example, Gingerich, 1974, 1976, 1977, 1980b, 1983a; Bookstein and others, 1977; Rose and Bown, 1984, 1986, 1991; Bown and Rose, 1987, 1991; Bown and Beard, 1990); and (4) phylogenetic diversity among early Eocene mammals (for example, Cope, 1884; Matthew, 1915, 1918; Jepsen, 1930; Van Houten, 1945; Radinsky, 1963, 1964; Gingerich, 1981, 1982, 1983c, 1986; Gunnell and Gingerich, 1981; Gingerich and Gunnell, 1979; Bown, 1974, 1979, 1980; Schankler, 1980; Rose, 1981a, 1981b; Rose and Bown, 1984; Rose and others, 1977; Bown and Rose, 1976, 1979, 1984, 1987, 1991). Concomi- tant studies of the stratigraphic contexts of Willwood mam- mals (for example, Gingerich, 1974, 1976, 1977; Gingerich and Simons, 1977; Gingerich and Gunnell, 1979; Bown, 1979; Schankler, 1980, 1981; Rose, 19813, 1981b; Rose and Bown, 1986; Bown and Rose, 1987; Bown and Beard, 1990) have facilitated the construction of a denser, more compre- hensive empirical picture of mammalian evolution than has hitherto been obtainable by traditional studies of samples from separate and disparate localities (or even basins), with little or no stratigraphic or paleoenvironmental control. Studies of Willwood turtles (Hutchison, 1980), plants (Wing, 1980, 1984a, 1984b), and trace fossils (Bown and Kraus, 1983) from the study area have substantially supple- mented studies of the fossil mammals. Some advantages that study of the Willwood mamma- lian fauna has conferred on paleobiology have been the result of the extraordinarily rich Willwood vertebrate fossil accumulations and unusually extensive and continuous Will- wood exposures. Paleontological studies have also been augmented considerably by sustained paleobotanical, sedi— mentological, and paleopedological investigations during the past 25 years (for example, Neasham, 1967, 1970; Neas- ham and Vondra, 1972; Bown, 1979, 1985; Bown and Kraus, 1981a, 1981b, 1987, 1993; Bown and others, 1991; Kraus, 1980, 1985; Butler and others, 1981; Kraus and Bown, 1986, 1988, and in press; Wing, 1980, 1984a; Wing and Bown, 1985). Most recently, the extraordinary Will- wood record of fossil mammal associations in paleosols has led to empirically testable means by which to examine tem- porally controlled small-scale geographic differences in fos- sil mammal composition, evolution, and taphonomy (Bown, 1987; Bown and Beard, 1990). Vertebrate paleontology has differed from invertebrate paleontology in that the origin, development, and evolution of its biostratigraphy were accomplished with little reference to the empirical control of measured stratigraphic sections. The reasons for this dichotomy appear to be historical: (1) From the beginning, vertebrate paleontologists tended to emphasize the biological rather than the geological aspects of their discipline; (2) most early collecting was done by museum scientists interested more in obtaining quality museum specimens than in recording detailed stratigraphic information; (3) vertebrate fossils were often thought (to some extent erroneously) to be too rare to be of much bios- tratigraphic value; (4) paleontological exploration of the 4 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Table l. Provisional list of fossil mammals from the Willwood Formation of the south—central and southeastern Bighorn Basin, central Wyoming. [List based on collections at the US. Geological Survey and the Yale Peabody Museum] Class Mammalia Class Manmtalia——Continued Subclass Allotheria Subclass Theda—Continued Order Multituberculata lnfraclass Eulheria—Continued Subordcr Ptilodontoidea Magnorder Preptotheria—Continued Family Neoplagiaulacidae Order Crcodonta—Continued Ectypodus tardus (Jcpscn) Parectypodus lunatus Krause Parectypodus simpsoni Jcpscn Subordcr Taeniolabidoidea Family Eucosmodontidae Neoliotomus ultimus (Granger and Simpson) Subclass Theria lnfraclass Metatheria Order Marsupialia Subordcr Didelphoidea Family Didelphidae Peratherium macgrewi Bown Peratlterr'um marsupium Troxcll Peradectes cllesleri (Gazin) Mimopemdecles labrus Bown and Rose Infraclass Eutheria Magnorder Emotheria Grandorder lctopsia Family Leptictidae Prodiacodon Iauricinerei (Jcpscn) Prodiacodon, sp. nov. Palaeictops bicuspis (Cope) Grandorder Anagalida? Order cf. Macroseelidea? Haplomylus speirianus (Cope) Haplomylus, sp. nov. Magnorder Preptotheria Order Cimolesta Subordcr Palaeoryctoidea Family Palaeoryctidae Palaeoryctes sp., cf. P. punclams Van Valen Pararycter, sp. nov. Pararycles sp. Family Didclphodontidae Didelphodus absarokae (Cope) Didelphodus sp., cf. D. venumus Matthew Subordcr Pantolesta Family Pantolestidae Palaeorinopa incerta Bown and Scltankler Palaeosinopa Iurreola Matthew Palaeosinopa veterrima Matthew Subordcr Apatotheria Family Apatemyidae Labidolemur kayi Simpson Labidolemur sp., cf. L. serus Gingerich Apatemys cltardt‘rti (Jepsen) Apatemys bellus Marsh Apalemys bellulus Marsh Apatemyr rodens Troxell Order Creodonta Family Hyaenodontidae Arfia opislholoma (Matthew) Arfia shoshoniertsis (Matthew) Tritemnodon Ilians (Cope) Tritemnodon strenua (Cope) Family Hyaenodontidae—Continued Tritenmodon, sp. nov. Protolomus mordax (Matthew) Prototomus sp., cf. P. multicuspis (Cope) Prototomus sp., cf. P. vulpecula (Matthew) Family Limnocyonidac Pralimnocyon atavus Matthew Prolinmocyon sp., cf. P. robustus Matthew Family Oxyaenidae Oxyaemt Iransiens Matthew Oxyaena forcipala Cope Ontaena gulo Matthew 0.x)‘(tenrt sp., cf. 0. Iupina Cope Dipsalidiclides amplus (Jcpscn) Palaeonictir sp., cf. P. occidentalis (Osborn) Ambloctonus sp. Order Arctocyonia Family Arctocyonidae Tito'placodon antiquus Matthew Thryptacodon sp., cf. 7‘. loisi Kelley and Wood Cltriacus, sp. nov. 1 Cltriacus, sp. nov. 2 Cltriacus sp. cf. Tricemes sp. Family incerlae scdis Anacodon ursidens Cope Anacodon sp., cf. A. cultridenx Matthew Anacodon, sp. nov. Order Mesonychia Family Mesonychidae cf. Dissacus sp. Pachyaena gracilis Matthew Pachyaerta gigantea Osborn Pacltyaena orsifmga Cope Hapalodecles leprogmu/Ius (Osborn) Hupulodectes, sp. nov. Order Camivora Family Viverravidae Viverravus aculus (Matthew) Viverravus bowm‘ Gingerich Viverravus politur Matthew Viverravus lulosus Gazin Vivermvur, sp. nov. Didymictis protenus (Cope) Didymictis lysitertsis Matthew Didymictis, sp. nov. Family Miacidae Vulpavui~ australis Matthew Vulpuvus canavur (Cope) Miacis exiguur Matthew Miacis pelilur Gingerich Uinmcyon masselericus (Cope) Uinmcyon rudis Matthew Uirtlacyon sp., cf. U. (trodes Gazin Varsacyon promicrodon (Wortman) INTRODUCTION 5 Table l. Provisional list of fossil mammals from the Willwood Formation of the south-central and southeastern Bighorn Basin, central Wyoming—Continued. Class Mammalia—Continued Subclass Theda—Continued lnfraelass Eutheria—Continued Magnorder Preptotheria—Cominued Order Plesiadapiformes—Continued Class Mammalia—Continued Subclass Theda—Continued Infraclass Eutheria—Continued Magnorder Preptotheria—Continued Order Creodonta—Continucd Family Miacidae—Continued cf. Oddectes, sp. nov. miacine, gen. et sp. nov. Order Erinaceomorpha Family Dormaaliidae Macrocram'on nitens (Matthew) Scenopagus hewettensir Bown and Schankler Scenopagus sp. dormaaliid, sp. nov. Family Erinaceidae Leipsanolestes sp. Eolestes simpsoni (Bown) Darloniusjepseni (McKenna) Order Erinaceomorpha, incerme sedis Talpavoides dartoni Bown and Schanklcr Order Soricomorpha Family Nyctitheriidae Pontifactor sp. Plagioctenodon krausae Bown Plagioctenodon ravagei Bown and Schankler Plagioctenoider microlesles Bown Family Geolabididae Centetodon patratus Bown and Schankler Centetodon neaslmmi Bown and Schankler Family Aptemodontidae Parapternodus antiquur Bown and Schankler Order Plesiadapiformes Suborder Mixodectoidea Family Plagiomenidae Plagiomene multicuspis Matthew Worlandia inurimta Bown and Rose Suborder Microsyopoidea Family Microsyopidae Subfamily Microsyopinae Arctodomomys wilsom' (Szalay) Arctodontomys nuplus (Cope) Microsyops angurlidens Matthew Microsyops [widens (Cope) Microryops cardiorestes Gunnell Subfamily Uintasoricinae Niptomonzys doreenae Mckenna Niptomomys thelmae Gunnell and Gingerich Niptonwmys, sp. nov. Family Paromomyidae Ignaciur graybullianus Bown and Rose Phenacolemur simonsi Bown and Rose Phenacolemur praecox Matthew Phenacolemur sp., cf. P. jepsem' Phenacolemur, sp. nov. 1 Phenacolemur, sp. nov. 2 Phenacalemur, sp. nov. 3 paromomyid, gen. et sp. nov. Suborder Mixodectoidea—Continued Family, incenae .redix Tinimomys greybulliensis Szalay Micromomys willwoodensis Rose and Bown Chalichomomys amilucanus Beard Order Primates Infraorder Omomyiformes Family Omomyidae Subfamily Anaptomorphinae Teilhardina americana Bown Teilhardina crarridens Bown and Rose Teilhardina Ienuicula (Jcpsen) ?Teillzardina, sp. nov. Chlororhysis incomptus Bown and Rose Anemorhyris pallersom' Bown and Rose Anemorltysis wortmam’ Bown and Rose Anemorhysis sp.. cf. A. pearcei Gazin Arapahovius advena Bown and Rose Tetom'us mmthewi Bown and Rose Tetonius homunculus (Cope) Telom'us sp. Pseudotetonius ambiguus (Matthew) Tatnmm'us szalayi Bown and Rose Absarokius memecus Bown and Rose Absarokius abbom' (Loomis) SIrigor/Iysis sp., cf. S. bridgerensis Bown Subfamily Omomyinae Steiru‘us vesperlinus (Matthew) Steinius armectens Bown and Rose Inf raorder Adapiformes Family Notharctidae Camius torresi Gingerich Canlius ralstom‘ Matthew Camius mckennai Gingerich and Simons Cantius Irigonodux Matthew Camius abditus Gingerich and Simons Camius frugivorus (Cope) Camius, sp. nov. Pelycodus jarrovii (Cope) cf. Copelemur sp. cf. Nolllarctus sp. Order Palacanodonta Family Mctacheiromyidae Palaeanodon ignavus Matthew Palaeanodon, sp. nov. Family Epoicotheriidae Alocodonlulum atopum (Rose, Bown, and Simons) Alocodonlulum, sp. nov. Order Rodcntia Family Ischyromyidac Paramys excavalus Loomis Paramys sp., cf. P. francesi Wood cf. Paramys, very large sp. Reithroparamys sp., cf. R. arwateri (Loomis) F ranimys sp. 6 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Table 1. Provisional list of fossil mammals from the Willwood Formation of the south-central and southeastem Bighorn Basin, central Wyoming—Continued. Class Mammalia—Continued Subclass Theria—Continued Infraclass Eutheria—Continued Magnorder Preptothcria—Continucd Order Rodentia—Continued Family Ischyromyidae—Continued cf. Microparamys sp. ischyromyid, medium sp. ischyromyid, very small sp. ischyromyid, minute sp. Order Tillodontia Family Esthonychidae Esthonyx grangeri Simpson Est/tony): spatularius Cope Esthonyx bisulcatus Cope Est/Ionyx acutidens Cope Megalesrhonyx hopsoni Rose Order Taeniodonta Family Stylinodontidae Ectoganus sp., cf. E. glirifomu'r Cope stylinodontid, indet. sp. Order Pantodonta Family Coryphodontidae Coryphodon, sp. 1 Coryphodon, sp. 2 Coryphodon, sp. 3 Coryphodon, sp. 4 Order Dinocerata Probalhyopsir? Iysitensis Kelley and Wood dinoceratan, gen. et sp. nov. Order Condylarthra Family Phenacodontidae Eclocion osbomianur Cope Ectocion, sp. nov. Phenacodus primaevus Cope Phenacodus vormiam' Cope Copecion brachyptemus (Cope) Phenacodus, sp. nov. Family Hyopsodontidae Hyopsodus sp., cf. H. loomiri McKenna Hyopsodus min'culur (Cope) Hyopsodus minor (Loomis) Hyopsodus sp., cf. H. [widens Denison Hyopsodus sp., cf. H. b‘silensis Matthew Hyopsodus, sp. nov. "Hyopsodur ” powellianus Cope Aphelircus sp., cf. A. nitidur Simpson Class Mammalia—Conlinued Subclass Thcria—Continued Infraclass Euthcria—Continucd Magnorder Prcptolheria—Continued Order Condylanhra—Continued Family Pcntacodontidae Apheliscus wapiriensis (Van Valen) Apheliscus sp., cf. A. inridiosus (Cope) Aplteliscus, sp. nov. 1 Order Perissodactyla Suborder Hippomorpha Family Hyracolheriidae Hymcotllen‘um sp., cf. H. anguslidens (Cope) Hyracollterium sp., Cf. H. etsagicum (Cope) Hyracothen'um sp., cf. H. borealis Granger Hymcolllerium sp., cf. H. craspt'dolum (Cope) Hyracotherium, sp. nov. Xenicohippus grangeri Bown and Kihm Family Palacothcriidac Lambdolherium popoagicum Cope Suborder Tapiroidca Family lseclolophidae Homogalar prompirinus (Worlman) Homogrrlar sp., cf. H. semi/rims (Cope) Homogalax, sp. nov. iscctolophid, gen. et sp. nov. Family Helaletidae Heplodon calciculus Cope Heplodon posticus (Cope) helalclid?, gen. et sp. nov. Order Artiodactyla Family Dichobunidac Diacodexis melsiacus Cope Diacodexis, sp. nov. Diacodexis roburtus Sinclair cf. Hexacodur sp. “liunophorus,” small sp. “Burlap/torus.“ large sp. Wasalchia grangeri Sinclair Waralcllia .rinclain' Guthrie Magnordcr Prcptothcria, inccrtac scdis Creolarsur Iepidur Matthew American West was linked to geographic exploration, and logistical support was too small for continuous field seasons or time—consuming section measuring; and (5) vertebrate paleontology did not have the stratigraphically directed eco- nomic incentive afforded invertebrate paleontology by the rapid expansion of the American oil industry from'about 1880 to 1920 (see also discussions in Tedford, 1970; Inter- national Subcommission on Stratigraphic Classification, 1976). Three of the first synopses of general mammalian bios- tratigraphy for the Tertiary of North America were published by Matthew (1899) and Osborn (1909, 1929). These were commendable early efforts that, although lacking explicit section information, approximated closely the occurrences of fossil mammals in rock units. The Wood committee report (Wood and others, 1941) offered the first real hope for advancing North American mammal biostratigraphy and was used as a general reference on the subject for about 50 years. Even so, it appeared about a century after detailed, section-controlled invertebrate biostratigraphies first began to appear in Europe. Woodburne (1987) is a substantial improvement over Wood and others (1941), but it remains curious to us that there is yet so little general interest in a vertebrate INTRODUCTION 7 biostratigraphy based on measured sections and in one more detailed than the rather crude, somewhat anachronis- tic resolution afforded by land-mammal ages. This is not to say that there has been no interest (see, for example, Reus- berger, 1971, 1973; Savage and others, 1972; Emry, 1973; West, 1973, 1979; Skinner and others, 1977; Wilson, 1977, 1986; Stevens and others, 1984; Skinner and Johnson, 1984; Stucky, 1984a, 1984b); however, progress toward this worthy goal has been very slow for vertebrate fossils and, in many instances, still lacks not only detailed sections but a reliable systematic base for the mammals as well. Earlier general efforts toward developing a section- controlled biostratigraphy of the Willwood Formation include work on the basal Willwood Formation of the south- east Bighorn Basin (Bown, 1979, 1980), on the lower and middle parts of the Willwood Formation in the Clarks Fork region of the northern Bighorn Basin (for example, Ginger- ich and others, 1980; Rose, 1981a, 1981b; Gingerich and Klitz, 1985), and on the complete Willwood section of the south-central and southern Bighorn Basin (Schankler, 1980; Bown, 1980; and this paper). Though most groups of Will- wood mammals still require considerable systematic revi- sion, Schankler’s (1980) work remains the most useful and comprehensive effort at a general Willwood mammal bios- tratigraphy for the Wasatchian of the central Bighorn Basin. It was complemented in 1981 by Rose’s biostratigraphic documentation of Clarkforkian rocks of the northern Big- horn Basin, and by Gingerich (1983b). In the study of the evolution of the omomyid primates (Rose and Bown, 1984, 1986; Bown and Rose, 1987) and other groups of Willwood mammals, it has become increas- ingly obvious that precise locality information, preferably coupled with good stratigraphic documentation, is essential to conduct meaningful investigations of tempo and mode of mammalian evolution as well as to pursue systematic and phylogenetic studies. Publication at this time of all current Willwood mammal locality and stratigraphic information will relieve future students of Willwood mammals of many of the vexing data gaps and quandaries earlier experienced. Paramount among these problems are instances in which fossils (including types and many outstanding specimens) have no or inadequate locality data and, therefore, no bios- tratigraphic data. Moreover, with the advent of paleonto- logical studies involving correlation of fossil vertebrates with pedofacies (Bown, 1987; Bown and Beard, 1990; Bown and others, 1992), and concomitant knowledge of the differential distributions of fossil mammals in paleosols, even more precise field documentation is necessary now and in the future in order to determine exactly which kinds of paleosols yield which kinds of fossils. Such documenta— tion requires considerable time to perform in the field, and the consequent decrease in collecting time decreases the size of samples that can be recovered in a field season. However, most necessary field information is now of such a nature that it cannot be reliably reconstructed now that the majority of the exceptionally rich fossil lag concentrations in the Willwood Formation have been exhausted. Although it seems true that the fossil mammal resources in Willwood paleosols are virtually infinite using current collecting and sediment-processing techniques (Bown, 1979), the largest samples of fossils have been recovered from erosional-surface lag accumulations that appear to have required many hundreds or even thousands of years to form. Consequently, thorough site documenta- tion at this time is important, even more than for the initial studies involving mammalian evolutionary mechanisms in light of the pedofacies and other as yet untested innova- tions. We also hope, by the stratigraphic documentation of numerous additional Willwood fossil-mammal sites in the present work, to assist in placing vertebrate and plant bios- tratigraphies on firmer and more respectable footings rela- tive to those of the invertebrates, and to provide a dense stratigraphic data framework from which to pursue empiri- cal studies of mammalian evolution. Studies of the recon- structed time stratigraphy of the Willwood Formation are also well underway (Bown and others, 1992; Bown and Kraus, 1993; Kraus and Bown, in press). Willwood plant fossils document a number of impor- tant patterns. First, like the mammalian faunas that occur in the same sections, Willwood floras demonstrate the transi- tion from Paleocene assemblages of archaic appearance to assemblages dominated by more modern forms. Floristi- cally, this transition involves a decrease in the diversity and importance of conifers and increase in the diversity and eventual dominance of various angiosperm groups, includ- ing many species attributable to extant genera. Second, plant megafossils from the Willwood Formation indicate a vegeta- tional shift from essentially deciduous forests in the latest Paleocene to mixed evergreen and deciduous broad-leaved forests by the end of Willwood time (Wing and others, 1991). This vegetational shift is significant both as a context for compositional change in the mammalian fauna and as a proxy for climatic change in this region during the early Eocene. In general, the floral trends are consistent with increasing warmth through the early Eocene, perhaps a reflection of the globally warmer climate inferred from pale- obotanical data and oxygen isotope studies of marine micro- fossils (for example, Wolfe and Poore, 1982). A third pattern, visible within single strata for tens to hundreds of meters, appears to relate to small-scale variation in the orig- inal composition of the flood-plain vegetation (Wing, 1984a). The preservation of compositional information at this small scale permits some reconstruction of forest heter- ogeneity, species-area relationships, and successional pro- cesses, ecological characteristics that cannot commonly be inferred for vegetation of this age. As a result, Willwood flo- ras may have the potential to play an important role in under- standing the evolution of forest structure over geologically long periods of time. 8 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Abbreviations used within the text.——DPC, Duke Uni- versity Primate Facility (Durham, NC); NM, National Museum of Natural History, Smithsonian Institution (Wash- ington, D.C.); UM, University of Michigan Museum ofPale- ontology (Ann Arbor, Mich.); US Geological Survey (Denver, Colo.; D in tables and plates); UW, University of Wyoming Geological Museum (Laramie, Wyo.; W in tables and plates); YPM, Yale Peabody Museum (New Haven, Conn.; Y in tables and plates); m, meters; MNI, minimum number of individuals. Acknowledgments—The authors thank H.H. Covert and R.K. Stucky for review of an earlier version of this manuscript, and M.J. Kraus and David Schankler for discus- sion. G.F. Gunnell contributed locality information regard— ing University of Michigan vertebrate localities. KC. McKinney assisted considerably with the organization of Willwood fossils in the US. Geological Survey collections. We are grateful to A.L. Isom for drafting the block diagram (fig. 12) showing the geometry of pedofacies. This study owes considerable debt to all of those who contributed to the recovery of Willwood vertebrate fossils from the southern Bighorn Basin, especially those who col— lected specimens now in the three largest institutional col- lections of fossil vertebrates from this region, the collections of the Yale Peabody Museum, the University of Wyoming Geological Museum, and the US. Geological Survey. The principal Yale Peabody Museum field-party members in 1961—74 were: Joe Alpert, Friderun Ankel- Simons, Ernie Bonebaker, Bruce E. Bowen, Thomas M. Bown, Hal Brown, Prithijit S. Chatrath, John G. Fleagle, Hal Frank, Michael F. Gibbons, Jr., Leonard Greenfield, Karen Hiiemae, Richard F. Kay, Troy Krieger, Paul Lemke, Jim Meade, Deborah Meinke, Grant E. Meyer, Marty Meyer, Wayne Meyer, Pete Parks, Dennis W. Pow- ers, Leonard Radinsky, Terry Radinsky, Stanley J. Riel, Kenneth D. Rose, Jeffrey Schweitzer, Richard Sheldon, Elwyn L. Simons (director), Ian M. Tattersall, Tom Wester- meier, Tom Walsh, Paul Whitehead, Scott L. Wing, Roy Winslow, Claire Zwell, and Michael Zwell. The principal University of Wyoming field-party members in 1973—76 were: Thomas M. Bown (director), Arliss Burtis, Malcolm C. Campbell, Ruth Henritze, Mary J. Kraus, Kenneth D. Rose, Eleanor Saunders, and Jeffrey Schweitzer. The prin- cipal US. Geological Survey field-party members in 1977—92 (jointly with the Johns Hopkins University School of Medicine after 1980) were: Andres Aslan, Kenneth C. Beard, Michael Bell, Brandon Bown, Thomas M. Bown (director), Mark Brown, Malcolm C. Campbell, Silvia E. Cornero, Robert Costello, Marian Dagosto, Michael Dia- mond, David Dunn, Al Fraser, Carolyn Garman, Daniel Gebo, Marc Godinot, Paul V. Gold, Ron Heinrich, lnés Horovitz, John Hunter, Howard Hutchison, Scott Johnson, Mary J. Kraus, Robert Kraus, John Kurtz, Lewis Ladocsi, Abd-el A. Latief-Houdab, Alexandra Ledesma, J. David Love, Richard Madden, Andrew C. McKenna, Bruce McKenna, John D. McPhee, Kevin C. McKinney, Adele Oakley, Fredericka Oakley, John Oakley, Robert W. O’Donnell, Maureen O’Leary, Charlotte Otts, Kathy Raf- ferty, D. Tab Rasmussen, Kenneth D. Rose (director), Jen- nie J. Rose, Sue Rose, Callum Ross, Jackie Runestad, Elise Schloeder, Sam Senturia, Myron Shekelle, Masako Shima- mura, David Simons, Elwyn L. Simons, Amy Verreault, Gustav Winterfeld, Virginia J. Yingling, Naoko Yokoyama, and Pan Yuerong. The principal Duke University Primate Center field-party members from 1979—90 were: Herbert H. Covert, Mario Gagnon, Pat Holroyd-Vychodil, David Simons, Elwyn L. Simons (director), Verne Simons, Michael Stuart, and Chris Tilden. We were assisted greatly in 1980 and 198] by J. Howard Hutchison and in various other seasons by visiting crews directed by J. David Archibald (San Diego State University), William S. Bartels (Albion College), Grant E. Meyer (Raymond M. Alf Museum), Michael J. Novacek (American Museum of Nat- ural History), Charles Schaff (Agassiz Museum), Wighart von Koenigsvald (Institut fiir Palaontologie, Bonn, Ger- many), and Craig B. Wood (Providence College). The senior author was assisted in measurement of stratigraphic sections of the Willwood Formation for the US. Geological Survey from 1981 to 1986 by Scott Johnson, Virginia J. Yingling, and especially Bruce Mckenna. The Yale sections of the Willwood Formation utilized here were measured by David Schankler and Scott L. Wing in 1976—78. In developing the fossil plant locali- ties, Scott L. Wing was assisted in 1978—87 by Natasha Atkins, David D’Argenio, Kevin C. McKinney, Arnold Powell, Ben Rose, Bruce H. Tiffney, and Steven B. Wing, and by visiting field parties directed by Bruce H. Tiffney. Mary J. Kraus contributed considerable geologic informa- tion from her unpublished sections of the Willwood Forma- tion along the Elk Creek Rim. In the initial stages, much of Bown’s work was sup- ported by a G.K. Gilbert Professional Fellowship with the US. Geological Survey, and later work was supported largely by National Geographic Society Grant 3985—89. Kenneth D. Rose acknowledges support from National Geographic Society Grant 2366—81, John J. Hopkins Fund and US National Institute of Health Biomedical Research Support Grant #RR5378 (through the Johns Hopkins University), and National Science Foundation Grants BSR—8215099 and BSR—8500732. Elwyn L. Simons was supported by grants from the J.T. Doneghy Fund (Yale University), The Boise Fund (Oxford University), and grants from the Duke University Research Council. Scott L. Wing acknowledges grants from Sigma Xi, the Smithso- nian Scholarly Studies Fund, the Smithsonian Research Opportunities Fund, the Roland Brown Fund (Smithsonian Institution), and a National Research Council Postdoctoral Fellowship with the US Geological Survey. David Schankler was assisted by grants from the J.T. Doneghy Fund and Sigma Xi. FOSSIL VERTEBRATE LOCALITIES 9 FOSSIL VERTEBRATE LOCALITIES GEOGRAPHIC LOCALITIES There is considerable variety of opinion as to just what constitutes a fossil vertebrate locality. This circumstance results less from conflicting opinions than from different field experience, commonly dictated by the natural disposi- tion of the fossils in different rocks in different basins. In the Willwood Formation of the south—central and southeast Big— horn Basin, all known sites are in one or more of the follow- ing categories, regardless of the mechanism responsible for concentrating the fossils: (1) Surface localities; (2) quarries; (3) wash sites; and (4) unusual concentrations of fossils that do not qualify as quarries, surface localities, or as wash sites. Surface localities are delimited by the areal extent of lag concentrations of fossils on hills, on slopes, in runnels and rills, and on flats at the bases of hills or surrounding them. They vary in size from about 1 square meter to several hectares (fig. 2). Quarries (figs. 3 and 4) and wash sites (fig. 5) generally occupy a few to several square meters in size and delimit places of high local concentration of fossils. Unusual concentrations specifically include calcareous steinkerns (fig. 6) of the holes of trees (Kraus, 1985, 1988) that are known to contain vertebrate remains in a number of sequences (for example, Carroll, 1967; Walker and others, 1986; Gingerich, 1987; Walker and Teaford, 1989), and thin (<3 cm) concentrations of fossils over but a few cubic centi- meters of surface exposure (for example, one area in locality D1830). All of these different kinds of localities are now recorded geographically by demarcating their areas as pre- cisely as possible on the best available maps (pls. l and 2) and, after 1992, will be recorded with a Magellan locating device; however, prior to about 1950, reliable large—scale topographic maps of the more remote badland areas of Will- wood Formation exposure in the Bighorn Basin were not available. No reliable locality mapping exists for most Will- wood localities established prior to about the middle of this century, except for sites known by tradition or by collecting continuity that have been, long after their discovery, recorded on maps. Lamentably, sites with poor, unreliable, or no recorded locality data include all of the principal local- ities of the early Cope expeditions and those of the American Museum of Natural History in the decade preceding World War I, from which important type materials were obtained (see discussions in Gingerich (1980a) and Bown and Rose (1987)). Although some localities were recorded on existing maps by Princeton University field parties under the direc- tion of W.J. Sinclair and G.L. Jepsen, many of those were inaccurately plotted, and the majority appear to have never been recorded. Therefore, the first reliable and systematically kept map records of the geographical situation of Willwood fossil mammal localities were maintained by E.L. Simons, who directed several Yale Peabody Museum expeditions in the Bighorn Basin from 1961 to 1975. In this endeavor, he was assisted by GE. Meyer from 1963 to 1971, and by the senior author from 1970 to 1972. These Yale localities possessed little geographic or stratigraphic control other than what could be obtained by circumscribing a general location on a map. Nonetheless, this information was recorded faithfully every collecting day, and at least as early as 1968 (and prob- ably earlier), the considerable time necessary to pinpoint new sites on maps became as important a part of the collect— ing routine as prospecting for fossils. Even so, the Yale localities commonly incorporated rather large geographic areas with only modest control on stratigraphic position. They are here termed geographic localities and, as shown in Schankler’s (1980) correlation of YPM sites in the south- central Bighorn Basin, most cannot be stratigraphically cor- related more accurately than to the nearest 10 m. STRATIGRAPHIC LOCALITIES In the area of exposure of the Willwood Formation, as in most badland areas where fossils commonly accumulate in surficial lags, it can be very difficult to determine from exactly where in a sequence an exposed fossil came. In the Willwood Formation, the majority of fossils were collected from lag accumulations on flats or at the bases of hills, accu- mulations that were produced over many years of weather- ing, erosion, and concentration. Only rarely, or when productive beds have been located (Bown, 1979), are remains found in place (fig. 7). Although it is commonplace procedure for paleontologists to follow the strike of the pro- ducing beds in outcrop in search of more fossils, during the Yale expeditions little attempt was made to either discern or to limit the stratigraphic provenance of fossils collected, except to constrain collecting efforts to the circumscribed geographic localities. Even so, great care was normally taken to prevent wandering of crew members in steep topography in the interest of stratigraphic conservation. In 1974, it was discovered that a suite of geographic localities in the Sand Creek-No Water Creek area of Will- wood badlands (pl. 2) yielded abundant vertebrate fossils from a single, exceptionally continuous bed (Bown, 1975, 1979). Further collecting in that area in 1975 demonstrated that the vast majority of Willwood fossils there could be pre- cisely related to the beds that produced them, and several localities were given names to reflect this discovery (for example, Slick Creek quarry beds, Two Head Hill quarry beds, Supersite quarry beds; Bown, 1979). All of these important units are geographically widespread within that part of the Bighorn Basin, and all produce abundant fossil vertebrates throughout their area of exposure. Shortly there- after, other exceptionally productive, stratigraphically explicit fossil occurrences were also discovered in Willwood rocks exposed in the drainages of Elk and Fifteenmile 10 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Figure 2. Surface (geographic) localities, Willwood Formation. southern Bighorn Basin. Wyoming. A. U.S. Geological Survey locality D1473, 556-m level. Locality has a sequence of levee deposits and immature paleosols at the floor of the valley and extending to the base of badland hills in the far distance. View to the north. B. Yale Peabody Museum locality Y104, 140-m level. Locality has a paleosol imme— diately above the flats at the base of the exposure. as well as several anthills (arrow). View to the north. Creeks (pl. 1), and it was found that their origin was due to passive paleosol lag accumulations (Bown, 1977, 1979, 1980; Bown and Kraus, 1981a, 1981b). Recent collecting operations in the Fifteenmile Creek drainage, beginning under University of Wyoming auspices in late 1973 and continuing with the U.S. Geological Survey and joint U.S. Geological Survey-Johns Hopkins University School of Medicine expeditions through 1992, were under- taken, following the 1974 season, with the specific goal of collecting large samples of Willwood vertebrates with tight stratigraphic controls tied to fossil provenances in paleosols. Field collecting began to be consciously restricted to specific FOSSIL VERTEBRATE LOCALITIES ll Figure 3. Fossil vertebrate quarry sites, Willwood Formation. southern Bighorn Basin, Wyoming. A. US. Geological Survey locality D1340Q, 364-m level. Fossils are concentrated in intraclastic mudrock conglomerate above the base of the scour (arrows). View to the south. B. US Geological Survey locality D1762Q. estimated at the 414-m level. Fossils are in whitish sandy mudrock filling the scour throughout the small valley but are most abundant at the edge of the hill where the people are digging. View to the north. 12 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Figure 4. Rose quarry. US. Geological Survey locality Dl460Q, 41 l-m lcvcl ofthe Willwood Formation. A. View to the southeast of the entire quarry site: more than 1000 specimens ofsmall mammals were found in the area bounded by the men and the arrows. B. Close view of quarry operations and working surface in 1983. The site is so small (about 9 m2) that it was difficult to apply the efforts of more than a few people at a time. FOSSIL VERTEBRATE LOCALITIES Figure 5. Teakettle Hill, Yale Peabody Museum locality 363, l90-m level of the Willwood Formation, southern Bighorn Basin, Wyoming. A. Chopping the A horizon of the productive paleosol and gathering matrix: view to the east-northeast. B and C. Screen-washing operations on the Bighom River at Worland, Wyo.. in 1984. Sediment was soaked in buckets (B). then poured in a slurry through screens and washed in river water (C). Concentrate was picked initially while drying (B). then packed for transport to the laboratory. 13 14 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING Figure 6. Calcareous steinkems of the holes of trees. A, in the Fort Union Formation. on the Polecat Bench north of Powell, Wyo., and B, at US. Geological Survey locality D1799, Willwood Formation, at geology pick. Specimen in B is rich in fossil vertebrate remains. A is courtesy of MJ. Kraus. FOSSIL VERTEBRATE LOCALITIES 15 Figure 7. Mandible of a small species of Coryphodon (Mammalia, Pantodonta) in place in mudrock at U.S. Geological Survey locality D1583, 556-m level of the Willwood Formation, southcm Bighorn Basin, Wyoming. stratigraphic intervals that could be related to fossil prove- nances, and these are almost invariably in paleosols. Thus, since 1974, Willwood specimens in the University of Wyo- ming and U.S. Geological Survey collections have, for the most part, been collected stratigraphically, the producing beds sought out and recorded at the time of collection. This technique has afforded greater stratigraphic resolution than was possible in the study of Schankler (1980), in his correla- tion of the strictly geographic YPM localities (nearest 1.0 m instead of 10.0 m), for which bed provenance was unknown and commonly could not be reconstructed. The UW and U.S. Geological Survey localities, therefore, are both geographic and stratigraphic localities (fig. 8). The complete listing for U.S. Geological Survey, YPM, DPC, UM, and UW geo- graphic and stratigraphic localities is presented in tables 2—6 (following “References Cited”). SEDIMENTOLOGIC LOCALITIES With increasing knowledge of Willwood Formation depositional mechanisms and temporal-depositional con- trols on Willwood sediment-accumulation rates (Bown and others, 1991, 1992; Bown and Kraus, 1993; Kraus and Bown, in press), it has also become important to qualify geo- graphic and stratigraphic localities in the field by some mea- sure of their sedimentologic attributes. It became clear that it was necessary to establish a new type of fossil vertebrate locality after recognition that the various fossil-bearing Will- wood paleosols are all basically the same kind of paleosol and that their morphological differences reflect considerably varying amounts of time required to form them (that is, some are more mature than others). Bown (1985) and Bown and Kraus (1987) designated five stages of maturation in Will- wood paleosols, numbered 1—5 in order of increasing matu- rity. A sixth and least mature stage (numbered 0) was added by Kraus (1987) for Willwood sediment that was relatively unaltered pedogenetically, and to this scheme Bown and Kraus (1993) have added stage 6 for the most mature Will- wood paleosols. The relative maturities of the paleosols were discovered to be more or less directly proportional to their relative lat- eral distances from contemporary stream-channel deposits; that is, very immature stage 0 and stage 1 paleosols are typ- ical of more proximal channel, levee, and meander-belt deposits, whereas stages 5 and 6 paleosols (the most mature) l6 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Figure 8. Stratigraphic fossil vertebrate localities, Willwood Formation, southern Bighorn Basin, Wyoming. A, US. Geological Survey locality D1454, 409—m level; man is collecting vertebrate fossils from surface lag accumulations derived from a stage 3 paleosol. Open arrow, A horizon; black arrow, upper part of B horizon of paleosol. B, Surface collecting and quarrying fossil vertebrates from stage 5 pal- eosol at University of Wyoming locality W44, 57-m level. Open arrow, A horizon, black arrow, upper part of B horizon of paleosol. FOSSIL VERTEBRATE LOCALITIES l7 typically formed on sediments on the most distal part of the contiguous flood plain. Stages 2, 3, and 4 paleosols occupy areas intermediate between the proximal deposits proper and the most distal flood plain. Because maturity of Willwood paleosols was controlled by deposition, a means had there- fore been found by which to integrate paleosols and paleosol time with deposition and sediment-accumulation time. Those means were embodied in the concept of the pedofa- cies (Bown and Kraus, 1987; Kraus, 1987), and the time- stratigraphic reconstruction of the Willwood Formation (Bown and others, 1992; Bown and Kraus, 1993; Kraus and Bown, in press). Studies of evolution in lineages of the adapid primates Cantius and “Copelemur” and different species of the hyop- sodontid condylarth Hyopsodus were undertaken in paleosol sequences with exceptionally rich fossil localities at the 438-442-m and 546—m levels of the Willwood Formation. It was discovered that the differential MNI abundances of tem- porally sympatric species are directly related to the different maturation stages of the paleosols in which they occur (Bown, 1987; Bown and Beard, 1990). Because, by the ped- ofacies concept, paleosol stage reflects proximity to nearby coeval stream channels (Bown and Kraus, 1987), the abun- dance differences between temporally sympatric species appear to record small-scale, intrabasinal geographic (and probably floral) controls on fauna] composition. Further examination of fossil mammal and pedofacies associations suggests that it is necessary to record even more locality information in the field to refine evolutionary studies further. Thus, beginning in 1987, the U.S. Geological Survey—Johns Hopkins University expeditions have recorded paleosol stage and other sedimentological and pedofacies information for all new localities and have begun a program of reconstructing this information from all older localities for which sufficient geographic and stratigraphic data exist to make such areconstruction plausible. These are new types of localities for the Willwood Formation, localities whose doc- umentation includes not only geographic area and strati- graphic provenance, but also sufficient information to assign paleosol stage and position in the local pedofacies complex. These sites are best termed sedimentologic localities (fig. 9). Sedimentologic locality information was published for vari- ous sites at the 438—442-m, 546-m, and 556-m levels by Bown (1987) and Bown and Beard (1990), and has now been compiled for about 1,000 additional localities. Some sedi- mentologic locality information is presented in tables accompanying the following section. AVERAGE AND NOTEWORTHY LOCALITIES All numbered fossil vertebrate localities in the Will— wood Formation yield isolated jaws, teeth, and bones in vari- able abundance and in various stages of preservation. The most commonly encountered elements are teeth, followed first by jaw fragments and second by identifiable bone frag- ments. Associations of several bones, of dental remains and bones of the same individual, or of associated right and left rami or maxillae are relatively uncommon. Skulls and partial skeletons are quite rare. Although the outcome of prospect- ing for fossils in the Willwood Formation cannot be pre- dicted with precision, the following estimates can be made, based on data compiled by the senior author for more than 22,000 specimens (partial listings occur in Bown and Kraus (1981b) and Bown and Beard (1990)). An average locality, after an average day of collecting by a party of six persons, might yield 50 teeth and one-tooth jaw fragments, 50 jaw fragments with two or more teeth, and perhaps 15 identifi- able fragments of postcranial bones. Our field crews also might expect to find a group of associated bones of one indi- vidual fossil animal (or an association of teeth and bones) once a week; two partial skulls might surface in a field sea- son; and a substantial part of a skeleton appears, on the aver— age, slightly more often than once per eight-week season. For the past 10 seasons, a single yearly 8-week expedition has found an average of about 3,000 teeth and one-tooth jaw fragments, 2,200 jaw fragments with two or more teeth, 930 identifiable postcranial bone fragments, 9 noteworthy post- cranial or dental-postcranial associations, 2 partial skulls, and 1—2 partial skeletons. The vast majority of Willwood fossil-mammal sites are average surface localities in which the whole known sample was taken in one or two days, and the locality is not revisited unless: (1) Particularly significant or unusual mammals are later found to have come from there; (2) there is evidence that the site is richer than could be demonstrated when found; (3) there is evidence that the productive unit or units at the locality is more or equally productive farther afield (in areas in which the locality might be geographically extended); or (4) after relating the site to the measured strati- graphic section, the site is found to occupy a stratigraphic position for which little (or not enough) material is known. Other localities, however, have yielded enough fossils and(or) sufficient unusual fossils that they are quite extraor- dinary. Still others are so large and(or) so productive that they continue to yield excellent fossil material season after season and are revisited to increase sample sizes for studies of anatomical variability and fauna] diversity. Data for the most important of these highly significant localities are given in table 7, and mammalian faunal lists and composi- tions for some of them are provided in tables 8—14. FAUNAL COMPOSITION A detailed analysis of the composition of Willwood mammalian assemblages is beyond the scope of this report, but a few remarks based on a preliminary assessment of the data at hand seem worthwhile. Basic data and diversity indi- ces are given in table 15 for the assemblages summarized in 18 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING Figure 9. Sedimentologic fossil vertebrate locality complex. Willwood Formation, southern Bighom Basin. Wyoming. A, Yale Peabody Museum locality Yl92. 546 m-level; fossils come from an approximately lO—m-thick levee sequence containing stage 0—1 paleosols and bounded by crevasse-splay and crevasse-channel deposits. Meter levels for localities in such levee sequences are de- termined by recording the stratigraphic position of the middle of the sequence (bounded by arrows in figure). B, US. Geological Survey locality D1583. 551-m level; most fossils come from the A horizon ofa stage 3 paleosol (arrows), from which the men are collecting. Both localities Yl92 and D1583 are in the same pedofacies; however, Yl92 is proximal to the channel system that formed the deposit, and D1583 is considerably distal to it. Both localities are part of the D1256 locality complex. and both are sedimentologic localities because their pedofaeies positions have been determined. in addition to their geographic and stratigraphic positions. STRATIGRAPHIC SECTIONS 19 tables 8—14. As indications of mammalian faunal diversity, we employ species richness (the number of species present), the Whittaker index (chiefly a measure of species evenness), and the Shannon-Wiener index (a commonly used measure of mixed diversity, that is, evenness and species richness). (For the use of these measures of diversity, see Whittaker, 1972, 1977; Feet, 1974; May, 1976; Rose, 1981b.) Sufficient samples are known for all the faunal assem- blages so that all but the rarest species likely have been recorded. An exception is the rarity of species with very small body size, but because all these samples were collected primarily by surface prospecting, this bias should be about the same for all. Although screen washing at some sites may signifi- cantly affect the composition by revealing an unsuspected abundance of microfaunal taxa (for example, Winkler, 1983), it is unlikely that this procedure would fundamentally alter the diversity indices in table 15. Still, the assemblages display quite a large range in species richness, and one that is generally proportional to sample size. This range indicates that even the relatively large samples from the Willwood Formation are probably incomplete with regard to species, and smaller samples may provide an inadequate impression of species richness. It is probable, however, that as sample size increases, the only species added are the rarest elements of the fauna. The diversity indices, despite generally larger samples than previously analyzed for Wasatchian assemblages, are surprisingly low compared to those of previously analyzed faunas (Rose, 1981a, 1981b). In relative diversity, the less diverse assemblages are more comparable with that of Clark- forkian faunas than with Wasatchian ones. Whether this lower diversity reflects local differences in ecological stabil- ity or local habitat has yet to be investigated. STRATIGRAPHIC SECTIONS MEYER-RADINSKY SECTION (1965) The abundance of fossil vertebrates in the Willwood Formation of the Bighorn Basin was apparent as early as the Princeton University and American Museum of Natural His- tory expeditions led by W.J. Sinclair and Walter Granger (Sinclair and Granger, 1911, 1912; Granger, 1914); how- ever, it was not until more than a half-century later that the first large numbers of fossil localities were related to one another in a stratigraphic section. In 1965, GE. Meyer and LB. Radinsky (both then at Yale University) measured a section at the base of the formation along Antelope Creek, south of Basin, Wyo. (pl. 1). This (unpublished) section ter- minated at the contact of the Willwood Formation with the overlying Tatman Formation on the Squaw Teats Divide, and related 83 localities to one another through a measured thickness of 1,690 feet (515 m). Although there now appears to have been a rather severe error in measuring the formation (it is the thinnest of the complete measured sections of the formation by about 600 feet (183 m)), the Meyer-Radinsky section was the first of several attempts to relate the hun- dreds of early Eocene fossil vertebrate sites in the southern Bighorn Basin. Even though later studies have demonstrated that the actual meter levels recorded in the Meyer-Radinsky section are incorrect, their section did provide a relatively accurate. stratigraphic arrangement of the localities with respect to one another, and it was utilized by Gingerich (1974) in his seminal study of dental evolution in the condy- larth Hyopsodus. NEASHAM-VONDRA SECTION (1966-69) From 1966 to 1969, J .W. Neasham and CF. Vondra of Iowa State University measured sections of the Willwood Formation. One of their sections was begun at the contact with the underlying Fort Union Formation on Antelope Creek but, rather than turning south at the Elk Creek Rim and crossing the Buffalo Basin as did the Meyer-Radinsky sec- tion, they instead brought their line of section westward up the drainage of Elk Creek, crossed the south face of Sheep Mountain, and culminated with a thickness of 2,300 feet (70] m) at the Willwood Formation-Tatman Formation con- tact on the east side of Tatman Mountain (pl. 1). This section was measured partly in cooperation with EL. Simons’ 1968 Yale Peabody Museum expedition to the Willwood Forma- tion, and 37 YPM fossil vertebrate localities were related to it, including 19 not correlated previously by Meyer and Rad- insky (Neasham, 1970). It was also in the course of this field work that Willwood paleosols were first recognized (Neas- ham, 1967, 1970; Neasham and Vondra, 1972). In 1976, Gingerich published a second account of his Hyopsodus study in conjunction with other work. This new study utilized nearly all fossil localities correlated by the combined Meyer-Radinsky and Neasham-Vondra sections and added stratigraphic plots of tooth dimensions in the diminutive mammal Haplomylus and the adapid primate Pelycodus (=Cantius). In these and several later depictions of stratigraphically correlated dental dimensions of Will- wood mammals from the central and southern Bighorn Basin (for example, Gingerich, 1977, 1980b, 1983a; Gingerich and Simons, 1977), Gingerich utilized data for fossils from 114 additional localities that were “***interpolated into mea- sured sections on basis of geographic proximity to a locality in the measured sections and/or the morphology of the Hyop- sodus from that locality” (Gingerich, 1976, p. 8). As observed by Bown (1979, p. 135), Willwood rocks through- out most of the central Bighorn Basin are not flat lying, as had been assumed by Gingerich, and an error of a single degree of dip from the actual rock inclination produces a stratigraphic error of more than 17 m/km (kilometer). More- over, the procedure of utilizing tooth-size data to infer 20 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 7. The most significant fossil vertebrate localities in the Willwood Formation of the southern Bighorn Basin, Wyoming, and syn— opsis of stratigraphic position, paleosol maturation stage (if known), and vertebrate remains. [Sample sizes given include only identified remains; number of mammalian jaws given are mostly dcntary or maxillary fragments with two or more teeth. MNI, minimum number of individuals; USGS, US. Geological Survey] Locality number, name, and year of discovery: D1162, Chri- acus locality, 1979. Stratigraphic position: Paleosol stage: 1 and 2. Sample size: 1,346 specimens, including 447 mammal jaw frag— ments. Significant specimens: Chriacus sp., nearly complete articulated skeleton (USGS 2353; Rose, 1987); Esrhonyx sp., cf. E. bisulca- tus, skull and mandible (USGS 5285); Palaeasinopa veterrima, skull and jaw fragments (USGS 302). Remarks: See faunal list, table 8. Locality Y40, nearby, repre- sents the same level. 481 m. Locality number, name, and year of discovery: D1177, Purple Hills, 1976. Stratigraphic position: Paleosol stage: 4. Sample size: 1,014 specimens, including 257 mammalian jaw fragments. Significant specimens: Vulpavus sp., cf. V. canavus, skull and jaws (USGS 206); Xenicohippus grangeri, holotype mandible (USGS 292). Remarks: D1177 is stratigraphically the highest known richly fossiliferous stage 4 paleosol in the southern Bighorn Basin. Other nearby localities in the same paleosol are D1315, D1316, Y253, UMRBl, and UMRBZ. See faunal list, table 9. 481m. Locality number, name, and year of discovery: D1198 com- plex, Reservoir Creek Bonanza (includes Y45 and Y4SS), 1962, as Y45. Stratigraphic position: 470 m. Paleosol stage: Sample size: fragments. Significant specimens: Cf. Prodiacodon, dentaries and partial skeleton (USGS 16493); Anemorhysis pattersom', holotype den- tary (USGS 476; Bown and Rose, 1984); Absarokius metoecus, holotype dentary (USGS 492; Bown and Rose, 1987); Miacis sp., cf. M. exiguus, dentary and partial skeleton (USGS 7161). Remarks: D1198 consists of eight separate sites, D1198A through D1198H, all in the same sequence of levee deposits ex- tensively exposed along the drainage of Reservoir Creek. D1198A is the same as Y45, and D1198C is the same as Y45S; the remaining localities are US. Geological Survey extensions in equivalent beds and are accorded the same locality number. Other sites that produce fossil mammals from the same levee de- posits are D1160, D1160N, D1244, and D1314. The D1198 complex is dominated faunally by Hyopsodus, two species com— prising almost 50 percent (MNI) of the fauna. See faunal list, ta- ble 10. Levee deposits; median position is 1 and 2. 4,865 specimens, including 1,629 mammalian jaw Locality number, name, and year of discovery: D1204, Kraus Flats, 1976. Stratigraphic position: Paleosol stage: 438—444 in. 3 and 3+ (3 paleosols). Sample size: More than 1,800 specimens, including about 750 mammalian jaw fragments. Significant specimens: Oxyaena gulo, partial skull and skeleton (USGS 7186); Steinius vespertinus, best known upper dentition (USGS 502; Bown and Rose, 1984). Remarks: D1204 is the richest fossil vertebrate site in the upper part of the Bunophorus Interval Zone of Schankler (1980). D1204 is characterized by an abundance of Hyopsodus and Can- tius, both of which are represented by two species and were uti- lized by Bown and Beard (1990) in their study of fossil vertebrate distribution in paleosols. Hyopsodus constitutes near- ly 40 percent of the fossil mammal fauna at D1204. Nearby lo- calities in the same paleosols are D1203. D1693, and Y338. See faunal list, table 11. Locality number, name, and year of discovery: D1230, Fossil Hollow Bonanza (equal to UMRBIO), 1976. Stratigraphic position: 490 m. Paleosol stage: Unknown. Sample size: More than 300 specimens, including more than 200 mammalian jaw fragments. Significant specimens: Many jaws of small mammals that are rare at this level of the Willwood Formation, including Apate- mys, Phenacolemur, and Didelphodus. Remarks: D1230 is locally extremely rich in vertebrate remains. The locality was established by a joint University of Wyoming- University of Michigan field party as UMRB 10. Locality number, name, and year of discovery: D1256 com- plex. Bobcat Draw Bonanza (fig. 9A) 1971 as Y192. Stratigraphic position: 541—551 m. Paleosol stage: 1 through 3+ (Bown and Beard, 1990). Sample size: 5,537 specimens. including more than 2,400 mam- malian lower jaws. Significant specimens: Hapaladectes Ieptognathus, dentition and associated postcrania (USGS 5912); numerous mandibular and maxillary associations and some dental and postcranial as- sociations. Remarks: The D1256 complex is developed at the richest fossil vertebrate horizon known in the southern Bighorn Basin. This pedofacies complex includes: D1256 proper, D1464, D1467, D1574, D1575, D1576, D1581, 01582, D1583, DPC15, DPC16, Y181, Y190, Y192. Y193, and Y315. The discovery site in the principal collecting area was Y192. Y181 and Y190 were discovered earlier but not extended; the remaining sites are extensions of Y192. See faunal list, table 12. Locality number, name, and year of discovery: Cottonwood Bonanza, 1980. Stratigraphic position: 425 m. Paleosol stage: 3. Sample size: About 650 specimens, including 327 mammalian jaw fragments. Significant specimens: Microsyops angusn’a’ens, snout and den- tary (USGS 3793); Didymicris sp., cf. D. protenus, dentaries and partial skeleton (USGS 5024). D1326, Dry STRATIGRAPHIC SECTIONS 21 Table 7. The most significant fossil vertebrate localities in the Willwood Formation of the southern Bighorn Basin, Wyoming, and syn- opsis of stratigraphic position, paleosol maturation stage (if known). and vertebrate remains—Continued. Remarks: D1326 is dominated by one species of Hyracotherium (MNI 21 percent), and two species of Hyopsodus (MNI 15 per- cent and 14 percent, respectively). The locality yields the strati- graphically lowest occurrences of Absarokius (A. memecus). Anacodon (A. ursidens), and Xenicohippus (X. grangeri). See faunal list, table 13. Locality number, name, and year of discovery: D1350, Gill Locality, 1976. Stratigraphic position: Paleosol stage: 1 and 2. Sample size: 57 specimens. Significant specimens: Hyracorherium sp., partial articulated skeleton (USGS 5901); Palaeanodon ignavus. dentaries and partial skeleton (USGS 7209). Remarks: Although D1350 is not a rich site, it is noteworthy for skeletal associations noted above and for a small quarry (D1350Q) at the southern margin of the site, which has yielded a small mammal fauna (including a new species of Phenacole- mur) from a stage-1 paleosol. 408—410 in. Locality number, name, and year of discovery: D1389, no name, 1981. Stratigraphic position: Paleosol stage: 4. Sample size: 117 specimens. including 65 jaw fragments of very small mammals. Significant specimens: Teronius-Pseudoteronius intermediate (stage 2), complete dentary (USGS 3841; Bown and Rose, 1987); several well-preserved lower jaw fragments of didelphid marsupials and lipotyphlans. Remarks: D1389 is stratigraphically the lowest locality above Biohorizon A (Schankler, 1980) that yields a diverse microfauna. 264 m. Locality number, name, and year of discovery: D1454, Potala Bonanza (fig. 8A), 1982. Stratigraphic position: 409 m. Paleosol stage: 3. Sample size: 1,687 specimens, including 776 mammalian jaw fragments and numerous associations of dentitions with postcra- nial bones (sample size includes fossils from nearby D1460, which produces from the same paleosol). Significant specimens: cf. Prodiacodon sp., 3 nearly complete skulls; Cantius trigonodus, snout and partial skeleton (USGS 5900; Rose and Walker, 1985); Cantius trigonodus, partial skel— eton (USGS 21832); Palaeanodon ignavus, dentaries and partial skeleton (USGS 16471): Esrhonyx bisulcatus, skull, mandible, and associated bones (USGS 7551, juvenile); Hyracorherium sp., jaw fragments and partial skeleton (USGS 21858); 14 man- dibular fragments of Apatemys sp.; 8 unusually complete lower jaws of Cantius trigonodus (at D1460). See faunal list, table 14. Remarks: The productive level at D1454 is exceptionally rich and extensive. Locality number, name, and year of discovery: D 1460Q, Rose quarry (fig. 4), 1982. Stratigraphic position: 411 m. Paleosol stage: 1. Sample size: More than 1,000 specimens, including 150 mam- malian jaw fragments. Significant specimens: Numerous well-preserved dentitions of very small mammals, including Apheliscus, Macrocranion, Tal- pavoides, and Peratlectes. Remarks: The fauna ofDl460Q is dominated by thejaws of very small mammals, of which the otherwise rare Macrocranion ni- tens and Aphelr’scus sp. nov. predominate (more than 20 jaws each). Faunal composition at D1460 differs considerably from that of the surrounding stage-3 paleosol (D1460 proper). Locality number, name, and year of discovery: D1473, Hoover Renner Reservoir Bonanza (fig. 2A), 1983. Stratigraphic position: 556 m. Paleosol stage: 0—1. Sample size: 1.119 specimens, including more than 750 mamma- lian jaw fragments. Significant specimens: 6554). Remarks: Locality D1473 produced more than 500 mammalian jaws in the first two days. D1504 and D1781 to the south have yielded large numbers of fossil mammals from the same levee sequence. Anemorhysis worrmani holotype. USGS Locality number, name, and year of discovery: D1510. Crook- ed Creek Bonanza, 1983. Stratigraphic position: 482 m. Paleosol stage: 1. Sample size: At least 1,000 specimens, including more than 800 mammalian jaw fragments. Significant specimens: Vulpavus canavus. skull and partial skel- eton (USGS 16488). Remarks: Locality D1510 was locally extremely rich. In the first two days at the site, five collectors discovered 602 mammal jaws with two or more teeth (175 the first day, 427 the second day); during the next season 200 additional jaws were collected there. The fauna is dominated by Hyopsodus. Locality number, name, and year of discovery: D1583, Bownanza (figs. 7, 9B), 1984. Stratigraphic position: 551 m. Paleosol stage: 3+. Sample size: 1,186 specimens, including at least 800 mammalian jaw fragments. Significant specimens: Didymictis protenus, snout and dentary (USGS 5909); very rich in a rare adapid primate similar to Copelemur. Remarks: Locally very productive; five collectors found more than 300 jaw fragments the first day in 1984, and 200 additional jaws were collected in one day the following season. Locality number, name, and year of discovery: D1651, Goose— berry Creek quarry, 1986. Stratigraphic position: Approximately 636 m. Paleosol stage: 1. Sample size: 315 specimens, including 75 mammalian jaw fragments. 22 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Table 7. The most significant fossil vertebrate localities in the Willwood Formation of the southern Bighorn Basin, Wyoming, and syn- opsis of stratigraphic position, paleosol maturation stage (if known), and vertebrate remains—Continued. Significant specimens: Phenacolemur sp., dentaries and partial skeleton (USGS 17847). Remarks: Locality D1651 is stratigraphically the highest known productive small-mammal locality in the Willwood Formation of the southern Bighorn Basin and yields a late Wasatchian fau- na. Locality D1651Q is a small hill within the locality that yield- ed more than 200 specimens, including more than 50 jaw fragments of small mammals. Locality number, name, and year of discovery: D1675Q, Elk Creek Rim quarry, 1986. Stratigraphic position: 493 m. Paleosol stage: 3. Sample size: About 30 specimens, including 15 mammalian jaw fragments. Significant specimens: Micrasyops sp., partial skull and com- plete dentary (USGS 28050); several well-preserved lower jaws of Microsyops and Apheliscus; partial skull of small hyaenodon— tid creodont. Remarks: Locality D1675Q is an important site because it yields well-preserved small mammals of middle Wasatchian age. The quarry site is contained within locality D1563, which yielded a partial skull and skeleton of Oxyaena sp., cf. 0. forci- pata (USGS 16484) from the same bed. Locality number, name, and year of discovery: D1699, no name, 1986. Stratigraphic position: Paleosol stage: 1. Sample size: 558 specimens, including 373 mammalian jaw frag- ments. Significant specimens: Hadrianus nuzjusculus, most of cara- pace, plastron, and postcranial skeleton (University of Califor- nia Museum of Paleontology 134931); Protoromus sp., dentaries and partial skeleton (USGS 16475); Anacodon ursidens, partial forelimb (USGS 21857). Remarks: Localities D1737, D1776, D1776N, D1833. and D1881 (see separate entry for D1737) are also very rich and oc- cur in the same levee deposits farther north. 463 m. Locality number, name, and year of discovery: D1717, no name, 1987. Stratigraphic position: Paleosol stage: 0. Sample size: 48 specimens. Significant specimens: Three partial skulls of Coryphodon and several well-preserved upper and lower jaws of Heptodon and Lambdotherium (all uncatalogued). Remarks: Stratigraphically one of the highest productive verte- brate localities in the Willwood Formation. Considerable future promise, especially for more remains of Coryphodon. Produc- tive unit (proximal levees with splay sands) extends to the north and includes locality D1718. Unknown; above 636 m. Locality number, name, and year of discovery: D1737, no name, 1987. Stratigraphic position: Paleosol stage: 463 m and 469 m. 1 (lower) and 3 (upper). Sample size: ments. Significant specimens: Pararyctes sp., skull (USGS 23824); Didymictis sp., cf. D. prorenus, skull and mandible (USGS 21864); Hyracotherium sp., partial hind-limb skeleton (USGS 21860). Remarks: Localities D1699 (to the northeast) and D1776 and D1776N (to the north of D1737) yield mammals from the same levee deposits (see separate entry for loc. D1699). Locality D1776 produced two partial skeletons of Palaeanodon ignavus (USGS 21876 and 21930) and a partial skeleton of Coryphodon (USGS 21935). Locality Y100, just to the southeast, lies in a stage-4 paleosol below locality D1737 (455-m level), and pro- duced an important partial skeleton of Anacodon ursidens (USGS 21856). 236 specimens, including 111 mammalian jaw frag- Locality number, name, and year of discovery: D1762Q, McKinney quarry (fig. 3B), 1988. Stratigraphic position: Approximately 414 m. Paleosol stage: 0. Sample size: About 1,000 specimens, including 73 mammalian jaw fragments. Significant specimens: Several well—preserved lower jaws of li- potyphlans, didelphid marsupials, and the omomyids Steinius vespertinus and Arapahovius advena (Bown and Rose, 1991; Rose and Bown, 1991). Remarks: Locality D1762Q has considerable potential as a mi- cromammal quarry. It is notable in that it has yielded several specimens of the rare omomyids Arapahovius and Steim'us at a stratigraphic level at which all omomyids are quite rare. Locality number, name, and year of discovery: Y55, Howard's Hill and Diacodexis locality, 1962. Stratigraphic position: Approximately 501 m. Paleosol stage: 1 and 2. Sample size: 168 specimens, including about 110 mammalian jaw fragments. Significant specimens: Diacodexis metsiacus skeleton (USGS 2352: Rose, 1982, 1985): Howard's Hill, a small pocket in a stage 2 paleosol in the Y55 levee sequence, yielded 40 micro- mammal jaws, more than 150 teeth, and about 200 bones. Locality number, name, and year of discovery: no name, 1963. Y104 (fig. 23), Stratigraphic position: 140 m. Paleosol stage: 4. Sample size: 79 specimens in U.S. Geological Survey collection, and a significant collection (sample size unknown) at the Yale Peabody Museum. Significant specimens: Teilhardina, T. americana-T. crassidens intermediate, only complete anterior dentition of Teilhardina (USGS 512; Bown and Rose, 1987); Pachyaena ossifraga, pal- atal dentition (USGS 7185, from loc. D1640, a site to the east de- veloped in the same paleosol); Plagioctenodon savagei, holotype dentary (YPM 34257; Bown and Schankler, 1982). Locality number, name, and year of discovery: Y356, Hyopso- dus Hill, 1972. STRATIGRAPHIC SECTIONS 23 Table 7. The most significant fossil vertebrate localities in the Willwood Formation of the southern Bighorn Basin, Wyoming, and syn- opsis of stratigraphic position, paleosol maturation stage (if known), and vertebrate remains—Continued. Stratigraphic position: Approximately 360 m. Paleosol stage: 2. Sample size: Unknown; probably more than 200 mammalian jaw fragments. Significant specimens: Unknown. Remarks: This site is noteworthy for its remarkable concentra— tion of jaw fragments of Hyopsodus and Microsyaps (most of the collection from the site) collected from a small hill by the 1972 Yale Peabody Museum field crew. About 60 more jaws were re- covered by the U.S. Geological Survey-Johns Hopkins Univer- sity School of Medicine field party in 1981, but the locality now appears to be worked out. Locality number, name, and year of discovery: Y363, Teaket— tle Hill (fig. 5A), 1972. Stratigraphic position: Paleosol stage: 4. Sample size: Unknown, but probably well in excess of 400 mam- malian jaw fragments. Significant specimens: Unknown. Remarks: Locality Y363 has produced one of the most important samples of small mammals in the upper part of the lower Hap- lomylus—Ectocion Zone (Schankler, 1980). It is especially rich in omomyid primates and is one of very few sites in the Willwood Formation that yield three contemporaneous omomyid species Teilhardina crassidens, Tetom'us matrhewi, Tetonius sp.; Bown and Rose, 1987). 190m. Locality number, name, and year of discovery: Y370A, Banjo Quarry, 1972. Stratigraphic position: Paleosol stage: 0. Sample size: Unknown but probably exceeds 100 mammalian jaw fragments and 500 teeth. Significant specimens: Paraprernodus ann‘quus, holotype den- tary (YPM 31169; Bown and Schankler, 1982): numerous spec- imens of small lipotyphlans, neoplagiaulacid multituberculates. didelphid marsupials, and primates. Remarks: Locality Y370 was the first major micromammal quan'y, whose location is known, to be developed in the Will- wood Formation. 70 m. Locality number, name, and year of discovery: W22, Slick Creek quarry beds, 1974. Stratigraphic position: 46 m. Paleosol stage: 4. Sample size: Unknown but exceeds 400 mammalian jaw frag— ments and 1,000 teeth. Significant specimens: Teilhardina americana (holotype den- tary, UW 6896; Bown, 1976; Bown and Rose, 1987): Talpavoid- es dartoni, holotype dentary (UW 9624; Bown and Schankler. 1982); numerous mandibular and maxillary fragments of lipo- typhlans, didelphid marsupials, and other small mammals. Remarks: Locality W22 is quite extensive areally and yields fos- sils throughout. Slick Creek Quarry was an exceptionally pro- ductive pocket in the paleosol. Locality number, name, and year of discovery: W27, Stone- henge quan‘y beds. 1974. Stratigraphic position: 30 m. Paleosol stage: 4+. Sample size: Unknown but exceeds 300 mammalian jaw frag- ments and 800 teeth. Significant specimens: very small mammals. Remarks: Locality W27 is areally limited but remains an excep— tionally rich locality. Stonehenge Quarry was a highly productive pocket in the paleosol. Locality D1296, just to the southwest, is in the same paleosol. Numerous jaw fragments and teeth of Locality number, name, and year of discovery: W37, Super- site quan'y beds. 1975. Stratigraphic position: Paleosol stage: 5. Sample size: More than 4,000 identified specimens, including more than 900 mammalian jaw fragments and 2.500 teeth. Significant specimens: Plagioctenoides microlestes, holotype dentary (UW 9694; Bown, 1979); several mandibular and max— illary specimens of the minute, rare plesiadapiformes Nipto- momys and Tinimomys. Remarks: Locality W37 is the richest known site in the southern Bighorn Basin for small mammals. and it is by far the most pro- ductive site in the Haplomylus-Ectocion zone and in the lower part of the Willwood Formation. It has almost limitless opportu— nities for development as a wash site. Locality W34 (Two Head Hill quarry beds) and extensions are farther south in the same pa- leosol and yielded the holotype dentary of Peratherium macgrewi (UW 9564; Bown, 1979). 34 m. Locality number, name, and year of discovery: W44, Wadi Kraus Quarry (fig. 8B), 1975. Stratigraphic position: 57 m. Paleosol stage: 5. Sample size: Approximately 150 mammalian jaw fragments and 500 teeth. Significant specimens: Jaw fragments of many lipotyphlans, pri- mates, and other small mammals, including holotype dentary of Plagioctenodon krausae (UW 9682; Bown. 1979) Remarks: Though of limited area, locality W44 is an exception— ally rich site. For its size, it is the most productive locality in the Sand Creek-No Water Creek area. both as a quarry and as a wash locality. Locality number, name, and year of discovery: 1976. Stratigraphic position: Paleosol stage: 4+. Sample size: Approximately 600 specimens, including about 150 mammalian jaw fragments. Significant specimens: Teilhardina crassidens, holotype den- tary (USGS 8959; Bown and Rose. 1987); numerous jaws of small mammals. especially lipotyphlans and omomyid primates. Remarks: Locality W125 is stratigraphically the highest produc- tive site in the lower Hap/omyIus-Ecrocion zone in the Fifteen— mile Creek section and, like Y363. yields three species of contemporaneous omomyid primates (Teilhardina crassidens, Tetonius marrhewi. and Tetom'us sp.). w125, Big w, 180 m. 24 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING Table 8. Provisional faunal list and fossil mammal composition, U.S. Geological Survey locality D1162 (includes locality Y40), 481-m level of the Willwood Formation, southern Bighorn Basin. Wyoming. [MNI minimum number of individuals. Includes data through 1983] Percent of MNI as Identified total percent Fauna elements elements MNI of fauna Class Mammalia .................. 858 100.05 241 99.88 Magnorder Preptotheria ............ 85 8 100.05 241 99.88 Order Cimolesta ................ 16 1.87 9 3.81 Suborder Pantolesta ............. 13 1.52 7 2.90 Family Pantolestidae .......... 13 1.52 7 2.90 Palaeosinopa veterrima ....... 13 1.52 7 2.90 Suborder Apatotheria ............ 1 .12 1 .41 Family Apatemyidae .......... 1 .12 1 .41 Apatemys rodens ............ 1 .12 1 .41 Suborder Palaeoryctoidea ......... 2 .23 1 .50 Family Didelphodontidae ........ 2 .23 1 .50 Didelphodus absarokae ........ 2 .23 1 .50 Order Creodonta ................ 7 .82 5 2.07 Family Hyaenodontidae ......... 2 .24 2 .82 Tritemnodon sp., cf. T. hians . . . . 1 .12 l .41 Prototomus sp .............. 1 .l2 1 .41 Family Limnocyonidae ......... 1 .12 1 .41 Prolimnocyon sp. ........... 1 .12 1 .41 Family Oxyaenidae ........... 4 .47 2 .83 Oxyaena sp. .............. 4 .47 2 .83 Order Arctocyonia ............... 10 1.17 5 2.07 Family Arctocyonidae ......... 10 1.17 5 2.07 Ithptacodon sp., cf. T. loisi . . . . 47 .47 2 .83 Chriacus, sp. nov. .......... 2 .23 2 .83 Anacodon ursidens .......... 4 .47 1 .41 Order Camivora ................ 21 2.45 11 4.46 Family Miacidae ............. 21 2.45 11 4.56 Didymictis sp. ............. 7 .82 2 .83 Viverravus sp., cf. V. acutus . . . . 5 .58 3 1.24 Vulpavus sp. .............. 8 .93 5 2.07 Miacis sp., cf. M. exiguus ...... 1 .12 1 .41 Order Erinaceomorpha ............ 1 .12 1 .41 Family Dormaaliidae .......... 1 .12 1 .41 Macrocranion nitens ......... 1 .12 1 .41 Order Plesiadapiformes ............ 10 1.17 8 3.31 Family Microsyopidae ......... 9 1.05 7 2.90 Microsyops latidens .......... 9 1.05 7 290 Family Paromomyidae ......... 1 .12 l .41 Phenacolemur, sp. nov. ....... 1 .12 l .41 Order Primates ................. 43 5.01 19 7.87 Infraorder Omomyiforrnes ........ 16 1.86 7 2.90 Family Omomyidae ........... 16 1.86 7 2.90 Absarokius abboni .......... 16 1.86 7 2.90 Infraorder Adapiformes .......... 27 3.15 12 4.97 Family Notharctidae .......... 27 3.15 _. 12 4.97 Cantius abditus ............ 26 3.03 11 4.56 cf. Copelemur sp. ........... 1 . 12 1 .41 STRATIGRAPHIC SECTIONS 25 Table 8. Provisional fauna] list and fossil mammal composition. US. Geological Survey locality D1 162 (includes locality Y40). 481-m level of the Willwood Formation, southern Bighorn Basin, Wyoming—Continued. Percent of MN] as Identified total percent Fauna elements elements MNI of fauna Order Palaeanodonta ............. 4 .47 2 .83 Family Metacheiromyidae ....... 4 .47 2 .83 Palaeanodon ignavus ......... 4 .47 2 .83 Order Rodentia ................. 19 2.21 7 2.90 Family Ischyromyidae ......... 19 2.21 7 2.90 cf. Paramys, large sp. ........ 4 .47 2 .83 cf. Paramys, medium sp. ...... 4 .47 2 .83 cf. Paramys, small sp. ........ 9 1.05 2 .83 ischyromyid, very small sp. ..... 2 .23 1 .41 Order Tillodontia ............... 24 2.80 8 3.32 Family Esthonychidae ......... 24 2.80 8 3.32 Esthonyx bisulcatus .......... 24 2.80 8 3.32 Order Pantodonta ............... 3 .35 1 .41 Family Coryphodontidae ........ 3 .35 1 .41 Coryphodon sp. ............ 3 .35 1 .41 Order Dinocerata ............... 1 .12 1 .41 dinoceratan, gen. et sp. nov. . . . . 1 .12 1 .41 Order Condylarthra .............. 252 29.37 80 33.20 Family Hyopsodontidae ......... 224 26.11 66 27.38 Hyopsodus sp., cf. H. miticulus . . 169 19.70 53 21.99 Hyopsodus sp., cf. H. minor . . . . 55 6.41 13 5.39 Family Pentacodontidae ........ 3 .35 3 1.24 Apheliscus, sp. nov. ......... 3 .35 3 1.24 Family Phenacodontidae ........ 25 2.92 11 4.56 Phenacodus vortmani ......... 24 2.80 10 4.15 Phenacodus brachypternus ..... 1 .12 1 .41 Order Perissodactyla ............. 396 46.15 62 25.73 Family Hyracotheriidae ......... 376 43.83 51 21.16 I-Iyracotherium, large sp ........ 53 6.18 8 3.32 I-Iyracozherium, small sp. ...... 323 37.65 43 17.84 Family Helaletidae ........... 20 2.33 11 4.56 Heptodon calciculus. ......... 16 1.86 9 3.73 helaletid, gen. et sp. nov. ...... 4 .47 2 .83 Order Artiodactyla ............... 54 6.29 24 9.96 Family Dichobunidae .......... 54 6.29 24 9.96 Diacodexis metsiacus ........ 48 5.59 21 8.71 "Bunopharus", small sp. ....... 6 .70 3 1.24 stratigraphic position and then using the stratigraphy so derived to plot tooth size and infer evolutionary patterns is inherently circular. Nonetheless, Gingerich’s work was instrumental in documenting the importance of tight strati- graphic control in empirical evolutionary studies using fossil mammals. It was also the first study to demonstrate the potential of the Willwood fauna in that regard. What was really needed was a major new measured sec- tion of the Willwood Formation, measured with the specific purpose of correlating as many fossil localities as accurately as possible. Such sections were published for Willwood localities in the Sand Creek-No Water Creek area and the central Bighorn Basin only three and four years later, respectively. 26 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING Table 9. Provisional fauna] list and fossil mammal composition, US. Geological Survey locality D1177 (includes localities D1315, D1316, Y253, UMRBl, and UMRBZ), 481-m level of the Willwood Formation, southern Bighorn Basin, Wyoming. [MNL minimum number of individuals. Includes data through 1983] Percent of MNl as Identified total percent Fauna elements elements MNI of fauna Class Mammalia .................. 459 100.24 136 100.75 Magnorder Emotheria ............. 3 .66 2 1.47 Grandorder letopsia .............. 3 .66 2 1.47 Family Leptictidae ........... 3 .66 2 1.47 Palaeictops bicuspis ........ 3 .66 2 1.47 Magnorder Preptotheria ............ 456 99.35 134 98.53 Order Cimolesta ............... 2 .44 2 1.47 Suborder Pantolesta ............ 1 .22 1 .74 Family Pantolestidae ......... 1 .22 1 .74 Palaeosinopa veterrima ...... 1 .22 1 .74 Suborder Palaeoryctoidea ........ 1 .22 1 .74 Family Didelphodontidae ....... 1 .22 1 .74 Didelahodus absarokae ....... 1 .22 1 .74 Order Creodonta ............... 5 1.09 3 2.22 Family Hyaenodontidae ....... 4 .87 2 1.47 Tritemnodon sp., of. T. hians . . . 2 .44 1 .74 cf. Prototomus sp. ......... 2 .44 1 .74 Family Oxyaenidae .......... 1 .22 1 .74 Oxyaena sp. ............. 1 .22 1 .74 Order Arctocyonia .............. 4 .87 2 1.47 Family Arctocyonidae ........ 4 .87 2 1.47 Chriacus, sp. nov. ......... 1 .22 1 .74 Anacodon ursidens ......... 3 .66 1 .74 Order Camivora ............... 26 5.68 12 8.82 Family Miacidae ............ 26 5.68 12 8.82 Didymictis sp. ............ 8 1.75 2 1.47 Viverravus aculus .......... 3 .66 2 1.47 Vulpavus australis .......... 1 .22 1 .74 Vulpavus canavus .......... 6 1.31 2 1.47 Miacis exiguus ............ 3 .66 2 1.47 Vassacyon sp., cf. V. promicrodon 1 .22 1 .74 Uintacyon sp. ............ 4 .87 2 1.47 Order Plesiadapiformes ........... 17 17.72 6 4.42 Family Microsyopidae ........ 15 3.28 5 3.68 Microsyops latidens ......... 15 3.28 5 3.68 Family Paromomyidae ........ 2 .44 1 .74 Phenacolemur, sp. nov. ...... 2 .44 1 .74 Order Primates ................ 31 6.77 16 11.77 lnfraorder Omomyiforrnes ....... 2 .44 1 .74 Family Omomyidae .......... 2 .44 1 .74 Absarokius metoecus ........ 2 .44 1 .74 lnfraorder Adapiformes ......... 29 6.33 15 11.03 Family Notharctidae ......... 29 6.33 15 11.03 Cantius abdilus ........... 29 6.33 15 11.03 STRATIGRAPHIC SECTIONS 27 Table 9. Provisional faunal list and fossil mammal composition. US. Geological Survey locality D1177 (includes localities D1315, D1316. Y253, UMRB], and UMRBZ), 481—m level of the Willwood Formation. southern Bighorn Basin, Wyoming—Continued. Percent of MNI as Identified total percent Fauna elements elements MNI of fauna Order Rodentia ................ 9 1.97 6 4.41 Family lschyromyidae ........ 9 1.97 6 4.41 ischyromyid, large sp. ....... 1 .22 1 .74 ischyromyid, medium sp. ..... 2 .44 2 1.47 ischyromyid, small sp. ....... 6 1.31 3 2.21 Order Tillodontia .............. 9 1.97 4 2.94 Family Esthonychidae ........ 9 1.97 4 2.94 Esthonyx sp. ............. 9 1.97 4 2.94 Order Pantodonta .............. 2 .44 2 1.47 Family Coryphodontidae ....... 2 .44 2 1.47 Coryphodon sp. ........... 2 .44 2 1.47 Order Condylarthra ............. 121 26.42 41 30.15 Family Hyopsodontidae ....... 95 20.74 35 25.73 Hyapsodus sp., cf. H. miticulus 85 18.56 31 22.79 Hyopsoa'us sp., cf. H. minor 10 2.18 4 2.94 Family Phenacodontidae ....... 26 5.68 6 4.42 Phenacodus vortmani ........ 24 5.24 5 3.68 Phenacodus brachypternus ..... 2 .44 1 .74 Order Perissodactyla ............ 200 43.67 32 23.53 Family Hyracotheriidae ........ 199 43.45 31 22.80 Hyracolherium, large sp. ..... 27 5.90 7 5.15 Hyracolherium, small sp. ..... 161 35.15 20 14.71 Xenicohippus grangeri ....... 11 2.40 4 2.94 Family Helaletidae .......... 1 .22 1 .74 helaletid, gen. et sp. nov. ..... 1 .22 1 .74 Order Artiodactyla ............. 30 6.55 9 6.62 Family Dichobunidae ......... 30 6.55 9 6.62 Diacodexis melsiacus ........ 26 5.68 7 5.15 "Bunophorus", small sp. ...... 4 .87 2 1.47 SAND CREEK-NO WATER CREEK (BOWN) SECTIONS (1974—75) In 1973 the senior author, then with the University of Wyoming Geological Museum (UW), began collecting operations in the extensive Willwood badlands southeast of Worland, Wyo., largely from exposures along the drainages of Sand Creek, Slick Creek, and the East Fork of No Water Creek (pl. 2). That region had earlier been prospected by Yale Peabody Museum field parties in 1964 and 1972; how- ever, no very productive sites had been found, except for Banjo quarry (Y370A, pl. 2) in 1972. The University of Wyoming expeditions established 76 fossil vertebrate local- ities. These incorporated the then richest known and best documented basal Willwood sites in the Bighorn Basin (including 35 sites below the stratigraphically lowest corre- lated YPM locality at the 50-m level). Stratigraphic sections relating 60 of the UW sites were published by Bown (1979), and the occurrence of most Willwood fossil vertebrates as lag accumulations in paleosols was first recognized (Bown, 1975, 1977, 1979). The University of Wyoming expeditions also initiated new collecting operations between Gooseberry Creek and the Greybull River (pl. 1), beginning in 1973. UW sites W124—W127 at the 180-m level of the Willwood Formation west of the Bighorn River were related to the 60 correlated sites in the Sand Creek-No Water Creek area east of the Big- horn River by well legs (Wyoming Geological Association, 1968; Bown, 1979). This correlation of clusters of Willwood localities on either side of the Bighorn River valley provided an accurate datum for the base of the Fifteenmile Creek sec- tions measured later and set the stage for the eventual integration of the Sand Creek-No Water Creek sections with the Schankler-Wing section, discussed below. 28 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Table 10. Provisional faunal list and fossil mammal composition. US. Geological Survey locality D1198 (includes localities D1160, D1160N, D1244, D1314, Y45, and Y4SS). 470-m level of the Willwood Formation, southern Bighom basin, Wyoming. [MNL minimum number of individuals. Includes data through 1983] Percent of MN I as Identified total percent Fauna elements elements MNI of fauna Class Mammalia ................. 2,972 99.97 797 100.05 Magnorder Emotheria ............. 9 .30 4 .51 Grandorder Ictopsia .............. 9 .30 4 4.51 Family Leptictidae ........... 9 .30 4 .51 Palaeictaps bicuspis ........ 9 .30 4 .51 Magnorder Prcptotheria ............. 2,963 99.70 793 99.49 Order Cimolesta ............... 18 .60 7 .89 Suborder Apatotheria ........... 2 .06 2 .26 Family Apatemyidae ......... 2 .06 2 .26 Apatemys bellulus .......... 1 .03 1 .13 Apatemys rodens ........... 1 .03 1 .13 Suborder Palaeoryctoidea ........ 16 .54 5 .63 Family Didelphodontidae ....... 16 .54 5 .63 Didelphodus sp. ........... 16 .54 5 .63 Order Creodonta ............... 37 1.24 17 2.13 Family Hyaenodontidae ....... 23 .77 11 1.39 Trilemnodon sp., cf. T. hians . . . 11 .37 7 .88 Prolotomus vulpecula ........ 6 .20 3 .38 Prototomus sp ............. 6 .20 1 .13 Family Limnocyonidae ........ 5 .17 2 .25 Prolimnocyon sp. .......... 5 .17 2 .25 Family Oxyaenidae .......... 9 .30 4 .50 Oxyaena sp., cf. 0.forcipala . . . 9 .30 4 .50 Order Arctocyonia .............. 3 .10 3 .38 Family Arctocyonidae ........ 3 .10 3 .38 Ilnyptacodon sp., cf. T. loisi . . . 1 .03 1 .13 Chriacus, sp. nov. ......... 1 .03 1 .13 Anacoa'on ursidens ......... 1 .03 1 .13 Order Carnivora ............... 107 3.60 38 4.77 Family Miacidae ............ 107 3.68 38 4.77 Dia'ymictis sp. ............ 42 1.41 10 1.25 Viverravus sp., cf. V. acums . . . 30 1.01 12 1.51 Viverravus lulosus .......... 3 .10 2 .25 Vulpavus australis .......... 15 .50 5 .63 Vulpavus canavus .......... 3 .10 2 .25 Miacis exiguus ............ 5 .17 2 .25 Vassacyon promicroa'on ...... 5 .17 2 .25 Uinlacyon sp., cf. U. asodes . . . 2 .07 1 .13 cf. Oodectes sp. ........... 2 .07 2 .25 Order Erinaceomorpha ........... 1 .03 1 .13 Family Dormaaliidae ......... 1 .03 1 .13 Macrocranion m'tens ........ 1 .03 1 .13 Order Plesiadapiformes ........... 86 2.90 28 3.52 Family Microsyopidae ........ 73 2.46 25 3.14 Microsyops lalidens ......... 73 2.46 25 3.14 Family Paromomyidae ........ 13 .44 3 .38 Phenacolemur, sp. nov. ...... 13 .44 3 .38 STRATIGRAPHIC SECTIONS 29 Table 10. Provisional faunal list and fossil mammal composition. US. Geological Survey locality D1198 (includes localities D1160. D1160N, D1244, D1314, Y45. and Y458). 470-m level of the Willwood Formation, southern Bighorn basin. Wyoming—Continued. Percent of MNl as Identified total percent Fauna elements elements MNI of fauna Order Primates ................ 182 6.13 55 6.90 Infraorder Omomyiformes ....... 12 .41 7 .88 Family Omomyidae .......... 12 .41 7 .88 Anemorhysis pattersoni ....... 2 .07 1 .13 Absarokius metoecus ........ 10 .34 6 .75 lnfraorder Adapiformes ......... 170 5.72 48 6.02 Family Notharctidae ......... 170 5 .72 48 6.02 Cantius abditus ........... 170 5.72 48 6.02 Order Palaeanodonta ............ 2 .07 2 .25 Family Metacheiromyidae ...... 2 .07 2 .25 Palaeanodon ignavus ........ 2 .07 2 .25 Order Rodentia ................ 65 2.19 24 3.01 Family lschyromyidae ........ 65 2.19 24 3.01 ischyromyid, large sp. ....... 16 .54 4 .50 ischyromyid, medium sp. ..... 43 1.45 17 2.13 ischyromyid, very small sp. . . . . 6 .20 3 .38 Order Tillodontia .............. 36 1.21 6 .75 Family Esthonychidae ........ 36 1.21 6 .75 Esthonyx sp. ............. 36 1.21 6 .75 Order Taeniodonta .............. 1 .03 1 .13 Family Stylinodontidae ........ 1 .03 1 .13 Ectoganus sp., cf. E. gliriformis . 1 .03 1 .13 Order Pantodonta .............. 19 .64 5 .26 Family Coryphodontidae ...... 19 .64 5 .26 Coryphodon, large sp ........ 16 .54 3 .38 Caryphodon, small sp. ...... 3 .10 2 .25 Order Condylarthra ............. 1,295 43.57 402 50.44 Family Hyopsodontidae ....... 1,253 42.16 392 49.18 Hyopsodus sp., cf. H. miticulus . 741 24.93 236 29.61 I-Iyopsodus sp., cf. H. minor . . . 512 17.23 156 19.57 Family Phenacodontidae ....... 42 1.41 10 1.25 Phenacodus vortmani ........ 42 1.41 10 1.25 Order Perissodactyla ............ 961 32.34 140 17.57 Family Hyracotheriidae ........ 862 29.00 113 14.18 Hyracotherium, very large sp. . . 2 .07 1 .13 Hyracotherium, large sp. ..... 200 6.73 26 3.26 Hyracotherium, small sp. ..... 651 21.90 82 10.29 Xenicohippus grangeri ....... 9 .30 4 .50 Family Isectolophidae ......... 1 .30 1 .13 cf. Homogalax sp. ......... 1 .30 1 .13 Family Helaletidae .......... 38 1.28 8 1.00 Heptodon calciculus ........ 38 1.28 8 1.00 Order Artiodactyla ............. 153 .15 64 8.03 Family Dichobunidae ......... 153 .15 64 8.03 Diacodexis metsiacus ........ 124 4.17 55 6.90 Diacodexis robustus ......... 4 .13 2 .25 "Bunophorus", large sp. ...... 22 .74 7 .88 30 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING Table 11. Provisional faunal list and fossil mammal composition. U.S. Geological Survey locality D1204 (includes localities D1203, D1208, and Y338), 438—444-m levels of the Willwood Formation. southcm Bighorn Basin, Wyoming. [MN], minimum number of individuals Includes data through 1987] Percent of MNI as Identified total percent Fauna elements elements MNI of fauna Class Mammalia .................... 984 99.72 308 99.95 Magnorder Emotheria ............... 8 .81 5 1.62 Grandorder Ictopsia ................ 7 .71 4 1.30 Family Leptictidae ............. 7 .71 4 1.30 Prodiacodon tauricinerei ........ 7 .71 4 1.30 Grandorder Anagalida .............. 1 .71 1 .32 Order cf. Macroscelidea ............ 1 .10 l .32 Haplomylus sp. ............. 1 .10 1 .32 Magnorder Preptotheria .............. 976 99.19 303 98.38 Order Cimolesta ................. 1 .10 1 .32 Suborder Apatotheria ............. 1 .10 1 .32 Family Apatemyidae ........... 1 .10 1 .32 Apatemys rodens ............. l .10 1 .32 Order Creodonta ................. 16 2.74 8 2.60 Family Hyaenodontidae ......... 20 2.03 9 2.92 Tritemnodon sp. ............. 4 .41 2 .65 Tritemnodon, sp. nov. ......... 2 .20 2 .65 Prototomus sp ............... 14 1.42 5 1.62 Family Limnocyonidae .......... 3 .30 2 .65 Prolimnocyon atavus .......... 3 .30 2 .65 Family Oxyaenidae ............ 4 .41 2 .65 Oxyaena sp. ............... 4 .41 2 .65 Order Camivora ................. 53 5.39 20 6.49 Family Miacidae .............. 53 5.39 20 6.49 Didymictis sp. .............. 11 1.11 2 .65 Viverravus acutus ............ 9 .91 6 1.95 Viverravus politus ............ 1 .10 1 .32 Vulpavus australis ............ 20 2.03 5 1.62 Vulpavus canavus ............ 2 .20 1 .32 Miacis exiguus .............. 8 .81 3 .97 cf. Oodectes sp. ............. 1 .10 1 .32 cf. Uintacyon sp. ............ 1 .10 1 .32 Order Erinaceomorpha ............. 1 .10 1 .32 Family Geolabididae ........... 1 .10 1 .32 Centetodon neashami .......... 1 .10 1 .32 Order Plesiadapiformes ............. 7 .71 4 1.30 Family Microsyopidae .......... 3 .30 3 .97 Microsyops angustidens ........ 3 .30 3 .97 Family Paromomyidae .......... 4 .41 1 .32 Phenacolemur sp. ............ 4 .41 l .32 STRATIGRAPHIC SECTIONS 31 Table 11. Provisional fauna] list and fossil mammal composition. U.S. Geological Survey locality D1204 (includes localities D1203, D1208, and Y338), 438—444-m levels of the Willwood Formation. southern Bighorn Basin, Wyoming-Continued. Percent of MNI as Identified total percent Fauna elements elements MNI of fauna Order Primates .................. 108 10.98 38 12.34 lnfraorder Omomyiformes ......... l .10 1 .32 Family Omomyidae ............ 1 .10 1 .32 Steinius vesperlinus ........... 1 .10 1 .32 lnfraorder Adapiformes ........... 107 10.87 37 12.01 Family Notharctidae ........... 107 10.87 37 12.01 Cantius trigonodus ........... 104 10.57 35 11.36 Cantius sp., cf. C. abditus ...... 3 .30 2 .65 Order Palaeanodonta ............... 3 .30 2 .65 Family Metacheiromyidae ........ 3 .30 2 .65 Palaeanodon sp., cf. P. ignavus . 3 .30 2 .65 Order Rodentia .................. 5 .51 3 .97 Family Ischyromyidae .......... 5 .51 3 .97 ischyromyid, large sp. ......... 2 .20 1 .32 ischyromyid, medium sp. ....... 3 .30 2 .65 Order Tillodontia ................ 5 .51 2 .65 Family Esthonychidae .......... 5 .51 2 .65 Esthonyx sp. ............... 5 .51 2 .65 Order Taeniodonta ................ 2 .20 2 .65 Family Stylinodontidae .......... 2 .20 2 .65 stylinodontid sp. ............. 2 .20 2 .65 Order Pantodonta ................ 13 1.32 4 1.30 Family Coryphodontidae ......... 13 1.32 4 1.30 Coryphadon sp. ............. 13 1.32 4 1.30 Order Condylarthra ............... 362 36.69 127 41.24 Family Hyopsodontidae ......... 361 36.49 126 40.92 Hyopsodus sp., cf. H. latidens . . . . 361 36.49 126 40.92 Family Pentaeodontidae ......... l .10 1 .32 Apheliscus, sp. nov. .......... 1 .10 1 .32 Order Perissodactyla .............. 289 29.37 56 18.18 Family Hyracotheriidae .......... 266 27.03 43 13.96 Hyracotherium, large sp. ....... 50 5 .08 7 2.27 Hyracotherium, small sp. ....... 216 21.95 36 11.69 Family Helaletidae ............ 23 2.34 13 4.22 helaletid, gen. et sp. nov. ....... 23 2.34 13 4.22 Order Artiodactyla ............... 97 9.86 29 9.42 Family Dichobunidae ........... 97 9.86 29 9.42 Diacodexis metsiacus .......... 73 7.42 22 7.14 Diacodexis robustus ........... 24 2.44 7 2.27 32 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN. WYOMING Table 12. Provisional faunal list and fossil mammal composition. U.S. Geological Survey locality D1256 (includes localities D1463, D1583, Y192, Y193, and Y315), 546-m level of the Willwood Formation, southern Bighorn Basin. Wyoming. [MNL minimum number of individuals. Includes data through 1984] Percent of MNI as Identified total percent Fauna elements elements MNI of fauna Class Mammalia ................... 3,216 99.99 788 100.02 Magnorder Emotheria .............. 8 .25 4 .51 Grandorder Ictopsia ............... 8 .25 4 .51 Family Leptictidae ............ 8 .25 4 .51 Palaeictops multicuspis ........ 8 .25 4 .51 Magnorder Preptotheria ............. 3,208 99.75 784 99.49 Order Cimolesta ................ 7 .22 4 .51 Suborder Apatotheria ............ 2 .06 2 .25 Family Apatemyidae ........... 2 .06 2 .25 Apatemys sp., cf. A. bellulus . . . . 2 .06 2 .25 Suborder Palaeoryctoidea ......... 5 .16 2 .25 Family Didelphodontidae ........ 5 .16 2 .25 Didelphodus sp. ............ 5 .16 2 .25 Order Creodonta ................ 30 .93 12 1.52 Family Hyaenodontidae ........ 17 .53 8 1.01 cf. Tritemnodon sp. .......... 11 .34 5 .63 Prototomus sp .............. 6 .19 3 .38 Family Limnocyonidae ......... 2 .06 1 .13 Prolimnocyon sp. ........... 2 .06 1 .13 Family Oxyaenidae ........... 11 .34 3 .38 Oxyaena sp. .............. 11 .34 3 .38 Order Mesonychia ............... 3 .09 2 .25 Family Mesonychidae .......... 3 .09 2 .25 cf. Dissacus sp. ............ 1 .03 1 .13 Hapalodectes leptognathus ...... 2 .06 1 .13 Order Arctocyonia ............... l .03 1 .13 Family Arctocyonidae ......... 1 .03 1 .13 Chriacus sp. .............. 1 .03 1 .13 Order Camivora ................ 83 2.58 26 3.30 Family Miacidae ............. 83 2.58 26 3.30 Didymictis lysilensis .......... 50 1.55 10 1.27 Viverravus acums ........... 6 .19 6 .76 Vulpavus australis ........... 3 .09 1 .13 Vulpavus canavus ........... 18 .56 6 .76 Miacis sp ................. 2 .06 1 .13 Uintacyon sp., of. U. asades . . . . 4 .12 2 .25 miacine, gen. et sp. nov. ...... 1 .03 l .13 Order Plesiadapiformes ............ 100 3.11 36 4.56 Family Microsyopidae ......... 91 2.83 34 4.31 Microsyops latidens .......... 91 2.83 34 4.31 Family Paromomyidae ......... 9 .28 2 .25 Phenacolemur, sp. nov. ....... 9 .28 2 .25 STRATIGRAPHIC SECTIONS 33 Table 12. Provisional faunal list and fossil mammal composition. US. Geological Survey locality D1256 (includes localities D1463, D1583, Y192. Y193, and Y315). 546-m level of the Willwood Formation. southern Bighorn Basin. Wyoming—Continued. Percent of MNI as Identified total percent Fauna elements elements MNl of fauna Order Primates ................. 205 6.38 63 1.54 lnfraorder Omomyiformes ........ 16 .50 8 1.02 Family Omomyidae ........... 16 .50 8 1.02 Anemorhysis wortmani ........ 1 .03 1 .13 Absarokius abbotti .......... 15 .47 7 .89 Infraorder Adapiformes .......... 189 5.88 55 6.98 Family Notharctidae .......... 189 5.88 55 6.98 Order Palaeanodonta ............. 1 .03 1 .13 Family Metacheiromyidae ....... 1 .03 1 .13 Palaeanodon sp ............. 1 .03 1 .13 Order Rodentia ................. 7 2.21 20 2.54 Family Ischyromyidae ......... 71 2.21 20 2.54 ischyromyid, large sp. ........ 7 .22 2 .25 ischyromyid, medium sp. ...... 41 1.27 8 1.02 ischyromyid, small sp. ........ 18 .56 8 1.02 ischyromyid, very small sp. ..... 4 .12 1 .13 ischyromyid, minute sp. ....... 1 .03 1 .13 Order Tillodontia ............... 41 1.27 7 .89 Family Esthonychidae ......... 41 1.27 7 .89 Esthonyx sp. .............. 41 1.27 7 .89 Order Pantodonta ............... 13 .40 3 .38 Family Coryphodontidae ........ 13 .48 3 .38 Coryphodon, large sp. ........ 12 .37 2 .25 Coryphodon, very small sp ...... 1 .03 1 .13 Order Condylarthra .............. 1,147 35.67 350 44.42 Family Hyopsodontidae ........ 1,132 35.20 342 43.40 "lb/opsodus" powellianus ...... 495 15.39 134 17.01 Hyapsodus sp., cf. H. lysitensis . . 630 19.59 202 25.63 Hyopsodus, sp. nov. ......... 7 .22 6 .76 Family Phenacodontidae ........ 15 .46 8 1.02 Phenacodus sp., cf. P. vortmam' . . 12 .37 6 .76 Phenacodus sp., of. P. primaevus . 1 .03 1 .13 Phenacodus brachypternus ...... 2 .06 1 .13 Order Perissodactyla ............. 1,302 40.49 192 24.37 Family Hyracotheriidae ......... 1,143 35.54 146 18.53 Hyracotherium, large sp. ...... 177 5.50 30 3.81 Hyracotherium, small sp. ...... 966 30.04 116 14.72 Family Helaletidae ........... 159 4.94 46 5.84 Heptodon sp. .............. 59 1.83 17 2.16 helaletid, gen. et sp. nov. ...... 100 3.11 29 3.68 Order Artiodactyla .............. 203 6.31 66 8.38 Family Dichobunidae .......... 203 6.31 66 8.38 Diacodexis sp., of. D. metsiacus . . 173 5.38 57 7.23 "Burtophorus" sp. ........... 27 .84 8 1.02 Wasatch ia sp. ............. 3 .09 1 . 13 34 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING Table 13. Provisional faunal list and fossil mammal composition. US. Geological Survey locality D1326, 425-m level of the Willwood Formation, southern Bighom Basin, Wyoming. [MN], minimum number of individuals. Includes data through 1989] Percent of MN I as Identified total percent Fauna elements elements MNI of fauna Class Mammalia .................. 662 100.02 194 99.99 Magnorder Preptotheria ............ 662 100.02 194 99.99 Order Cimolesta ................ 3 .45 3 1.55 Suborder Pantolesta ............. 2 .30 2 1.03 Family Pantolestidae .......... 2 .30 2 1.03 Palaeosinopa veterrima ....... 2 .30 2 1.03 Suborder Palaeoryctoidea ......... 1 .15 1 .52 Family Didelphodontidae ........ 1 .15 1 .52 Dideéuhodus absarokae ........ 1 .15 1 .52 Order Creodonta ................ 6 .91 2 1.03 Family Hyaenodontidae ......... 6 .91 2 1.03 Tritemnodon sp. ............ 4 .60 1 .52 Prototomus mordax .......... 2 .30 1 .52 Order Arctocyonia ............... 2 .30 2 1.03 Family Arctocyonidae ......... 2 .30 2 1.03 Chriacus, sp. nov. .......... 1 .15 1 .52 Anacodon ursidens .......... 1 .15 l .52 Order Camivora ................ 18 2.72 10 5.15 Family Miacidae ............. 18 2.72 10 5.15 Didymictis sp., cf. D. protenus . . 3 .45 1 .52 Viverravus sp. ............. 7 1.06 3 1.55 Vulpavus sp. .............. 5 .76 3 1.55 Miacis sp., cf. M. exiguus ...... 2 .30 2 1.03 cf. Uintacyan sp. ........... 1 .15 1 .52 Order Plesiadapiformes ............ 32 4.83 10 5.15 Family Microsyopidae ......... 32 4.83 10 5.15 Microsyops latidens .......... 32 4.83 10 5 . 15 Order Primates ................. 54 8.15 23 11.85 Infraorder Omomyiformes ........ 3 .45 2 1.03 Family Omomyidae ........... 3 .45 2 1.03 Absarokius metoecus ......... 3 .45 2 1.03 Infraorder Adapiformes .......... 51 7.70 21 10.82 Family Notharetidae .......... 51 7.70 21 10.82 Order Rodentia ................. 15 2.27 7 3.61 Family Ischyromyidae ......... 15 2.27 7 3.61 ischyromyid, large sp. ........ 4 .60 2 1.03 ischyromyid, medium sp. ...... 10 1.51 4 2.06 ischyromyid, small sp. ........ 1 .15 1 .52 Order Tillodontia ............... 24 3.63 9 4.64 Family Esthonychidae ......... 24 3.63 9 4.64 Esthonyx sp., cf. E. bisulcatus . . . 24 3.63 9 4.64 Order Pantodonta ............... 7 1.06 2 1.03 Family Coryphodontidae ........ 7 1.06 2 1.03 Coryphodon sp. ............ 7 1.06 2 1.03 STRATIGRAPHIC SECTIONS 35 Table 13. Provisional faunal list and fossil mammal composition, US. Geological Survey locality D1326. 425—m level of the Willwood Formation, southern Bighorn Basin, Wyoming—~Continued. Percent of MNI as Identified total percent Fauna elements elements MNI of fauna Order Condylarthra .............. 206 31.12 3 32.47 Family Hyopsodontidae ......... 185 27.95 56 28.87 I-Iyopsodus sp., cf. H. miticulus 111 16.77 29 14.95 Hyapsodus sp., cf. H. minor . . . . 74 11.18 22 13.92 Family Phenacodontidae ........ 21 3.17 7 3.61 Phenacadus vortmani ......... 21 3.17 7 3.61 Order Perissodactyla ............. 252 38.07 5 25.77 Family Hyracotheriidae ......... 241 36.41 47 24.23 Hyracotherium, large sp ........ 1 .15 1 .52 Hyracotherium, small sp. ...... 232 35.05 41 21.13 Xenicohippus grangeri ........ 8 1.21 5 2.58 Family Helaletidae ........... 11 1.66 3 1.55 helaletid, gen. et sp. nov. ...... 11 1.66 3 1.55 Order Artiodactyla ............... 43 6.50 13 6.70 Family Dichobunidae .......... 43 6.50 13 6.70 Diacodexis metsiacus ......... 37 5.59 11 5.67 Diacodexis robustus .......... 1 .15 1 .52 "Bunophorus", large sp. ....... 5 .76 1 .52 SCHANKLER-WING SECTION (1976—78) For his dissertation work at Yale University, David Schankler investigated the mammalian biostratigraphy of the central Bighorn Basin Willwood Formation, using the then largest fossil samples from the formation (at the Yale Peabody Museum) and the best controlled locality data then available (the 477 YPM localities). Schankler recognized early in his studies that measuring a new Willwood section was necessary, both to resolve conflicts between the Meyer- Radinsky and Neasham-Vondra sections and to correlate substantially more of the YPM sites to obtain denser biostratigraphic control. Assisted by S.L. Wing, Schankler began in 1976 and completed his new section of the Willwood Formation in 1978, having related 243 YPM sites to a 773-m Willwood section. Schankler’s (1980) section and locality correlations permitted him to produce the first section-controlled vertebrate biostratigraphy of the Willwood Formation and perhaps the most detailed strati- graphic documentation of the ranges of fossil vertebrate taxa ever published. By virtue of both the number of localities correlated and the admirable constraint of the author, Schankler’s Will- wood biostratigraphy remains quite useful despite knowl- edge that most groups of Willwood mammals still require considerable systematic revision. Schankler adeptly side- stepped the archaic, largely unsubstantiated, and putatively biostrati graphic terminology that had been retained for Will- wood rocks and faunas by Wood and others (1941) by refusing to endorse Granger’s (1914) traditional Willwood Formation subdivisions (Sand Coulee and Gray Bull beds), or the borrowed Wind River Formation rock and faunal sub- divisions (Lysite and Lost Cabin Members or Lysitean and Lostcabinian age). Using approved biostratigraphic proce- dure and nomenclature, Schankler (1980) instead applied new names to three biostrati graphic zones: The Haplomylus- Ectocion Range Zone (lower and upper); the Bunophorus Interval Zone; and the Heptodon Range Zone (lower, mid- dle, and upper). These zones were properly based on the stratigraphic occurrences of taxa characterizing them and were separated by Schankler by three so-called horizons apparently recording marked faunal change: Biohorizon A, Biohorizon B, and Biohorizon C. As shown by Bown and others (1991) and Bown and Kraus (1993), Biohorizons B and C as viewed by Schankler almost certainly document the same episode of faunal turnover. The Schankler-Wing section was a marked improve- ment over earlier sections in terms of detail and density of fossil localities and contributed a novel and still useful bio- stratigraphic zonation as well as preliminary faunal analysis based on this new biostratigraphy. Nonetheless, this section is not without problems, some of which will affect its future utility. Paramount among these is that a map record- ing the lines of his sections has not been published. More- over, “***The localities were grouped into ten-meter intervals, the maximum resolution thought possible” (Schankler, 1980, p. 102). The latter (10-m-interval) manipulation is both good and bad; by honest implication 36 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 14. Provisional faunal list and fossil mammal composition. US. Geological Survey locality D1454 (includes locality D1460 but not D1460Q), 409-m level of the Willwood Formation. southern Bighorn Basin. Wyoming. [MN‘L minimum number of individuals. Includes data through 1983] Percent of MNI as Identified total percent Fauna elements elements MNI of fauna Class Mammalia .................... 831 100.01 251 100.02 Magnorder Emotheria ............... 2 .24 2 .80 Grandorder lctopsia ................ 2 .24 2 .80 Family Leptictidae ............. 2 .24 2 .80 Prodiacodon tauricinerei ........ 2 .24 2 .80 Magnorder Preptotheria .............. 829 99.76 249 99.20 Order Cimolesta ................. 8 .96 6 2.39 Suborder Apatotheria ............. 6 .72 4 1.59 Family Apatemyidae ........... 6 .72 4 1.59 Apatemys sp. ............... 6 .72 4 1.59 Suborder Palaeoryctoidea .......... 2 .24 2 .80 Family Didelphodontidae ......... 2 .24 2 .80 Didelphodus absarokae ......... 2 .24 2 .80 Order Creodonta ................. 15 1.81 9 3.59 Family Hyaenodontidae ......... 3 .36 3 1.20 Tritemnodon sp. ............. 1 .12 1 .40 Prototomus sp ............... 2 .24 2 .80 Family Limnocyonidae .......... 7 .84 4 1.59 Prolimnocyon sp. ............ 7 .84 4 ' 1.59 Family Oxyaenidae ............ 5 .60 2 .80 Oxyaena sp. ............... 5 .60 2 .80 Order Arctocyonia ................ 2 .24 2 .80 Family Arctocyonidae .......... 2 .24 2 .80 Thryptacodon sp., cf. T. antiquus 1 .12 1 1.40 Chriacus sp. ............... 1 .12 1 .40 Order Camivora ................. 47 5.66 21 8.37 Family Miacidae .............. 47 5.66 21 8.37 Didymictis protenus ........... 19 2.29 6 2.39 Viverravus acutus ............ 6 .72 3 1.20 Vulpavus australis ............ 15 1.81 8 3.19 Vulpavus canavus ............ 1 .12 1 .40 Miacis exiguus .............. 3 .36 1 .40 Vassacyon promicrodon ........ 1 .12 1 .40 Uintacyon rudis ............. 2 .24 1 .40 Order Plesiadapiformes ............. 25 3.01 10 3.99 Family Microsyopidae .......... 21 2.53 8 3.19 Microsyops sp. cf. M. angustidens . . 20 2.41 7 2.80 Microsyops minuta ........... 1 .12 1 .40 Family Paromomyidae .......... 4 .48 2 .80 Phenacolemur, sp. nov. ........ 4 .48 2 .80 Order Primates .................. 84 10.11 32 12.75 Infraorder Adapiformes ........... 84 10.11 32 12.75 Family Notharctidae ........... 84 10.11 32 12.75 Cantius abditus ............. 82 9.87 31 12.35 cf. Copelemur sp. ............ 2 .24 ‘ 1 .40 STRATIGRAPHIC SECTIONS Table 14. 37 Provisional faunal list and fossil mammal composition. U.S. Geological Survey locality D1454 (includes locality D1460 but not D1460Q), 409-m level of the Willwood Formation. southern Bighorn Basin. Wyoming—Continued. Percent of MNI as Identified total percent Fauna elements elements MNI of fauna Order Palaeanodonta .............. 3 .36 2 .80 Family Metacheiromyidae ........ 3 .36 2 .80 Palaeanodon ignavus .......... 3 .36 2 .80 Order Rodentia .................. 32 3.85 7 2.79 Family Ischyromyidae .......... 32 3.85 7 2.79 ischyromyid, large sp. ......... 10 1.20 1 .40 ischyromyid, medium sp. ....... 16 1.93 3 1.20 ischyromyid, small sp. ......... 3 .36 1 .40 ischyromyid, minute sp. ........ 3 .36 2 .80 Order Tillodontia ................ 33 3.97 9 3.59 Family Esthonychidae .......... 33 3.97 9 3.59 Esthonyx sp., cf. E. bisulcatus . . . . 33 3.97 9 3.59 Order Pantodonta ................ 4 .48 1 .40 Family Coryphodontidae ......... 4 .48 l .40 Coryphodon sp. ............. 4 .48 l .40 Order Condylarthra ............... 224 26.96 71 28.29 Family Hyopsodontidae ......... 214 25.75 67 26.69 Hyopsodus sp., cf. H. latidens . . . . 214 25.75 67 26.69 Family Phenacodontidae ......... 10 1.20 4 1.59 Phenacodus primaevus ......... 10 1.20 4 1.59 Order Perissodactyla .............. 218 26.23 38 15.14 Family Hyracotheriidae .......... 212 25.51 36 14.35 Hyracotherium, large sp. ....... 39 4.69 8 3.19 Hyracotherium, small sp. ....... 173 20.82 28 11.16 Family Isectolophidae ........... 6 .72 2 .80 Homogalax sp., cf. H. protapirinus . 6 .72 2 .80 Order Artiodactyla ............... 134 16.13 42 16.73 Family Dichobunidae ........... 134 16.13 42 16.73 Diacodexis sp., cf. D. metsiacus . . . 130 15.64 40 15.94 Diacodexis robustus ........... 2 .24 1 .40 "Bunophorus", large sp. ........ 2 .24 1 .40 that more precise resolution may not be possible (all of the YPM localities are geographic localities, as defined above), the actual measured record was sacrificed. That record was positively a more accurate empirical stratigraphic docu- mentation of localities, whether the precision was on the order of 1 m or 10 m. Lacking publication of the original section, the lines of section, and the record of bed correla- tions, the Schankler-Wing section offers nothing to assist future biostratigraphic correlations of the Willwood Forma- tion other than by use of what exists in Schankler (1980). Inability to cross reference exact beds in the Schankler- Wing section has led to some difficulty in correlating that section with the Fifteenmile Creek section, especially in the region of the Elk Creek Rim, as discussed below. FIFTEENMILE CREEK (BOWN) SECTIONS (1980—92) GENERAL CONSIDERATIONS FORT UNION-WILLWOOD CONTACT Pedofacies relations (Bown and Kraus, 1987) and a variety of paleogeomorphological attributes of Willwood sediment accumulation present a suite of problems for corre- lation of Willwood vertebrate fossil localities that have rarely or never received attention. Some problems that were encountered almost daily in the field were treated in the course of section studies (see below), but others of broader 38 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Table 15. Diversity indices for mammalian faunal assemblages listed in tables 8—14, southern Bighorn Basin, Wyoming. [Rankings of relative diversity are shown in parentheses. Numbers in parentheses are MN], minimum number of individuals] Assemblage Number of Number of Whittaker Shannon-Wiener (meter level) specimens MNl species index index D1162 (481 m) ........ 858 241 39 22.56 (2) 2.87 (1) D1177 (481 m) ........ 459 157 34 22.85 (1) 2.87 (1) D1198 (470 m) ........ 2,972 797 47 19.95 (3) 2.44 (6) D1204 (438-444 m) ..... 984 308 35 16.67 (7) 2.30 (7) D1256 (546 m) ........ 3,216 788 45 19.60 (5) 2.57 (5) D1326 (425 m) ........ 662 194 29 18.13 (6) 2.61 (3) D1454 (409 m) ........ 831 251 36 19.67 (4) 2.60 (4) import cannot yet be resolved. For example, little is known about the nature of the pre-Willwood paleotopography and relative rates of sediment accumulation, and their relation- ship to each other, between the base of the Willwood section in the Antelope Creek drainage (the area of the base of the Meyer—Radinsky, Neasham-Vondra, and Schankler-Wing sections) and the base of the Willwood section in the Sand Creek-No Water Creek area. Differences in either of these parameters would affect relative thicknesses of Willwood sections begun in different places. Development of a time- stratigraphic section of the Willwood Formation for the southern Bighorn Basin (Bown and Kraus, 1993; Kraus and Bown, in press) has partly resolved these problems. Although it has long been known that the Fort Union Formation—Willwood Formation contact is time transgres- sive, correlation of the contact from one area to another is not a simple matter of correlating time-transgressive strata in one direction or another. For example, the stratigraphic con- tact lies well beneath the Clarkforkian-Wasatchian faunal boundary in the Clarks Fork area (in the north; Rose, 1981a), and well above it in the Gould Butte area (in the middle; Wing and Bown, 1985), whereas the formation contact and the faunal boundary appear to be essentially coincident in the Sand Creek-No Water Creek area (in the south; Bown, 1979). The reasons for these complex and varying bound- aries might become known with more knowledge of the causes of the geographically disparate distributions and tem- porally diachronous onsets of Willwood-type soil (paleosol) formation. A particular kind of paleosol development pro- duced varicolored beds, which are, by definition (Van Houten, 1944, 1948; Bown, 1979), typical of the Willwood Formation in contrast to Fort Union rocks. At present (1992), the causes of onset of soil formation producing paleosols typical of the Willwood Formation are simply unknown but are probably indicative of both climatic change and decreased sediment-accumulation rates (Bown and Kraus, 1993; Kraus and Bown, in press). They may also have been related to relative original (early Eocene) paleotopography and drainage or to geographic position with respect to the evolving early Eocene Bighorn Basin axis (hence, resulting in different sediment-accumulation rates in different areas). There is currently no way to determine or judge the relative effects of either factor. Kraus (in press) documented basement lineament con- trol on sedimentation and sedimentary facies development in Willwood rocks in the central and southeast Bighorn Basin in which adjacent lineament-bounded regions contain differ- ent Willwood facies and different suites of paleosols. Because some of the facies differences are differences in paleosol development, movement along basin lineaments and resulting different sediment-accumulation rates might well have been responsible for the geographically and tem- porally disjunct onsets of characteristic Willwood paleosol development around the Bighorn Basin. CUT-A ND-FILL SEQUENCES To the extent now possible, principles of time and rock stratigraphy must also be applied to the correlation of the fossil-mammal localities of the Willwood Formation. Where they are directly and most commonly applicable to Will- wood sections is in the stratigraphic resolution of cut-and-fill sequences, hereafter termed “cuts” (Bown and others, 1983; Kraus and Middleton, 1987). Willwood cuts are of two kinds. Sandstone-floored cuts (f1 g. 10A) formed by excavation and subsequent channel fill- ing during stream relocation (probably avulsion) and by cre- vasse channeling. Mudstone-floored cuts (fig. 103) formed by excavation of generally distal flood-plain areas by erosive streams, followed by rapid fill of the cuts with fine-grained sediment. Some preliminary evidence suggests that whereas the excavation of cuts with sandstone floors is obviously a normal part of the depositional alluvial regime, the excava— tion of cuts with mudstone floors (or at least many of them) was associated with temporary intervals of lowered base lev- els and degradational regimes. Both types of cuts vary in breadth and profundity. Sandstone-floored cuts in the Will- wood Formation range from a few meters wide and 1 m deep to more than 1 km wide and 30 m deep. Mudstone cuts have a similar lower limit in size; however, although they rarely attain more than 10 m in depth, some of them (or zones of STRATIGRAPHIC SECTIONS 39 Figure 10. Depositional and erosional cuts in the Willwood Formation, southern Bighorn Basin, Wyoming. A, Depositional (sandstone- floored) cut; SW 1/4 sec. 15, T. 49 N., R. 95 W. (pl. 1). B, Erosional (mudstone-floored) cut; SE 1/4 sec. 16. T. 48 N., R. 94 W. (pl. 1). Bases of scours emphasized in places with arrows. 40 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BlGI-IORN BASIN. WYOMING such cuts) reach a width of several kilometers (Kraus and Bown, in press). Both sandstone- and mudstone-floored cuts are com- mon in the Willwood Formation, even though they have received little attention in the literature (for example, Bown, 1984). Their occurrence in nearly every measured section directs that their stratigraphic and temporal effects must be resolved to correctly and completely situate fossil vertebrate localities with respect to one another, both in terms of simple meter-level determinations and geologic time. Given current levels of resolution, meter levels are an adequate base from which to construct section-controlled biostratigraphies (for example, Bown, 1979; Schankler, 1980; Rose, 1981a). How- ever, meter levels alone are not sufficient for estimating evo- lutionary rates, because rates are dependent on sediment- accumulation rates and relative time, and relative time requires some control on temporal resolution. Adequate tem- poral resolution is not available from simple meter-level bio- stratigraphies because there are no controls on varying sediment-accumulation rates in different geographic areas and in different parts of the rock column. A preliminary time-stratigraphic reconstruction of Willwood deposition was presented by Bown and Kraus (1993). All units in alluvial sequences might be considered to have unconforrnable or, at the very least, paraconformable contacts because alluvial sediment accumulation is sporadic (see discussion in Kraus and Bown (1986) and references therein). Of interest to biostratigraphers concerned with pre- cise correlations is the magnitude of time represented by deposition of the sediments making up the rocks and the time represented by hiatuses and lacunae separating rock bodies (for example, Wheeler, 1958). Bown (1985), Kraus and Bown (1986), and Bown and Kraus (1987) suggested that most geologic time bound up in the development of alluvial rock sequences was occupied by soil formation and that rel- atively little of the geologic time required to form alluvial sequences was expended during active sedimentation. That is, the prior and traditional view that soils (paleosols in the rock record) are rare and record pauses in a more-or-less continuous process of sediment accumulation is incorrect. Rather, alluvial sediment accumulation is rare, of short dura- tion, and punctuates lengthy intervals of soil development. Kraus and Bown (1986) and Bown and Larriestra (1990) indicated that stages of maturity of paleosols offer means of establishing relative temporal correlations in alluvial rocks. These means also apply to the reconstruction of hiatal and lacunal time (Bown and Larriestra, 1990; Bown and Kraus, 1993; Kraus and Bown, in press). To return to the problem of cuts in the Willwood For- mation, it is clear from figure 10 that simple meter-level relations of sites lying in and adjacent to cuts produce erro- neous stratigraphic correlations and potentially even more serious relative temporal correlations. The relative temporal picture of cuts is complicated even further by the fact that paleosols developed on the fill in most (but not all) of them are dominated by immature forms. The relative temporal resolution of the Willwood fossil vertebrate localities by holostrome reconstruction using paleosols (see Bown and Larriestra, 1990, for method) is well beyond the scope of this report and was published by Bown and Kraus (1993). However, for the Willwood sections discussed here, locali- ties affected by cuts are completely resolved stratigraphi- cally (fig. 11) but incompletely restored temporally (see temporal restoration of Willwood meter-level stratigraphy in Bown and Kraus, 1993). PEDOFACIES SECTION MEASUREMENT The identification of sedimentologic localities in the field based on pedofacies relationships has necessitated development of a consistent procedure for identifying strati- graphic positions of fossil vertebrate localities in paleosols occurring in different parts of local pedofacies. Pedofacies are prismatic rock bodies containing paleosols (fig. 12). The thickest part of the pedofacies rock prism is on the alluvial ridge, which contains numerous superposed immature paleosols. The thinnest part of the pedofacies prism is on the distal flood plain, which generally contains one or two very mature paleosols. Therefore, although there is temporal equivalence between proximal and distal parts of the pedofa- cies prism (the few mature distal paleosols being the time equivalent of the many immature proximal ones), there is no stratigraphic equivalenCe (in terms of meter levels) across the pedofacies because the alluvial ridge sediments are thicker than those of the distal flood plain. Alluvial ridge sediments are dominated by channel- belt, levee, crevasse—channel, and crevasse-splay deposits. Pedologically, Willwood channel-belt and levee deposits are generally characterized by stage 0—2 paleosols and are dom- inated by stage 1 paleosols (fig. 12). Other alluvial-ridge deposits are overwhelmingly dominated by stage 0 paleo- sols. Though they are cut by crevasse channels and inter- tongue with crevasse-splay deposits, fining-upwards sequences of sand and mud are the volumetrically predomi- nant component of Willwood channel-belt and levee depos- its. Because of the sporadic nature of alluvial overbank deposition, each major fining upwards sequence in most Willwood channel-belt and levee deposits has an immature paleosol (generally stage 1) developed on it, and the sandy base of the succeeding fining-upwards sequence marks the base of the parent sediment for the succeeding, younger paleosol. Levee and channel-belt deposits, consisting of several fining-upwards sequences and their paleosols, typically weather into steep ridges. Therefore, it is very difficult to find areas in which faunas can be reliably attributed to spe- cifically one or another of the levee and channel-belt paleo- sols. In areas in which the specific paleosol from which a fossil vertebrate sample came cannot be determined, the meter level of the middle of the sequence is used for STRATIGRAPHIC SECTIONS 41 Time SITE A SITE B Time Time to remove : '''''''''' Time to deposit units 13 (part) pa" °l "n” 19 and 14—21, form soils on them, remove units 13 (part) and 14-21, deposit sequence A—F, and form soils on sequence A-F 12 1 1 10 9 . 8 Time to remove “m...” panofunit7 ""“""' _-—-7 6 Time to deposit units 5-7 and part 5 of 4, form soils on them, and to remove units 5-7 and part of 4 unit 4 3 2 1 EXPLANATION EXPLANATION EXPLANATION E 3E 1E m Missing time A horlzon of Lower B horizon Missing time paleosol of paleosol C Time represented by sediments or paleosols 2E Upper B horizon of paleoeol Sandstone C Time represented by sediments or paleosols Figure 11. Effects of paleosols and cuts on Willwood biostratigraphy in two different exposures of Willwood Formation sandstone and mudrock in the same stratigraphic interval. Note that in such areas, simple meter levels record very different temporal stratigraphy at sites A and B. Numbers are bed numbers. stratigraphic correlation (fig. 9A). Weathering poses little problem for identifying stratigraphic positions of fossils from very mature paleosols (stages 4 and 5), because these soils are generally confined, both above and below, by boundaries of the preceding and succeeding pedofacies. Temporal resolution, however, is affected; faunas from channel-belt and levee deposits generally cannot be resolved temporally at levels finer than that of the whole sequence containing them. Using the pedofacies model, whole chan- nel-belt sequences represent the same amount of time as the most mature paleosols of the distal floodbasin, or, for the Willwood paleosols, about 25,000—100,000 years (stages 4—6). Therefore, except in extraordinary localities (where individual paleosols might be resolved at an order of magni- tude of about 1,000 years), fossil mammals from channel- belt and levee deposits with very immature paleosols are resolvable only at levels comparable to those of the most mature paleosols. The most precise temporal resolution is possible in paleosols of intermediate maturities (stages 2—3+), at intermediate lateral positions (distal alluvial ridge and proximal flood plain, Bown and Kraus, 1987) in the ped- ofacies sequence. UNRESOLVED AGGRADATIONAL BIOSTRATIGRAPHY In examining the mechanisms by which sediment accu- mulated during Willwood time, it is clear that the mecha- nisms have introduced an inherent element that precludes determinations of precise relative temporal positions of localities based on relative meter-level correlations. In aggrading meandering stream systems, continued overbank deposition during flooding builds up raised prisms of sedi- ment flanking channels—the natural levees. During extreme flooding, the levees may be breached by the flooded channel, so that ( 1) the active channel is relocated to a lower, more distal position on the flood plain, and (2) that part of the hith- erto active channel downstream from the breach in the levee is stranded above the flood plain and only rarely (or much 42 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING EXPLANATION Stage 0 soils Stage 1 soils Stage 2 soils Stage 3 soils Stage 4 soils ‘ Stage 5 soils — W Stage 0 paleosol Stage 1 paleosol Stage 2 paleosol Illlllllll m Stage 3 paleosol Stage 4 paleosol Stage 5 paleosol Figure 12. Relationships of five hypothetical Willwood Formation pedofacies (pedofacies A through D; pedofacies B is detailed in cross section). The fifth pedofacies is being developed at the surface. The block diagram is schematic and highly ideali7ed. The width of the left face of the diagram is about 20 km; height of the diagram axis is about 70 m: the vertical exaggeration is about X150. later) receives additional sediment. The new and topograph- ically lower part of the active channel begins to form chan- nel-belt deposits and levees of its own, so that the channel- belt, levee, and flood-plain deposits associated with the new channel position lie topographically lower than the old. Ini- tially, this meter-level disparity might be as much as 20 m (fig. 13). With continued sediment accumulation, the origi- nal channel deposits become engulfed by those of the new channel and are juxtaposed against them laterally. In such a rock sequence, it is clear that measured sec— tions will include some deposits of both the older and younger channels in the same meter interval. Thus, on a small scale, the faunas of the Willwood Formation and like alluvial systems are partly superposed and partly juxta- posed. This phenomenon may have played a role in causing the oscillation of the mean of tooth area plots of Willwood mammals that are plotted against a stratigraphic (and puta- tively temporal) axis (for example, Bookstein and others, 1978, figs. 4 and 7). Detailed pedofacies analysis likely can resolve such inherent small-scale temporal biostratigraphic problems; however, the field work involved would be formidable. SECTION CORRELATIONS The Fifteenmile Creek master section was begun in 1980 at locality W125 (equal to D1224) and was carried to the spud of the Gulf-Teeters well, in sec. 28, T. 47 N., R. 93 W., in which was recorded a thickness of 790 feet (240 m) of Willwood rocks. This initial section (C—C', pl. 1) established W125 at the base of the Fifteenmile Creek section at the STRATIGRAPHIC SECTIONS 43 l‘___— 10 KILOMETEHS VERTICAL EXAGGEHATION ABOUT X 115 Figure 13. Diagram showing how sediment accumulation in an aggrading regime accommodating avulsion from an alluvial ridge constrains meter-level alluvial stratigraphy. Relocation of drainage A to a lower position (B) on the distal floodbasin results in older al- luvial-ridge sediments (C) at higher meter—level positions than allu- vial deposits (D) being formed by the younger channel. By the Willwood Formation pedofacies model, the inherent stratigraphic error would not exceed the height of the alluvial ridge, or about 20 m. Patterns show highly schematic bed geometries. 180-m level, approximately 50 In higher than any Willwood localities in the Sand Creek-No Water Creek area studied by Bown (1975, 1979). The US. Geological Survey Willwood expeditions (1977—79) and the joint US. Geological Survey- Johns Hopkins University School of Medicine expeditions (1980—1992) continued the intensive collecting operations in the lowest part of the Willwood section exposed along Fifteenmile Creek (pl. 1), near the confluence of Fifteenmile Creek with the Bighorn River, begun in 1973. In general, collecting emphasis from 1980—84 was directed farther westward each succeeding field season to allow fossil pros- pecting and the establishment of new localities to be in advance of the measured section. Sections were measured using a Jacob’s staff in areas characterized by high or variable dips, and(or) in regions with a great density of localities. Localities correlated by this procedure include about 96 percent of all sites correlated. A few extraneous localities were correlated in areas with a low density of localities or with little variability of low dips, and across poorly exposed areas, where dips could be estimated from peripheral exposures and section position calculated by solving three-point problems (for example, Billings, 1965). Locality position was determined to the nearest meter for stratigraphic and sedimentologic localities. For geographic localities at which fossil provenance could not be established with confidence, the locality meter level was determined by averaging the lowest and highest meter levels occurring within the circumscribed geographic areas. All sites that were correlated without use of estimated meter levels (tables 2—5) were related to one another by walking out the beds, and beds were also walked out to relate the 44 Fifteenmile Creek spur sections (table 16) to one another. US. Geological Survey localities established in 1977—79 are, like all the YPM localities, strictly geographic localities. They were established by circumscribing areas on maps without recording data necessary to later place them precisely in measured sections. These are sites D1128 through D1252. Several of those sites were exceptionally rich and were revisited frequently enough that sufficient stratigraphic and sedimentologic information was gathered some years after the sites were discovered. The most impor- tant of such localities are D1162, D1177, D1198, D1204, and D1230. At localities established between 1980 and 1984 (D1253-D1584), records were kept regarding which beds at the sites actually produced the fossils, and most 1985—92 localities (D1585—D1986) have documentation of both paleosol stage and pedofacies position. As of this writing (1992), 1,474 fossil vertebrate local- ities have been established by the five major institutions working in the Willwood Formation in the central and southern Bighorn Basin since 1961. Most of those in the area south of the Greybull River are depicted on plates 1 and 2, and all of the localities known to us are listed in tables 2—6 at the end of this report. Nine hundred and twenty-eight localities are tied to the composite measured sections of the Willwood Formation in the central and southern Bighorn Basin. Of these, 678 localities have been related directly to the section, whereas the positions of 250 additional sites have been estimated using incomplete sec- tion data or using broader paleosol (that is, pedofacies; Bown and Kraus, 1987) correlations for short distances in poorly exposed areas. A synopsis of these localities by institution, depicting their correlation status, is presented in table 17, and the stratigraphic distribution of all correlated sites is depicted in table 18. CORRELATION WITH THE SCHANKLER-WING SECTION In his portrayal of the Schankler-Wing section, Schan- kler (1980) placed localities Y45 and Y227 at the 530-m level. In correlating localities in the Fifteenmile Creek drain- age, it was found that these sites lay at 470 and 457 m, respectively, in the sections measured by Bown. The Schan- kler-Wing and Bown sections are confluent near Y227 at the top of the Elk Creek Rim. The Schankler-Wing section recorded two localities at the bottom of the rim (Y226 and Y269) at 410 m and 420 m, respectively, whereas the Bown section places Y226 at 385 m and Y269 at 394 m. The dis- crepancy in meter levels (barring human error and consider- ations of the Fort Union-Willwood contact discussed above) was due to differences in measuring the Willwood section on the Elk Creek Rim. Accordingly, two sections (at ECR—ECR’, pl. 1) were measured up the rim between local- ities Y226 and Y227 and between Y269 and Y227 by US. Geological Survey personnel in 1986 and 1989. Those sec- tions record thicknesses of 63 and 71 m, respectively, 57 m and 49 in less than in the Schankler-Wing section. The 457-m stratigraphic level was adopted for Y227, resulting in a discrepancy of 49—57 m between all Schankler- Wing localities and all Bown localities lying stratigraphi- cally higher than Y227. These include numerous localities lying along the high topographic outliers west of Y227 44 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 16. Names and locations of measured spur stratigraphic sections of the Fifteenmile Creek master section of the Willwood Forma— tion, south-central and southeast Bighorn Basin, Wyoming. [Locations given to quarter sections: exact locations appear on plates 1 and 2. USGS, US. Geological Survey section; UW, University of Wyoming section; YPM, Yale Peabody Museum section (probable lines of section reconstructed by T.M. Bown)] Section symbol and name: (YPM). Location of bases: NW V4 sec. 32, T. 51 N., R. 93 W.; NE V4 sec. 36, T.51N., R. 94 W.; and NE V4 sec. 1, T. 50 N., R. 94 W., Or- chard Bench quadrangle. Location of tops: SW V4 sec. 7, T. 50 N., R. 93 W.; and NE V4 sec. 12, T. 50 N., R. 94 W., Orchard Bench quadrangle. AC—AC’—-—Antelope Creek section Section symbol and name: BB—BB'——Buffalo Basin section (YPM). Location of bases: NE V4 sec. 21, SW V4 sec. 21, NE V4 sec. 28, and NW V4 sec. 30, T. 49 N., R. 97 W.; NE V4 sec. 26 and NE V4 sec. 22, T. 49 N., R. 98 W., Dutch Nick Flat NW quadrangle. Location of tops: NW V4 sec. 16, T. 49 N., R. 97 W.; NE V4 sec. 1, SE V4 sec. 14, and NE V4 sec. 22, T. 49 N., R. 98 W., Dutch Nick Flat NW quadrangle. Section symbol and name: BD—BD’——Bobcat Draw section (YPM). Location of bases: SW V4 sec. 6 and SW1/4 sec. 8, T. 48 N., R. 96 W.; SW1/4 sec. 6, T. 48 N., R. 97 W., Dutch Nick Flat NW quadrangle. Location of tops: NW V4 sec. 20, T. 48 N., R. 96 W.; SE V4 sec. 11 and SW V4 sec. 24, T. 48 N., R. 97 W., Dutch Nick Flat NW quadrangle. Section symbol and name: BJ—BJ’—Banjo section (UW). Location of bases: SW V4 sec. 16 and NE V4 sec. 33, T. 47 N., R. 91 W., Worland SE quadrangle; NE V4 sec. 9, T. 46 N., R. 91 W., Banjo Flats East quadrangle. Location of top: NW V4 sec. 6, T. 46 N., R. 91 W., Banjo Flats East quadrangle. Section symbol and name: BW—BW’—Brinkcrhoff Well sec- tion (USGS). Location of bases: SW V4 sec. 2, T. 48 N., R. 95 W. and SE V4 sec. 36. T. 49 N., R. 95 W., Schuster Flats NW quadrangle. Location of top: SE V4 sec. 15, T. 49 N., R. 95 W., Sucker Dam quadrangle. Section symbol and name: C—C’—Canal section (USGS). Location of bases: SW V4 sec. 21 and SE V4 sec. 27, T. 47 N., R. 93 W., Schuster Flats SE quadrangle. Location of top: SE V4 sec. 28, T. 47 N., R. 93 W., Schuster Flats SE quadrangle. Section symbol and name: CD—CD’—Crooked Draw section (USGS). Location of base: NE V4 sec. 21, T. 47 N., R. 93 W., Schuster Flats SE quadrangle. Location of top: SW V4 sec. 9, T. 47 N., R. 93 W., Schuster Flats SE quadrangle. Location of base: SW V4 sec. 8, T. 47 N., R. 93 W., Schuster Flats SE quadrangle. Location of top: SW V4 sec. 6, T. 47 N., R. 93 W., Schuster Flats SE quadrangle. Section symbol and name: CR—CR’—Crooked Creek section (USGS). Location of bases: NWV4 sec. 26, T. 48 N., R. 96 W., Dutch Nick Flat quadrangle: SW V4 sec. 14, T. 48 N., R. 96 W., Sucker Dam quadrangle. Location of top: SW V4 sec. 19, T. 48 N., R. 96 W., Dutch Nick Flat SW quadrangle. Section symbol and name: D—D’—Divide section (USGS). Location of base: SE V4 sec. 29, T. 48 N., R. 93 W., Schuster Flats SE quadrangle. Location of top: NE V4 sec. 31, T. 48 N., R. 93 W., Schuster Flats SE quadrangle. Section symbol and name: (YPM). Location of base: ervoir quadrangle. Location of tops: NW1/4 sec. 5, T. 50 N., R. 94 W.; SE V4 sec. 2, NE1/4 sec. 11, NW V4 sec. 11, NW V4 sec. 14, and center sec. 10, T. 50 N., R. 95 W., Jones Reservoir quadrangle; SW V4 sec. 6, T. 50 N., R. 95 W., Wardel Reservoir quadrangle. DC—DC'——Dorscy Creek section SE14 sec. 26, T. 51 N., R. 95 W., Jones Res- Section symbol and name: DN—DN’——Dutch Nick section (USGS). Location of base: SW V4 sec. 2, T. 47 N., R. 96 W., Dutch Nick Flat quadrangle. Location of top: SW V4 sec. 32, T. 48 N.. R. 96 W., Dutch Nick Flat SW quadrangle. Section symbol and name: EC—EC'—Elk Creek section (YPM). Location of base: SE V4 sec. 17, T. 50 N.. R. 93 W., Orchard Bench quadrangle. Location of tops: NE V4 sec. 16 and NW V4 sec. 28, T. 50 N., R. 93 W., SE V4 sec. 23, T. 50 N., R. 94 W., Orchard Bench quad- rangle; NW V4 sec. 6, SE 1/4 sec. 7, NE V4 sec. 10, SE V4 sec. 22, NW1/4 sec. 27, T. 50 N., R. 94 W., NWV4 sec. 12, T. 50 N., R. 95 W., Jones Reservoir quadrangle. Section symbol and name: ECR—ECR’—Elk Creek Rim sec- tion (USGS). Location of base: SW V4 sec. 30, T. 50 N.. R. 95 W., Wardel Res- ervoir quadrangle. Location of top: NE V4 sec. 35, T. 50 N., R. 96 W., Wardel Res- ervoir quadrangle. Section symbol and name: CDW—CDW’—Crooked Draw West section (USGS). Section symbol and name: ECW—ECW'—Elk Creek West sec— tion (YPM? and USGS). STRATIGRAPHIC SECTIONS 45 Table 16. Names and locations of measured spur stratigraphic sections of the Fifteenmile Crcck master section of the Willwood Formation, south-central and southeast Bighorn Basin, Wyoming—Continued. Location of base: SW 1/4 sec. 13, T. 50 N., R. 95 W., Jones Res- ervoir quadrangle. Location of top: SE 1/4 sec. 29, T. 50 N., R. 95 W.. Wardel Res- ervoir quadrangle. Location of base: NE 1/4 sec. 13, T. 49 N., R. 96 W., Sucker Dam quadrangle. Location of top: SE 1/4 sec. 26. T. 50 N.. R. 96 W.. Wardel Res— ervoir quadrangle. Section symbol and name: ER—ER’—Elk Creek Rim East sec— tion (USGS). Location of base: SW 1/4 sec. 29, T. 50 N., R. 95 W.. Wardel Res- ervoir quadrangle. Location of top: SW Ma sec. 33, T. 50 N., R. 95 W.. Wardel Res— ervoir quadrangle. Section symbol and name: RB—RB’-—Rcd Butte section (USGS). Location of base: Dam quadrangle. Location of top: SW 1/4 sec. 33. T. 50 N., R. 95 W., Wardel Res- ervoir quadrangle. SW ‘/4 sec. 15, T. 49 N., R. 95 W., Sucker Section symbol and name: ERD—ERD’—East Ridge section (USGS). Location of base: SE1/4 sec. 26, T. 47 N., R. 97 W.. Dutch Nick Flat SW quadrangle. Location of top: NE 1/4 sec. 21, T. 47 N., R. 97 W.. Dutch Nick Flat quadrangle. Section symbol and name: FM—FM’—Fifteenmilc section (YPM). Location of base: NW 1/4 sec. 5, T. 48 N., R. 96 W., Dutch Nick Flat NW quadrangle. Location of tops: NW 1/4 sec. 26 and SE1/4 sec. 36, T. 49 N., R. 97 W., Dutch Nick Flat NW quadrangle. Section symbol and name: NF—NF'—North Fork Fifteenmile Creek section (USGS). Location of base: NE 1/4 sec. 24, T. 48 N., R. 95 W.. Schuster Flats NW quadrangle. Location of top: NE 1/4 sec. 31, T. 49 N.. R. 94 W.. Schuster Flats NW quadrangle. Section symbol and name: NFE—NFE’—North Fork Fifteen- mile Creek East section (USGS). Location of base: Center sec. 19, T. 48 N., R. 94 W.. Schuster Flats NW quadrangle. Location of top: NW1/4 sec. 31, T. 49 N., R. 94 W.. Schuster Flats NW quadrangle. Section symbol and name: RBS—RBS’——Red Butte South sec- tion (USGS). Location of base: Dam quadrangle. Location of top: quadrangle. Center sec. 21, T. 49 N., R. 95 W.. Sucker SE‘/4 sec. 15, T. 49 N., R. 95 W., Sucker Dam Section symbol and name: RC—RC’——Reservoir Creek section (USGS). Location of base: SE 1/4 sec. 33, T. 49 N., R. 95 W., Sucker Darn quadrangle. Location of top: SW 1/4 sec. 22, T. 49 N., R. 95 W., Sucker Dam quadrangle. Section symbol and name: RS-RS'——Rcd Spires section (USGS) Location of bases: NE 1/4 sec. 9 and SE 1/4 sec. 10. T. 49 N., R. 96 W.. Dutch Nick Flat NW quadrangle. Location of top: SW I/4 sec. 8, T. 49 N., R. 96 W., Dutch Nick Flat NW quadrangle. Section symbol and name: RSA—RSA’—Rcd Spires Approach section (USGS). Location of base: Dam quadrangle. Location of tops: NW1/4 sec. 33, T. 50 N., R. 96 W., Sheep Mountain quadrangle. NW 1/4 sec. 31, T. 49 N., R. 95 W., Sucker Section symbol and name: NT—NT’~—North Fork Tenmile Creek section (USGS). Location of bases: SW 1/4 sec. 6 and SW 1/4 sec. 8, T. 48 N., R. 93 W., Schuster Flats NE quadrangle. Location of top: SW 1/4 sec. 31, T. 49 N., R. 93 W., Schuster Flats NE quadrangle. Section symbol and name: RWC-RWC'—Rock Waterhole Creek section (USGS). Location of base: SE 1/4 sec. 24. T. 49 N., R. 97 W., Dutch Nick Flat NW quadrangle. Location of tops: SE 1/4 see. 1 and SE 1/4 sec. 11, T. 49 N., R. 97 W., Dutch Nick Flat NW quadrangle. Section symbol and name: (YPM and USGS). Location of bases: SW 1/4 sec. 3, T. 48 N., R. 96 W., Sucker Dam quadrangle; and NE 1/4 sec. 30, T. 49 N., R. 96 W., Dutch Nick Flat NW quadrangle. Location of top: SE1/4 sec. 7, T. 49 N., R. 96 W.. Dutch Nick Flat NW quadrangle. PD—PD’—Phelp’s Drift section Section symbol and name: PSB—PSB'—Peterson School Bus section (USGS). Section symbol and name: S—S'—Schuster section (USGS). Location of base: NE 1/4 sec. 3, T. 47 N., R. 94 W., Schuster Flats quadrangle. . Location of top: SW 1/4 sec. 32, T. 49 N., R. 94 W.. Schuster Flats NW quadrangle. Section symbol and name: SD—SD’—Sucker Dam section (USGS). Location of base: quadrangle. SE 1/4 sec. 16. T. 48 N., R. 95 W., Sucker Dam 46 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Table 16. Names and locations of measured spur stratigraphic sections of the Fifteenmile Creek master section of the Willwood Forma- tion. south-central and southeast Bighorn Basin, Wyoming—Continued. Location of top: SW 1/4 see. 34, T. 49 N., R. 95 W., Sucker Dam quadrangle. Section symbol and name: SF—SE—Schuster Flats section (USGS). Location of base: NW1/4 sec. 4, T. 47 N., R. 94 W., Schuster Flats quadrangle. Location of tops: NE l/4 sec. 18, T. 47 N., R. 94 W., and SE l/4 sec. 12, T. 47 N., R. 95 W., Schuster Flats quadrangle. Section symbol and name: SFE—SFE'——South Fork Elk Creek section (YPM and USGS). Location of bases: SW 1/4 sec. 28, NW1/4 sec. 33, and SW 1/4 sec. 34, T. 50 N., R. 93 W., Orchard Bench quadrangle. Location of tops: SW 1/4 sec. 26 and SE 1/4 sec. 34, T. 50 N., R. 94 W., Jones Reservoir quadrangle. Section symbol and name: SL—SL'——Slick Creek section (UW). Location of bases: SW 1/4 sec. 1, T. 46 N., R. 92 W.: SE 1/4 sec. 26 and NW 1/4 sec. 35, T. 47 N., R. 92 W., Banjo Flats East quad- rangle. Location of tops: NE 1/4 sec. 6, T. 46 N., R. 91 W., Banjo Flats East quadrangle; and SE 1/4 sec. 30, T. 47 N.. R. 91 W., Worland SE quadrangle. Section symbol and name: SM—SM’—Sixmilc Creek section (USGS). Location of base: NE quadrangle. Location of top: NE 1/4 sec. 6, T. 48 N., R. 93 W., Schuster Flats NE quadrangle. SE 1/4 sec. 8, T. 48 N., R. 93 W., Schuster Flats Section symbol and name: SMW—SMW’—Sixmile Creek West section (USGS). Location of base: NW1/4 sec. 8, T. 48 N., R. 93 W., Schuster Flats NE quadrangle. Location of top: NE 1/4 sec. 6, T. 48 N., R. 93 W., Schuster Flats NE quadrangle. Section symbol and name: ST—ST’—South Fork Tenmile Creek section (USGS). Location of base: SW 1/4 sec. 29, T. 48 N., R. 93 W., Schuster Flats NE quadrangle. Location of top: SE 1/4 sec. 30, T. 48 N., R. 93 W., Schuster Flats NE quadrangle. Section symbol and name: (USGS). TC—TC’—Triple Catch section Location of base: SE 1/4 sec. 3, T. 47 N., R. 94 W., Schuster Flats SE quadrangle. Location of top: NE l/4 sec. 2, T. 47 N., R. 94 W., Schuster Flats SE quadrangle. Section symbol and name: TM—TM’—Tenmile section (USGS). Location of bases: NE1/4 sec. 16, T. 48 N., R. 93 W., Schuster Flats NE quadrangle, and NE 1/4 sec. 30. T. 48 N., R. 93 W., Schuster Flats SE quadrangle. Location of top: NE V4 sec. 2, T. 48 N.. R. 94 W., Schuster Flats NE quadrangle. Section symbol and name: TW-TW’—Triple Catch West sec- tion (USGS). Location of base: NWl/4 sec. 2, T. 47 N., R. 94 W., Schuster Flats SE quadrangle. Location of top: NW 1/4 sec. 2, T. 47 N., R. 94 W., Schuster Flats SE quadrangle. Section symbol and name: UD-UD’—-Upper Divide section (USGS). Location of base: SE 1/4 sec. 31, T. 48 N.. R. 93 W., Schuster Flats SE quadrangle. Location of top: NE '/4 sec. 31. T. 48 N.. R. 93 W., Schuster Flats SE quadrangle. Section symbol and name: W~W’—Wardel section (USGS ex— tensions of MJ. Kraus sections). Location of bases: NW 1/4 sec. 23 and NE 1/4 sec. 25, T. 50 N., R. 96 W., Wardel Reservoir quadrangle. Location of tops: SE 1/4 sec. 19, T. 50 N., R. 95 W.; NE 1/4 sec. 14 and SE ]/4 sec. 24, T. 50 N., R. 96 W., Wardel Reservoir quad- rangle. Section symbol and name: WG-WG’—Worland Gulch section (USGS). Location of base: SE quadrangle. Location of top: SW V4 sec. 31, T. 48 N., R. 93 W., Schuster Flats SE quadrangle. SW 1/4 sec. 7, T. 47 N., R. 93 W., Schuster Flats Section symbol and name: WW~WW’—Worland Gulch West section (USGS). Location of base: SE quadrangle. Location of top: NWI/4 sec. 31, T. 48 N., R. 93 W., Schuster Flats SE quadrangle. SW '/4 sec. 2, T. 47 N., R. 94 W., Schuster Flats known as Red Spires, as well as most localities in the Buffalo Basin (between Tatman Mountain and the Squaw Teats Table), and those lying between Gooseberry Creek and the Buffalo Basin. The Bown section along Red Spires adjusted this discrepancy to 79 m; thus most sites in the Schankler- Wing section recorded by Schankler (1980) as lying at 530 m and above are here recorded at meter levels given by Schankler (1980) minus 79 In. Section measuring of the Willwood Formation and correlation of localities in the Elk Creek, South Fork of Elk Creek, Buffalo Basin, and Squaw Teats Table areas reveal only insignificant differences in meter levels between the two sections in those areas. STRATIGRAPHIC SECTIONS 47 Table 17. Fossil vertebrate localities related to measured sections of the Willwood Formation in the southern Bighom Basin, Wyoming, with respect to institutions housing the fossils. [DPC, Duke University Primate Center, Durham, NC. (localities founded by expeditions directed by E.L. Simons); UM, University of Michigan Museum of Paleontology, Ann Arbor, Mich. (localities founded by expeditions directed by PD. Gingerich); USGS, U.S. Geological Survey, Denver, Colo. (localities founded by expeditions directed by T.M, Bown and K.D. Rose); UW, University of Wyoming Geological Museum, Laramie, Wyo. (localities founded by expeditions directed by T.M. Bown); YPM, Yale Peabody Muse- um, New Haven, Conn. (localities founded by expeditions directed by E.L. Simons). Data included through 1992 field season] DPC UM USGS UW YPM Total Total localities .............. 19 29 843 86 495 1,472 Uneorrelated ............... 11 17 325 12 166 531 Directly correlated ............ 5 11 359 66 238 679 Total correlated ............ 8 12 518 74 329 941 Estimated within 10 m ......... 3 1 124 8 66 202 Estimated within 20 m ......... 0 0 35 0 24 59 Total estimated ............. 3 1 159 8 90 261 Cataloged specimens .......... 11,000 11,500 245,418 4,300 l20,400 72,618 lEstimated; less than 2 percent are isolated teeth and most are jaw fragments with two or more teeth. 2Does not include an estimated 30,000 additional uncatalogued specimens. Bown and Rose (1987) published a study of the evolu- tion of Willwood anaptomorphine primates, using meter lev- els from both Bown’s Fifteenmile Creek section and the Schankler-Wing section for biostratigraphic control. The plot of the area of the lower second molar of these primates is depicted in figure 14, as it appeared in their figure 54. A second plot of the area of the same tooth, using the revised section data, is presented in figure 15. It is clear from exam- ination of the two plots that the picture of gradual evolution of dental characters in the Bighorn Basin omomyid primates is not changed by the information from the revised section. Rather, the effect of replotting the omomyid tooth dimen- sions has simply been to contract the plots stratigraphically (temporally), resulting in an even denser distribution of the biostratigraphic data. CORRELATION WITH THE CLARKS FORK BASIN SECTIONS During much of the time that UW, YPM, and US. Geo- logical Survey localities were being correlated to measured sections in the south-central and southeast Bighorn Basin, similar and equally important developments were taking place in the Clarks Fork region of the northern Bighorn Basin. In 1974, a program of vertebrate fossil collecting was initiated there by the University of Michigan Museum of Paleontology (UM), under the direction of PD. Gingerich. Rose (1981a) published a map locating 249 localities in the Fort Union and Willwood Formations and stratigraphic sec- tions correlating 194 of those localities (161 in the Willwood Formation, 62 of which are of Wasatchian age). Gingerich and Klitz (1985) later published a map recording all locali- ties, including those established between 1981 and 1984. The fossil mammals from the Clarks Fork area have been instrumental in the empirical documentation of tempo and mode of evolution in late Paleocene and early Eocene mammals (see, for example, papers by Gingerich and Rose cited in the “Introduction” of this report) and in definition of the Clarkforkian land-mammal age (Rose, 1981a). The Clarks Fork lower Tertiary section is additionally important because it is there that Paleocene fossil mammals were first known in some abundance beneath the lower Eocene sec- tion. Moreover, because they are geographically somewhat extraneous with respect to Willwood fossil mammal locali- ties of the south-central and southeast Bighorn Basin, Will- wood mammal sites in the Clarks Fork area have also proven important in corroborating evolutionary patterns seen in Willwood mammals with the records from farther south (for example, Bown and Rose, 1987). There is no continuous exposure of Willwood rocks between the Clarks Fork area and the south-central Bighorn Basin, and adequate Tertiary well-log data do not exist. Nonetheless, precise correlation between the Willwood sec- tions of the south-central and southeast Bighorn Basin and the Clarks Fork area is of obvious interest because of the abundance of vertebrate fossils from these areas and their prominent role in investigation of rates and modes of mam- mal evolution. Because Wasatchian mammals of the greater Bighorn Basin (including the Clarks Fork area) were part of a regional fauna existing in a single depositional basin (Gin- gerich, 1983a), biostratigraphic correlation based on mam- mals holds the most promise. Although existing collections are probably quite ade- quate to produce a relatively precise correlation, few groups or lineages have yet been studied in the detail necessary to provide a compelling correlation. However, we offer a pre- liminary attempt here (fig. 16, table 19) based on several taxa 48 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 18. Stratigraphic distribution of fossil vertebrate and plant localities in the Fort Union, Willwood, and Tatman Forma- tions of the southern Bighorn Basin, Wyoming. [Position is shown in meter levels above the base of the Willwood Formation. Local- ities from three separate master sections are represented: (l) the Sand Creek-Banjo section southeast of Worland, Wyo. (Bown, 1979); (2) the Fifteenmile Creek section in the south-central Bighorn Basin (all new data, section measured and localities cor- related by TM. Bown)‘. and (3) the Antelope Creek»Elk Creek-Buffalo Basin section measured by David Schankler and S.L. Wing in 1976—78 (Schankler. 1980). Local- ities in the Sand Creek-Banjo section include all University of Wyoming localities, except W124—W127. All localities originally in Schankler‘s (1980) Antelope Creek- Elk Creek-Buffalo Basin section are shown underlined, as are DPC, UMRB, and USGS localities that are in the line of this section and which were added in their ap- propriate places by Bown. Note that Schankler's stratigraphic sections along the Elk Creek Rim have been considerably modified, based on new sections by Dawn and by MJ. Kraus. All other localities are in the Fifteenmile Creek master section. mea- sured by Bown in 1981—92. D, US. Geological Survey (USGS) localities; DPC, Duke Primate Center localities; NM, US. National Museum fossil plant localities; UMRB, University of Michigan Red Butte localities; W, University of Wyoming Geological Museum (UW) localities; Y, Yale Peabody Museum (YPM) localities; ‘, stratigraphic position estimated and probably within 10 m; “‘, stratigraphic position estimated and probably within 20 m. The letters A through H following locality names designate different areas assigned to the same locality. N, S, E, and W indi- cate compass direction. U, M, and L indicate stratigraphic positions recognized with- in individual localities (upper, middle, and lower, respectively), and Q designates a quarry site] Meter level Localities Tatman Formation 740 .............. NM37686, NM37687. Willwood Formation 719 .............. NM37682, NM37683, NM37684, NM37685. 706 .............. NM37679, NM37680. 641 .............. 17. 636 .............. D1651**, D1651Q**. 626 .............. Y172**, NM37677. 621 .............. NM37669, NM37672, NM37673, NM37674, NM37675. 611 .............. 123, m. 601 .............. E, m, 1&1, m. w, Y198, NM37667, NM37668. that are: (1) Known well enough that their taxonomy is con- sistent and reliable; (2) common or distinct enough to be readily and unambiguously identified in both areas; and (3) restricted in temporal range or with abrupt first or last appearances. We consider first and last appearances to be equally useful for intrabasinal correlation, assuming that species had potentially unrestricted and geologically instan— taneous dispersal throughout the basin. Under this assump- tion, it is very unlikely that a species’ first or last appearance would be widely discordant in the two parts of the basin. It is acknowledged that first or last appearances could be mis- leading if they are tied to certain local paleoenvironments. For example, if paleosols indicate that local habitats differed in the two parts of the basin, this method of correlation would be inappropriate. Table 18. Stratigraphic distribution of fossil vertebrate and plant localities in the Fort Union. Willwood, and Tatman Forma- tions of the southern Bighorn Basin, Wyoming—Continued. Meter level Localities 591 .............. D1596**, D1646**, D1647**, D1686**, Xé, m, Y162A, Y162B, Y162C, L196, m, M- 571 .............. n, g, 116;. 566 .............. D1772. 561 .............. D1735*,m*,X1_65,_Y_1_8_3_. 559 .............. D1622*. 556 .............. D1172*, D1473, D1504, D1558*, D1781, D186o,11_8_7, DPC14. 553 .............. D1674. 551 .............. D1583, fl, x_1_o, m, m, 2212*- 550 .............. D1503, D1505, D1506. 546 .............. D1212*, D1256, D1463, D1464, D1465*, Dl467, D1481*, D1574, D1575, D1576, D1581*, D1582*, D1828, D1890, Egg, Y192s, m, _Y193E, 1M. X119, DPClS, DPC16. 544 .............. D1918. 543 .............. D1945. 542 .............. D1764*. 541 .............. D1482*, D1613, m, m, 11.6, m. m. we M, M, M, 1.19—0- 539 .............. D1919. 537 .............. D1765*. 536 .............. D1173*, D1534*, DPC11*. 531 .............. D1170*, D1567*, D1673, £14, Y1_75.X1E, Y_17§, Y1_85. 1.1%. 530 .............. D1920. 529 .............. D1831, D1914. 528 .............. D1566*, D1843, DPC17*. 526 .............. D117l*. 521 .............. D1170*, m, xl_9, Y_36_. 516 .............. D1176*, D1304, D1438, D1466*, D1608**, D1625, D1985. 513 .............. D1623*, £5685. 511 .............. D1167, D1176, D1375*, D1437*, D1573*, 01754, D1834, m, m. M’“. Y_1_7_3., m. m, M- 510 .............. D1769*. 509 .............. D1285, D1513, D1986. 507 .............. D1624*, 1251*. 505 .............. D1609**, D1612*, UMRBS. 504 .............. D1984. STRATIGRAPHIC SECTIONS 49 Table 18. Stratigraphic distribution of fossil vertebrate and plant localities in the Fort Union, Willwood, and Tatman Forma- tions of the southern Bighorn Basin, Wyoming—Continued. Meter level Localities 501 .............. D1174*, D1175, D1431, D1432, D1433, D1435, D1468, D1755, D1829, D1830, fl, .YLS’ m) 15.552 _Y_§_§*1 £173,375, Y76, Y77,X16_8, M- 499 .............. D1337*. 496 .............. D1434*, D1474*, D1475*, D1782 495 .............. D1672 494 .............. D1408, D1507, D1508, D1910. 493 .............. D1563, D1675Q. 492 .............. D1436, D1982. 491 .............. D1163*, D1169*, D1338*, D1338N*, D1344*, D1345, D1346, D1469, D1470, D1471, D1773, D1966, Y18A, ____Y26A1 m, m. m. Y73, Y74, Y317. 490 .............. D1230, D1255“, D1426*, D1562, Y49**, UMRBlO. 489 .............. D1286, D1734*, D1825, Y47, Y47A, UMRB6. 488 .............. D1983. 486 .............. D1165*, D1257, D1305, D1491. 485 .............. D1531*, D1532*, D1552, D1564*, D1565*, UMRB4. 483 .............. D1307, D1312, D1317, D1331, D1397, D1586, Y14A. 482 .............. D1156, D1158, D1159, D1246, D1510, UMRBl2. 481 .............. D1162, D1166*, D1177, D1197, w, D1316, D1336, 149, m, m, 33*, v72, Y253, UMRB1,UMRBIA. 480 .............. Y249**. 479 .............. D1826. 478 .............. D1157, D1511, D1605, D1727, Y99, Y318. 477 .............. D1245. 476 .............. D1164, D1667. 475 .............. D1617, D1767*. 474 .............. D1490, D1671, D1777, D1778, D1783, D1885*, Y61. 472 .............. D1161*, D1889*. 471 .............. D1670. Table 18. Stratigraphic distribution of fossil vertebrate and plant localities in the Fort Union, Willwood, and Tatman Forma- tions of the southern Bighorn Basin, Wyoming—Continued. Meter level Localities 470 .............. D1128, Dll60, D1160N, D1198A, D1198B, D1198C, D1198D, D1198E, D1198F, D119SG, D1198H, D1244, D1314, D1315, D1662, D1663, D1677*, Y45, Y4SS, Y52*, UMRB2, UMRB3. 469 .............. D1737(U), Y34. 468 .............. NM37560. 466 .............. D1592*. 465 .............. D1425*. 464 .............. D1495, D1669, D1676. 463 .............. D1462**, D1602, D1603, D1604, D1699, D1726, D1737(L), D1776, D1833, D1881, D1890, D1936, Y44. 461 .............. D1250. 460 .............. D1668, UMRB9*. 458 .............. D1210*. 457 .............. Y227, Y227N. 455 .............. D1409, D1430, D1698, D1784, YIOO. 454 .............. Y353. 452 .............. D1209, D1339, D1497, Y339. 450 .............. D1536*, M! 449 .............. D1537, D1599. 448 .............. D1207, D1308, D1451*. 446 .............. D1429, D1439, Y340*. 445 .............. D1629“, Y270**. 444 .............. D1204(U), D1587. 443 .............. D1657. 442 .............. D1204(M), D1310, D1311, D1407, D1588, D1659, D1660, D1682, D1688*, D1937*. 440 .............. D1428, D1452*, D1684, Y250*, Y252*. 438 .............. D1203, D1204(L), D1206*, D1208, D1319, D1320, D1321, D1322, D1323, D1325, D1398, D1400, D1401, D1404, D1405, D1459*, D1687*, D1693, D1748, D1899*, Y338, Y448’“, DPCl. 436 .............. D1377, D1406, UMRB7. 435 .............. D1570**, D1571“, D1628**, D1694, D1742, D1876**, D1883*, Y224*, Y225*, Y325**. 50 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING Table 18. Stratigraphic distribution of fossil vertebrate and plant localities in the Fort Union, Willwood, and Tatman For- mations of the southern Bighorn Basin, Wyoming—Contin- ued. Meter level Localities 434 .............. D1399. 433 .............. D1749. 432 .............. D1487. 431 .............. D1347. 430 .............. D1348, D1349, D1376, D1378, D1379, D1380, D1381, D1382, D1486, D1545*, D1689, m, m, Y222*, Y223, Y236*, Y248*, Y251", Y261*, Y321, Y325**, w", m“. 428 .............. D1598, D1330, D1897*. 426 .............. D1309, D1822. 425 .............. D1234, D1326, D1550*, Y247, Y268*, UMRBs. 424 .............. D1295, D1324. 423 .............. Y320*, D1848*, D1866*, NM37662. 422 .............. D1946. 420 .............. D1396, D1402, D1403, D1443, D1529", D1530", D1597, fl, Y324", NM37661. 418 .............. D1410(U), D1526“. 416 .............. D1410(M), D1484*, D1554, D1821, Y51. 415 .............. D1483*, D1747*. 414 .............. D1235*, D1528“, D1541, D1680*, D1762“, D1762Q**, D1863, Y69*, Y85*. 413 .............. D1774". 412 .............. D1217, D1411, D1779“, Y221, Y237, Y319“. 411 .............. D1460Q, D1804*. 410 .............. D1261*, D1306, D1350(U), D1350Q, D1410(L), D1527", D1539, D1549*, D1658, D1859*, Y234, Y463. 409 .............. D1454, D1460, D1524“, D1823, D1895*, Y267. 408 .............. D1240“, D1350(L), Y266. 407 .............. D1894“, D1896*, D1947, Y230A, Y230B. 406 .............. D1824. 405 .............. D1538, D1547*, D1559*, D1805*, Y78, Y220, Y461. 404 .............. D1744, Y235. 402 .............. D1951. 400 .............. D1222, D1458, D1551*, D1952, Y324*, X348", Y271, Y462. 399 .............. D1540. 397 .............. D1556, D1716*, Y219, Y262, Y263 . Table 18. Stratigraphic distribution of fossil vertebrate and plant localities in the Fort Union, Willwood, and Tatman For- mations of the southern Bighorn Basin, Wyoming—Continued. Meter level Localities 394 .............. D1555, D1864*, Y50, Y265, Y269. 392 .............. D1218, D1219, D1385, D1413, D1560, Y460. 390 .............. D1342, D1548*, D1712*, D1745*, m, Y127, mt 385 .............. D1743, D1792*, D1803*, Y226, Y264. 384 .............. D1221, D1341, D1370, D1421(U). 383 .............. D1741. 382 .............. D1652. 380 .............. D1216, D1259“, D1514*, Y67, Y84. 1.152, M“. 379 .............. D1242, D1421(L). 378 .............. D1251, D1300, 01301, D1414, D1453. 377 .............. D1553*. 376 .............. D1293*. 374 .............. D1283. 370 .............. D1200, D1220, D1371, D1422, D1494, D1635, Y82A, Mt, m. 211, m. m, 1282, Y_T9_8. m, m. M". $1.12! 368 .............. D1292“. 364 .............. D1340Q, D1412. 362 .............. D1561, D1923*. 361 .............. D1636*. 360 .............. D1303, D1332, D1333, D1334, D1387, D1388, D1417, D1420, _Y_8_1, Yl32, m, EEK L51". ms. Q72, w. 32M. 13%“. 359 .............. Y136. 357 .............. D1653, D1924, D1967. 356 .............. D1205, D1372, D1391, D1557, Y447, Y449. 354 .............. D1415*, D1416*, Y158**. 353 .............. 01950, NM37656. 352 .............. D1282, D1299, Y274. 351 .............. D1700. 348 .......... -. . . . D1243*, Y131(U). 346 .............. D1287, D1335(U), D1850. 345 .............. D1882*. 344 .............. D1201, D1201N, D1386, D1449", D1493, Dl498*, D1811, Y131(L). 343 .............. Y135, Y157(U). 342 .............. D1289, D1294, D1313, D1384. 340 .............. Y125*, Y216*. STRATIGRAPHIC SECTIONS 51 Table 18. Stratigraphic distribution of fossil vertebrate and plant localities in the Fort Union, Willwood, and Tatman Forma- tions of the southern Bighorn Basin, Wyoming—Continued. Meter level Localities 338 .............. D1284, D1373(U). 336 .............. D1288(U), D1”""VU. D1373(L) D1374, Y157(M). 335 .............. ME 334 .............. D1302**, D1499*. 332 .............. D1288(L), Y459. 329 .............. D1775. 324 .............. D1202**, D1395**, Y133**, Y458. 322 .............. D1500**, Y157(L)*. 315 .............. D1931*. 312 .............. NM37655. 311 .............. D1577**, NM37654. 310 .............. D1938*, D1880*, Y156**, X1651. 305 .............. w*. 300 .............. D1145*, D1146*. 296 .............. D1393, D1441. 292 .............. D1328, D1369, D1392. 290 .............. D1141*, D1183*, D1501**, w. m, M, w, L50 288 .............. D1258*. 285 .............. D1144*, D1266*. 282 .............. D1290, D1418. 280 .............. D1143*, _Y_2_8__5_, _Y_2_89., __Y_2£5., X291- 278 .............. D1298, D1390, D1678*. 275 .............. D1142*. 270 .............. D1241, D1383,12fi,_Y_29_4. 264 .............. D1389. 262 .............. D1297(U). 260 .............. D1291, D1297(M+L), D1419, D1711*. 255 .............. D1644*. 250 .............. D1709*, D1935* Y373 245 .............. D1710*. 240 .............. D1645, m, m, m, L55 230 .............. m, M’“, M“, m“. 227 .............. Y300. 220 .............. w, m, m, m. 215 .............. £68“. 213 .............. D1872**, Y412. 210 .............. MK m, M“, M”, $3.61“- 205 .............. Y416** 200 .............. D1631* 195 .............. Y323** Table 18. Stratigraphic distribution of fossil vertebrate and plant localities in the Fort Union, Willwood. and Tatman For- mations of the southern Bighorn Basin, Wyoming— Continued. Meter level Localities 190 .............. D1630*, D1847", Y111, Y214, Y215W‘, Y363. 182 .............. Y347*. 180 .............. D1224, D1461*, D1816", W124, W125, W126, W127, Y345, Y369“, Y377, Y388, M- 175 .............. D1189*. 17o .............. D1192, D1193.X§2. X2132- 165 .............. 30413111911. 160 .............. D1178, 191, 114_5, 11.49. 1321, 19.5.2. $3.73. 3%". ME“, M‘- 155 .............. M“. 150 .............. m, M“, M”, Y359, M", M. Y395*. fl“. 149 .............. m. 145 .............. win 140 .............. D1188“, 131194*,131195*, 131262, 13164012, x23, m. 19.6. )QZ. m. M“. m. m. m, m. m. m. m, M. m. 130 .............. D1190, 0119114, D1632*, 131648, W30, x395. 124 .............. NM37650. 119 .............. W55, W84. 115 .............. m*. 113 .............. D1447*, W29, W54, W61, W111, Y342, Y343*. 112 .............. NM37639, NM37640, NM37641, NM37643, NM37645, NM37648. 100 .............. Y9OB, Y119, Y120, Y201. Y202. X222, 3.224. 1225, NM37638. 97 .............. W20, WZOA, W208, W52, Y137*. 95 .............. m*. 94 .............. W87 90 .......... I. . . . Y90A. 88 .............. W49, W51, W82. 82 .............. Y276*. s1 .............. W83, W129. 80 .............. m. 77 .............. W81, Y139*. 75 .............. W46. 70 .............. W16A, Y370A. 66 .............. W50. 64 .............. W16B, W17. 52 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING Table 18. Stratigraphic distribution of fossil vertebrate and plant localities in the Fort Union, Willwood, and Tatman Forma- tions of the southern Bighorn Basin, Wyoming—Continued. Meter level Localities 63 .............. W48. 61 .............. W16C, W86. 57 .............. W44, W90*, W91*, Y48*. 50 .............. m. 48 .............. W24, W24A. 46 .............. W22, W32, W45, W63, W78*, W80, W92*. 41 .............. W38, Y138*. 40 .............. W35, W110. 39 .............. W53, W60. 36 .............. W36 34 .............. W33, W34, W34N1, W34N2, W37, W77. 31 .............. W23, W66, W130. 30 .............. D1296*, W27, W41*, W76, Y115*, Y306*. 27 .............. W62. 26 .............. W67*, W105. 24 .............. W25, W26, W42*. 23 .............. W39, W85. 20 .............. W43*, W96. 18 .............. D1485*, W28. 10 .............. D1199*, W95, Y275*. 9 .............. W19. 5 .............. D1579, D1887. 4 .............. W59. 3 .............. D1888. Base of Willwood Formation Fort Union Formation -20 .............. NM37627. -24 .............. Y307*. -25 .............. D1578 Willwood Formation deposition began much earlier in the northern Bighorn Basin than in the south; hence the Will- wood section in the Clarks Fork area includes several hun- dred meters of sediment of Clarkforkian age as well as overlying deposits of Wasatchian age. The Wasatchian part of the Clarks Fork Basin Willwood Formation section (which represents only the earlier Wasatchian) is about the same thickness (about 720 m) as the entire Willwood section of the central Bighorn Basin, a section that represents the entire Wasatchian. The events and ranges used for our corre— lation show comparable offsets in the two sections (as indi- cated by the roughly parallel correlation lines in fig. 16). Most biostratigraphic events occur at meter levels 50—75 percent higher relative to the beginning of the Wasatchian in the Clarks Fork section; that is, the Clarks Fork section is generally at least 50 percent thicker per unit of time than the combined sections from the southern Bighorn Basin. This greater thickness reflects a more rapid (though not necessar- ily constant) rate of sediment accumulation in the Clarks Fork area, which probably was controlled by its closer prox- imity to the basin depositional axis (Kraus, 1980; Gingerich, 1983b). These data also suggest that sediment accumulation there was more rapid earlier in Wasatchian time than later. It is also evident from our correlation (fig. 16) that the Clarks Fork area Wasatchian section is essentially restricted to the Haplomylus-Ectocion Range Zone of Schankler (1980). Only a few relatively poor localities, at the top of the Clarks Fork section and succeeding an unfossiliferous inter- val of about 100 m (from about 2,100—2,240 m), have pro- duced a fauna belonging to Schankler’s Bunophorus Interval Zone. Because of the gap, the level of the beginning of the Bunophorus Interval Zone, as well as the first and last appearances of several taxa (that occur in the 360—400 In interval in the southern Bighorn Basin) cannot yet be deter- mined with any precision. Reliability of biostratigraphic events used in correlation is enhanced if two or more events coincide in both sections. Of the events listed in table 19, probably the most reliable for correlating the two sections more precisely are the coinci- dent events at 190 m in the southern Bighorn Basin section involving two lineages of omomyid primates and one of a microsyopid plesiadapiforrn. As currently understood, the last occurrence of the microsyopid Arctodontomys wilsoni (Gunnell, 1985) in the southern part of the basin (190 m) was synchronous with the last occurrence of the omomyid Teil- hardina crassidens and the transition from stage 1 to stage 2 in the Tetom'us mazthewi—Pseudotetonius ambiguus transi- tion (a nonarbitrary transition marked by the loss of the sec- ond lower premolar, documented to have occurred in a 10-m interval, Bown and Rose, 1987). In the Clarks Fork section, Teilhardina crassidens last appears at 330 m (1,850 m in Gingerich’s 1982 section), coinciding with the first known stage 2 Tetom'us and possibly with the last stage 1 Tetonius matthewi. Unfortunately, the record is too sparse for confi- dence; the stage l-stage 2 transition could have occurred slightly earlier. The last occurrence of Arctodontomys wil- soni, however, is conspicuously lower (at 240 m) in the Clarks Fork section. Although A. wilsom' may have persisted much longer in the southern Bighorn Basin than in the north, our correlation suggests that its range was similar in the Clarks Fork area, and that it may eventually be found in beds as high as 1,850 m. In either case, it seems very improbable that two separate lineages of omomyid primates would con- temporaneously show identical temporally restricted mor- phologic stages at a much later time in the Clarks Fork area. The events just discussed are approximately synchro- nous with an apparent extinction-immigration event termed Biohorizon A by Schankler (1980). In a critical examination STRATIGRAPHIC SECTIONS 53 700 l | I | I 1 I | I . O O O — o o o o oo — a. ‘3} O . 8 5% ($2) 8 go 0 O 600 — . (g5) 0 g 0 _ O 63 o _ g go g 8) g g CB 0 o o _ g o 8 8 O 0 o o o _ . .— 500 . . F. . g * O : ’ .0919 o (as o 00 o a _ O o g o co _, 40° _ EXPLANATION __ |.IJ E D I I0. - O Absaroklus abbottl _ a: _ 0 00. n 0 Q 0 Abaaroklua metaecus E 0 at Anemorhysle wortmani E 300 — 0 0 0 0 as Anemorhysis pattcuoni — 8 o g 3 8 g 0 Stelntun veapertinus _ 0 0 O Pseudotetonlus amblguua I Tetoniua matthcwl 200 _ 0 T matthewl-P. amblguua _ 63 63 63 I I ' 6 ® ‘ I I .i I I I intermediates _ 9 9 T t _ 0 o 0 G O 0 0 O I . . 610" ll! sp. 0 O I O Tetlhardlna sp. 100 —‘ O 00 9 O 9 Q : I I I GB Tellhardlna crauldena " Q G 8 0° 0 O I I I I e Tellhardlna amerlcana ‘ e gag e e 8 O T. amerlcana—T. crauldens — e 9| Q 9 9t e | l Intelrmedlates l l | l l I (6.8 1.0 1.2 1.4 1.6 1.8 2.0 LOG NORMAL (LENGTH TIMES WIDTH) OF LOWER SECOND MOLAR Figure 14. Plot of area of second lower molar in omomyid primates from the Willwood Formation of the south—central and southeast Big— horn Basin, using stratigraphic data from Schankler (1980) and Bown and Rose (1987, table 2 and fig. 54). of Biohorizon A in the Clarks Fork area, Badgley and Gin- gerich (1988) correctly portrayed the Biohorizon A events as embracing an interval (1,750—1,790 m) but questioned its validity, suggesting that it could be an artifact of sampling. More recently, Badgley (1989) concluded (partly on the basis of the omomyid primate correlation summarized above) that Biohorizon A may occur higher in the Clarks Fork area, about 1,860 m. The latter assessment conforms much better with the correlation proposed here. Certain other distinctive taxa have restricted strati- graphic ranges that appear to be useful in the correlation of the two areas. We regard omomyids and microsyopids to be particularly useful because of recent studies (cited above) that place specimens into both sections and relate characteristic morphologies to specific stratigraphic levels. The ranges of stage 5 Pseudotetonius ambiguus and of the microsyopids Arctodontomys nuptus and Microsyops angustidens are tem- porally quite restricted and suggest a correlation consistent with that based on the events discussed above. Approximately coincident with the last appearance of Pseudotetonius in the southern Bighorn Basin were the last occurrences of the hyaenodontid creodont Arfia and the phenacodontid condy- larth Ectocion, as well as the first occurrence of the dichobunid artiodactyl Bunophorus (all events occur in a 20- m interval). Although these events all appear to have taken place at 2,100 m or above in the Clarks Fork area (Bunophorus is unknown below 2,240 m), it is impossible to be precise because of the very poor record above this level. Based on the other data in table 18, Bunophorus almost certainly was present much earlier than the record indicates. It will probably be found eventually as low as 2,100 m. If the correlation shown in figure 16 is correct, the meter level of a Wasatchian event in the Clarks Fork section may be estimated as 1.50—1.75 times its stratigraphic level in meters in the southern Bighorn Basin sections, the larger fac- tor evidently applicable in the lower two-thirds of the section (a factor of 2 may be a better estimate for the lowest 200 m of the section). More precise correlation should be possible when cer- tain other groups are known in more detail. We believe the most useful taxa for better correlation will be rodents, the adapiform primate Cantius, Phenacodus, and, especially, the hyracotheriid perissodactyl Hyracotherium and the hyops- odontid condylarth Hyopsodus. The study of Cantius by Gingerich and Simons (1977) allows a general correlation, but much new evidence (specimens and new taxa as well as revised stratigraphic data) is now available. Detailed corre- lation is dependent on knowledge of precise meter levels or intervals associated with recognizable morphologic shifts or transitions. 54 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING 700 l I I I I O I _ A _ 600 — 0 8° 0 O o _ 0 o oo _ “i no 00 9‘8 0 _ ” 00 8 8 §88§ e 5. e 08 o 8%, O O O 500 — 0 .§ (fl‘93%@§ ?§2%%OO 8 GD . _ 4‘ O O o. 0 008820.. 53:00.08 00: co _ “ o o . O o o. 0 ° ° EXPLANATION E 400 _ a A Strtgorhyaia cf. bridgerenal? 5.: _ O -.9 ‘ -§- - 0 Abcaroklus abbottl 5 y 00 ’0? V? 00 Q o Absoroktus metoeeus E 0 a Anemorhysls wortmanl 2 300 _ o 0 0 0 0 n» Anemorhyaio patteraont _ 8 0 § g g 0 Steinlus vespertlnus _ 0 0 O Paedotetonlus ambiguua 200 Q 0 l Tetonlus manhewl _ _ 69 EB 63 ‘ IL A A I I 0 T. matthewl-P. amblguua 063 O 63 u I I A I I I I intermediates ‘ Q g Q Q Q Q 90 e I A A Tetontua sp. _ GO I I) Tellhardina sp. 100 -* Q a O O ‘ ‘ l I l 69 Tellhardlna crauldem Q Q I I I I e Teilhardlna amerlcana — e 8 § @ge Q T. amerlcana-T. crauldena _ | @I | I I . intermediates %.8 1.0 1.2 1.4 1.6 1.8 2.0 LOG NORMAL (LENGTH TIMES WIDTH) OF LOWER SECOND MOLAR Figure 15. Plot of area of second lower molar in omomyid primates from the Willwood Formation of the south-central and southeast Big— horn Basin, using new and revised sections presented in this report. Note that the overall gradual picture of omomyid evolution presented by Bown and Rose (1987) is unchanged; the net effect has been to compress stratigraphically the points from localities in the Schankler- Wing section above the 530-m level. Information for omomyid specimens collected in 1987 and 1988 has been added. FOSSIL PLANT LOCALITIES PALEOBOTANICAL SAMPLING As is clear from the foregoing discussion of vertebrate localities, the predominant lithologies of the Willwood For- mation are pedogenically modified mudstone and various kinds of sandstone. Carbonaceous debris is rare, probably comprising 2—5 percent of the formation as a whole, but car- bonaceous sediments are locally abundant in the lower and upper parts of the formation (figs. 17 and 18). Unlike vertebrate fossils, plant remains in the Will- wood Formation do not accumulate in lags at the bottom of fossiliferous exposures. The necessity of quarrying for plant remains (fig. 19), in addition to the specific and clearly iden- tifiable horizons, has from the beginning forced collectors to be aware of precise geographic position, stratigraphic posi- tion, and sedimentological context. The geographic position of all plant localities has been recorded on topographic quad- rangle maps to the maximum degree of accuracy thought possible for the local terrain and the map scale. Beginning in 1989, some localities have been mapped on 1220,000-scale aerial photographs. The stratigraphic position of each locality is known to whatever level of accuracy the bed con- taining it can be correlated with the established measured sections. Finally, virtually all ofthe approximately 100 latest Paleocene—early Eocene plant localities in the Bighorn Basin are “sedimentological” localities, as the term is informally used above. That is, the physical characteristics of the fossil- iferous sediment are noted with the locality information, and for most localities lithological descriptions of fresh (man- made) exposures are accomplished for the l—-3-m thick inter- val enclosing the locality. Because of the small-scale lateral Figure 16 (facing page). Relative correlation of Willwood For- mation sedimentary rocks and time between A. the study area, and B, the Clarks Fork Basin area of the Bighorn Basin, northwest Wy- oming. using fossil mammal distributions. Datum (base of diagram) is base of Willwood Formation (O—m level) in the southern Bighorn Basin and is the 1,520-m level of the Tertiary (Gingerich, 1983c) in the Clarks Fork area. The datum represents the base of the Wasatch- ian land-mammal age in both areas (Clarksforkian-Wasatchian boundary). Note that the net Willwood sediment-accumulation rate in thc Clarks Fork area is about 1.5—2.0 times that of the study area for most of the interval studied. Correlation lines dashed and que- ried where uncertain. A SOUTHERN BIGHORN BASIN METERS 000 300 — 200 —1llllIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Tetonlua matthewl, A06 stage 2 (first) Teflhardlna crauldena Tetonlua mutthewl, stage 1 — Arctodontornys wllaonl (last appearances) 100 _ Eathonyx gmngerl ( last) FOSSIL PLANT LOCALITIES B CLARKS FORK BASIN Bunophonu/Waeatchla (first) 55 METE HS Haplomylul lpeirlanua Ectoclon oabomtanua Arfla opiathotorna (last appearances) 2200 EXPLANATION I Haplomylua apelrlamu _ e Ectoclon oabornlanua 0 Arfla opiathotorna A Bunophorua/Waaatchia 0 Abaaroklua, Anacodon, and 2100 Xenlcohlppua 63 Tetoniua matthewi, stage 1 A Tetoniua matthewi. atage 2 O Heptodon calciculua . Eathonyx grangefi fl Arctodontomya wHaoni Q Teflhardina craaaldena — 2000 Teflhardlna crauldena Tetonhu matthewl, stage 1 (last appearances) Tetonlul matthewl, stage 2 (first) - 1900 — 1800 Biohorizon A interval? Arctodontomya wflaonl (last) Eathanyx gmngcrl ( last) - 1700 — 1600 DATUM 1520 56 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 19. Mammalian taxa of potential biostratigraphic significance for correlating Willwood Formation measured sections of the south- ern Bighorn Basin and the Clarks Fork area in the northern Bighorn Basin, Wyoming. [Clarks Fork levels are in sections of Gingerich (1982) and Badgley and Gingerich (1988); figures in parentheses are meter levels in Wasatchian part of Clarks Fork section; ?. uncertain meter level] Taxon and event Esthonyx grangeri, last .................... Arctodontomys wiLsoni, last ................. Teilhardina crassidens, last ................. Tetanius matthewi, last stage 1 ............... Tetom'us matthewi, first stage 2 ............... "Biohorizon A" ........................ Arctodontomys nupzus, range ................ Pseudotetonius ambiguus, range of stage 5 ........ Micrasyaps angustidens, range ............... Arfia opisthotoma, last .................... Bunophorus/ Wasatchia, first ................. Ectocion, last .......................... "Biohorizon B" ......................... Haplomylus, last ........................ Absarokius, Anacodon, Xenicohippus, first ........ Heptodon, first ......................... Southern Bighorn Basin Clarks Fork area 971 ....... 1,7202 (200) 1903 ....... 1,7603 (240) 190‘ ....... 1,850‘ (330) 1904 ....... 1,815,?1,850‘ (295, 7330). 1904 ....... 1,850‘ (330) About 2005 . . . 1,750-1,790'5 (195—210!) (230-270) 1,8607 (340). 260-2903 1,970~2,010‘ (450490). 346-374‘ ?2050—20954 (?530—575). 350-4103 2,050—2,1003 (1 specimen, (530-580). 440)3 3605 ....... 2,1002 (580) 365‘ ....... 2,2408 (720) 3791 ....... 2,1002 (580) About 3905 . . . About 2,2003 (380') (680). 400l ....... 2,1002 (580) 425 ‘ ....... Not present. 4301 ....... Not present. lT.M. Bown and K.D. Rose, unpublished data. 2RD. Gingerich, written commun., May, 1989: new record (UM78944) extends range 80 m higher than indicated by Badgley and Gingerich (1988). 3Gunnell (1986), using section data provided by T.M. Bown. ‘Bown and Rose (1987). SSchankler (1980). 6Badgley and Gingerich (1988). 7Badgley (1989). E‘P.D. Gingerich and G.F. Gunnell, written commun., 1989. variations in floral composition, localities more than 3 m apart in the same bed are given separate designations. Given the great abundance of plant fossils where they are preserved at all, it is not practical to collect all identifiable specimens. Most museum collections result from a compromise collecting strategy that tries to repre- sent the relative abundances of the species at a locality but that favors well-preserved specimens and rare species. To preserve accurate information about relative abundances, censuses have been made at about 20 of the Willwood localities. In these censuses only leaves are counted, and each identifiable specimen complete enough to represent more than half a leaf is assigned to the appropriate species. Studies of untransported leaf litter in living forests show that such counts reflect the surrounding forest with considerable accuracy, both in terms of composition and relative abundance of species (Bumham and Wing, 1989; Johnson, 1989). DEPOSITIONAL SETTINGS OF PLANT FOSSILS Wing ( 1980, 1984a) defined two kinds of carbonaceous units: (1) Lenticular deposits (fig. 17) representing the accu- mulation of plant debris in abandoned channel scours, and FOSSIL PLANT LOCALITIES 57 Figure 17. Lenticular carbonaceous shale. locality NM37560. 468-m level of the Willwood Formation, southern Bighorn Basin. Wyo- ming. Carbonaceous shale (the black unit in the middle distance) is underlain by a poorly consolidated medium-grained sandstone. The sinuous form of the ridge top apparently conforms to the original shape of the abandoned channel segment. Figure 18. Tabular carbonaceous shale, 621-m level of the Willwood Formation, southern Bighorn Basin, Wyoming. This exposure of carbonaceous shale is part of an outcrop area of at least 52 kmz. 58 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING *W ‘W Figure 19. Plant—fossil quarry and trench at locality NM37656, southern Bighorn Basin, Wyoming, in a tabular carbonaceous shale unit at the 353-m level of the Willwood Formation, southern Bighorn Basin, Wyoming. Note underclay subunit (below whisk broom), carbon- aceous shale subunit (above whisk broom), and overlying drab mudstone (immediately above hammer). The 353-m level is the approximate top of the range for many Paleocene-earliest Eocene plants. and the bottom of the range for several late early and middle Eocene species. FOSSIL PLANT LOCALITIES 59 (2) widespread tabular deposits (fig. 18), representing plant debris accumulating in extensive floodbasin backswamps. Most lenticular deposits were thought to occur in the 270—457-m interval (270—530-m interval of the Schankler— Wing section; Wing, 1980), but subsequent work has shown that they are present throughout the formation and that they are also abundant between 621 m and the contact with the Tatman Formation. The two types of carbonaceous units represent differ- ent kinds of samples of the original flood-plain vegetation. The numerically predominant floral elements in lenticular deposits are generally aquatic and(or) riparian species. Typ- ically, the aquatic element includes floating plants such as Salvinia and Azolla, and emergent aquatics such as species of the families Alismataceae and Typhaceae. These are plants that probably colonized oxbow ponds following stream abandonment. The other abundant elements in these assemblages are stream-side trees or shrubs typical of dis- turbed sites, for example Platanus, Averrhoites, and Popu- lus. The high abundance and common occurrence of these taxa in lenticular deposits probably reflects their abundance on point bars of meander bends before abandonment. The better known lenticular deposit assemblages each contain perhaps 20—40 other species, but many of these are unique to particular sites, and some are represented by only one specimen each. These species were probably derived from the cutbank or levee side of the oxbow and are the best record we have of the vegetation of the typical oxidized Willwood flood plain. Such species include a diversity of Leguminosae and a large number of forms not yet identi- fied even at the familial level. The palynofloras of lenticu- lar units are characterized by a higher level of pine pollen and reworked Cretaceous marine dinoflagellates than is seen in the tabular units of the Willwood (Farley, 1987, and in press). There are also substantial compositional differ- ences between different lenticular unit palynofloras, proba- bly reflecting the diversity and heterogeneity of the vegetation on the cutbank sides of the oxbow ponds. The floral assemblages derived from tabular deposits represent a wider array of depositional settings and local floras than do those of the lenticular deposits. Two litho- logic types within the tabular units produce identifiable plant fossils: carbonaceous shale, and interlaminated fine sand and silt. The carbonaceous shale lithology was inter- preted by Wing (1984a) as representing deposition in flood- plain backswamps distal to the channel belt. The large quan- tity of apparently unsorted plant debris, such as compressed leaves, flowers, seeds, and horizontal trunks and branches, was taken as evidence that these assemblages were essen- tially autochthonous, or untransported. This interpretation is also consistent with the fine grain size of the shale (mostly clay), the delicate nature of much of the plant debris, and the small-scale lateral variations in the composition of the flora of individual depositional units. Tree trunks and stumps have been observed rooted in or on similar carbonaceous shales in various parts of the Willwood and Fort Union Formations (Kraus, 1988, and personal observa- tion) but have not yet been detected in association with car- bonaceous shales producing compression fossil assemblages. The apparent absence of trees in place in most Willwood carbonaceous shales is surprising if the compres- sion assemblages are indeed autochthonous—how were leaves preserved while trunks decayed? At least two possi- ble explanations exist. One, modern weathering may make the trunk casts difficult to detect, because the carbonaceous shales commonly crop out as ledges, whereas the mudstones above them into which the trunks would project are more deeply weathered. Second, the carbonaceous shale assem- blages may represent deposition in laterally extensive but very shallow lakes, the plant material having been derived from trees growing on the shoreline. The latter explanation is not consistent with the observed small-scale lateral varia- tion in floral composition but is consistent with the fine grain size of the deposits, their tabular form, and the pres- ence of abundant unsorted plant matter. Regardless of the genesis of carbonaceous shale, mega- floras and microfloras found in it are distinct from those recovered from lenticular units. Typical localities in the car- bonaceous shale produce 10—20 species, commonly with strongly predominant taxodiaceous conifers Glyptostrobus or Metasequoia, or the broad-leaved trees Alnus, Platycarya, or Dombeya. Several species of ferns and the gingerlike monocot Zingiberopsis are also locally abundant. Floating aquatic and emergent aquatic plants are rare in the carbon- aceous shale. Palynofloras from this depositional setting reflect the composition of the megaflora reasonably well, being dominated by pollen of Taxodicaeae, the broad-leaved genera mentioned above, and fern spores. Reworked palyno- morphs and those possibly derived from more distant vege- tation (for example, Pinus) are relatively rare in the carbonaceous shale (Farley, 1987, and in press). The interlaminated silt and sand was interpreted by Wing (19843) as representing deposition in regions closer to the channel, for example upper point bars, levees, or splays. Recent field work has shown that some of the bedforms preserved in this lithology were generated by oscillatory rip- ples (Erik Kvale, written commun., 1989). This genesis again raises the possibility of deposition in a body of stand- ing water, although waves within a channel could have been responsible. Whatever the depositional environment of this lithology, it preserves floras distinct from those of carbon- aceous shales at equivalent stratigraphic levels. Generally taxodiaceous conifers are less important, and a variety of taxa that today occupy streamside habitats are predominant (for example, Platanus, Populus, Cercidiphyllum). As with the carbonaceous shale assemblages, floating aquatic plants are quite rare. Presumably assemblages derived from this depositional environment reflect vegetation growing in coarser, less inundated soils than those of the distal flood- plain backswamp. 60 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING EXCEPTIONAL LOCALITIES Several levels within the Willwood Formation have been especially productive of plant megafossils. A tabular carbonaceous shale at the 112-m level of the Sehankler— Wing section is exposed along the east side of the South Fork of Elk Creek. The collections made from this unit (from localities NM37639—NM37650, pl. 1) are the best sample of the earliest Eocene flora of North America. Palynologically, this level is considered to be just above the Paleocene- Eocene boundary because it is the first appearance datum for Platycarya pollen (Wing, 1984b). The composition of the flora at this level is very similar to typical Paleocene floras reported from the upper part of the Fort Union Formation (Brown, 1962; Hickey, 1977), with the addition of a few Eocene megafloral indicators such as Lygodium kaulfussi and Cnemadaria magna. The flora of this bed also clearly shows the effect of depositional environment on megafloral and palynofloral composition (Wing, 1981; Farley, 1987). Four especially productive lenticular deposits are at localities NM37654 (311 m), NM37661 and SW882 (429 m), and NM37560 (468 In). Each of these floras has the floating aquatic species characteristic of pond assemblages as well as riparian elements. The number of species pre- served in these deposits rises up through the section from 22 at the 31 l-m level, to 25 or 30 at the 429-m level, to approx- imately 35 at the 468-m level. As yet there are too few len- ticular unit localities at each stratigraphic level to know if this relationship represents a true up-section increase in flo- ral diversity. A 1—3—m-thick tabular carbonaceous unit that crops out on the south side of Fifteenmile Creek (localities NM37669—NM37675, SW8826—SW8828, and others; 621- m level) is the most productive plant-fossil bed in the Will- wood Formation. As of 1989 this bed had been traced to the east side of the Squaw Buttes Divide (pl. 1), documenting an east-west lateral extent of more than 1 1 km. The bed extends north-south at least 4.8 km, and if a similar bed on Tatman Mountain (pl. 1) proves to be the same unit, the north-south dimension would be increased to about 13 km. Over most of the outcrop area, this layer produces plant megafossils, and in some regions the preservation is excellent, with both cuti- cle and fine venation present on many specimens. Overall, the geometry and lithology of this bed are similar to those of tabular carbonaceous units in the lower part of the Willwood Formation, although the bed is thicker and more laterally extensive. The flora of the Fifteenmile Creek carbonaceous shale has more species than those of shale lower in the for- mation, both at individual localities and for the combined floras of whole beds. As with the lenticular beds, there is an indication of up—section increase in number of species even within similar depositional environments. The flora of this level includes several species (Populus wyomingiana, Platy- carya castaneopsis, Dalbergia sp., and Eugenia americana) known from parts of the Wind River Formation (Wind River Basin) and Green River Formation (Green River Basin) in central and southern Wyoming that produce late Wasatchian mammal faunas. The location and stratigraphic distribution of the most important Paleocene and Eocene fossil plant localities in the southern Bighorn Basin are given in table 20, and a prelimi- nary list of the Willwood megaflora is presented in table 21. REFERENCES CITED Badgley, Catherine, 1989, A statistical assessment of last appear- ances in the fossil record of Eocene mammals, in Bown, T.M., and Rose, K.D., eds., Dawn of the age of mammals in the northern part of the Rocky Mountain interior, North America: Geological Society of America Special Paper 243, p. 153-168. Badgley, Catherine, and Gingerich, PD, 1988. Sampling and fau- nal turnover in Early Eocene mammals: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 63. p. 41—57. Billings, M.P., 1965, Structural geology (2nd ed.): Englewood Cliffs, N.J., Prentice-Hall, 514 p. Bookstein, F.L., Gingerich, P.D., and Kluge, A.G.. 1977, Hierar- chical linear modeling of the tempo and mode of evolution: Paleobiology, v. 4, p. 120—134. Bown, T.M., 1974, Notes on some early Eocene anaptomorphine primates: Contributions to Geology, v. 13, p. 19—26. 1975, Paleocene and lower Eocene rocks in the Sand Creek- No Water Creek area, Washakic County, Wyoming: Wyoming Geological Association. 27th Annual Field Conference Guide— book, p. 55—61. 1977, Geology and mammalian paleontology of the Sand Creek facies, lower Willwood Formation (lower Eocene), Washakic County, Wyoming [abs.]: Dissertation Abstracts International, v. 38, p. 597. 1979, Geology and mammalian paleontology of the Sand Creek facies, lower Willwood Formation (lower Eocene), Washakic County, Wyoming: Geological Survey of Wyoming Memoir 2, 151 p. 1980, The Willwood Formation (lower Eocene) of the south— ern Bighorn Basin, Wyoming, and its mammalian fauna, in Gingerich, P.D., ed., Early Cenozoic paleontology and stratig- raphy of the Bighorn Basin. Wyoming: University of Michigan Museum Papers on Paleontology 24, p. 127—138. 1982, Geology, paleontology, and correlation of Eocene vol- caniclastic rocks, southeast Absaroka Range, Hot Springs County, Wyoming: U.S. Geological Survey Professional Paper 1201—A, 75 p. 1984, Biostrati graphic significance of haselevel changes dur- ing deposition of the Willwood Formation (lower Eocene). Bighorn Basin, Wyoming [abs.]: Geological Society of Amer— ica. Rocky Mountain Section Annual Meeting, Abstracts, v. 16. p. 216. 1985, Maturation sequences in lower Eocene alluvial paleo- sols. Willwood Formation. in Flores, R.M., and Harvey, M., eds., Field guidebook to modern and ancient fluvial systems in the United States: Third lntemational Fluvial Sedimentology Conference, Fort Collins, Colo., Guidebook, p. 20—26. REFERENCES CITED 6] Table 20. US National Museum fossil plant localities in the Fort Union and Willwood Formations of the south—central Bighorn Basin, Wyoming. [Localities NM37686 and NM37687 are in the Tatman Formation, and locality NM37627 is in the Fort Union Formation; all other localities are in the Willwood Formation. m, meter level; B, Bown section; S, Schankler-Wing section; K, Kraus section; EB, estimated into Bown section; 7. unknown. Localities are given to the nearest quarter section and shown on plate 1. All quadrangles have US. Geological Survey 7 lIZ-minute topographic maps at scale 1:24.000. Localities represent collecting efforts by S.L. Wing from 1976 to 1990] Locality Stratigraphic Topographic No. position Location quadrangle NM37560 457 m B SW14 sec. 25, T. 50 N., R. 96 W. Wardel Reservoir. NM37627 -20 m S SW14 sec. 29, T. 51 N., R. 93 W. Orchard Bench. NM37638 100 m S NE14 sec. 31, T. 51 N., R. 93 W. Orchard Bench. NM37639 112 m S SW14 sec. 16, T. 50 N., R. 93 W. Orchard Bench. NM37640 112 m S NE14 sec. 29, T. 50 N., R. 93 W. Orchard Bench. NM37641 112 m S SE14 sec. 20, T. 50 N., R. 93 W. Orchard Bench. NM37643 112 m S NE14 sec. 20, T. 50 N., R. 93 W. Orchard Bench. NM37645 112 m S NE14 sec. 20, T. 50 N., R. 93 W. Orchard Bench. NM37648 112 m S SE% sec. 17, T. 50 N., R. 93 W. Orchard Bench. NM37650 124 m S SW14 sec. 21, T. 50 N., R. 93 W. Orchard Bench. NM37654 311 m S SE1/4 sec. 34, T. 50 N., R. 94 W. Jones Reservoir. NM37655 312 m S SW14 sec. 25, T. 51 N., R. 95 W. Jones Reservoir. NM37656 353 m S NW'A sec. 1‘, T. 50 N., R. ‘95 W. Jones Reservoir. NM37661 420 m S SE14 sec. 25, T. 50 N., R. 96 W. Wardel Reservoir. NM37662 423 m K NE14 sec. 3, T. 50 N., R. 96 W. Sheep Mountain. NM37667 601 m S NE14 sec. 26, T. 49 N., R. 98 W. Dead Indian Hill. NM37668 601 m S NE14 sec. 26, T. 49 N., R. 98 W. Dead Indian Hill. NM37669 621 m S SW14 sec. 25, T. 49 N., R. 98 W. Dead Indian Hill. NM37672 621 m S SE'A sec. 31, T. 49 N., R. 97 W. Dead Indian Hill. NM37673 621 m S SW14 sec. 25, T. 49 N., R. 98 W. Dead Indian Hill. NM37674 621 m S NE14 sec. 35, T. 49 N., R. 98 W. Dead Indian Hill. NM37675 621 m S SW14 sec. 25, T. 49 N., R. 98 W. Dead Indian Hill. NM37677 626 m S NW'4 sec. 6, T. 48 N., R. 97 W. Dead Indian Hill. NM37679 706 m S SE14 sec. 1, T. 48 N., R. 97 W. Dead Indian Hill. NM37680 706 m S SE14 sec. 1, T. 48 N., R. 97 W. Dead Indian Hill. NM37682 719 m S SW14 sec. 35, T. 49 N., R. 97 W. Dutch Nick Flat NW. NM37683 719 m S SE% sec. 35, T. 49 N., R. 97 W. Dutch Nick Flat NW. NM37684 719 m S SE14 sec. 35, T. 49 N., R. 97 W. Dutch Nick Flat NW. NM37685 719 m S SW1/4 sec. 35, T. 49 N., R. 97 W. Dutch Nick Flat NW. NM37686 740 m S SW14 sec. 6, T. 49 N., R. 97 W. Dead Indian Hill. NM37687 740 m S SW14 sec. 6, T. 49 N., R. 97 W. Dead Indian Hill. SW881 ?m NE14 sec. 31, T. 49 N., R. 97 W. Dead Indian Hill. SW882 ?m SW'4 sec. 15, T. 48 N., R. 94 W. Schuster Flats NW. SW8826 ?m NE14 sec. 31, T. 49 N., R. 97 W. Dead Indian Hill. SW8827 ?m SE14 sec. 31, T. 49 N., R. 97 W. Dead Indian Hill. SW8828 ?m SE14 sec. 31, T. 49 N., R. 97 W. Dead Indian Hill. SW8831 344 m EB NE14 sec. 32, T. 48 N., R. 93 W. Schuster Flats SE. 62 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 21. Provisional megafloral taxa of the Willwood Formation. southern Bighorn Basin, Wyoming. [Range is in meters above the contact of the Willwood Formation and the Fort Union Formation. A range bottom of 0 is assigned to species known to occur in rocks stratigraphically below the base of the Willwood Formation. Binomials within quotation marks refer to informal designations in Wing (1981) and are not validly published binomials. Generic names followed by queries indicate that the name is valid but the generic assignment is questionable; names in parentheses indicate alternative generic assignments that reflect other au- thors' interpretations of generic boundaries; and names within quotation marks are valid. but the assignment to this genus is incorrect. Taxa assigned to Roman numerals were cited as incertae sedis forms by Wing (1981), and names in parentheses following the Roman numerals are best guesses at familial assignments. Species names with an asterisk were not mentioned by Wing (1981). Continued collection of the flora of the Willwood Formation has resulted in an ever-increasing number of species. This list does not include at least 20 species of dicotyledonous leaves alone, and if fruits and flowers represent species not seen in the leaf flora. the total number of species not represented in this list could be as many as 50] Species Range 1 Alismataceae? sp. ("Sparganium" stygium) .......................................... 0-740 2 Allanloidiopsis erosa ........................................................ 0—719 3 Alnus sp. ("A/nus atkinsii" of Wing, 1981) .......................................... 0-740 4 Ampelopsis? acerifalia ....................................................... 0-112 5 Apocynaceae sp. ("Apocynophyllum palustrum" of Wing, 1981) ............................. 621 6 Averrhoites afi‘inis .......................................................... 0-706 7 Azolla sp.* .............................................................. 420 8 Betulaceae sp. ("Catryla schankleri" of Wing, 1981) .................................... 112-420 9 Cercidiphyllum (Jofi'rea?) genetrix ............................................... 0—621 10 Cnemidaria (Hemitelia) magna ................................................. 15-719 11 Camus hyperborea ......................................................... 0-20 12 Dalbergia? sp. (Leguminosae) Dicotyledones incertae sedis .................................................. 468-621 13 [(Annonaceac?) .......................................................... 621—740 14 II ................................................................... 621 15 III (Magnoliaceae?) ........................................................ 601-719 16 IV ................................................................... 112 17 V ................................................................... 150 18 VI (Burseraceae?) ......................................................... 112—311 19 X ................................................................... 621—706 20 XI ................................................................... 621 21 XII (Magnoliaceac?) ........................................................ 621 22 XIV (Menispcrmaceac?) ..................................................... 468 23 XV (Cucurbitaccae?) ....................................................... 311 24 XVI (Sapindaceac?, Anacardiaccae?, Juglandaccae?) .................................... 420 25 XVII (Lauraccae?) ......................................................... 353—621 26 XVIII ................................................................. 150 27 XIX .................................................................. 420 28 XX (Leguminosae?, Sapindaceac?, Burseraceac?) ..................................... 20-311 29 XXI (Tiliaceae?) .......................................................... 112 30 XXII (Lauraccae?) ......................................................... 621 31 XXIII (aff. Zizyplms) ....................................................... 353 32 XXIV (Aquifoliaceae?, Monimiaceae?) .......... > .................................. 150 33 XXV (Icacinaceac7, Malpighiaccae?) ............................................. 621—719 34 XXVI ................................................................. 112 35 XXVII (Malvaceac?, Tiliaceae?, Sterculiaccac?) ...................................... 621 36 Dombeya? novi—mundi (Malvaceac, Sterculiaceae, Tiliaccae) ............................... 311-740 REFERENCES CITED 63 Table 21. Provisional megafloral laxa of the Willwood Formation. soulhcm Bighorn Basin, Wyoming—Continued. Species Range 37 Equisetum sp. .................................................................... 0-740 38 Eugenia? americana* (Myrtaceae) ...................................................... 621 39 Fagopsis cf. undulata* .............................................................. 60-740 40 Flacourtiaceae sp. 1 ("Idesia canutaurensis" of Wing, 1981) .................................... 150 41 Flacourtiaceae sp. 2 ("Populus" wyomingiana)* ............................................. 621 42 Flacourtiaceae sp. 3 ("Salix paucisecondaria" of Wing, 1981) ................................... 420 43 Ginkgo adiantoides ................................................................ 0-420 44 Glyptostrobux europaeus ............................................................ 0-621 45 Hamamelidaceae sp. ("Churchillia crenata" of Wing, 1981) .................................... 0-353 46 Juglandaceae Sp. 1 (aff. "Carya" antiquorum) .............................................. 0-353 47 Juglandaceae sp. 2 ("Vinea basinensis" of Wing (1981) ....................................... 420 48 Leguminosae sp. 1 ("Leguminosites alcerivalis" of Wing, 1981) ................................. 420 49 Leguminosae sp. 2 (DICOT IX of Wing, 1981) ............................................. 468 50 Leguminosae sp. 3 (DICOT VIII of Wing, 1981) ............................................ 468 51 Leguminosae sp. 4 (DICOT VII of Wing, 1981) ............................................ 420 52 Leguminosae sp. 5 (microphyllous)* .................................................... 468 53 Lygodium kaulfussi ................................................................ 112-740 54 "Meliosma" langifolia (Platanaceae) ..................................................... 0-311 55 Menispermaceae sp. ("Menispermites afevius" of Wing, 1981) .................................. 150 56 Menispermites parvareolatus .......................................................... 0-429 57 Metasequoia occidentalis ............................................................ 0-353 58 Palmae incertae xedix (indetenninable palm) ............................................... 0—740 59 Palmae incertae xedis (indeterminable fan palm) ............................................ 0-740 60 Penosphyllum cordatum ............................................................. 0-30 61 Perxites arqutus ................................................................... 0—112 62 Phoebe? sp. (Lauraceae) ............................................................. 10-353 63 Platanus (Macqinitiea) brownii ........................................................ 420 64 Platanus cf. quillelmae .............................................................. 420-601? 65 Platanus (Macqinitiea) gracilis ........................................................ 0-621 66 Platanus raynoldsii ................................................................ 0-626 67 Platycarya castaneopxis ............................................................. 621-740 68 Polyptera sp.* .................................................................... 100 69 Populus cf. meeqsii ................................................................ 112—740 70 Potamogeton Sp. 1 ................................................................. 10 71 Potamogelon Sp. 2* ................................................................ 420-468 72 Pteropsida incertae sedis (indeterminate fem of Wing, 1981) ................................... 621 73 Salvinia preauriculata .............................................................. 100-621 74 Sapindaceae sp. (Acer-like samaras) ..................................................... 0-353 75 Schoepfia? cf. republicensis (Acrovena laevis of Wing, 1981) ................................... 621 76 Spirodela magna .................................................................. 420 77 Theaceae sp. 1 (DICOT XXVIH of Wing, 1981) ............................................ 621 78 Thelypteris iddz'ngsii ................................................................ 621-740 79 Thelypteris weedii“ ................................................................ 621-740 80 aff. Typha ....................................................................... 0-740 81 Ulmus (Chaeloptelea) microphyllum ..................................................... 0-353 82 Woodwardia gravida ............................................................... 0-112 83 Zingiberopsis isonervosa ............................................................ 0-740 64 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN. WYOMING 1987, The mammalian pedofacies; a novel approach to detailed vertico-lateral and temporal controls in vertebrate facies distribution and mammalian evolution [abs]: Geologi- cal Society of America, Rocky Mountain Section, 40th Annual Meeting, Abstracts with Programs, v. 19, no. 5, p. 262. 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Wood, H.E., 11, Chaney, R.W., Clark, John, Colbert, E..H. Jepsen, G.L., Reeside, J.B., Jr., and Stock, Chester, 1941, Nomencla- ture and correlation of the North American continental Terti- ary: Geological Society of America Bulletin. v. 52, p. 1—48. Woodhume, M.O., ed., 1987, Cenozoic mammals of North Ameri- ca; geochronology and biostratigraphy: Berkeley, University of California Press, 336 p. Wyoming Geological Association, 1968, Tertiary well-logs in all Wyoming basins; Log #4, Washakie County. Gulf Oil Corpo- ration. #1, Teeters: Wyoming Geological Association, well log. 1 sheet. 68 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 2. US Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south— ern Bighorn Basin, Wyoming. [All localities are in the Willwood Formation except D1578 and D1580. m, meter level (minus values denote position beneath top of Fort Union Formation); B, Bown sections; S, Schankler-Wing sections; K. Kraus sections; E, stratigraphic position estimated during Bown‘s sectioning; EB, into Bown sections; EK, into Kraus sections; ES, into Schankler- Wing sections; 7, unknown. Localities are given to the nearest quarter section and are shown on plates 1 and 2. Names of topographic quadrangles in which the localities occur follow locality information. All are US. Geological Survey 7 1rz-minute topographic maps at scale 1:24,000. unless otherwise indicated. Names in parentheses following the quad— rangle names are other names by which the localities are known or equivalent localities established by other institutions. Localities represent collecting efforts of the US. Geological Survey in 1977—79 and of the joint US. Geological Survey-Johns Hopkins University School of Medicine expeditions from 1980 to 1992] Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1128 470 m B NW14 sec. 33, T. 49 N., R. 95 W. Sucker Dam. D1136 ?m ......... NW14 sec. 28, T. 54 N., R. 100 W. Vocation. D1137 ?m ......... SW14 sec. 22, T. 54 N., R. 100 W. Vocation. D1138 7m ......... SW14 sec. 22, T. 54 N., R. 100 W. Vocation. D1139 ?m ......... SW14 sec. 22, T. 54 N., R. 100 W. Vocation. D1140 ?m ......... SE14 sec. 29, T. 54 N., R. 100 W. Vocation. D1141 290 m ES . . . . SW14 sec. 32, T. 51 N., R. 94 W. Jones Reservoir. D1142 275 m EB . . . . SW14 sec. 32, T. 51 N., R. 94 W. Jones Reservoir. D1143 280 m ES . . . . NE14 sec. 31, T. 51N., R. 94 W. Jones Reservoir. D1144 285 m ES . . . . SW14 sec. 31, T. 51 N., R. 94 W. Jones Reservoir. D1145 300 in BB . . . . SE14 sec. 36, T. 51 N., R. 95 W. Jones Reservoir. D1146 300 m EB . . . . SW14 sec. 31, T. 51 N., R. 94 W. Jones Reservoir. D1147 ?m ......... NE14 sec. 24, T. 54 N., R. 100 W. Ralston Reservoir. D1148 ?m ......... NW14 sec. 33, T. 53 N., R. 99 W. Stone Barn Camp. D1149 ?m ......... SE14 sec. 33, T. 53 N., R. 99 W. Stone Barn Camp. D1150 ?m ......... SE14 sec. 1, T. 54 N., R. 99 W. Gilmore Hill NW. D1151 ?m ......... SW14 sec. 1, T. 54 N., R. 99 W. Gilmore Hill NW. D1152 ?m ......... NE‘A sec. 11, T. 54 N., R. 99 W. Gilmore Hill NW. D1153 ?m ......... NW14 sec. 15, T. 53 N., R. 100 W. Corbet Dam. D1154 ?m ......... NE14 sec. 11, T. 47 N., R. 95 W. Schuster Flats. D1155 ?m ......... NW14 sec. 4, T. 47 N., R. 95 W. Dutch Nick Flat. D1156 482 m B ..... SW14 sec. 23, T. 48 N., R. 96 W. Dutch Nick Flat. D1157 478 m B ..... NW14 sec. 23, T. 48 N., R. 96 W. Dutch Nick Flat. D1158 482 m B ..... SW14 sec. 23, T. 48 N., R. 96 W. Dutch Nick Flat. D1159 482 m B ..... SW14 sec. 23, T. 48 N., R. 96 W. Dutch Nick Flat. D1160 470 m B ..... NW14 sec. 28, T. 49 N., R. 95 W. Sucker Dam. D1160N 470 m B ..... SW14 sec. 21, T. 49 N., R. 95 W. Sucker Dam. D1161 472 m EB . . . . SW14 sec. 18, T. 48 N., R. 95 W. Sucker Dam. D1162 481 m S ..... SW14 sec. 34, T. 49 N., R. 96 W. Dutch Nick Flat NW (Chriacus locality). D1163 491 m EB . . . . SW14 sec. 5, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1164 476 m B ..... SE14 sec. 34, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1165 486 m EB . . . . NW'A sec. 5, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1166 481 in ES . . . . SW14 sec. 33, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1167 511 m B ..... NW% sec. 31, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1168 ?m ......... SE14 sec. 8, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1169 491m EB . . . . SW14 sec. 5, T. 48 N., R. 96 W. Dutch Nick Flat NW. Table 2. em Bighorn Basin, Wyoming—Continued. TABLES 2—6 69 US Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1170 531 m ES . . . . NE54 sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1171 526 m EB . . . . NE54 sec. 36, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1172 556 m EB . . . . SE54 sec. 36, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1173 536 m EB NE54 sec. 36, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1174 501 m ES NE54 sec. 13, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1175 501 m ES . . . . SE14 sec. 12, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1176 511 m EB . . . . SW54 sec. 12, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1177 481 m B ..... NE54 sec. 28, T. 49 N., R. 95 W. Sucker Dam (Purple Hills). D1178 160 m S ..... SE54 sec. 30, T. 50 N., R. 93 W. Orchard Bench. D1179 ?m ......... SW54 sec. 35, T. 54 N., R. 97 W. Gilmore Hill SE. D1180 ?m ......... NW54 sec. 5, T. 53 N., R. 96 W. Emblem. D1181 ?m ......... NW54 sec. 35, T. 54 N., R. 96 W. Emblem. D1182 ?m ......... SW54 sec. 3, T. 50 N., R. 94 W. Jones Reservoir. D1183 290 m ES SW54 sec. 25, T. 51 N., R. 95 W. Jones Reservoir. D1184 ?m ......... SW'/4 sec. 15, T. 51 N., R. 94 W. Gould Butte (Deerfly locality). D1185 ?m ......... NW54 sec. 14, T. 51 N., R. 94 W. Gould Butte. D1186 ?m ......... SW54 sec. 18, T. 46 N., R. 94 W. Chimney Gulch. D1187 7m ......... NW54 sec. 30, T. 46 N., R. 94 W. Chimney Gulch. D1188 140 m EB . . . . SE54 sec. 29, T. 50 N., R. 93 W. Orchard Bench. D1189 175 m EB . . . . NE54 sec. 32, T. 50 N., R. 93 W. Orchard Bench. D1190 130 m S ..... SE14 sec. 29, T. 50 N., R. 93 W. Orchard Bench. D1191 130 m EB . . . . NE54 sec. 29, T. 50 N., R. 93 W. Orchard Bench. D1192 170 m S ..... NE14 sec. 32, T. 50 N., R. 93 W. Orchard Bench. D1193 170 m S ..... SE‘4 sec. 32, T. 50 N., R. 93 W. Orchard Bench. D1194 140 m EB SW'4 sec. 7, T. 50 N., R. 93 W. Orchard Bench. D1195 140 m EB . NE'A sec. 30, T. 50 N., R. 93 W. Orchard Bench. D1196 ?m ......... NW54 sec. 34, T. 47 N., R. 94 W. Schuster Flats SE. D1197 481m S ..... NE54 sec. 10, T. 48 N., R. 96 W. Sucker Dam. D1198A 470 m B ..... NW54 sec. 33, T. 49 N., R. 95 W. Sucker Dam. D119SB 470 m B ..... NW54 sec. 33, T. 49 N., R. 95 W. Sucker Dam (equal to Y45). D1198C 470 m B ..... SW54 sec. 5, T. 48 N., R. 95 W. Sucker Dam (equal to Y45). D1198D 470 m B ..... SW54 sec. 28, T. 49 N., R. 95 W. Sucker Dam. D1198E 470 m B ..... NE54 sec. 33, T. 49 N., R. 95 W. Sucker Dam. D1198F 470 m B ..... NW14 sec. 33, T. 49 N., R. 95 W. Sucker Dam. D119SG 470 m B ..... NE54 sec. 5, T. 48 N., R. 95 W. Sucker Dam. D1198H 470 m B ..... NW54 sec. 5, T. 48 N., R. 95 W. Sucker Dam. D1199 10 m EB ..... NE54 sec. 27, T. 47 N., R. 91 W. Worland SE. D1200 370 m B ..... NW54 sec. 3, T. 47 N., R. 94 W. Schuster Flats. D1201 344 m B ..... NE54 sec. 6, T. 48 N., R. 93 W. Schuster Flats NE. D1201N 344 m B ..... NE54 sec. 6, T. 48 N., R. 93 W. Schuster Flats NE. D1202 324 m EB NW54 sec. 30, T. 49 N., R. 93 W. Schuster Flats NE (equal to Y133). D1203 438 m B ..... SE54 sec. 7, T. 48 N., R. 94 W. Schuster Flats NW (Rose Flats). 70 Table 2. cm Bighorn Basin, Wyoming—Continued. FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN, WYOMING US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south— Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1204 444 m B, upper; NW54 sec. 8, T. 48 N., R. 94 W. Schuster Flats NW 442 m B, middle; (Kraus Flats 438 m B, lower. Bonanza). D1205 356 m B ..... SE54 sec. 34, T. 48 N., R. 94 W. Schuster Flats SE. D1206 438 m EB . NW54 sec. 15, T. 48 N., R. 94 W. Schuster Flats NE. D1207 448 m B ..... SE54 sec. 6, T. 48 N., R. 94 W. Schuster Flats NW. D1208 438 m B ..... SW54 sec. 5, T. 48 N., R. 94 W. Schuster Flats NW. D1209 452 m B ..... NE54 sec. 6, T. 48 N., R. 94 W. Schuster Flats NW. D1210 458 m EB SW54 sec. 29, T. 49 N., R. 94 W. Schuster Flats NW. D1211 ?m ......... SW54 sec. 27, T. 54 N., R. 96 W. Jack Homer Reservoir. D1212 546 m EB . . . . NE54 sec. 27, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1213 7m ......... SW54 sec. 6, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1214 ?m ......... NW54 sec. 6, T. 49 N., R. 96 W. Sheep Mountain. D1215 7m ......... NW54 sec. 5, T. 49 N., R. 96 W. Sheep Mountain. D1216 380 m B ..... NW54 sec. 33, T. 48 N., R. 94 W. Schuster Flats. D1217 412 m B ..... NE54 sec. 20, T. 48 N., R. 94 W. Schuster Flats. D1218 392 m B ..... SW54 sec. 28, T. 48 N., R. 94 W. Schuster Flats. D1219 392 m B ..... SW54 sec. 21, T. 48 N., R. 94 W. Schuster Flats. D1220 370 m B ..... SE54 sec. 33, T. 48 N., R. 94 W. Schuster Flats. D1221 384 m B ..... NW54 sec. 33, T. 48 N., R. 94 W. Schuster Flats. D1222 400 m B ..... NE54 sec. 21, T. 48 N., R. 94 W. Schuster Flats. D1223 180 m B ..... SE'A sec. 27, T. 47 N., R. 93 W. Schuster Flats SE. D1224 180 m B ..... NW54 sec. 27, T. 47 N., R. 93 W. Schuster Flats SE (equal to Big "W", W125). D1225 180 m B ..... NE‘A sec. 28, T. 47 N., R. 93 W. Schuster Flats SE. D1226 180 m B ..... SE54 sec. 27, T. 47 N., R. 93 W. Schuster Flats SE. D1227 ?m ......... NW54 sec. 10, T. 47 N., R. 92 W. Worland. D1228 81 m B ...... NW54 sec. 4, T. 46 N., R. 91 W. Banjo Flats East. D1229 481 m S ..... SW54 sec. 3, T. 48 N., R. 96 W. Sucker Dam (Moocow Hollow locality, equal to Y42). D1230 490 m B ..... SW54 sec. 14, T. 48 N., R. 96 W. Sucker Dam (Fossil Hollow Bonanza, includes UMRB-lO). D1231 7m ......... SW54 sec. 26, T. 53 N., R. 96 W. Emblem. D1232 ?m ......... NE54 sec. 21, T. 52 N., R. 99 W. Oregon Basin (scale 1:62,500). D1233 ?m ......... NE54 sec. 16, T. 52 N., R. 99 W. Oregon Basin (scale 1:62,500). D1234 425 m K ..... NW54 sec. 14, T. 50 N., R. 96 W. Wardel Reservoir (includes Y247). D1235 414 EK ...... SE54 sec. 15, T. 50 N., R. 96 W. Wardel Reservoir (includes Y69). D1236 ?m ......... NE54 sec. 16, T. 51 N., R. 94 W. Gould Butte. D1237 ?m ......... NW54 sec. 36, T. 52 N., R. 95 W. Gould Butte. D1238 ?m ......... SW54 sec. 36, T. 52 N., R. 95 W. Gould Butte. TABLES 2—6 71 Table 2. US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south— ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1239 ?m ......... SE54 sec. 22, T. 51 N., R. 95 W. Wardel Reservoir. D1240 408 m EK SE54 sec. 22, T. 50 N., R. 96 W. Sheep Mountain. D1241 270 m B ..... SW54 sec. 9, T. 47 N., R. 93 W. Schuster Flats SE. D1242 379 m B ..... SW54 sec. 31, T. 49 N., R. 93 W. Schuster Flats NE. D1243 348 m EB SW54 sec. 5, T. 48 N., R. 93 W. Schuster Flats NE. D1244 470 m B ..... NW54 sec. 8, T. 48 N., R. 95 W. Sucker Dam. D1245 477 m B ..... SE54 sec. 28, T. 49 N., R. 95 W. Sucker Dam (Oxyaena locality). D1246 482 m B ..... SE54 sec. 28, T. 49 N., R. 95 W. Sucker Dam (Esthonyx locality). D1247 ?m ......... NW54 sec. 16, T. 47 N., R. 96 W. Dutch Nick Flat SW. D1248 ?m ......... Center sec. 28, T. 53 N., R. 96 W. Emblem. D1249 ?m ......... SW54 sec. 27, T. 48 N., R. 93 W. Schuster Flats SE. D1250 461 m B ..... SW54 sec. 35, T. 50 N., R. 96 W. Wardel Reservoir. D1251 378 m B ..... NW54 sec. 33, T. 48 N., R. 94 W. Schuster Flats. D1252 ?m ......... SW54 sec. 20, T. 52 N., R. 96 W. Burlington. D1253 ?m ......... SW54 sec. 24, T. 47 N., R. 95 W. Schuster Flats. D1254 ?m ......... SW54 sec. 25, T. 47 N., R. 95 W. Schuster Flats. D1255 490 m EB . . . . NE54 sec. 10, T. 47 N., R. 95 W. Schuster Flats. D1256 546 m S ..... NE54 sec. 12, T. 48 N., R. 97 W. Dutch Nick Flat NW (Bobcat Draw Bonanza). D1257 486 m B ..... NW54 sec. 35, T. 49 N., R. 95 W. Schuster Flats (Brinkerhoff Well locality). D1258 288 m ES SW54 sec. 35, T. 50 N., R. 94 W. Jones Reservoir. D1259 380 m EB . . . . SW54 sec. 3, T. 50 N., R. 95 W. Wardel Reservoir. D1260 ?m ......... NW54 sec. 34, T. 51 N., R. 96 W. Sheep Mountain. D1261 410 m EK . . . . SE54 sec. 22, T. 50 N., R. 96 W. Wardel Reservoir. D1262 140 m B ..... NW54 sec. 19, T. 50 N., R. 93 W. Orchard Bench. D1264 ?m ......... NW54 sec. 33, T. 51 N., R. 96 W. Sheep Mountain. D1265 ?m ......... NE54 sec. 2, T. 55 N., R. 101 W. Elk Basin SW. D1266 285 m ES NE54 sec. 34, T. 50 N., R. 94 W. Jones Reservoir. D1267 ?m ......... SE54 sec. 13, T. 50 N., R. 94 W. Orchard Bench. D1280 ?m ......... NW54 sec. 9, T. 51 N., R. 97 W. Y-U Bench NE. D1281 7m ......... SE54 sec. 10, T. 51 N., R. 97 W. Burlington. D1282 352 m B ..... NW54 sec. 31, T. 48 N., R. 93 W. Schuster Flats SE. D1283 374 m B ..... SW54 sec. 30, T. 48 N., R. 93 W. Schuster Flats SE. D1284 338 m B ..... NE54 sec. 2, T. 47 N., R. 94 W. Schuster Flats SE. D1285 509 m B ..... SW% sec. 15, T. 49 N., R. 95 W. Sucker Dam. D1286 489 m B ..... NW54 sec. 22, T. 49 N., R. 95 W. Sucker Dam. D1287 346 m B ..... SE54 sec. 3, T. 47 N., R. 94 W. Schuster Flats SE. D1288 336 m B, upper; NW54 sec. 2, T. 47 N., R. 94 W. Schuster Flats SE. 332 m B, lower. D1289 342 m B ..... SE54 sec. 2, T. 47 N., R. 94 W. Schuster Flats SE. D1290 282 m B ..... SE% sec. 6, T. 47 N., R. 93 W. Schuster Flats SE. D1291 260 m B ..... NW54 sec. 8, T. 47 N., R. 93 W. Schuster Flats SE. 72 Table 2. cm Bighorn Basin, Wyoming—Continued. FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING U.S. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south— Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1292 368 m EB . . . . SW14 sec. 34, T. 48 N., R. 94 W. Schuster Flats SE. D1293 376 m EB . . . . NW14 sec. 27, T. 48 N., R. 94 W. Schuster Flats SE. D1294 342 m B ..... SW14 sec. 2, T. 47 N., R. 94 W. Schuster Flats SE. D1295 424 m B ..... SW14 sec. 13, T. 48 N., R. 95 W. Schuster Flats NW. D1296 30 m EB ..... NE14 sec. 12, T. 46 N., R. 92 W. Banjo Flats East. D1297 262 m B, upper; NW14 sec. 7, T. 47 N., R. 93 W. Schuster Flats SE. 260 m B, middle; and lower. D1298 278 m B ..... SW14 sec. 6, T. 47 N., R. 93 W. Schuster Flats SE. D1299 352 m B ..... NE‘4 sec. 2, T. 47 N., R. 94 W. Schuster Flats SE. D1300 378 m B ..... NW14 sec. 13, T. 48 N., R. 94 W. Schuster Flats NE. D1301 378 m B ..... NW14 sec. 13, T. 48 N., R. 94 W. Schuster Flats NE. D1302 334 m EB NE14 sec. 25, T. 49 N., R. 94 W. Schuster Flats NE. D1303 360 m B ..... SE14 sec. 30, T. 48 N., R. 93 W. Schuster Flats SE. D1304 516 m B ..... SE14 sec. 15, T. 49 N., R. 95 W. Sucker Dam. D1305 486 m B ..... SE14 sec. 27, T. 49 N., R. 95 W. Sucker Dam. D1306 410 m B ..... NE14 sec. 24, T. 48 N., R. 95 W. Schuster Flats. D1307 483 m B ..... NW14 sec. 29, T. 49 N., R. 95 W. Sucker Dam. D1308 448 m B ..... NE14 sec. 6, T. 48 N., R. 94 W. Schuster Flats NW. D1309 426 m B ..... NE14 see. 19, T. 48 N., R. 94 W. Schuster Flats. D1310 442 m B ..... SE14 sec. 36, T. 49 N., R. 95 W. Schuster Flats NW (Bell Bonanza). D1311 442 m B ..... NW14 sec. 2, T. 48 N., R. 95 W. Schuster Flats NW (Brinkerhoff Bonanza). D1312 483 m B ..... SW14 sec. 20, T. 49 N., R. 95 W. Sucker Dam. D1313 342 m B ..... NE‘A sec. 2, T. 47 N., R. 94 W. Schuster Flats SE. D1314 470 m B ..... NW14 sec. 28, T. 49 N., R. 95 W. Sucker Dam. D1315 470 m B ..... SE14 sec. 21, T. 49 N., R. 95 W. Sucker Dam. D1316 481 m B ..... SE14 sec. 21, T. 49 N., R. 95 W. Sucker Dam. D1317 483 m B ..... SW14 sec. 21, T. 49 N., R. 95 W. Sucker Dam. D1318 ?m ......... SE14 sec. 13, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1319 438 m B ..... SE14 sec. 2, T. 48 N., R. 95 W. Schuster Flats NW. D1320 438 m B ..... SW14 sec. 1, T. 48 N., R. 95 W. Schuster Flats NW. D1321 438 m B ..... NE14 sec. 1, T. 48 N., R. 95 W. Schuster Flats NW. D1322 438 m B ..... NE14 sec. 2, T. 48 N., R. 95 W. Schuster Flats NW. D1323 438 m B ..... NW14 sec. 2, T. 48 N., R. 95 W. Schuster Flats NW. D1324 424 m B ..... SE14 sec. 12, T. 48 N., R. 95 W. Schuster Flats NW. D1325 438 m B ..... NE14 sec. 11, T. 48 N., R. 95 W. Schuster Flats NW. D1326 425 m B ..... SW14 sec. 13, T. 49 N., R. 96 W. Sucker Dam (Dry Cottonwood Bonanza). D1327 ?m ......... SW'A sec. 24, T. 48 N., R. 99 W. Hillberry Rim. , D1328 292 m B ..... NW14 sec. 9, T. 47 N., R. 93 W. Schuster Flats SE. D1329 ?m ......... SW14 sec. 33, T. 48 N., R. 93 W. Schuster Flats SE. D1330 428 m B ..... SW% sec. 19, T. '49 N., R. 95 W. Sucker Dam. D1331 483 m B ..... SE14 sec. 29, T. 49 N., R. 95 W. Sucker Dam. TABLES 2—6 73 Table 2. US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- cm Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1332 360 m B ..... SE14 sec. 30, T. 48 N., R. 93 W. Schuster Flats SE. D1333 360 m B ..... SE14 sec. 30, T. 48 N., R. 93 W. Schuster Flats SE. D1334 360 m B ..... NW% sec. 31, T. 48 N., R. 93 W. Schuster Flats SE. D1335 346 m B, upper; SE54 sec. 31, T. 48 N., R. 93 W. Schuster Flats SE. 336 m B, lower. D1336 481 m B ..... NW% sec. 3, T. 48 N., R. 96 W. Sucker Dam. D1337 499 m EB . . . . NWIA sec. 29, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1338 491 m EB . . . . NE‘A sec. 29, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1338N 491 m EB . . . . NE‘Asec. 29, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1339 452 m B ..... NW% sec. 6, T. 48 N., R. 94 W. Schuster Flats NW. D1340Q 364 m B ..... NW'A sec. 32, T. 48 N., R. 93 W. Schuster Flats SE (Howard’s Quarry). D1341 384 m B ..... NW‘A sec. 33, T. 48 N., R. 94 W. Schuster Flats. D1342 390 m B ..... SW'A sec. 28, T. 48 N., R. 94 W. Schuster Flats. D1343 ?m ......... SW'A sec. 21, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1344 491 m EB . . . . NW'A sec. 20, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1345 491 m B ..... NW'A sec. 20, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1346 491 m B ..... SW% sec. 17, T. 49 N., R. 96 W. Dutch Nick Flat NW - (Anacodon locality). D1347 431 m B ..... NE‘A sec. 30, T. 49 N., R. 95 W. Sucker Dam. D1348 430 m B ..... NW% sec. 30, T. 49 N., R. 95 W. Sucker Dam. D1349 430 m B ..... SW'A sec. 30, T. 49 N., R. 95 W. Sucker Dam. D1350 410 m B, upper; Center sec. 19, T. 48 N., R. 94 W. Schuster Flats. 408 m B, lower. D13SOQ 410 m B ..... SW% sec. 19, T. 48 N., R. 94 W. Schuster Flats. D1369 292 m B ..... NE‘A sec. 11, T. 47 N., R. 94 W. Schuster Flats SE. D1370 384 m B ..... NW‘A sec. 33, T. 48 N., R. 94 W. Schuster Flats. D1371 370 m B ..... NW‘A sec. 3, T. 47 N., R. 94 W. Schuster Flats. D1372 356 m B ..... SE56 sec. 34, T. 48 N., R. 94 W. Schuster Flats SE. D1373 338 m B, upper; SW‘A sec. 8, T. 48 N., R. 93 W. Schuster Flats NE. 336 m B, lower. D1374 336 m B ..... SW14 sec. 5, T. 48 N., R. 93 W. Schuster Flats NE. D1375 511 m ES SW‘A sec. 12, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1376 430 m B ..... NE% sec. 18, T. 48 N., R. 94 W. Schuster Flats NW. D1377 436 m B ..... SW% sec. 7, T. 48 N., R. 94 W. Schuster Flats NW. D1378 430 m B ..... SE14 sec. 30, T. 49 N., R. 95 W. Sucker Dam. D1379 430 m B ..... SE% sec. 30, T. 49 N., R. 95 W. Sucker Dam. D1380 430 m B ..... SW'A sec. 30, T. 49 N., R. 95 W. Sucker Dam. D1381 430 m B ..... SE14 sec. 24, T. 49 N., R. 96 W. Sucker Dam. D1382 430 m B ..... SW‘A sec. 30, T. 49 N., R. 95 W. Sucker Dam. D1383 270 m B ..... SW‘A sec. 8, T. 47 N., R. 93 W. Schuster Flats SE. D1384 342 m B ..... NE‘A sec. 1, T. 47 N., R. 94 W. Schuster Flats SE. D1385 392 m B ..... NE'A sec. 29, T. 48 N., R. 94 W. Schuster Flats. D1386 344 m B ..... NE‘A sec. 30, T. 48 N., R. 93 W. Schuster Flats SE. D1387 360 m B ..... NE‘A sec. 30, T. 48 N., R. 93 W. Schuster Flats SE. 74 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 2. US Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1388 360 m B ..... NW56 sec. 30, T. 48 N., R. 93 W. Schuster Flats SE. D1389 264 m B ..... SW56 sec. 7, T. 47 N., R. 93 W. Schuster Flats SE. D1390 278 m B ..... NW56 sec. 7, T. 47 N., R. 93 W. Schuster Flats SE. D1391 356 m B ..... SW56 sec. 35, T. 48 N., R. 94 W. Schuster Flats SE. D1392 292 m B ..... NE56 sec. 11, T. 47 N., R. 94 W. Schuster Flats SE. D1393 296 m B ..... SE56 sec. 2, T. 47 N., R. 94 W. Schuster Flats SE. D1394 ?m ......... NE56 sec. 6, T. 51 N., R. 94 W. Gould Butte. D1395 324 m EB NE56 sec. 14, T. 47 N., R. 94 W. Schuster Flats SE. D1396 420 m B ..... SE56 sec. 13, T. 48 N., R. 95 W. Schuster Flats NW. D1397 483 m B ..... NE56 sec. 29, T. 49 N., R. 95 W. Sucker Dam. D1398 438 m B ..... NE56 sec. 14, T. 48 N., R. 95 W. Schuster Flats NW. D1399 434 m B ..... NE56 sec. 14, T. 48 N., R. 95 W. Schuster Flats NW. D1400 438 m B ..... SE56 sec. 11, T. 48 N., R. 95 W. Schuster Flats NW. D1401 438 m B ..... NW56 sec. 11, T. 48 N., R. 95 W. Schuster Flats NW. D1402 420 m B ..... NW56 sec. 24, T. 48 N., R. 95 W. Schuster Flats. D1403 420 m B ..... SW56 sec. 13, T. 48 N., R. 95 W. Schuster Flats NW. D1404 438 m B ..... SW56 sec. 6, T. 48 N., R. 94 W. Schuster Flats NW. D1405 438 m B ..... SW56 sec. 7, T. 48 N., R. 94 W. Schuster Flats NW. D1406 436 m B ..... SW56 sec. 9, T. 48 N., R. 94 W. Schuster Flats NW. D1407 442 m B ..... NW56 sec. 31, T. 49 N., R. 95 W. Schuster Flats NW. D1408 494 m B ..... SW56 sec. 23, T. 49 N., R. 95 W. Schuster Flats NW. D1409 455 m B ..... SE56 sec. 8, T. 48 N., R. 95 W. Sucker Dam. D1410 418 m B, upper; SE56 sec. 17, T. 48 N., R. 94 W. Schuster Flats NW. 416 m B, middle; 410 m B, lower. D1411 412 m B ..... NE56 sec. 20, T. 48 N., R. 94 W. Schuster Flats. D1412 364 m B ..... NE56 sec. 24, T. 48 N., R. 94 W. Schuster Flats SE. D1413 392 m B ..... SE56 sec. 14, T. 48 N., R. 94 W. Schuster Flats SE. D1414 378 m B ..... SE56 sec. 12, T. 48 N., R. 94 W. Schuster Flats NE. D1415 354 m EB . . . . NW56 sec. 7, T. 48 N., R. 93 W. Schuster Flats NE. D1416 354 m EB . . . . SE'A sec. 7, T. 48 N., R. 93 W. Schuster Flats NE. D1417 360 m B ..... SW56 sec. 7, T. 48 N., R. 93 W. Schuster Flats NE. D1418 282 m B ..... NE56 sec. 7, T. 47 N., R. 93 W. Schuster Flats SE. D1419 260 m B ..... NW56 sec. 8, T. 47 N., R. 93 W. Schuster Flats SE. D1420 360 m B ..... SW56 sec. 12, T. 48 N., R. 94 W. Schuster Flats NE. D1421 384 m B, upper; NE56 sec. 2, T. 48 N., R. 94 W. Schuster Flats NE. 379 m B, lower. D1422 370 m B ..... NE56 sec. 1, T. 48 N., R. 94 W. Schuster Flats NE. D1423 ?m ......... NE56 sec. 27, T. 49 N., R. 94 W. Schuster Flats NW. D1424 ?m ......... SW56 sec. 27, T. 49 W., R. 94 W. Schuster Flats NW. D1425 465 m EB SE56 sec. 30, T. 49 N., R. 94 W. Schuster Flats NW. D1426 490 m EB . NW56 sec. 30, T. 49 N., R. 94 W. Schuster Flats NW. D1427 ?m ......... NE56 sec. 14, T. 49 N., R. 94 W. Schuster Flats NE. D1428 440 m B ..... NW56 sec. 14, T. 49 N., R. 96 W. Sucker Dam. D1429 446 m B ..... SW56 sec. 11, T. 49 N., R. 96 W. Sucker Dam. D1430 455 m B ..... SE56 sec. 15, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1431 501 m S ..... NE56 sec. 24, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1432 501 m S ..... NE56 sec. 24, T. 49 N., R. 97 W. Dutch Nick Flat NW. TABLES 2—6 Table 2. U.S. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and southern Bighorn Basin, Wyoming—Continued. Towgraphic Locality Stratigraphic quadrangle No. position Location (other names) D1433 501 m S ..... NE14 sec. 24, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1434 496 m EB . . . . N814 sec. 19, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1435 501 m S ..... NW14 sec. 18, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1436 492 m S ..... SE14 sec. 12, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1437 511 m EB NE14 sec. 12, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1438 516 m B ..... NE14 sec. 15, T. 49 N., R. 95 W. Sucker Dam. D1439 446 m B ..... SE‘A sec. 10, T. 49 N., R. 96 W. Sucker Dam. D1440 7m ......... NE14 sec. 14, T. 49 N., R. 96 W. Sucker Dam. D1441 296 m B ..... SW14 sec. 1, T. 47 N., R. 94 W. Schuster Flats SE. D1442 No data ...... No data ................. No data. D1443 420 m B ..... NE‘A sec. 23, T. 48 N., R. 95 W. Schustcr Flats. D1444 No data ...... No data ................. No data. D1445 ?m ......... SW14 sec. 35, T. 51 N., R. 97 W. Sheep Mountain. D1446 7m ......... SW14 sec. 22, T. 52 N., R. 96 W. Burlington. D1447 113 m EB . . . . NW14 sec. 6, T. 46 N., R. 91 W. Banjo Flats East. D1448 ?m ......... NW14 sec. 9, T. 47 N., R. 94 W. Schuster Flats. D1449 344 m EB . . . . NW14 sec. 23, T. 47 N., R. 94 W. Schuster Flats SE. D1450 7m ......... NW14 sec. 20, T. 47 N., R. 94 W. Schuster Flats. D1451 448 m EB . . . . NW‘A sec. 18, T. 47 N., R. 94 W. Schuster Flats. D1452 440+ in BB . . . NE14 sec. 18, T. 47 N., R. 94 W. Schuster Flats. D1453 378 m B ..... SW14 sec. 13, T. 48 N., R. 94 W. Schuster Flats NE. D1454 409 m B ..... NE‘A sec. 7, T. 47 N., R. 94 W. Schuster Flats (Potala Bonanza). D1455 ?m ......... NW14 sec. 4, T. 52 N., R. 95 W. Emblem SE. D1456 ?m ......... NE14 sec. 19, T. 47 N., R. 93 W. Schuster Flats SE. D1457 ?m ......... NE14 sec. 19, T. 47 N., R. 93 W. Schuster Flats SE. D1458 400 m B ..... NW‘A sec. 8, T. 47 N., R. 94 W. Schuster Flats. D1459 438+ m EB . . . NE14 sec. 18, T. 47 N., R. 94 W. Schuster Flats. D1460 409 m B ..... SW14 sec. 8, T. 47 N., R. 94 W. Schuster Flats. D1460Q 411 m B ..... SW14 see. 8, T. 47 N., R. 94 W. Schuster Flats (Rose Quarry). D1461 180 in BB . . . . SE14 sec. 20, T. 47 N., R. 93 W. Schuster Flats SE. D1462 463 m EB . . . . NE14 sec. 13, T. 47 N., R. 95 W. Schuster Flats. D1463 546 m S ..... NW‘A sec. 7, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1464 546 m S ..... NE14 sec. 7, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1465 546 m ES SW14 sec. 8, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1466 516 m ES NE14 sec. 18, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1467 546 m S ..... SE14 sec. 7, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1468 501 m S ..... NE14 sec. 18, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1469 491 m B ..... SW14 sec. 17, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1470 491 m B ..... NW14 sec. 17, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1471 491 m BS NE'A sec. 8, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1472 ?m ......... SW14 sec. 9, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1473 556 m B ..... NW'A sec. 20, T. 48 N., R. 96 W. Dutch Nick Flat SW (Hoover Renner Reservoir Bonanza). D1474 496 m EB . . . . NE14 sec. 19, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1475 496 m EB . . . . SE14 sec. 18, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1476 ?m ......... NE14 sec. 24, T. 48 N ., R. 97 W. Dutch Nick Flat SW. 76 Table 2. FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN. WYOMING US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1477 7m ......... NW54 sec. 19, '1‘. 48 N., R. 96 W. Dutch Nick Flat SW. D1478 ?m ......... SE54 sec. 31, T. 50 N., R. 96 W. Sheep Mountain. D1479 ?m ......... NW54 sec. 31, T. 50 N., R. 96 W. Sheep Mountain. D1480 7m ......... SE54 sec. 32, T. 48 N., R. 95 W. Dutch Nick Flat. D1481 546 m EB . . . . NE54 sec. 2, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1482 541 m EB . . . . NW54 sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1483 415 m EK . . . . NE54 sec. 14, T. 50 N., R. 96 W. Wardel Reservoir. D1484 416 m EK . . . . NW54 sec. 23, T. 50 N., R. 96 W. Wardel Reservoir. D1485 18 m EB ..... NW54 sec. 2, T. 48 N., R. 92 W. Worland SE. D1486 430 m B ..... NW54 sec. 25, T. 50 N., R. 96 W. Wardel Reservoir. D1487 432 m B ..... NW54 sec. 25, T. 50 N., R. 96 W. Wardel Reservoir. D1488 ?m ......... NW54 sec. 12, T. 50 N., R. 95 W. Jones Reservoir. D1489 7m ......... NW54 sec. 34, T. 48 N., R. 92 W. Worland. D1490 474 m B ..... SW54 sec. 26, T. 49 N., R. 95 W. Schuster Flats NW. D1491 486 m B ..... NW54 sec. 25, T. 49 N., R. 95 W. Schuster Flats NW. D1492 ?m ......... SW54 sec. 17, T. 47 N., R. 94 W. Schuster Flats. D1493 344 m B ..... SE54 sec. 6, T. 48 N., R. 93 W. Schuster Flats NE. D1494 370 m B ..... NE54 sec. 2, T. 48 N., R. 94 W. Schuster Flats NE. D1495 464 m B ..... SW54 sec. 35, T. 50 N., R. 96 W. Wardel Reservoir. D1496 ?m ......... SE54 sec. 34, T. 50 N., R. 96 W. Sheep Mountain. D1497 452 m B ..... SW54 sec. 3, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1498 344 m EB . . . . SW14 sec. 32, T. 49 N., R. 93 W. Schuster Flats NE. D1499 334 m EB NE54 sec. 32, T. 49 N., R. 93 W. Schuster Flats NE. D1500 322 m EB NW% sec. 32, T. 49 N., R. 93 W. Schuster Flats NE. D1501 290 m EB SE54 sec. 29, T. 49 N., R. 93 W. Schuster Flats NE. D1502 ?m ......... SE54 sec. 20, T. 47 N., R. 93 W. Schuster Flats SE. D1503 550 m B ..... NW54 sec. 22, T. 48 N., R. 96 W. Dutch Nick Flat. D1504 556 m B ..... SW54 sec. 21, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1505 550 m B ..... SW54 sec. 21, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1506 550 m B ..... SW54 sec. 21, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1507 494 m B ..... NE54 sec. 22, T. 48 N., R. 96 W. Dutch Nick Flat. D1508 494 m B ..... NE54 sec. 22, T. 48 N., R. 96 W. Dutch Nick Flat. D1509 ?m ......... NW54 sec. 28, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1510 482 m B ..... SW54 sec. 23, T. 48 N., R. 96 W. Dutch Nick Flat (Crooked Creek Bonanza). D1511 478 m B ..... SE54 sec. 22, T. 48 N., R. 96 W. Dutch Nick Flat. D1512 ?m ......... NE54 sec. 2, T. 49 N., R. 95 W. Jones Reservoir. D1513 509 m B ..... NW54 sec. 4, T. 49 N., R. 95 W. Wardel Reservoir. D1514 380 m EK . . . . SE54 sec. 12, T. 50 N., R. 96 W. Wardel Reservoir. D1515 ?m ......... NE54 sec. 6, T. 47 N., R. 95 W. Dutch Nick Flat. D1516 ?m ......... SE54 sec. 11, T. 47 N., R. 95 W. Schuster Flats. D1517 ?m ......... SE54 sec. 11, T. 47 N., R. 95 W. Schuster Flats. D1518 436 m B ..... NW54 sec. 16, T. 48 N., R. 94 W. Schuster Flats NW. D1519 ?m ......... NE54 sec. 16, T. 48 N., R. 94 W. Schuster Flats NW. D1520 ?m ......... SE54 sec. 16, T. 48 N., R. 94 W. Schuster Flats NW. D1521 ?m ......... . SW54 sec. 9, T. 47 N., R. 96 W. Dutch Nick Flat SW. TABLES 2—6 77 Table 2. US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1522 7m ......... SE14 sec. 4, T. 47 N., R. 96 W. Dutch Nick Flat SW. D1523 ?m ......... SW14 sec. 3, T. 47 N., R. 96 W. Dutch Nick Flat. D1524 409 m EB . . . . NE14 sec. 36, T. 49 N., R. 94 W. Schuster Flats NE. D1525 ?m ......... SW14 sec. 34, T. 49 N., R. 94 W. Schuster Flats NW. D1526 418 m EB . . . . NW14 sec. 3, T. 48 N., R. 94 W. Schuster Flats NW. D1527 410 m EB . . . . SW14 sec. 3, T. 48 N., R. 94 W. Schuster Flats NW. D1528 414 m EB . . . . SW14 sec. 3, T. 48 N., R. 94 W. Schuster Flats NW. D1529 420 m EB . . . . SE14 sec. 4, T. 48 N., R. 94 W. Schuster Flats NW. D1530 420 m EB . . . . SE14 sec. 4, T. 48 N., R. 94 W. Schuster Flats NW. D1531 485 m EB . . . . NE14 sec. 30, T. 49 N., R. 94 W. Schuster Flats NW. D1532 485 m EB . . . . NW14 sec. 25, T. 49 N., R. 95 W. Schuster Flats NW. D1533 438 m B ..... SW14 sec. 14, T. 48 N., R. 95 W. Schuster Flats NW. D1534 536 m ES Center sec. 17, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1535 ?m ......... SW14 see. 24, T. 48 N., R. 96 W. Dutch Nick Flat. D1536 450 m EB Center sec. 28, T. 48 N., R. 95 W. Dutch Nick Flat. D1537 449 m B ..... SE14 sec. 16, T. 48 N., R. 95 W. Sucker Dam. D1538 405 m B ..... NE14 sec. 30, T. 48 N., R. 94 W. Schuster Flats. D1539 410 m B ..... SW14 sec. 25, T. 48 N., R. 95 W. Schuster Flats. D1540 399 m B ..... NW14 sec. 36, T. 48 N., R. 95 W. Schuster Flats. D1541 414 m K ..... NW14 sec. 30, T. 50 N., R. 96 W. Wardel Reservoir. D1542 ?m ......... NW14 sec. 3, T. 47 N., R. 96 W. Dutch Nick Flat. D1543 7m ......... NE14 sec. 3, T. 47 N., R. 96 W. Dutch Nick Flat. D1544 ?m ......... SE14 sec. 3, T. 47 N., R. 96 W. Dutch Nick Flat. D1545 430 m EK NW14 sec. 31, T. 50 N., R. 95 W. Wardel Reservoir. D1546 ?m ......... SW14 sec. 2, T. 47 N., R. 95 W. Dutch Nick Flat. D1547 405 m EK . . . . NE14 sec. 23, T. 50 N., R. 96 W. Wardel Reservoir. D1548 390 m EK . . . . SE14 sec. 3, T. 50 N., R. 96 W. Sheep Mountain. D1549 410 m EK . . . . SW14 sec. 3, T. 50 N., R. 96 W. Sheep Mountain. D1550 425 m EK . . . . NW14 sec. 10, T. 50 N., R. 96 W. Sheep Mountain. D1551 400 m EK . . . . NW14 sec. 10, T. 50 N., R. 96 W. Sheep Mountain. D1552 485 m B ..... NE14 sec. 21, T. 49 N., R. 95 W. Sucker Dam. D1553 377 m EK . . . . SE14 sec. 10, T. 50 N., R. 96 W. Wardel Reservoir. D1554 416 m K ..... SE14 sec. 10, T. 50 N., R. 96 W. Sheep Mountain. D1555 394 m K ..... SW14 sec. 30, T. 50 N., R. 96 W. Wardel Reservoir. D1556 397 m K ..... NE'A sec. 30, T. 50 N., R. 96 W. Wardel Reservoir. D1557 356 m B ..... SE14 sec. 35, T. 48 N., R. 94 W. Schuster Flats SE. D1558 556 m ES NE14 sec. 13, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1559 405 m ES . . . . SW14 sec. 20, T. 50 N., R. 95 W. Wardel Reservoir. D1560 392 m B ..... SE14 sec. 29, T. 48 N., R. 94 W. Schuster Flats. D1561 362 m B ..... NW14 sec. 19, T. 48 N., R. 94 W. Schuster Flats SE. D1562 490 m B ..... SE14 sec. 9, T. 49 N., R. 95 W. Sucker Dam. D1563 493 m B ..... NW14 sec. 9, T. 49 N., R. 95 W. Sucker Dam. D1564 485 m EB . . . . SW14 sec. 16, T. 49 N., R. 95 W. Sucker Dam. D1565 485 m EB . . . . NE14 sec. 21, T. 49 N., R. 95 W. Sucker Dam. D1566 528 m B ..... NE14 sec. 11, T. 49 N., R. 97 W. Dutch Nick Flat NW. 78 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING Table 2. U.S. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin. Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1567 531 in ES NE'A sec. 11, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1568 7m ......... NE‘A sec. 32, '1‘. 51 N., R. 96 W. Sheep Mountain. D1569 7m ......... SE14 sec. 32, T. 51 N., R. 96 W. Sheep Mountain. D1570 435 m EK . . . . SE14 sec. 4, T. 50 N., R. 96 W. Sheep Mountain. D1571 435 m EK . SE14 sec. 4, T. 50 N., R. 96 W. Sheep Mountain. D1572 ?m ......... NE‘A sec. 23, T. 48 N., R. 96 W. Dutch Nick Flat. D1573 511 in ES . . . . NEM sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1574 546 m S ..... NE‘A sec. 12, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1575 546 m S ..... NEW sec. 12, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1576 546 m S ..... NW% sec. 12, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1577 311 m EB . . . . NW‘A sec. 5, T. 47 N., R. 93 W. Schuster Flats SE. D1578 -25 m B ..... NW% sec. 26, T. 46 N., R. 91 W. Cabin Fork. D1579 5 m B ....... SW56 sec. 24, T. 46 N., R. 91 W. Cabin Fork. D1580 -?m ........ NW‘A sec. 4, T. 45 N., R. 90 W. Cabin Fork. D1581 546 m ES NW% sec. 17, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1582 546 m ES . . . . NE% sec. 18, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1583 551 m S ..... SE16 sec. 17, T. 48 N., R. 96 W. Dutch Nick Flat NW (Bownanza). D1584 ?m ......... NE'A sec. 13, T. 51 N., R. 94 W. Greybull South (equal to Y405). D1585 7m ......... SE'A sec. 26, T. 48 N., R. 99 W. Hillberry Rim. D1586 483 m B ..... SE14 sec. 17, T. 49 N., R. 95 W. Sucker Dam. D1587 444 m B ..... SW14 sec. 1, T. 49 N., R. 96 W. Sucker Dam. D1588 442 m B ..... NE% sec. 2, T. 49 N., R. 96 W. Sucker Dam (Peterson School Bus locality). D1589 ?m ......... SE‘A sec. 26, T. 51 N., R. 97 W. Sheep Mountain. D1590 ?m ......... SE‘A sec. 25, '1‘. 51 N., R. 97 W. Sheep Mountain. D1591 ?m ......... SE'A sec. 25, T. 51 N., R. 97 W. Sheep Mountain. D1592 466 m ES NW'A sec. 24, T. 50 N., R. 96 W. Wardel Reservoir. D1593 ?m ......... SW'A sec. 33, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1594 ?m ......... NE% sec. 5, T. 47 N., R. 96 W. Dutch Nick Flat SW. D1595 ?m ......... NW'A sec. 4, T. 47 N., R. 96 W. Dutch Nick Flat SW. D1596 591 m EB . . . . SE14 sec. 32, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1597 420 m B ..... NW‘A sec. 26, T. 48 N., R. 95 W. Schuster Flats. ' D1598 428 m B ..... SW'A sec. 15, T. 48 N., R. 95 W. Schuster Flats. D1599 449 m B ..... NE'A sec. 17, T. 48 N., R. 95 W. Sucker Dam. D1600 ?m ......... SW‘A sec. 34, T. 51 N., R. 98 W. Sheets Flat. D1601 ?m ......... SE'A sec. 34, T. 51 N., R. 98 W. Tatman Mountain. D1602 463 m B ..... SW'A sec. 10, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1603 463 m B ..... SW‘A sec. 10, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1604 463 m B ..... SE'A sec. 16, T. 49 N., R. 96 W. Dutch Nick Flat NW (possibly equal to Y44). D1605 478 m B ..... SW'A sec. 10, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1606 ?m ......... SW14 sec. 28, T. 50 N., R. 96 W. Sheep Mountain. TABLES 2—6 79 Table 2. US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south— em Bighorn Basin, Wyoming—Continued. Topographic Locath Stratigraphic quadrangle No. position Location (other names) D1607 7m ......... SE54 sec. 29, T. 50 N., R. 96 W. Sheep Mountain. D1608 516 m EB . . . . NE54 sec. 36, T. 50 N., R. 97 W. Sheep Mountain. D1609 505 m EB . . . . SE54 sec. 36, T. 50 N., R. 97 W. Sheep Mountain. D1610 ?m ......... NE54 sec. 3, T. 50 N., R. 98 W. Tatman Mountain. D1611 ?m ......... SW54 sec. 34, T. 51 N., R. 98 W. Tatman Mountain. D1612 505 m EB . . . . NW54 sec. 31, T. 50 N., R. 96 W. Sheep Mountain. D1613 541 m S ..... NE54 sec. 21, T. 49 N., R. 97 W. Dead Indian Hill. D1614 7m ......... SW54 sec. 16, T. 49 N., R. 97 W. Dead Indian Hill. D1615 ?m ......... SE54 sec. 16, T. 49 N., R. 97 W. Dead Indian Hill. D1616 ?m ......... SE54 sec. 16, T. 49 N., R. 97 W. Dead Indian Hill. D1617 475 m B ..... SE54 sec. 33, T. 49 N., R. 95 W. Sucker Dam. D1618 ?m ......... NW54 sec. 10, T. 51 N., R. 97 W. Y-U Bench NE. D1619 ?m ......... NW54 sec. 20, T. 51 N., R. 97 W. Y-U Bench NE. D1620 ?m ......... SE54 sec. 17, T. 51 N., R. 97 W. Y-U Bench NE. D1621 7m ......... SW54 sec. 28, T. 51 N., R. 97 W. Tatman Mountain. D1622 559 m ES NW54 sec. 21, T. 49 N., R. 97 W. Dead Indian Hill. D1623 513 m ES SW54 sec. 13, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1624 507 in ES . . . . NW54 sec. 13, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1625 516 m S ..... SW54 sec. 12, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1626 7m ......... SE54 sec. 2, T. 46 N., R. 95 W. Chimney Gulch. D1627 7m ......... NW54 sec. 12, T. 46 N., R. 95 W. Chimney Gulch. D1628 435 m EK . . . . NW54 sec. 27, T. 50 N., R. 96 W. Sheep Mountain. D1629 445 m EK . . . . NW54 sec. 27, T. 50 N., R. 96 W. Sheep Mountain. D1630 190 m ES NE54 sec. 14, T. 50 N., R. 94 W. Orchard Bench. D1631 200 m ES SE54 sec. 15, T. 50 N., R. 94 W. Jones Reservoir. D1632 130 m ES . . . . SE54 sec. 18, T. 50 N., R. 93 W. Orchard Bench. D1633 149 m S ..... NW54 sec. 7, T. 50 N., R. 93 W. Orchard Bench. D1634 ?m ......... SE54 sec. 22, T. 51 N., R. 94 W. Gould Butte. D1635 370 m S ..... SE54 sec. 10, T. 50 N., R. 95 W. Wardel Reservoir. D1636 361 m ES SE54 sec. 15, T. 50 N., R. 95 W. Wardel Reservoir. D1637 ?m ......... SE54 sec. 22, T. 51 N., R. 95 W. Otto. D1638 ?m ......... SW54 sec. 23, T. 51 N., R. 95 W. Gould Butte. D1639 ?m ......... NW54 sec. 24, T. 51 N., R. 95 W. Gould Butte. D1640 140 m S ..... NW54 sec. 18, T. 50 N., R. 93 W. Orchard Bench. D1641 ?m ......... SE54 sec. 9, T. 48 N., R. 96- W. Sucker Dam. D1642 ?m ......... NW54 sec. 15, T. 48 N., R. 96 W. Sucker Dam. D1643 7m ......... NE54 sec. 16, T. 48 N., R. 96 W. Sucker Dam. D1644 255 in ES . . . . SW14 sec. 36, T. 50 N., R. 94 W. Orchard Bench. D1645 240 m S ..... NW54 sec. 36, T. 50 N., R. 94 W. Orchard Bench. D1646 591 m EB . . . . SW54 sec. 32, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1647 591 m EB . . . . SW54 sec. 32, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1648 130 m S ..... SW54 sec. 28, T. 50 N., R. 93 W. Orchard Bench. D1649 ?m ......... SW54 sec. 27, T. 51 N., R. 96 W. Sheep Mountain. D1650 ?m ......... SW54 sec. 27, T. 51 N., R. 96 W. Sheep Mountain. D1651 636 m EB . . . . NE54 sec. 26, T. 47 N., R. 97 W. Dutch Nick Flat SW. 80 Table 2. FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING U.S. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and southern Bighorn Basin, Wyoming——Continued. Topographic locality Stratigraphic quadrangle No. position Location (other names) D1651Q 636 m EB . . . . NE14 sec. 26, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1652 382 m B ..... SE14 sec. 24, T. 48 N., R. 94 W. Schuster Flats SE. D1653 357 m B ..... NE14 sec. 19, T. 48 N., R. 93 W. Schuster Flats SE. D1654 7m ......... NE14 sec. 25, T. 48 N., R. 97 W. Dutch Nick Flat SW. D1655 ?m ......... NE14 sec. 30, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1656 7m ......... NW14 sec. 30, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1657 443 m B ..... SW14 sec. 1, T. 49 N., R. 96 W. Sucker Dam. D1658 410 m B ..... SE14 sec. 24, T. 48 N., R. 95 W. Schuster Flats. D1659 442 m B ..... SW14 sec. 1, T. 49 N., R. 96 W. Sucker Dam. D1660 442 m B ..... NE14 sec. 2, T. 49 N., R. 96 W. Wardel Reservoir. D1661 ?m ......... SE14 sec. 1, T. 47 N., R. 95 W. Schuster Flats. D1662 470 m B ..... NW14 sec. 33, T. 50 N., R. 96 W. Sheep Mountain. D1663 470 m B ..... NW14 sec. 33, T. 50 N., R. 96 W. Sheep Mountain. D1664 7m ......... NE14 sec. 33, T. 50 N., R. 96 W. Sheep Mountain. D1665 ?m ......... NW14 sec. 12, T. 47 N., R. 95 W. Schuster Flats. D1666 ?m ......... NW14 sec. 15, T. 50 N., R. 95 W. Wardel Reservoir. D1667 476 m B ..... SW14 sec. 26, T. 50 N., R. 96 W. Wardel Reservoir. D1668 460 m B ..... NW14 sec. 35, T. 50 N., R. 96 W. Wardel Reservoir. D1669 464 m B ..... NW14 sec. 35, T. 50 N., R. 96 W. Wardel Reservoir. D1670 471 m B ..... NW14 sec. 35, T. 50 N., R. 96 W. Wardel Reservoir. D1671 474 m B ..... SW14 sec. 26, T. 50 N., R. 96 W. Wardel Reservoir. D1672 495 m B ..... SE14 sec. 5, T. 49 N., R. 95 W. Sucker Dam. D1673 531 m B ..... NW14 sec. 3, T. 49 N., R. 95 W. Sucker Dam. D1674 553 m B ..... SW14 sec. 3, T. 49 N., R. 95 W. Sucker Dam. D1675Q 493 m B ..... SW14 sec. 4, T. 49 N., R. 95 W. Sucker Dam (Elk Creek Rim Quarry). D1676 464 m B ..... NW14 sec. 35, T. 50 N., R. 96 W. Wardel Reservoir. D1677 470 m EB . . . . SW14 sec. 31, T. 50 N., R. 95 W. Wardel Reservoir. D1678 278 m EB . . . . SW14 sec. 12, T. 47 N., R. 94 W. Schuster Flats SE. D1679 7m ......... SE14 sec. 9, T. 50 N., R. 95 W. Wardel Reservoir. D1680 414 m EK . . . . SE14 sec. 13, T. 50 N., R. 96 W. Wardel Reservoir. D1681 ?m ......... SE14 sec. 5, T. 48 N., R. 93 W. Schuster Flats NE. D1682 442 m B ..... NE14 sec. 2, T. 49 N., R. 96 W. Wardel Reservoir (Elise's Pocket). D1683 ?m ......... SE14 sec. 13, T. 47 N., R. 95 W. Schuster Flats. D1684 440 m B ..... SW14 sec. 7, T. 47 N., R. 94 W. Schuster Flats. D1685 ?m ......... SW14 sec. 14, T. 47 N., R. 95 W. Schuster Flats. D1686 591 m EB . . . . SE14 sec. 32, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1687 438 m EB . . . . SE14 sec. 15, T. 48 N., R. 95 W. Schuster Flats NW. D1688 442 m EB . . . . SE14 sec. 15, T. 48 N., R. 95 W. Schuster Flats NW. D1689 430 m S ..... NE14 sec. 9, T. 50 N., R. 95 W. Wardel Reservoir (equal to Y83). D1690 ?m ......... NE14 sec. 16, T. 50 N., R. 95 W. Wardel Reservoir (equal to Y429). D1691 ?m ......... NE14 sec. 4, T. 50 N., R. 95 W. Wardel Reservoir. D1692 ?m ......... NE14 sec. 5, T. 48 N., R. 94 W. Schuster Flats NW. D1693 438 m B ..... NW14 sec. 8, T. 48 N., R. 94 W. Schuster Flats NW. D1694 435 m B ..... NW14 sec. 8, T. 48 N., R. 94 W. Schuster Flats NW. D1695 418 m B ..... NE14 sec. 8, T. 48 N., R. 94 W. Schuster Flats NW. TABLES 2—6 81 Table 2. US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1696 ?m ......... SW14 sec. 9, T. 47 N., R. 95 W. Dutch Nick Flat. D1697 ?m ......... SW16 sec. 8, T. 47 N., R. 95 W. Dutch Nick Flat. D1698 455 m B ..... SW14 sec. 33, T. 50 N., R. 96 W. Sheep Mountain. D1699 463 m B ..... SW16 sec. 33, T. 50 N., R. 96 W. Sheep Mountain. D1700 351 m B ..... SE16 sec. 3, T. 47 N., R. 94 W. Schuster Flats SE. D1701 ?m ......... NW'A sec. 18, T. 47 N., R. 95 W. Dutch Nick Flat. D1702 ?m ......... SW16 sec. 9, T. 47 N., R. 95 W. Dutch Nick Flat. D1703 ?m ......... SW14 sec. 4, T. 49 N., R. 98 W. Wilson Spring. D1704 ?m ......... NW14 sec. 3, T. 49 N., R. 98 W. Sheets Flat (equal to Y182). D1705 7m ......... SW14 sec. 19, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1706 ?m ......... SE16 sec. 25, T. 48 N., R. 97 W. Dutch Nick Flat SW. D1707 ?m ......... SE16 sec. 25, T. 48 N., R. 97 W. Dutch Nick Flat SW. D1708 ?m ......... NE14 sec. 24, T. 48 N., R. 97 W. Dutch Nick Flat SW. D1709 250 m ES SW14 sec. 29, T. 51 N., R. 94 W. Jones Reservoir. D1710 245 m ES SE16 sec. 30, T. 51 N., R. 94 W. Jones Reservoir. D1711 260 m ES NW14 sec. 32, T. 51 N., R. 94 W. Jones Reservoir. D1712 390 m ES SE14 sec. 33, T. 50 N., R. 94 W. Jones Reservoir. D1713 ?m ......... NW14 sec. 5, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1714 ?m ......... SE16 sec. 6, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1715 ?m ......... NW16 sec. 19, T. 49 N., R. 93 W. Schuster Flats NE. D1716 397 in ES . SW14 sec. 33, T. 50 N., R. 94 W. Jones Reservoir. D1717 ?m ......... NE16 sec. 22, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1718 ?m ......... NW14 sec. 22, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1719 ?m ......... NW16 sec. 22, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1720 ?m ......... SE% sec. 22, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1721 ?m ......... NE14 sec. 27, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1722 ?m ......... NE14 sec. 22, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1723 7m ......... SW14 sec. 14, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1724 ?m ......... SW14 sec. 14, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1725 ?m ......... SW16 sec. 14, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1726 463 m B ..... NE16 sec. 4, T. 49 N., R. 96 W. Sheep Mountain. D1727 478 m B ..... NE14 sec. 9, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1728 ?m ......... SE14 sec. 14, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1729 7m ......... NW‘A sec. 24, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1730 ?m ......... SW14 sec. 13, T. 47 N., R. 97 W. Dutch Nick Flat SW. D1731 No data ...... No data ................. No data. D1732 No data ...... No data ................. No data. D1733 ?m ......... NE14 sec. 9, T. 49 N., R. 95 W. Sucker Dam. D1734 489 m EB . . . . NW'A sec. 9, T. 49 N., R. 95 W. Sucker Dam. D1735 561 m ES NE14 sec. 11, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1736 ?m ......... SE14 sec. 10, T. 44 N., R. 96 W. Dutch Nick Flat. D1737 463 m, lower; . . SW14 sec. 4, T. 49 N., R. 96 W. Dutch Nick Flat NW. 469 m, upper. D1738 ?m ......... SW14 sec. 5, T. 49 N., R. 94 W. Schuster Flats NW. D1739 ?m ......... NW14 sec. 35, T. 51 N., R. 96 W. Wardel Reservoir. D1740 ?m ......... NE‘A sec. 35, T. 51 N., R. 96 W. Wardel Reservoir. 82 Table 2. FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south— ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1741 383 m K ..... NE14 sec. 28, T. 50 N., R. 95 W. Wardel Reservoir. D1742 435 m K ..... SE14 sec. 20, T. 50 N., R. 95 W. Wardel Reservoir. D1743 385 m K ..... SE14 sec. 29, T. 50 N., R. 95 W. Wardel Reservoir. D1744 404 m K ..... NW14 sec. 32, T. 50 N., R. 95 W. Wardel Reservoir. D1745 390 m EK . . . . SW14 sec. 29, T. 50 N., R. 95 W. Wardel Reservoir. D1746 7m ......... SW14 sec. 18, T. 50 N., R. 95 W. Wardel Reservoir. D1747 415 m EK . . . . NW14 sec. 24, T. 50 N., R. 96 W. Wardel Reservoir. D1748 438 m K ..... NW14 sec. 30, T. 50 N., R. 95 W. Wardel Reservoir. D1749 433 m K ..... NW14 sec. 30, T. 50 N., R. 95 W. Wardel Reservoir. D1750 519 m B ..... NW14 sec. 14, T. 49 N., R. 95 W. Schuster Flats NW. D1751 535 m B ..... NW14 sec. 14, T. 49 N., R. 95 W. Schuster Flats NW. D1752 526 m B ..... NE14 sec. 15, T. 49 N., R. 95 W. Sucker Dam. D1753 516 m B ..... NE14 sec. 15, T. 49 N., R. 95 W. Sucker Dam. D1754 511 m B ..... NE14 see. 12, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1755 497 m S ..... NE14 sec. 13, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1756 ?m ......... SW14 sec. 31, T. 49 N., R. 96 W. Sucker Dam. D1757 468 m ...... SW14 sec. 32, T. 49 N., R. 96 W. Sucker Dam. D1758 397 m EB . . . . NW14 sec. 29, T. 48 N., R. 94 W. Schuster Flats. D1759 393 m EB . NW14 sec. 29, T. 48 N., R. 94 W. Schuster Flats. D1760 ?m ......... NE14 sec. 26, T. 48 N., R. 94 W. Schuster Flats SE. D1761 ?m ......... SW14 see. 22, T. 48 N., R. 92 W. Worland. D1762 414 m EB . . . . NW14 sec. 10, T. 48 N., R. 94 W. Schuster Flats NW. D1762Q 414 m EB . . . . NW14 see. 10, T. 48 N., R. 94 W. Schuster Flats NW (McKinney Quarry). D1763 7m ......... SE14 sec. 16, T. 48 N., R. 94 W. Schuster Flats NW. D1764 542 m EB . . . . SE14 sec. 14, T. 49 N., R. 95 W. Schuster Flats NW. D1765 537 m EB . . . . NW14 sec. 13, T. 49 N., R. 95 W. Schuster Flats NW. D1766 7m ......... SW14 sec. 13, T. 49 N., R. 95 W. Schuster Flats NW. D1767 475 m EB . . . . NE14 sec. 26, T. 49 N., R. 95 W. Schuster Flats NW. D1768 ?m ......... SW14 sec. 24, T. 49 N., R. 95 W. Schuster Flats NW. D1769 510 m EB . . . . SW14 see. 24, T. 49 N., R. 95 W. Schuster Flats NW. D1770 ?m ......... SW14 sec. 10, T. 49 N., R. 95 W. Sucker Dam. D1771 586 m EB . . . . NW14 sec. 13, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1772 566 m S ..... NE14 sec. 13, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1773 491 m B ..... SE14 sec. 8, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1774 413 m EB . . . . NE14 see. 9, T. 48 N., R. 94 W. Schuster Flats NW. D1775 329 m B ..... NE14 sec. 29, T. 48 N., R. 93 W. Schuster Flats SE. D1776 463 m B ..... NW14 sec. 4, T. 49 N., R. 96 W. Sheep Mountain. D1776N 463 m B ..... NW14 sec. 32, T. 50 N., R. 96 W. Sheep Mountain. D1777 474 m B ..... NW14 sec. 5, T. 49 N., R. 96 W. Sheep Mountain. D1778 474 m B ..... SW% sec. 33, T. 50 N., R. 96 W. Sheep Mountain. D1779 412 m EK . . . . SW14 sec. 13, T. 50 N., R. 96 W. Wardel Reservoir. D1780 ?m ......... NE14 sec. 1, T. 50 N., R. 96 W. Wardel Reservoir. D1781 556 m B ..... SE sec. 20, T. 48 N., R. 96 W. Dutch Nick Flat SW. D1782 496 m B ..... SW14 sec. 22, T. 48 N., R. 96 W. Dutch Nick Flat. D1783 474 m B ..... SE14 sec. 8, T. 49 N., R. 96 W. Dutch Nick Flat NW. TABLES 2—6 83 Table 2. US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin. Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1784 455 m B ..... SE54 sec. 8, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1785 ?m ......... SE54 sec. 5, T. 48 N., R. 94 W. Schuster Flats NW. D1786 ?m ......... SW54 sec. 4, T. 48 N., R. 94 W. Schuster Flats NW. D1787 ?m ......... NE'A sec. 36, T. 49 N., R. 98 W. Dead Indian Hill. D1788 566 m S ..... NE54 sec. 29, T. 49 N., R. 97 W. Dead Indian Hill. D1789 7m ......... SW54 sec. 1, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1790 7m ......... SW54 sec. 1, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1791 7m ......... NW54 sec. 1, T. 49 N., R. 97 W. Sheep Mountain. D1792 385 m EK NE'A sec. 10, T. 50 N., R. 96 W. Sheep Mountain. D1793 7m ......... NW54 sec. 17, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1794 7m ......... NW54 sec. 17, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1795 ?m ......... NE54 sec. 17, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1796 7m ......... NE‘A sec. 17, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1797 ?m ......... NE54 sec. 29, T. 49 N., R. 94 W. Schuster Flats NW. D1798 7m ......... NE54 sec. 29, T. 49 N., R. 94 W. Schuster Flats NW. D1799 ?m ......... NW54 sec. 24, T. 49 N., R. 95 W. Schuster Flats NW. D1800 ?m ......... NE54 sec. 20, T. 49 N., R. 94 W. Schuster Flats NW. D1801 ?m ......... NW54 sec. 19, T. 49 N., R. 94 W. Schuster Flats NW. D1802 ?m ......... NE54 sec. 24, T. 49 N., R. 95 W. Schuster Flats NW. D1803 385 m EK . . . . SE54 sec. 10, T. 50 N., R. 96 W. Sheep Mountain. D1804 411 m EK . . . . NE54 sec. 19, T. 50 N., R. 95 W. Wardel Reservoir. D1805 405 m EK . . . . NW54 sec. 29, T. 50 N., R. 95 W. Wardel Reservoir. D1806 7m ......... NE54 sec. 12, T. 50 N., R. 95 W. Jones Reservoir. D1807 7m ......... NW‘A sec. 9, T. 50 N., R. 94 W. Jones Reservoir. D1808 7m ......... SW54 sec. 27, T. 48 N., R. 92 W. Worland. D1809 360 m B ..... NE54 sec. 31, T. 48 N., R. 93 W. Schuster Flats SE. D1810 452 m B ..... NE‘A sec. 31, T. 48 N., R. 93 W. Schuster Flats SE. D1811 344 m B ..... NW54 sec. 29, T. 48 N., R. 93 W. Schuster Flats SE. D1812 7m ......... SE54 sec. 7, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1813 ?m ......... SW54 sec. 5, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1814 7m ......... NW54 sec. 29, T. 49 N., R. 97 W. Dead Indian Hill. D1815 7m ......... NW54 sec. 33, T. 51 N., R. 94 W. Jones Reservoir. D1816 180 m EB . . . . SW54 sec. 12, T. 50 N., R. 94 W. Orchard Bench. D1817 ?m ......... SW54 sec. 15, T. 51 N., R. 94 W. Gould Butte. D1818 ?m ......... SE54 sec. 15, T. 50 N., R. 94 W. Jones Reservoir. D1819 ?m ......... SW54 sec. 15, T. 50 N., R. 94 W. Jones Reservoir. D1820 ?m ......... SW54 sec. 23, T. 50 N., R. 94 W. Orchard Bench. D1821 416 m B ..... NE54 sec. 17, T. 48 N., R. 94 W. Schuster Flats NW. D1822 426 m B ..... SW54 sec. 17, T. 48 N., R. 94 W. Schuster Flats NW. D1823 409 m B ..... SE54 sec. 25, T. 48 N., R. 95 W. Schuster Flats. D1824 406 m B ..... SE54 sec. 25, T. 48 N., R. 95 W. Schuster Flats. D1825 489 m B ..... SW54 sec. 22, T. 49 N., R. 95 W. Sucker Dam. D1826 479 m B ..... SW54 sec. 23, T. 49 N., R. 95 W. Schuster Flats NW. D1827 ?m ......... SW54 sec. 20, T. 50 N., R. 94 W. Jones Reservoir. D1828 546 m B ..... SW54 sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. 84 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING Table 2. US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin. Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1829 501 m B ..... NE'A sec. 6, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1830 501 m B ..... SW16 sec. 32, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1831 529 m B ..... NE‘A sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1832 7m ......... Center sec. 29, T. 50 N., R. 96 W. Sheep Mountain. D1833 463 m B ..... SW16 sec. 29, T. 50 N., R. 96 W. Sheep Mountain. D1834 511 m B ..... NW‘A sec. 25, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1835 7m ......... SE14 sec. 16, T. 46 N., R. 92 W. Banjo Flats West. D1836 7m ......... NElA sec. 35, T. 50 N., R. 94 W. Orchard Bench. D1837 ?m ......... NWM sec. 21, T. 50 N., R. 96 W. Sheep Mountain. D1838 7m ......... NW‘A sec. 21, T. 50 N., R. 96 W. Sheep Mountain. D1839 7m ......... NEM sec. 32, T. 50 N., R. 96 W. Sheep Mountain. D1840 ?m ......... NE'A sec. 32, T. 50 N., R. 96 W. Sheep Mountain. D1841 ?m ......... NEM sec. 32, T. 50 N., R. 96 W. Sheep Mountain. D1842 ?m ......... SW'A sec. 16, T. 50 N., R. 96 W. Sheep Mountain. D1843 528 m S ..... NW% sec. 31, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1844 ?m ......... NW‘A sec. 21, T. 50 N., R. 96 W. Sheep Mountain. D1845 7m ......... SE% sec. 31, T. 49 N., R. 95 W. Sucker Dam. D1846 ?m ......... NE‘A sec. 1, T. 48 N., R. 96 W. Sucker Dam. D1847 190 m EB SW14 sec. 9, T. 49 N., R. 93 W. Schuster Flats NE. D1848 423 m EK NW% sec. 35, T. 51 N., R. 96 W. Wardel Reservoir. D1849 7m ......... Unsurveyed area in T. 51 N., R. 92 W. Gould Butte. D1850 346 m B ..... NW‘A sec. 1, T. 47 N., R. 94 W. Schuster Flats SE. D1851 7m ......... Center SE14 sec. 33, T. 49 N., R. 94 W. Schuster Flats NW. D1852 ?m ......... NE'A sec. 5, T. 48 N., R. 94 W. Schuster Flats NW. D1853 ?m ......... SE14 sec. 29, T. 49 N., R. 93 W. Schuster Flats NE. D1854 ?m ......... NW% sec. 33, T. 49 N., R. 93 W. Schuster Flats NE. D1855 ?m ......... SW'A sec. 24, T. 49 N., R. 94 W. Schuster Flats NE. D1856 7m ......... SW‘A sec. 24, T. 49 N., R. 94 W. Schuster Flats NE. D1857 ?m ......... NE‘A sec. 30, T. 51 N., R. 94 W. Jones Reservoir. D1858 7m ......... Center NW‘A sec. 21, T. 49 N., R. 94 W. Schuster Flats NW. D1859 410 m EB . Center NW'A sec. 10, T. 48 N., R. 94 W. Schuster Flats NE. D1860 556 m B ..... Center SE'A sec. 2, T. 48 N., R. 97 W. Dutch Nick Flat NW. D1861 ?m ......... NE% sec. 36, T. 51 N., R. 98 W. Tatman Mountain. D1862 ?m ......... NW% sec. 1, T. 50 N., R. 98 W. Tatman Mountain. D1863 414 m K ..... SE'A sec. 24, T. 50 N., R. 96 W. Wardel Reservoir. D1864 394 m K ..... NE‘A sec. 24, T. 50 N., R. 96 W. Wardel Reservoir. D1865 ?m ......... NW% sec. 35, T. 51 N., R. 97 W. Sheep Mountain. D1866 423 m EK . . . . SW% sec. 34, T. 51 N., R. 96 W. Sheep Mountain. D1867 ?m ......... NE% sec. 36, T. 51 N., R. 97 W. Sheep Mountain. D1868 ?m ......... NE‘A sec. 36, T. 51 N., R. 97 W. Sheep Mountain. D1869 ?m ......... NW‘A sec. 35, T. 51 N., R. 96 W. Wardel Reservoir. D1870 ?m ......... NE‘A sec. 35, T. 51 N., R. 96 W. Wardel Reservoir. D1871 ?m ......... NE‘A sec. 16, T. 48 N., R. 96 W. Dutch Nick Flat NW. D1872 213 in ES SW% sec. 28, T.'51 N., R. 94 W. Jones Reservoir. D1873 ?m ......... Center N'AS'A sec. 21, T. 51 N., R. 94 W. Jones Reservoir. Table 2. TABLES 2-6 85 US. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1874 ?m ......... SW‘A sec. 22, T. 51 N., R. 94 W. Jones Reservoir. D1875 ?m ......... SW'A sec. 33, T. 51 N., R. 96 W. Sheep Mountain. D1876 435 m EK . . . . SE% sec. 4, T. 50 N., R. 96 W. Sheep Mountain. D1877 7m ......... SW‘A sec. 20, T. 50 N., R. 96 W. Sheep Mountain. D1878 ?m ......... NW‘A sec. 29, T. 50 N., R. 96 W. Sheep Mountain. D1879 ?m ......... NW‘A sec. 33, T. 51 N., R. 94 W. Jones Reservoir. D1880 310 m ES Center sec. 36, T. 51 N., R. 95 W. Jones Reservoir. D1881 463 m B ..... NWM sec. 32, T. 50 N., R. 96 W. Sheep Mountain. D1882 345 in ES SE%,sec. 35, T. 51 N., R. 95 W. Jones Reservoir. D1883 435 m EK NE% sec. 21, T. 50 N., R. 96 W. Sheep Mountain. D1884 7m ......... SW‘A sec. 22, T. 50 N., R. 96 W. Sheep Mountain. D1885 474 m BK SE14 sec. 27, T. 50 N., R. 96 W. Wardel Reservoir. D1886 ?m ......... SE'A sec. 20, T. 50 N., R. 96 W. Sheep Mountain. D1887 5 m B ....... SE‘A sec. 19, T. 46 N., R. 89 W. Castle Gardens. D1888 3 m B ....... SE‘A sec. 16, T. 47 N., R. 91 W. Worland SE. D1889 472 m EB . . . . SE‘A sec. 5, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1890 463 m B ..... SE'A sec. 4, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1891 ?m ......... Center SE54 sec. 36, T. 49 N., R. 98 W. Dead Indian Hill. D1892 7m ......... SW%NE%SE% sec. 36, T. 49 N., R. 98 W. Dead lndian Hill. D1893 ?m ......... SW%5W% sec. 7, T. 47 N., R. 94 W. Schuster Flats. D1894 407 m EB . . . . NW‘ASE‘A sec. 10, T. 48 N., R. 94 W. Schuster Flats NE. D1895 409 m EB . . . . Center Sl/zN'ANW‘A sec. 11, T. 48 N., R. 94 W. Schuster Flats NE. D1896 407 m EB . . . . SE%SW% sec. 3, T. 48 N., R. 94 W. Schuster Flats NE. D1897 428 m EK . . . . SE‘ASE‘A sec. 15, T. 50 N., R. 96 W. Sheep Mountain and Wardel Reservoir. D1898 ?m ......... Center NE‘A sec. 22, T. 50 N., R. 96 W. Sheep Mountain and Wardel Reservoir. D1899 438 m EK . . . . NE‘ANE'ANE'A sec. 22, T. 50 N., R. 96 W. Sheep Mountain. D1900 ?m ......... NW‘ANE‘A sec. 6, T. 50 N., R. 95 W. Wardel Reservoir. D1901 ?m ......... NW'ANE'ANW‘A sec. 6, T. 50 N., R. 95 W. Wardel Reservoir. D1902 7m ......... Center E'ASE'ASW‘A sec. 4, T. 50 N., R. 95 W. Wardel Reservoir. D1903 ?m ......... NW‘ANW‘A sec. 8, T. 50 N., R. 95 W. Wardel Reservoir. D1904 ?m ......... Center W'AW'ASW'ANE‘A sec. 27, T. 51 N., Tatman Mountain. R. 97 W. D1905 ?m ......... Center W%W‘/zNW% sec. 27, T. 51 N., R. 97 W. Tatman Mountain. D1906 ?m ......... Center NW‘ASW'ASE‘A sec. 3, T. 47 N., R. 96 W. Dutch Nick Flat. D1907 7m ......... Center SW%SW% sec. 2, T. 47 N., R. 96 W. Dutch Nick Flat. D1908 ?m ......... Center W1/8NW%SW% sec. 11, T. 47 N., R. 96 W. Dutch Nick Flat. D1909 ?m ......... NW%NW%SW%SE% and SE%SE%NW%SE% Dutch Nick Flat. sec. 10, T. 47 N., R. 96 W. D1910 494 m B ..... Center S'ANE‘ASE‘A and center N‘ASE‘ASE‘A Dutch Nick Flat NW. sec. 29, T. 49 N., R. 96 W. D1911 ?m ......... NE‘ANE‘ASW'ASW'A sec. 1, T. 50 N., R. 98 W. Tatman Mountain. D1912 ?m ......... SE %SW%SE% sec. 2, T. 50 N., R. 98 W. Tatman Mountain. D1913 ?m ......... SW%SW%NW%SE% sec. 2, T. 50 N., R. 98 W. Tatman Mountain. 86 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 2. U.S. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Towsmphic Locality Stratigraphic quadrangle No. position Location (other names) D1914 529 m B ..... Center SW‘ASWlé sec. 25, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1915 ?m ......... Center NE'ANE'ASW'A sec. 8, T. 49 N., R. 97 W. Dead Indian Hill. D1916 ?m ......... Center EMSEMSE'A sec. 5, T. 49 N., R. 97 W. Dead Indian Hill. D1917 ?m ......... Center W'ANW‘A NE‘A sec. 8, T. 49 N., R. 97 W. Dead Indian Hill. D1918 544 m B ..... SE%SE% sec. 26, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1919 539 m B ..... Center S‘ASW‘ASWM sec. 25, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1920 530 m B ..... Center SWMSWM sec. 25, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1921 7m ......... SEMNE'ASE'A sec. 8, T. 50 N., R. 95 W. Wardel Reservoir. D1922 ?m ......... Center SEMSE'ANW'A sec. 17, T. 49 N., R. 97 W. Dead Indian Hill. D1923 362 m EB SW%SE%NE% sec. 2, T. 50 N., R. 95 W. Jones Reservoir. D1924 357 m B ..... SW‘ASE'ASE'A sec. 2, T. 50 N., R. 95 W. Jones Reservoir. D1925 ?m ......... Center NléNE'ASW‘A sec. 17, T. 49 N., R. 97 W. Dead Indian Hill. D1926 ?m ......... SE ‘ASE'ASW‘ANW'A sec. 7, T. 50 N., R. 94 W. Jones Reservoir. D1927 ?m ......... NW'ANE‘ANE‘ANEK sec. 13, T. 50 N., R. 95 W. Jones Reservoir. D1928 ?m ......... Center SW%SW%SE% sec. 12, T. 50 N., R. 95 W. Jones Reservoir. D1929 7m ......... NEMNE'ASW'A sec. 12, T. 50 N., R. 95 W. Jones Reservoir. D1930 ?m ......... N'ASW‘ASW‘A sec. 7, T. 50 N., R. 94 W. Jones Reservoir. D1931 315 m ES NE‘ASW‘A and W'ANW‘ASW‘A sec. 7, T. 50 N., Jones Reservoir. R. 94 W. D1932 ?m ......... NE%SW%SW% sec. 4, T. 47 N., R. 96 W. Dutch Nick Flat SW. D1933 ?m ......... NW'ANW‘ANW'ANW‘A sec. 27, T. 48 N., R. 96 W. Dutch Nick Flat. D1934 ?m ......... SW%NW%SW%SW% sec. 35, T. 49 N., R. 96 W. Sucker Dam. D1935 250 m EB . . . . Center NE‘ASW‘A sec. 5, T. 50 N., R. 96 W. Jones Reservoir. D1936 463 m B ..... Center E'ASE‘ASW‘A sec. 20, T. 50 N., Sheep Mountain. R. 96 W. D1937 442 m EB NW%SW%SW%NW% sec. 31, T. 49 N., R. 94 W. Schuster Flats NW. D1938 310 m ES NE'ANE‘ANE‘A sec. 1, T. 50 N., R. 95 W. Jones Reservoir. D1939 ?m ......... SW'ASW‘ANW‘A sec. 31, T. 51 N., R. 94 W. Jones Reservoir. D1940 ?m ......... SE‘ASW'ASW'A sec. 17, T. 49 N., R. 94 W. Schuster Flats NW. D1941 7m ......... Center NE‘A sec. 17, T. 49 N ., R. 94 W. Schuster Flats NW. D1942 ?m ......... SW‘ANW'ANW'A sec. 16, T. 49 N., R. 94 W. Schuster Flats NW. D1943 ?m ......... NW'ANW‘ANW‘ANE'A sec. 20, T. 49 N., R. 94 W. Schuster Flats NW. D1944 ?m ......... NE'ANE‘ASW‘A sec. 1, T. 48 N., R. 98 W. Dead Indian Hill. D1945 ?m ......... NW'ANW‘ANW'A sec. 36, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1946 422 m B ..... E'ANEIANEM sec. 9, T. 48 N., R. 94 W. Schuster Flats NW. D1947 407 m B ..... Center NEM sec. 9, T. 48 N., R. 94 W. Schuster Flats NW. D1948 ?m ......... SE'ASEléSEK sec. 28, T. 48 N., R. 93 W. Schuster Flats SE. D1949 ?m ......... SW'ANW'ASE'ASE‘A sec. 28, T. 48 N., R. 93 W. Schuster Flats SE. D1950 353 m B ..... NWMNW‘ANW'ASE'ANE‘A sec. 3, T. 47 N., Schuster Flats SE. R. 94 W. D1951 402 m B ..... El/3NW‘ASE‘A sec. 21, T. 48 N., R. 94 W. Schuster Flats. D1952 400 m B ..... E1/3NW%SE% sec. 21, T. 48 N., R. 94 W. Schuster Flats. D1953 ?m ......... Center S'ASW‘ASE‘A sec. 33, T. 49 N., R. 94 W. Schuster Flats NW. D1954 ?m ......... SW‘ASWIANE'ANE‘A sec. 20, T. 49 N., R. 94 W. Schuster Flats NW. D1955 ?m ......... Center W% sec. 9, T. 49 N ., R. 94 W. Schuster Flats NE. D1956 ?m ......... SW'ASW'ANWMNE'A sec. 3, T. 49 N., R. 95 W. Wardel Reservoir. D1957 ?m ......... Center NEIA sec. 3, T. 49 N., R. 95 W. Wardel Reservoir. D1958 7m ......... NE‘A sec. 2, T. 49 N., R. 95 W. Jones Reservoir. TABLES 2—6 87 Table 2. U.S. Geological Survey (Denver) fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) D1959 7m ......... N'ANW'ASE'A and NW'ANW‘ASE'ASE'A sec. 3, Jones Reservoir. T. 50 N., R. 94 W. D1960 7m ......... Center SW16 see. 20, T. 48 N., R. 94 W. Schuster Flats. D1961 7m ......... NWMNE'A sec. 22, T. 48 N., R. 94 W. Schuster Flats SE. D1962 ?m ......... NW‘A sec. 13, T. 49 N., R. 94 W. Dutch Nick Flat. D1963 ?m ......... SW‘A sec. 12, T. 49 N., R. 94 W. Dutch Nick Flat. D1964 7m ......... Center N‘AS'A sec. 11, T. 50 N., R. 95 W. Jones Reservoir. D1965 7m ......... Center SE16 sec. 17, T. 49 N., R. 97 W. Dead Indian Hill. D1966 491 m B ..... NE'A sec. 30, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1967 357 m B ..... Center NW‘ASE‘A sec. 2, T. 50 N., R. 95 W. Jones Reservoir. D1968 7m ......... SE‘ASE‘ASE‘A sec. 9, T. 47 N., R. 94 W. Dutch Nick Flat. D1969 7m ......... NW‘ANW‘A sec. 16, T. 47 N., R. 96 W. Dutch Nick Flat SW. D1970 ?m ......... SW‘ASE‘A and SE‘ASWM sec. 35, T. 52 N., Gould Butte. R. 95 W. D1971 ?m ......... SW14 sec. 25, T. 52 N., R. 95 W. Gould Butte. D1972 7m ......... SE‘ASE'A sec. 26, T. 52 N., R. 95 W. Gould Butte. D1973 ?m ......... SE'ANW‘ASW‘ASW'A sec. 4, T. 47 N., R. 96 W. Dutch Nick Flat SW. D1974 ?m ......... NW'ANW‘ASW‘ASW‘A sec. 4, T. 47 N., R. 96 W. Dutch Nick Flat SW. D1975 7m ......... Center NE'ASE‘ASE‘A sec. 5, T. 47 N., R. 96 W. Dutch Nick Flat SW. D1976 7m ......... E‘ANE‘A sec. 8, T. 47 N., R. 96 W. Dutch Nick Flat SW. D1977 ?m ......... SE%SE% sec. 13, T. 46 N., R. 91 W. Cabin Fork. D1978 7m ......... SE‘ANE'ANEIA sec. 35, T. 51 N., R. 98 W. Tatman Mountain. D1979 7m ......... NE%NW%NE%SW% sec. 28, T. 50 N., R. 98 W. Sheets Flat. D1980 7m ......... Center NE'ANWlé and NWMNW‘ANWE‘NW'A Tatman Mountain. sec. 32, T. 51 N., R. 97 W. D1981 7m ......... NEléNE‘ASW'ASWlA sec. 6, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1982 492 m B ..... SE‘ASE'A sec. 1, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1983 488 m B ..... SW'ANW'A sec. 7, T. 49 N., R. 96 W. Dutch Nick Flat NW. D1984 504 m B ..... SW‘ASW'ASE‘A sec. 12, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1985 516 m B ..... SE%SE%SE%SE% sec. 11, T. 49 N., R. 97 W. Dutch Nick Flat NW. D1986 509 m B ..... SE‘ASE‘ANW‘A sec. 12, T. 49 N., R. 97 W. Dutch Nick Flat NW. 88 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN. WYOMING Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming. [Only locality Y307 is in the Fort Union Formation. m, meter level (minus values denote meter levels beneath top of Fort Union Formation); B, Bown sections; S, Schankler-Wing sections; K, Kraus sections; E, stratigraphic position estimated during Bown's sectioning; EB, into Bown's sections; EK, into Kraus's sections; ES, into Schankler-Wing sections; ? unknown. Localities are given to the nearest quarter section and are shown on plates 1 and 2. Names of topographic quadrangles in which the localities occur follow locality infor- mation. All are US. Geological Survey 7 l72-minute topographic maps at scale 1:24,000. Names in parentheses following the quadrangle names are other names by which the localities are known. Localities represent collecting efforts of the Yale Peabody Museum in 1961-65, 1968-72. 1974, and 1975] Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y1 571 m S ..... NE'A sec. 29, T. 49 N., R. 97 W. Dead Indian Hill. Y2 571 m S ..... SW‘A sec. 20, T. 49 N., R. 97 W. Dead Indian Hill. Y3 601 m S ..... NEM sec. 26, T. 49 N., R. 98 W. Dead Indian Hill. Y4 ?m ........ SW'A sec. 12, T. 49 N., R. 99 W. Wilson Spring. Y5 ?m ........ NE'A sec. 23, T. 50 N., R. 99 W. Sheets Flat (Rain). Y6 ?m ........ NW% sec. 20, T. 50 N., R. 98 W. Sheets Flat (Magpie). Y7 641 m S ..... SE‘A sec. 32, T. 49 N., R. 97 W. Dead Indian Hill. Y8 591 m S ..... NW‘A sec. 32, T. 49 N., R. 97 W. Dead Indian Hill. Y9 551 m S ..... NW% sec. 21, T. 49 N., R. 97 W. Dead Indian Hill. Y10 551 m S ..... NW% sec. 21, T. 49 N., R. 97 W. Dead Indian Hill. Y11 No data ..... No data ................. No data. Y12 ?m ........ SW% sec. 6, T, 48 N., R. 98 W. Wilson Spring. Y13 541 m S ..... 313% sec. 16, T. 49 N., R. 97 W. Dead Indian Hill. Y14A 483 m B ..... NE‘A sec. 32, T. 49 N., R. 95 W. Sucker Dam. Y14B No data ..... No data ................. No data. Y15 541 m S ..... SE‘A sec. 16, T. 49 N., R. 97 W. Dead Indian Hill. Y16 541 m S ..... NE'A sec. 27, T. 49 N., R. 97 W. Dutch Nick Flat NW. Y17 561 m ES . . . . NW'A sec. 35, T. 49 N., R. 97 W. Dutch Nick Flat NW. Y18A 491 m S ..... NE'A sec. 30, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y18B 521 m S ..... SE54 sec. 26, T. 49 N., R. 97 W. Dutch Nick Flat NW. Y19 521 m S ..... NW% sec. 25, T. 49 N., R. 97 W. Dutch Nick Flat NW. Y20 511 m S ..... NE‘A sec. 23, T. 49 N., R. 97 W. Dutch Nick Flat NW. Y21 501 m S ..... NW'A sec. 24, T. 49 N., R. 97 W. Dutch Nick Flat NW. Y22 551 m S ..... NE% sec. 27, T. 49 N., R. 97 W. Dead Indian Hill. Y23 511 m S ..... NW% sec. 13, T. 49 N., R. 97 W. Dutch Nick Flat NW. Y24 611 m S ..... SW‘A sec. 22, T. 49 N., R. 98 W. Wilson Spring. Y25 501 m S ..... SW% sec. 18, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y26A 491 m S ..... SW% sec. 20, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y26B 491 m S ..... SW‘A sec. 17, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y26C 491 m S ..... NW'A sec. 20, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y27 491 m S ..... NW‘A sec. 29, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y28 491 m S ..... SW'A sec. 29, T. 49 N., R. 96 W. Dutch Nick Flat NW (Windy Gap). Y29 No data ..... No data ................. No data. Y3O ?m ........ NWIA sec. 5, T. 48 N., R. 98 W. Wilson Spring. Y31 ?m ........ NE'A sec. 1, T. 49 N., R. 99 W. Wilson Spring. Y32 611 m S ..... NW'A sec. 22, T. 49 N., R. 98 W. Wilson Spring. Y33 601 m S ..... SE% sec. 22, T. 49 N., R. 98 W. Dead Indian Hill. Y34 469 m S ..... SW‘A sec. 10, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y35 No data ..... No data ................. No data. Y36 521 m S ..... NE% sec. 22, T. 49 N., R. 97 W. Dutch Nick Flat. TABLES 2—6 89 Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south— ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y37 ?m ........ SW14 sec. 4, T. 49 N., R. 97 W. Dead Indian Hill. Y38 7m ........ NE‘A sec. 8, T. 49 N., R. 97 W. Dead Indian Hill. Y39 501 m S ..... NW'A sec. 19, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y40 481 m S ..... SW16 sec. 34, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y41 481m S ..... SW‘A sec. 11, T. 48 N., R. 96 W. Sucker Dam. Y42 481 m S ..... SW14 sec. 3, T. 48 N., R. 96 W. Sucker Dam (Moocow Hollow). Y43 481 m ES . . . . NW% sec. 13, T. 48 N., R. 96 W. Sucker Dam. Y44 463 m B ..... SW14 sec. 15, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y45 470 m B ..... NW% sec. 33, T. 49 N., R. 95 W. Sucker Dam (called main stop on road to Worland on many museum labels). Y4SS 470 m B ..... SW‘A sec. 5, T. 48 N., R. 95 W. Sucker Dam. Y46 No data ..... No data ................. No data. Y47 489 m B ..... SW‘A sec. 15, T. 49 N., R. 95 W. Sucker Dam. Y47A 489 m B ..... NW'A sec. 22, T. 49 N., R. 95 W. Sucker Dam. Y48 57 m EB NW'A sec. 17, T. 46 N., R. 91 W. Banjo Flats East. Y49 490 m EB . . . . SW‘A sec. 2, T. 47 N., R. 95 W. Schuster Flats. Y50 394 m K ..... SW'A sec. 11, T. 50 N., R. 96 W. Wardel Reservoir. Y51 416 m K ..... NE% sec. 14, T. 50 N., R. 96 W. Wardel Reservoir. Y52 470 m EB . . . . SW54 sec. 32, T. 50 N., R. 95 W. Wardel Reservoir. Y53 No data ..... No data ................. No data. Y54 No data ..... No data ................. No data. Y55 501 m ES . . . . 813% sec. 6, T. 48 N., R. 96 W. Dutch Nick Flat NW. (Howard’s Hill and Diacodexis locality). Y56 501 m ES . . . . SE14 sec. 32, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y57 ?m ........ SW% sec. 9, T. 48 N., R. 96 W. Dutch Nick Flat NW. Y58 No data ..... No data ................. No data. Y59 491 m S ..... NW'A sec. 29, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y60 No data ..... No data ................. No data. Y61 474 m B ..... 85% sec. 9, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y62 No data ..... No data ................. No data. Y63 ?m ........ NE'A sec. 3, T. 49 N., R. 95 W. Wardel Reservoir. Y64 No data ..... No data ................. No data. Y65 No data ..... No data ................. No data. Y66 491 m S ..... SW% sec. 33, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y67 380 m K ..... SW'A sec. 12, T. 50 N., R. 96 W. Wardel Reservoir. Y68 420 m S ..... No data ................. No data. Y69 414 m EK . . . . SE'A sec. 15, T. 50 N., R. 96 W. Wardel Reservoir (Didelphodus locality). Y70 491 m S ..... SW‘A sec. 20, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y71A 501 m S ..... SW14 sec. 20, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y7lB 491 m S ..... NW% sec. 20, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y72* 481 m B ..... SE‘A sec. 4, T. 48 N., R. 96 W. Sucker Dam. Y73 491 m S ..... SE‘A sec. 18, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y74 491 m S ..... NW% sec. 17, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y75 501 m S ..... SW16 sec. 19, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y76 501 m S ..... NE'A sec. 24, T. 49 N., R. 97 W. Dutch Nick Flat NW. Y77 501 m S ..... NE% sec. 24, T. 49 N., R. 97 W. Dutch Nick Flat NW. Y78 405 m K ..... NE‘A sec. 23, T. 50 N., R. 96 W. Wardel Reservoir. 90 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN. WYOMING Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y79 ?m ........ 88% sec. 27, T. 51 N., R. 96 W. Wardel Reservoir. Y80 390 m S ..... NE'A sec. 10, T. 50 N., R. 95 W. Wardel Reservoir. Y81 360 m S ..... NW'A sec. 12, T. 50 N., R. 95 W. Jones Reservoir. Y82 No data ..... No data ................. No data. Y82A 370 m S ..... NW‘A sec. 13, T. 50 N., R. 95 W. Jones Reservoir. Y83 430 m S ..... NE‘A sec. 9, T. 50 N., R. 95 W. Wardel Reservoir. Y84 380 m K ..... NE‘A sec. 13, T. 50 N., R. 96 W. Wardel Reservoir. Y85 414 m EK . . . . SW'A sec. 18, T. 50 N., R. 95 W. Wardel Reservoir. Y86 430 m S ..... SW56 sec. 9, T. 50 N., R. 95 W. Wardel Reservoir. Y87 180 m S ..... NE'A sec. 31, T. 50 N., R. 93 W. Orchard Bench. Y88 180 m S ..... SW14 sec. 32, T. 50 N., R. 94 W. Orchard Bench. Y89 170 m S ..... SE56 sec. 32, T. 50 N., R. 93 W. Orchard Bench. Y90A 90 m S ...... SE14 sec. 20, T. 50 N., R. 93 W. Orchard Bench. Y90B 100 m S ..... NE% sec. 20, T. 50 N., R. 93 W. Orchard Bench Y91 160 m S ..... SE'A sec. 19, T. 50 N., R. 93 W. Orchard Bench. Y92 140 m S ..... NW'A sec. 19, T. 50 N., R. 93 W. Orchard Bench. Y93 140 m S ..... NE'A sec. 18, T. 50 N., R. 93 W. Orchard Bench. Y94 140 m S ..... NW'A sec. 20, T. 50 N., R. 93 W. Orchard Bench. Y95 50 m S ...... NE'A sec. 31, T. 51 N., R. 93 W. Orchard Bench. Y96 140 m S ..... SE'A sec. 6, T. 50 N., R. 93 W. Orchard Bench. Y97 140 m S ..... NW% sec. 7, T. 50 N., R. 93 W. Orchard Bench. Y98 180 m S ..... NE% sec. 24, T. 50 N., R. 94 W. Orchard Bench. Y99 478 m B ..... NE% sec. 9, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y100 455 m B ..... NE‘A sec. 9, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y101 180 m S ..... SW‘A sec. 19, T. 50 N., R. 93 W. Orchard Bench. Y102 No data ..... No data ................. No data. Y103 7m ........ NW'A sec. 36, T. 51 N., R. 97 W. Sheep Mountain. Y104 140 m S ..... NW% sec. 18, T. 50 N., R. 93 W. Orchard Bench. Y105 7m ........ NW'A sec. 23, T. 51 N., R. 94 W. Greybull South. Y106 140 m ES No data ................. No data. Y107 ?m ........ SW'A sec. 18, T. 49 N., R. 93 W. Schuster Flats NE. Y108 220 m S ..... NE% sec. 23, T. 50 N., R. 94 W. Orchard Bench. Y109 150 m S ..... NW% sec. 7, T. 50 N., R. 93 W. Orchard Bench. Y110 155 m ES . . . . NW% sec. 13, T. 50 N., R. 94 W. Orchard Bench. Y111 190 m S ..... SW% sec. 14, T. 50 N., R. 94 W. Orchard Bench. Y112 210 m ES . . . . NE‘A sec. 16, T. 50 N., R. 94 W. Jones Reservoir. Y113 220 m S ..... NE‘A sec. 18, T. 50 N., R. 94 W. Jones Reservoir. Y114 No data ..... No data ................. No data. Y115 30 m EB NW% sec. 24, T. 46 N., R. 92 W. Banjo Flats East. Y116 No data ..... No data ................. No data. Y117 No data ..... No data. . . .. ............. No data. Y118 No data ..... No data ................. No data. Y119 100 m S ..... NE'A sec. 36, T. 51 N., R. 94 W. Orchard Bench (Neoliotomus locality). Y120 100 m S ..... NE‘A sec. 36, T. 51 N., R. 94 W. Orchard Bench. Y121 150 m ES . . . . NE% sec. 26, T. 51 N., R. 94 W. Orchard Bench. TABLES 2—6 91 Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming-Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y122 ?m ........ NE'A sec. 27, T. 51 N., R. 94 W. Jones Reservoir. Y123 No data ..... No data ................. No data. Y124 No data ..... No data ................. No data. Y125 340 m ES . . . . SW'A sec. 13, T. 50 N., R. 95 W. Jones Reservoir. Y126* 370 m EK . . . . SW16 sec. 28, T. 50 N., R. 95 W. Wardel Reservoir. Y127 390 m K ..... SW% sec. 30, T. 50 N., R. 95 W. Wardel Reservoir. Y128 ?m ........ SW14 sec. 12, T. 49 N., R. 94 W. Schuster Flats NE. Y129 ?m ........ SE54 sec. 11, T. 49 N., R. 94 W. Schuster Flats NE. Y130 ?m ........ NE‘A sec. 13, T. 49 N., R. 94 W. Schuster Flats NE. Y131 348 m B, upper; SW54 sec. 29, T. 48 N., R. 93 W. Schuster Flats SE. 344 m B, lower. Y132 360 m B ..... SW14 sec. 30, T. 48 N., R. 93 W. Schuster Flats SE. Y133 324 m EB . . . . NW‘A sec. 30, T. 49 N., R. 93 W. Schuster Flats NE. Y134 ?m ........ NW'A sec. 8, T. 49 N., R. 94 W. Schuster Flats NW. Y135 343 m B ..... SW16 sec. 5, T. 48 N., R. 93 W. Schuster Flats NE. Y136 359 m B ..... NW'A sec. 6, T. 48 N., R. 93 W. Schuster Flats NE. Y137 97 m EB NE% sec. 9, T. 46 N., R. 91 W. Banjo Flats East. Y138 41 m EB NE'A sec. 4, T. 46 N., R. 91 W. Banjo Flats East. Y139 77 m EB NE'A sec. 32, T. 47 N., R. 91 W. Worland SE. Y140* ?m ........ SW'A sec. 11, T. 49 N., R. 94 W. Schuster Flats NW. Y141 ?m ........ SE% sec. 8, T. 49 N., R. 94 W. Schuster Flats NW. Y142 370 m S ..... NW'A sec. 33, T. 50 N., R. 94 W. Jones Reservoir. Y143 240 m S ..... SE54 sec. 26, T. 50 N., R. 94 W. Orchard Bench. Yl44 180 m S ..... NW‘A sec. 31, T. 50 N., R. 93 W. Orchard Bench. Y145 160 m S ..... NE‘A sec. 12, T. 50 N., R. 94 W. Orchard Bench. Y146 160 m S ..... NW% sec. 7, T. 50 N., R. 93 W. Orchard Bench. Y147 7m ........ NE‘A sec. 35, T. 51 N., R. 94 W. Orchard Bench. Y148 150 m ES . . . . NW% sec. 35, T. 51 N., R. 94 W. Orchard Bench. Yl49 360 m S ..... SE‘A sec. 2, T. 50 N., R. 95 W. Jones Reservoir (Pachyaena locality). YISO 360 m ES . . . . No data ................. No data. Y151 360 m ES . . . . No data ................. No data. Y152 380 m S ..... SW'A sec. 3, T. 50 N., R. 95 W. Wardel Reservoir. Y152N 380 m ES . . . . 515% sec. 3, T. 50 N., R. 95 W. Wardel Reservoir. Y153 ?m ........ SW'A sec. 13, T. 49 N., R. 94 W. Schuster Flats NE. Y154 7m ........ Center sec. 14, T. 49 N., R. 94 W. Schuster Flats NE. Y155 ?m ........ NW'A sec. 3, T. 48 N., R. 93 W. Schuster Flats NE. Y156 310 m ES . . . . NW‘A sec. 6, T. 50 N., R. 94 W. Jones Reservoir. Y157 343 m B, upper; NE'A sec. 8, T. 48 N., R. 93 W. Schuster Flats NE. 336 m B, middle; 322 m EB, lower. Y158 354 m EB . . . . No data ................. No data. Y159 ?m ........ NW'A sec. 13, T. 49 N., R. 94 W. Schuster Flats NE. Y160 591 m S ..... SE'A sec. 19, T. 49 N., R. 97 W. Dead Indian Hill. Y161 571 m S ..... NE'A sec. 29, T. 49 N., R. 97 W. Dead Indian Hill. Y162A 591 m S ..... NW'A sec. 19, T. 49 N., R. 97 W. Dead Indian Hill. Y16ZB 591 m ...... NW% sec. 19, T. 49 N., R. 97 W. Dead Indian Hill. Y162C 591 m ...... NE'A sec. 19, T. 49 N., R. 97 W. Dead Indian Hill. Y163 601 m S ..... NW% sec. 18, T. 49 N., R. 97 W. Dead Indian Hill. 92 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y164 ?m ........ SW‘A sec. 33, T. 49 N., R. 98 W. Wilson Spring. Y165 561 m S ..... NW'A sec. 28, T. 49 N., R. 97 W. Dead Indian Hill. Y166 601 m S ..... NW'A sec. 32, T. 49 N., R. 97 W. Dead Indian Hill. Y167 541 m S ..... NE‘A sec. 21, T. 49 N., R. 97 W. Dead Indian Hill. Y168 501 m S ..... SW56 sec. 19, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y169 ?m ........ NE‘A sec. 12, T. 49 N., R. 99 W. Wilson Spring. Y170 ?m ........ 313% sec. 5, T. 49 N., R. 98 W. Wilson Spring. Y171 511 m ES . . . . No data ................. No data. Y172 626 m ES . . . . NE'A sec. 15, T. 49 N., R. 98 W. Dead Indian Hill. Y173 511 m S ..... SE54 sec. 31, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y174 531 m S ..... NE% sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y175 531 m S ..... 88% sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW (Gray Flats locality). Y176 531 m S ..... SW'A sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y177 511 m S ..... NE‘A sec. 31, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y178 531 m S ..... SE% sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y179 541 m S ..... SE% sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y180 541 m S ..... SW'A sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y181 541 m S ..... NW‘A sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y182* ‘Im ........ NW% sec. 3, T. 50 N., R. 98 W. Sheets Flat. Y183 561 m S ..... NW'A sec. 27, T. 49 N., R. 97 W. Dead Indian Hill. Y184 541 m S ..... SW‘A sec. 26, T. 49 N., R. 97 W. Dutch Nick Flat NW. Y185 531 m S ..... SE‘A sec. 26, T. 49 N., R. 97 W. Dutch Nick Flat NW (Absarokius locality). Y186 511 m S ..... SW% sec. 30, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y187 556 m S ..... SE14 sec. 2, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y188 551 m S ..... NE‘A sec. 11, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y189 541 m S ..... SW‘A sec. 6, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y190 541 m S ..... NW'A sec. 7, T. 48 N., R. 96 W. Dutch Nick Flat NW. Y191 531 m S ..... SW54 sec. 31, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y192 546 m S ..... SE'A sec. 12, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y1928 546 m S ..... SW'A sec. 7, T. 48 N., R. 96 W. Dutch Nick Flat NW. Y193 546 m S ..... NE‘A sec. 12, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y193E 546 m S ..... NE'A sec. 12, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y194 No data ..... No data ................. No data. Y195 601 m S ..... 815% sec. 30, T. 49 N., R. 97 W. Dead Indian Hill. Y196 591 m S ..... NE% sec. 23, T. 49 N., R. 98 W. Dead Indian Hill. Y197 591 m S ..... SE'A sec. 14, T. 49 N., R. 98 W. Dead Indian Hill. Y198 601 m S ..... SE54 sec. 13, T. 49 N., R. 98 W. Dead Indian Hill. Y199 591 m S ..... NE‘A sec. 24, T. 49 N., R. 98 W. Dead Indian Hill. Y200 80 m S ...... NEl/4 sec. 31, T. 51 N., R. 93 W. Orchard Bench. Y201 100 m S ..... NE'A sec. 6, T. 50 N., R. 93 W. Orchard Bench. Y202 100 m S ..... NE'A sec. 6, T. 50 N., R. 93 W. Orchard Bench. Y203 100 m S ..... NE‘A sec. 6, T. 50 N., R. 93 W. Orchard Bench. Y204 100 m S ..... SE'A sec. 31, T. 51 N., R. 93 W. Orchard Bench. Y205 100 m S ..... SE‘A sec. 31, T. 51 N., R. 93 W. Orchard Bench. Y206 140 m S ..... SE'A sec. 6, T. 50 N., R. 93 W. Orchard Bench. TABLES 2—6 93 Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y207 140 m S ..... NW‘A sec. 7, T. 50 N., R. 93 W. Orchard Bench. Y208 ?m ........ SW‘A sec. 21, T. 50 N., R. 93 W. Orchard Bench. Y209 No data ..... No data ................. No data. Y210 No data ..... No data ................. No data. Y211 No data ..... No data ................. No data. Y212 230 m S ..... NE‘A sec. 23, T. 50 N., R. 94 W. Orchard Bench. Y212E 7m ........ NW‘A sec. 24, T. 50 N., R. 94 W. Orchard Bench. Y213 220 m S ..... NE‘A sec. 23, T. 50 N., R. 94 W. Orchard Bench. Y214* 190 m S ..... SW‘A sec. 14, T. 50 N., R. 94 W. Orchard Bench. Y215 210 m S ..... NE‘A sec. 15, T. 50 N., R. 94 W. Jones Reservoir. Y215W 190 m ES . . . . NW‘A sec. 15, T. 50 N., R. 94 W. Jones Reservoir. Y216 340 m ES . . . . SE‘A sec. 13, T. 50 N., R. 95 W. Jones Reservoir (Haplomylus locality). Y217 7m ........ NEK sec. 23, T. 50 N., R. 95 W. Jones Reservoir. Y218 ?m ........ SE54 sec. 15, T. 50 N., R. 95 W. Wardel Reservoir. Y219 397 m K ..... NW% see. 30, T. 50 N., R. 95 W. Wardel Reservoir. Y220 405 m K ..... NE'A see. 25, T. 50 N., R. 96 W. Wardel Reservoir. Y221 412 m K ..... SW% sec. 30, T. 50 N., R. 95 W. Wardel Reservoir. Y222 430 m EK . . . . NW'A sec. 31, T. 50 N., R. 95 W. Wardel Reservoir. Y223 430 m K ..... NE‘A sec. 36, T. 50 N., R. 96 W. Wardel Reservoir. Y224* 435 m EK . . . . NE'A sec. 36, T. 50 N., R. 96 W. Wardel Reservoir. Y225 435 m EK . . . . NW% see. 31, T. 50 N., R. 95 W. Wardel Reservoir. Y226 385 m K ..... 85% sec. 29, T. 50 N., R. 95 W. Wardel Reservoir. Y227 457 m B ..... NW‘A sec. 36, T. 50 N., R. 96 W. Wardel Reservoir. Y227N 457 m B ..... SW14 sec. 25, T. 50 N., R. 96 W. Wardel Reservoir. Y228 No data ..... No data ................. No data. Y229 No data ..... No data ................. No data. Y230A 407 m K ..... SW‘A sec. 24, T. 50 N., R. 96 W. Wardel Reservoir. YZSOB 407 m K ..... NE‘A sec. 25, T. 50 N., R. 96 W. Wardel Reservoir (Hyracotherium locality). Y231 ?m ........ NE‘A see. 17, T. 50 N., R. 96 W. Sheep Mountain. Y232 7m ........ NW'A sec. 17, T. 50 N., R. 96 W. Sheep Mountain. Y233 ?m ........ NE‘A sec. 17, T. 50 N., R. 96 W. Sheep Mountain. Y234 410 m K ..... NW'A sec. 25, T. 50 N., R. 96 W. Wardel Reservoir. Y235 404 m K ..... SW54 sec. 30, T. 50 N., R. 95 W. Wardel Reservoir. Y236 430 m EK . . . . NW‘A sec. 31, T. 50 N., R. 95 W. Wardel Reservoir. Y237 412 m K ..... NW'A sec. 31, T. 50 N., R. 95 W. Wardel Reservoir. Y238 No data ..... No data ................. No data. Y239 No data ..... No data ................. No data. Y240 ?m ........ 813% sec. 7, T. 50 N., R. 96 W. Sheep Mountain. Y241 ?m ........ SW% sec. 7, T. 50 N., R. 96 W. Sheep Mountain. Y242 ?m ........ SW'A sec. 7, T. 50 N., R. 96 W. Sheep Mountain. Y243 ?m ........ SE% sec. 13, T. 50 N., R. 97 W. Sheep Mountain. Y244 7m ........ SE14 sec. 18, T. 50 N., R. 96 W. Sheep Mountain. Y245 ?m ........ SW54 sec. 23, T. 50 N., R. 97 W. Sheep Mountain. Y246 No data ..... No data ................. No data. Y247 425 m K ..... NW% sec. 14, T. 50 N., R. 96 W. Wardel Reservoir. 94 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y248 430 m EK . . . . NW'A sec. 22, T. 50 N., R. 96 W. Sheep Mountain. Y249 480 m EK . . . . NEW sec. 35, T. 51 N., R. 97 W. Sheep Mountain. Y250 440 m EK . . . . NE'A sec. 36, T. 50 N., R. 95 W. Wardel Reservoir. Y251 430 m EK . . . . NW‘A sec. 22, T. 50 N., R. 96 W. Sheep Mountain. Y252 440 m EK . . . . SW14 see. 31, T. 50 N., R. 95 W. Wardel Reservoir. Y253 481 m B ..... SW‘A sec. 27, T. 49 N., R. 95 W. Sucker Dam. Y254 ?m ........ NE% sec. 6, T. 49 N., R. 96 W. Sheep Mountain. Y255 7m ........ NWM sec. 6, T. 49 N., R. 96 W. Sheep Mountain. Y256 513 m ES . . . . NW'A sec. 7, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y257 507 m ES . . . . NE% see. 7, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y258 ?m ........ SW‘A sec. 22, T. 51 N., R. 97 W. Tatman Mountain. Y259 ?m ........ 813% sec. 21, T. 51 N., R. 97 W. Tatman Mountain. Y260 7m ........ SW14 sec. 22, T. 51 N., R. 97 W. Tatman Mountain. Y261 430 m EK . . . . NE'A sec. 31, T. 50 N., R. 95 W. Wardel Reservoir. Y262 397 m K ..... NE'A sec. 30, T. 50 N., R. 95 W. Wardel Reservoir. Y263 397 m K ..... NE'A sec. 30, T. 50 N., R. 95 W. Wardel Reservoir. Y264 385 m K ..... SW‘A sec. 29, T. 50 N., R. 95 W. Wardel Reservoir. Y265 394 m K ..... 813% sec. 30, T. 50 N., R. 95 W. Wardel Reservoir. Y266 408 m K ..... SE'A sec. 30, T. 50 N., R. 95 W. Wardel Reservoir. Y267 409 m K ..... SE14 sec. 29, T. 50 N., R. 95 W. Wardel Reservoir. Y268 425 m EK . . . . 813% sec. 22, T. 50 N., R. 96 W. Sheep Mountain. Y269 394 m K ..... 513% sec. 30, T. 50 N., R. 95 W. Wardel Reservoir. Y270 445 m EK . . . . NE'A sec. 4, T. 50 N., R. 96 W. Sheep Mountain. Y271 400 m K ..... SE56 sec. 24, T. 50 N., R. 96 W. Wardel Reservoir. Y272 ?m ........ NE'A see. 8, '1‘. 47 N., R. 96 W. Dutch Nick Flat SW. Y273 ?m ........ SW16 sec. 4, T. 47 N., R. 94 W. Schuster Flats. Y274 352 m B ..... 813% sec. 35, T. 48 N., R. 94 W. Schuster Flats SE. Y275 10 m EB SW‘A sec. 22, T. 47 N., R. 91 W. Worland SE. Y276 82 m EB NW'A sec. 24, T. 47 N., R. 92 W. Worland SE. Y277 370 m S ..... NW% sec. 11, T. 50 N., R. 95 W. Jones Reservoir. Y278 360 m S ..... SE'A sec. 2, T. 50 N., R. 95 W. Jones Reservoir. Y279 360 m S ..... NE'A sec. 11, T. 50 N., R. 95 W. Jones Reservoir. Y280 370 m S ..... NW'A sec. 14, T. 50 N., R. 95 W. Jones Reservoir. Y281 360 m S ..... NE'A sec. 2, T. 50 N., R. 95 W. Jones Reservoir. Y282 370 m S ..... SW'A sec. 2, T. 50 N., R. 95 W. Jones Reservoir. Y283 370 m S ..... Center sec. 11, T. 50 N ., R. 95 W. Jones Reservoir. Y284 360 m S ..... NE'A sec. 11, T. 50 N., R. 95 W. Jones Reservoir. Y285 280 m S ..... NW% sec. 5, T. 50 N., R. 94 W. Jones Reservoir. Y286 270 m S ..... SW56 sec. 25, T. 51 N., R. 95 W. Jones Reservoir. Y287 290 m S ..... SE14 sec. 26, T. 51 N., R. 95 W. Jones Reservoir. Y288 290 m S ..... SW'A sec. 25, T. 51 N., R. 95 W. Jones Reservoir. Y289 280 m S ..... NW‘A sec. 31, T. 51 N., R. 94 W. Jones Reservoir. Y290 210 m ES . . . . NE‘A sec. 33, T. 51 N., R. 94 W. Jones Reservoir. Y291 7m ........ NW‘A sec. 34, T. 51 N., R. 94 W. Jones Reservoir. Y292 ‘Im ........ NE'A sec. 32, T. 51 N., R. 94 W. Jones Reservoir. TABLES 2—6 95 Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y293 ?m ........ NE% sec. 27, T. 51 N., R. 94 W. Jones Reservoir. Y294 270 m S ..... NW‘A sec. 32, T. 51 N., R. 94 W. Jones Reservoir. Y295 280 m S ..... NE'A sec. 31, T. 51 N., R. 94 W. Jones Reservoir. Y296 290 m S ..... NE‘A sec. 6, T. 50 N., R. 94 W. Jones Reservoir. Y297 290 m S ..... NE'A sec. 6, T. 50 N., R. 94 W. Jones Reservoir. Y298 370 m S ..... NW'A sec. 13, T. 50 N., R. 95 W. Jones Reservoir. Y299 370 m S ..... SW‘A sec. 12, T. 50 N., R. 95 W. Jones Reservoir. Y300 227 m B ..... SE‘A sec. 5, T. 50 N., R. 94 W. Jones Reservoir. Y301 280 m S ..... SW‘A sec. 31, T. 51 N., R. 94 W. Jones Reservoir. Y302 230 m ES SW14 sec. 4, T. 50 N., R. 94 W. Jones Reservoir. Y303 ?m ........ NW‘A sec. 22, T. 51 N., R. 94 W. Gould Butte. Y304 7m ........ NW‘A sec. 11, T. 50 N., R. 94 W. Jones Reservoir. Y305 130 m S ..... SE54 sec. 29, T. 50 N., R. 93 W. Orchard Bench. Y306 30 m EB NW‘A sec. 2, T. 46 N., R. 92 W. Banjo Flats East. Y307 -24 m EB NW'A sec. 26, T. 46 N., R. 91 W. Cabin Fork. Y308 7m ........ SW'A sec. 12, T. 47 N., R. 92 W. Worland SE. Y309 No data ..... No data ................. No data. Y310 No data ..... No data ................. No data. Y311 No data ..... No data ................. No data. Y312 No data ..... No data ................. No data. Y313 ?m ........ SE'A sec. 8, T. 49 N., R. 97 W. Dead Indian Hill. Y314 511 m S ..... NE'A sec. 1, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y315 546 m S ..... NE% sec. 12, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y316 546 m ES . . . . NW‘A sec. 12, T. 48 N., R. 97 W. Dutch Nick Flat NW. Y317* 491 m S ..... SW‘A sec. 8, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y318* 478 m B ..... SW'A sec. 9, T. 49 N., R. 96 W. Dutch Nick Flat NW. Y319 412 m EK . . . . NW‘A sec. 34, T. 51 N., R. 96 W. Sheep Mountain. Y320 423 m EK . . . . NWM sec. 3, T. 50 N., R. 96 W. Sheep Mountain. Y321 430 m K ..... NWM sec. 14, T. 50 N., R. 96 W. Wardel Reservoir. Y322 7m ........ NE‘A sec. 33, T. 51 N., R. 94 W. Jones Reservoir. Y323 195 m ES . . . . NW'A sec. 28, T. 51 N., R. 94 W. Jones Reservoir. Y324 400 m EK . . . . NE‘A sec. 4, T. 50 N., R. 96 W. Sheep Mountain. Y325 435 m EK . . . . SE‘A sec. 4, T. 50 N., R. 96 W. Sheep Mountain. Y326 7m ........ NE% sec. 25, T. 52 N., R. 95 W. Gould Butte. Y327 160 m S ..... SE54 sec. 33, T. 50 N., R. 93 W. Orchard Bench. Y328 ?m ........ SW% sec. 17, T. 49 N., R. 94 W. Schuster Flats NW. Y329 7m ........ SE‘A sec. 18, T. 49 N., R. 94 W. Schuster Flats NW. Y330 430 m ES NW'A sec. 30, T. 50 N., R. 94 W. Jones Reservoir. Y331 7m ........ SE'A sec. 18, T. 49 N., R. 94 W. Schuster Flats NW. Y332 ?m ........ SE% sec. 18, T. 49 N., R. 94 W. Schuster Flats NW. Y333 ?m ........ NW‘A sec. 21, T. 49 N., R. 94 W. Schuster Flats NW. Y334 370 m S ..... SW54 sec. 29, T. 50 N., R. 94 W. Jones Reservoir. Y335 335 m ES . NE'A sec. 19, T. 50 N., R. 94 W. Jones Reservoir. Y336 ?m ........ SE% sec. 12, T. 49 N., R. 94 W. Schuster Flats NE. Y337 140 m S ..... SW'A sec. 7, T. 50 N., R. 93 W. Orchard Bench. 96 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN. WYOMING Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y338 438 m B ..... NE‘A sec. 7, T. 48 N., R. 94 W. Schuster Flats NW. Y339 452 m B ..... SW14 sec. 33, T. 49 N., R. 94 W. Schuster Flats NW. Y340 446 m EB . . . . NW‘A sec. 29, T. 49 N., R. 94 W. Schuster Flats NW. Y341 140 m S ..... SW'A sec. 34, T. 50 N., R. 93 W. Orchard Bench. Y342 113 m EB . . . . E'A sec. 6, T. 46 N., R. 91 W. Banjo Flats East. Y343 113 m EB . . . . NE‘A sec. 5, T. 46 N., R. 91 W. Banjo Flats East. Y344 210 m ES . . . . NE% sec. 8, T. 50 N., R. 94 W. Jones Reservoir. Y345 180 m S ..... NE% sec. 14, T. 50 N., R. 94 W. Orchard Bench. Y346 140 m S ..... NE% sec. 13, T. 50 N., R. 94 W. Orchard Bench. Y347 182 m ES . . . . NE'A sec. 11, T. 50 N., R. 94 W. Orchard Bench. Y348 400 m ES . . . . SW14 sec. 33, T. 50 N., R. 94 W. Jones Reservoir. Y349 305 m ES . . . . SE14 sec. 7, T. 50 N., R. 94 W. Jones Reservoir. Y350 290 m S ..... SE14 sec. 7, T. 50 N., R. 94 W. Jones Reservoir. Y351 240 m S ..... SE14 sec. 5, T. 50 N., R. 94 W. Jones Reservoir. Y352 ?m ........ SW‘A sec. 19, T. 49 N., R. 94 W. Schuster Flats NW. Y353 454 m B ..... SE‘A sec. 26, T. 49 N., R. 95 W. Schuster Flats NW. Y354 240 m S ..... NE% sec. 35, T. 50 N., R. 94 W. Orchard Bench. Y355 240 m S ..... NE'A sec. 35, T. 50 N., R. 94 W. Orchard Bench. Y356 360 m ES NE% sec. 29, T. 50 N., R. 94 W. Jones Reservoir (Hyopsodus Hill). Y357 7m ........ SE'A sec. 15, T. 49 N., R. 93 W. Schuster Flats NE. Y358 140 m S ..... NE% sec. 1, T. 50 N., R. 94 W. Orchard Bench. Y359 150 m B ..... SW'A sec. 6, T. 50 N., R. 93 W. Orchard Bench. Y360 370 m ES . . . . NE% sec. 28, T. 50 N., R. 94 W. Jones Reservoir. Y361 430 m ES . . . . SW'A sec. 30, T. 50 N., R. 94 W. Jones Reservoir. Y362 160 m S ..... SE'A sec. 30, T. 50 N., R. 93 W. Orchard Bench. Y363 190 m S ..... SE54 sec. 25, T. 50 N., R. 94 W. Orchard Bench (Tcakcttle Hill). Y364 140 m B ..... NE‘A sec. 12, T. 50 N., R. 94 W. Orchard Bench. Y365 310 m S ..... SW‘A sec. 35, T. 50 N., R. 94 W. Jones Reservoir. Y366 ?m ........ NW‘A sec. 9, T. 53 N., R. 96 W. Emblem. Y367 210 m ES . . . . SW% sec. 31, T. 50 N., R. 93 W. Orchard Bench. Y368 215 in ES . . . . NE% sec. 6, T. 49 N., R. 93 W. Orchard Bench. Y369 180 m ES . . . . SE% sec. 10, T. 50 N., R. 94 W. Jones Reservoir. Y370 70 m B ..... SW'A sec. 33, T. 47 N., R. 91 W. Banjo Flats East (Banjo quarry, equal to W16A). Y371 ?m ........ SE‘A sec. 24, T. 50 N., R. 95 W. Jones Reservoir. Y372 220 m S ..... SE% sec. 23, T. 50 N., R. 94 W. Orchard Bench. Y373 250 m S ..... SE'A sec. 22, T. 50 N., R. 94 W. Jones Reservoir. Y374 160 m S ..... NE'A sec. 12, T. 50 N., R. 94 W. Orchard Bench. Y375 ?m ........ NE'A sec. 21, T. 50 N., R. 94 W. Jones Reservoir. Y376 ?m ........ NE% sec. 1, T. 52 N., R. 98 W. Gilmore Hill SE. Y377 180 m S ..... NW‘A sec. 30, T. 50 N., R. 93 W. Orchard Bench. Y378 No data ..... No data. . . .' ............. No data. Y379 No data ..... No data ................. No data. Y380 No data ..... No data ................. No data. Y381 115 m ES . . . . NW'A sec. 36, T. 51 N., R. 94 W. Orchard Bench. Y382 140 m S ..... SE‘A sec. 32, T. 50 N., R. 93 W. Orchard Bench. TABLES 2—6 97 Table 3. Yale University Peabody Museum fossil venebratc localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y383 140 m S ..... SE54 sec. 32, T. 50 N., R. 93 W. Orchard Bench. Y384 7m ........ SW54 sec. 5, T. 49 N., R. 93 W. Schuster Flats NE. Y385 ?m ........ SW54 sec. 5, T. 49 N., R. 93 W. Schuster Flats NE. Y386 230 m ES . . . . NE54 sec. 36, T. 50 N., R. 94 W. Orchard Bench. Y387 230 m ES . . . . SE54 sec. 36, T. 50 N., R. 94 W. Orchard Bench. Y388 180 m S ..... NW54 sec. 19, T. 50 N., R. 93 W. Orchard Bench. Y389 170 m S ..... SE54 sec. 32, T. 50 N., R. 93 W. Orchard Bench. Y390* ?m ........ SW54 sec. 2, T. 49 N., R. 93 W. Schuster Flats NE. Y391 ?m ........ SW54 sec. 2, T. 49 N., R. 93 W. Schuster Flats NE. Y392 ?m ........ SE54 sec. 3, T. 49 N., R. 93 W. Schuster Flats NE. Y393 150 m ES . . . . NE54 sec. 3, T. 50 N., R. 94 W. Jones Reservoir. Y394 150 m S ..... SW54 sec. 2, T. 50 N., R. 94 W. Jones Reservoir. Y395 150 m B ..... NW54 sec. 2, T. 50 N., R. 94 W. Orchard Bench. Y396 160 m ES . . . . NW54 sec. 12, T. 50 N., R. 94 W. Orchard Bench. Y397 150 m ES . . . . NE54 sec. 1, T. 50 N., R. 94 W. Orchard Bench. Y398 No data ..... No data ................. No data. Y399 95 m ES ..... SW54 sec. 30, T. 51 N., R. 93 W. Orchard Bench. Y400 ?m ........ SW'A sec. 3, T. 50 N., R. 94 W. Jones Reservoir. Y401 ?m ........ SW54 sec. 3, T. 50 N., R. 94 W. Jones Reservoir. Y402 ?m ........ SW54 sec. 3, T. 50 N., R. 94 W. Jones Reservoir. Y403 ?m ........ NW54 sec. 27, T. 51 N., R. 94 W. Jones Reservoir. Y404 165 m ES NE54 sec. 2, T. 50 N., R. 94 W. Orchard Bench. Y405 ?m ........ SE54 sec. 13, T. 51 N., R. 94 W. Greybull South. Y406 160 m ES NE54 sec. 12, T. 50 N., R. 94 W. Orchard Bench. Y407 145 m ES NW‘A sec. 7, T. 50 N., R. 93 W. Orchard Bench. Y408 180 m S ..... SW54 sec. 13, T. 50 N., R. 94 W. Orchard Bench. Y409 ?m ........ SE54 sec. 8, T. 49 N., R. 93 W. Schuster Flats NE. Y410 165 m ES . . . . NE54 sec. 2, T. 50 N., R. 94 W. Orchard Bench. Y411 160 m ES . . . . NW54 sec. 1, T. 50 N., R. 94 W. Orchard Bench. Y412 213 m ES . . . . SW54 sec. 28, T. 51 N., R. 94 W. Jones Reservoir. Y413 ?m ........ SW54 sec. 10, T. 53 N., R. 96 W. Emblem. Y414 ?m ........ NE54 sec. 17, T. 53 N., R. 96W. Emblem. Y415 ?m ........ SE54 sec. 34, T. 54 N., R. 97 W. Gilmore Hill SE. Y416 205 m ES SW54 sec. 28, T. 51 N., R. 94 W. Jones Reservoir. Y417 ?m ........ SE54 sec. 13, T. 53 N., R. 97 W. Emblem. Y418* ?m ........ SW54 sec. 35, T. 54 N., R. 97 W. Gilmore Hill SE. Y419 370 m ES NW54 sec. 5, T. 50 N., R. 95 W. Wardel Reservoir. Y420 ?m ........ NE54 sec. 6, T. 50 N., R. 95 W. Wardel Reservoir. Y421 390 m ES SE54 sec. 6, T. 50 N., R. 95 W. Wardel Reservoir. Y422 ?m ........ NW‘A sec. 29, T. 51 N., R. 96 W. Sheep Mountain. Y423 ?m ........ SE54 sec. 29, T. 51 N., R. 96 W. Sheep Mountain. Y424 7m ........ NE54 sec. 33, T. 51 N., R. 96 W. Sheep Mountain. Y425 ?m ........ SE54 sec. 2, T. 50 N., R. 96 W. Wardel Reservoir. Y426 ?m ........ SW54 sec. 4, T. 50 N., R. 95 W. Wardel Reservoir. Y427 450 m ES . . . . SW54 sec. 9, T. 50 N., R. 95 W. Wardel Reservoir. 98 FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y428 7m ........ NW'A sec. 16, T. 50 N., R. 95 W. Wardel Reservoir. Y429 ?m ........ NE'A sec. 16, T. 50 N., R. 95 W. Wardel Reservoir. Y430 ?m ........ NE'A sec. 15, T. 50 N., R. 95 W. Wardel Reservoir. Y43l ?m ........ SW34 sec. 16, T. 50 N., R. 95 W. Wardel Reservoir. Y432 ?m ........ NWK sec. 22, T. 50 N., R. 95 W. Wardel Reservoir. Y433 ?m ........ NW'A sec. 15, T. 50 N., R. 95 W. Wardel Reservoir. Y434 ?m ........ SE54 sec. 14, T. 50 N., R. 95 W. Jones Reservoir. Y435 No data ..... No data ................. No data. Y436 No data ..... No data ................. No data. Y437 No data ..... No data ................. No data. Y438 No data ..... No data ................. No data. Y439 No data ..... No data ................. No data. Y440 ?m ........ Unsurveyed area, SW54 Ralston. Y441 No data ..... No data ................. No data. Y442 No data ..... No data ................. No data. Y443 No data ..... No data ................. No data. Y444 ?m ........ NE‘A sec. 26, T. 54 N., R. 99 W. Gilmore Hill NW (Birthday locality). Y445A 9m ........ NW% sec. 8, T. 54 N., R. 99 W. Ralston. Y4458 ?m ........ SW14 sec. 9, T. 54 N., R. 99 W. Ralston. Y446 No data ..... No data ................. No data. Y447 356 m B ..... SE‘A sec. 34, T. 48 N., R. 94 W. Schuster Flats SE. Y448 438 m EB . . . . NW'A sec. 15, T. 48 N., R. 94 W. Schuster Flats NE. Y449 356 m B ..... NE'A sec. 3, T. 47 N., R. 94 W. Schuster Flats SE. Y450 ?m ........ SW14 sec. 24, T. 54 N., R. 99 W. Gilmore Hill NW. Y451 ?m ........ Unsurveyed area, SE54 ........ Emblem. Y452 7m ........ Center sec. 28, T. 53 N., R. 96 W. Emblem. Y453 No data ..... No data ................. No data. Y454 ?m ........ SW'A sec. 4, T. 52 N., R. 99 W. Stone Barn Camp. Y455 ?m ........ SW14 sec. 28, T. 52 N., R. 98 W. Y-U Bench. Y456 ?m ........ NE'A sec. 27, T. 54 N., R. 99 W. Ralston. Y457 7m ........ SE'A sec. 12, T. 54 N., R. 100 W. Ralston. Y458 324 m B ..... NE% sec. 12, T. 47 N., R. 94 W. Schuster Flats SE. Y459 332 m B ..... NW% sec. 6, T. 47 N., R. 93 W. Schuster Flats SE. Y460 392 m B ..... SE14 sec. 21, T. 48 N., R. 94 W. Schuster Flats. Y461 405 m B ..... NE'A sec. 17, T. 47 N., R. 94 W. Schuster Flats. Y462 400 m B ..... SE'A sec. 25, T. 48 N., R. 95 W. Schuster Flats. Y463 410 m B ..... NEK sec. 25, T. 48 N., R. 95 W. Schuster Flats. Y464 ?m ........ NE'A sec. 9, T. 53 N., R. 96 W. Emblem. Y465 ?m ........ SE56 sec. 34, T. 53 N., R. 97 W. Gilmore Hill SE. Y466 ?m ........ SW‘A sec. 35, T. 53 N., R. 97 W. Gilmore Hill SE. Y467 ?m ........ NE% sec. 24, T. 54 N., R. 100 W. Ralston. Y468 ?m ........ NWM sec. 10, T. 53 N., R. 96 W. Emblem. Y469 No data ..... No data ................. No data. Y470 No data ..... No data ................. No data. Y471 ?m ........ SE‘A sec. 26, T. 53 N., R. 100 W. Stone Barn Camp. TABLES 2—6 99 Table 3. Yale University Peabody Museum fossil vertebrate localities in the Fort Union and Willwood Formations of the central and south- ern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) Y472 ?m ........ SW56 sec. 13, T. 51 N., R. 99 W. Y-U Bench NW. Y473 7m ........ NE54 sec. 3, T. 51 N., R. 99 W. Y-U Bench NW. Y474 ?m ........ Unsurveyed area, SE54 ........ Gilmore Hill NW. Y475 ?m ........ Unsurveyed area, SE54 ........ Gilmore Hill NE. Y476* ?m ........ SW54 sec. 16, T. 54 N., R. 99 W. Ralston. Y477 ?m ........ Unsurveyed area, SE'A Emblem. *The Yale Peabody Museum maps give two different locations for these localities. The additional locations, which may represent vastly different meter levels, are shown below. We lack data for localities Y478-Y495, established by David Schankler. Locality Topographic No. Location quadrangle Y72 NE‘A sec. 4, T. 48 N., R. 96 W. Dutch Nick Flat NW. Y126 SE56 sec. 36, T. 50 N., R. 96 W. Wardel Reservoir. Y140 NE54 sec. 31, T. 50 N., R. 93 W. Orchard Bench. Y182 NW54 sec. 17, T. 49 N., R. 97 W. Dead Indian Hill. Y214 SW54 sec. 14, T. 50 N., R. 94 W. Jones Reservoir. Y224 SE‘A sec. 20, T. 50 N., R. 96 W. Sheep Mountain. Y317 NW54 sec. 28, T. 49 N., R. 97 W. Dead Indian Hill. Y318 NW54 sec. 28, T. 49 N., R. 97 W. Dead Indian Hill. Y390 SW56 sec. 20, T. 50 N., R. 93 W. Orchard Bench. Y418 NE54 sec. 2, T. 53 N., R. 97 W. Emblem. Y476 Unsurveyed area, SE54 ........ Gilmore Hill. Table 4. Duke University Primate Center fossil vertebrate localities in the Willwood Formation of the central and southem Bighorn Basin, Wyoming. [m, meter level; B, Bown sections; S, Schankler-Wing sections; EB, stratigraphic position estimated into Bown sections; ?, unknown. Localities are given to the nearest quarter section and are shown on plates 1 and 2. Names of topographic quadrangles in which the localities occur follow locality information. All are U.S. Geological Survey 7 10-minute topographic maps at scale 1224,000. Localities represent collecting efforts of the Duke University Primate Center during 1979—81] Locality Stratigraphic Topographic No. position Location quadrangle DPCl 438 m B . SE54 sec. 14, T. 48 N., R. 95 W. Schuster Flats NW. DPC2 No data . . . No data ................. No data. DPC3 No data . . . No data ................. No data. DPC4 No data . . . No data ................. No data. DPCS No data . . . No data ................. No data. DPC6 7m ...... SW54 sec. 6, T. 53 N., R. 97 W. Gilmore Hill SE. DPC7 No data No data ................. No data. DPC8 ?m ...... SE54 sec. 30, T. 53 N., R. 97 W. Gilmore Hill SE. DPC9 No data No data ................. No data. DPC10 ?m ...... SE54 sec. 25, T. 48 N., R. 97 W. Dutch Nick Flat SW. DPC11 536 m EB SW54 sec. 16, T. 48 N., R. 96 W. Dutch Nick Flat NW. DPC12 551 m EB SE54 sec. 17, T. 48 N., R. 96 W. Dutch Nick Flat NW. DPC13 501 m B NE56 sec. 22, T. 48 N., R. 96 W. Dutch Nick Flat. DPC14 556 m B . SE54 sec. 20, T. 48 N., R. 96 W. Dutch Nick Flat SW. DPC15 546 m S . . . SE54 sec. 7, T. 48 N., R. 96 W. Dutch Nick Flat NW. DPC16 546 m B NW54 sec. 18, T. 48 N., R. 96 W. Dutch Nick Flat NW. DPC17 528 m EB . NWIA sec. 17, T. 48 N., R. 96 W. Dutch Nick Flat NW. DPC18E ?m ...... SW54 sec. 9, T. 48 N., R. 96 W. Dutch Nick Flat NW. DPC18W ?m ...... NE54 sec. 17, T. 48 N., R. 96 W. Dutch Nick Flat NW. 100 FOSSIL MAMMAL AND PLANT LOCALITIES, SOUTHERN BIGHORN BASIN. WYOMING Table 5. University of Michigan fossil vertebrate localities in the Willwood Formation of the central and southern Bighorn Basin, Wyoming. [m. meter level; 8, Bown sections; EB, stratigraphic position estimated into Bown sections; ’2, unknown. Localities are given to the nearest quarter section and are shown on plates 1 and 2. Names of topographic quadrangles in which the localities occur follow locality information. All are US Geological Survey 7 lIz-minute topographic maps at scale 1:24.000. Localities represent collecting efforts of the University of Michigan in 1976 and 1981] Locality Stratigraphic Topographic No. position Location quadrangle Red Butte series of localities UMRBl 481 m B SE14 sec. 21, T. 49 N., R. 95 W. Sucker Dam. UMRBIA 481 m B NW'A sec. 27, T. 49 N., R. 95 W. Sucker Dam. UMRB2 481 m B SE14 sec. 21, T. 49 N., R. 95 W. Sucker Dam. UMRB3 470 m B NW‘A sec. 28, T. 49 N., R. 95 W. Sucker Dam. UMRB4 485 m B NE‘A sec. 17, T. 49 N., R. 95 W. Sucker Dam. UMRBS 505 m B SE14 sec. 4, T. 49 N., R. 95 W. Sucker Dam. UMRB6 489 m B NE% sec. 16, T. 49 N., R. 95 W. Sucker Dam. UMRB7 436 m B SW54 sec. 12, T. 49 N., R. 96 W. Sucker Dam. UMRB8 425 m B SE14 sec. 13, T. 49 N., R. 96 W. Sucker Dam. UMRB9 460 m EB Center sec. 8, T. 48 N., R. 95 W. Sucker Dam. UMRBlO 490 m B SW'A sec. 14, T. 48 N., R. 96 W. Sucker Dam. UMRBll ?m ..... SE‘A sec. 25, T. 48 N., R. 97 W. Dutch Nick Flat SW. UMRBlZ 482 m B SW'A sec. 23, T. 48 N., R. 96 W. Dutch Nick Flat. Greybull River series of localities GRl 'Im ..... NW‘A see. 5, T. 50 N., R. 95 W. Wardel Reservoir (equal to Y419). GR2 ?m ..... NE% sec. 6, T. 50 N., R. 95 W. Wardel Reservoir (equal to Y420). GR3 ?m ..... SW14 sec. 6, T. 50 N., R. 95 W. Wardel Reservoir (equal to Y421). GR4 ?m ..... NW'A sec. 4, T. 50 N., R. 96 W. Sheep Mountain. GRS 7m ..... NW‘A sec. 4, T. 50 N., R. 96 W. Sheep Mountain. GR6 ?m ..... NE'A sec. 5, T. 50 N., R. 96 W. Sheep Mountain. GR7 ‘Im ..... NE'A see. 5, T. 50 N., R. 96 W. Sheep Mountain. GR8 ?m ..... NE‘A sec. 5, T. 50 N., R. 96 W. Sheep Mountain. GR9 ?m ..... SW14 sec. 34, T. 51 N., R. 96 W. Sheep Mountain. GR10 ?m ..... 813% sec. 34, T. 51 N., R. 96 W. Sheep Mountain. GR11 ?m ..... SE'A sec. 5, T. 50 N., R. 96 W. Sheep Mountain. GR12 No data . No data ................. No data. GR13 ?m ..... NW% sec. 9, T. 50 N., R. 96 W. Sheep Mountain. GR14 ?m ..... NE‘A sec. 8, T. 50 N., R. 96 W. Sheep Mountain. GRIS ?m ..... SW54 sec. 4, T. 50 N., R. 96 W. Sheep Mountain. GR16 ?m ..... NE‘A sec. 9, T. 50 N., R. 96 W. Sheep Mountain. TABLES 2—6 101 Table 6. University of Wyoming fossil vertebrate localities in the Willwood Formation of the central and southern Bighorn Basin, Wyoming. [m, meter level; B, Bown sections; E, estimated; '3. unknown. Localities are given to the nearest quarter section and are shown on plates 1 and 2. Names of topographic quadrangles in which the localities occur follow locality information. All are US. Geological Survey 7 Ir2»minute topographic maps at scale 1:24.000. Names in parentheses following the quad- rangle names are other names by which the localities are known. Localities represent collecting efforts of the University of Wyoming Geological Museum in 1973—76. In the Wyoming Geological Museum catalogue, these localities have the prefix “V—73"; for example, V—73017 is W17, and V—73125 is W125. as used here] Topographic Locality Stratigraphic quadrangle No. position Location (other names) W16A 70 m B ..... SW14 sec. 33, T. 47 N., R. 91 W. Banjo Flats East (Banjo quarry), W16B 64 m B ..... SW'A sec. 33, T. 47 N., R. 91 W. Banjo Flats East (Banjo anthills). W16C 61 m B ..... SW'A sec. 33, T. 47 N., R. 91 W. Banjo Flats East. W17 64 m B ..... NW‘A sec. 4, T. 46 N., R. 91 W. Banjo Flats East. W19 9 m B ..... SW54 sec. 34, T. 48 N., R. 92 W. Worland (Canal). W20 97 m B ..... SW14 sec. 4, T. 46 N., R. 91 W. Banjo Flats East (Purple Valley). W20A 97 m B ..... NEM sec. 9, T. 46 N., R. 91 W. Banjo Flats East. W208 97 m B ..... NE‘A sec. 9, T. 46 N., R. 91 W. Banjo Flats East. W21 7m ........ SE‘A sec. 19, T. 46 N., R. 92 W. Banjo Flats West. W22 46 m B ..... SE14 sec. 36, T. 47 N., R. 92 W. Banjo Flats East (Slick Creek quarry beds; includes Slick Creek quarry). W23 31 m B ..... NWM sec. 1, T. 46 N., R. 92 W. Banjo Flats East. W24 48 m B ..... NEM sec. 1, T. 46 N., R. 92 W. Banjo Flats East (Campbell quarry). W24A 48 m B ..... NE‘A sec. 1, T. 46 N., R. 92 W. Banjo Flats East (Jeffrey’s extension of Campbell quarry). W25 24 m B ..... SW14 sec. 1 T. 46 N., R. 92 W. Banjo Flats East. W26 24 m B ..... SW14 sec. 1, T. 46 N., R. 92 W. Banjo Flats East. W27 30 m B ..... NE% sec. 12, T. 46 N., R. 92 W. Banjo Flats East (Stonehenge quarry beds, including Stonehenge quarry). W28 18 m EB SW'A sec. 29, T. 45 N., R. 92 W. Banjo Flats West. W29 113 m B ..... NE'A sec. 6, T. 46 N., R. 91 W. Banjo Flats East. W30 130 m B ..... SE14 sec. 30, T. 47 N., R. 91 W. Worland SE. W31 7m ........ SW14 sec. 6, T. 46 N., R. 91 W. Banjo Flats East. W32 46 m B ..... SW14 sec. 6, T. 46 N., R. 91 W. Banjo Flats East. W33 34 m B ..... SE14 sec. 1, T. 46 N., R. 92 W. Banjo Flats East. W34 34 m B ..... NW'A sec. 1, T. 46 N., R. 92 W. Banjo Flats East (Two Head Hill quarry beds). W34N1 34 m B ..... SW'A sec. 36, T. 47 N., R. 92 W. Banjo Flats East. W34N2 34 m B ..... NE‘A sec. 35, T. 47 N., R. 92 W. Worland SE. W35 40 m B ..... NW‘A sec. 3, T. 46 N., R. 91 W. Banjo Flats East. W36 36 m B ..... 813% sec. 26, T. 47 N., R. 92 W. Worland SE. W37 34 m B ..... NW'A sec. 35, T. 47 N., R. 92 W. Worland SE (Supersite quarry beds, including Supersite quarry). W38 41 m B ..... NE'A sec. 4, T. 46 N., R. 91 W. Banjo Flats East. W39 23 m B ..... SE14 sec. 21, T. 47 N., R. 91 N. Worland SE. W40 ?m ........ NE‘A sec. 9, T. 46 N., R. 91 W. Banjo Flats East. W41 30 m EB NE‘A sec. 24, T. 46 N., R. 92 W. Banjo Flats East. W42 24 m EB SE‘A sec. 24, T. 46 N., R. 91 W. Cabin Fork. W43 20 m EB SW'A sec. 11, T. 46 N., R. 91 W. Cabin Fork. W44 57 m B ..... NE‘A sec. 4, T. 46 N., R. 91 W. Banjo Flats East (Wadi Kraus quarry). 102 Table 6. University of Wyoming fossil vertebrate localities in the Willwood Formation of the central and southern Bighorn Basin, FOSSIL MAMMAL AND PLANT LOCALITIES. SOUTHERN BIGHORN BASIN, WYOMING Wyoming—Continued. Topographic Locafity Stratigraphic quadrangle No. position Location (other names) W45 46 m B ..... NE16 sec. 4, T. 46 N., R. 91 W. Banjo Flats East. W46 75 m B ..... NW16 sec. 33, T. 47 N., R. 91 W. Worland SE. , W47 ?m ........ NW16 sec. 7, T. 46 N., R. 91 W. Banjo Flats East. 1 W48 63 m B ..... SE16 sec. 4, T. 46 N., R. 91 W. Banjo Flats East. W49 88 m B ..... NW16 sec. 4, T. 46 N., R. 91 W. Banjo Flats East. W50 66 m B ..... SE16 sec. 4, T. 46 N., R. 91 W. Banjo Flats East. W51 88 m B ..... SW16 sec. 4, T. 46 N., R. 91 W. Banjo Flats East. W52 97 m B ..... SE16 sec. 5, T. 46 N., R. 91 W. Banjo Flats East. W53 39 m B ..... NW16 sec. 3, T. 46 N., R. 91 W. Banjo Flats East. W53A 7m ........ SE16 sec. 3, T. 46 N., R. 91 W. Cabin Fork. W54 113 m B ..... NE16 sec. 5, T. 46 N., R. 91 W. Banjo Flats East. W55 119 m B ..... NW16 sec. 5, T. 46 N., R. 91 W. Banjo Flats East. W56 ?m ........ NW16 sec. 8, T. 46 N., R. 91 W. Banjo Flats East. W57 ?m ........ NE16 sec. 10, T. 47 N., R. 92 W. Worland SE. W58 ?m ........ NW16 sec. 11, T. 47 N., R. 92 W. Worland SE. W59 4 m B ..... NE16 sec. 21, T. 47 N., R. 91 W. Worland SE. W60 39 m B ..... SW16 sec. 34, T. 47 N., R. 91 W. Banjo Flats East. W61 113 m B ..... SE16 sec. 6, T. 46 N., R. 91 W. Banjo Flats East. W62 27 m B ..... SE16 see. 35, T. 47 N., R. 92 W. Banjo Flats East. W63 46 m B ..... SW16 sec. 25, T. 47 N., R. 92 W. Worland SE. W66 31 m B ..... NW16 sec. 1, T. 46 N., R. 92 W. Banjo Flats East. W67 26 m EB SW16 sec. 1, T. 46 N., R. 92 W. Banjo Flats East. W76 30 m B ..... NW16 sec. 1, T. 46 N., R. 92 W. Banjo Flats East (finimomys Hills). W77 34 m B ..... NW16 sec. 1, T. 46 N., R. 92 W. Banjo Flats East. W78 46 m EB SW16 sec. 25, T. 47 N., R. 92 W. Worland SE. W80 46 m B ..... SE16 sec. 26, T. 47 N., R. 92 W. Worland SE. W81 77 m B ..... NW16 sec. 4, T. 46 N., R. 91 W. Banjo Flats East. W82 88 m B ..... SW16 sec. 33, T. 47 N., R. 91 W. Banjo Flats East. W83 81 m B ..... SW16 sec. 33, T. 47 N., R. 91 W. Banjo Flats East. W84 119 m B ..... SW16 sec. 31, T. 47 N., R. 91 W. Banjo Flats East. W85 23 m B ..... SW16 sec. 1, T. 46 N., R. 92 W. Banjo Flats East. W86 61 m B ..... NW16 sec. 4, T. 46 N., R. 91 W. Banjo Flats East (Lantern Hill). W87 94 m B ..... NW16 sec. 10, T. 46 N., R. 91 W. Banjo Flats East. W88 ?m ........ SW16 sec. 3, T. 45 N., R. 92 W. Banjo Flats West. W89 ?m ........ SW16 sec. 15, T. 46 N., R. 92 W. Banjo Flats West. W90 57 m EB NW16 sec. 17, T. 46 N., R. 91 W. Banjo Flats East. W91 57 m EB NW16 sec. 17, T. 46 N., R. 91 W. Banjo Flats East. W92 46 m EB SE16 sec. 18, T. 46 N., R. 91 W. Banjo Flats East. W95 10 m B ..... NW16 sec. 27, T. 47 N., R. 91 W. Worland SE. W96 20 m B ..... SW16 sec. 13, T. 46 N., R. 92 W. Banjo Flats East. W98 7m ........ SW16 sec. 8, T. 46 N., R. 91 W. Banjo Flats East. W105 26 m B ..... NE16 sec. 24, T. 46 N., R. 92 W. Banjo Flats East. W110 40 m B ..... SW16 sec. 3, T. 46 N., R. 91 W. Banjo Flats East. W111 113 m B ..... SE16 sec. 32, T. 47 N., R. 91 W. Banjo Flats East. W124 180 m B ..... SE16 sec. 27, T. 47 N., R. 93 W. Schuster Flats SE. TABLES 2—6 103 Table 6. University of Wyoming fossil vertebrate localities in the Willwood Formation of the central and southern Bighorn Basin, Wyoming—Continued. Topographic Locality Stratigraphic quadrangle No. position Location (other names) W125 180 m B ..... NW‘A sec. 27, T. 47 N., R. 93 W. Schuster Flats SE (Rose Bonanza, Big W). W126 180 m B ..... NEM sec. 28, T. 47 N., R. 93 W. Schuster Flats SE. W127 180 m B ..... SE‘A sec. 27, T. 47 N., R. 93 W. Schuster Flats SE. W128 ?m ........ NW'A sec. 10, T. 47 N., R. 92 W. Worland. W129 81 m B ..... NW% sec. 4, T. 46 N., R. 91 W. Banjo Flats East (Mary‘s Hill). W130 31 m B ..... NE‘A sec. 1, T. 47 N., R. 92 W. Worland SE. Published in the Central Region, Denver. Colorado Manuscript approved for publication May 6. 1993 Edited by Barbara Hillier Graphics by Wayne Hawkins Color design by Virginia D. Scott Photocomposition by Shelly A. Fields U. 8. DEPARTMENT OF THE INTERIOR - . PROFESSIONAL PAPEPIgggg U.S. GEOLOGICAL SURVEY o I II I I II o I I II I o I II 6 I , ,, o , y n I 10800773077 6 6 6 51 2730” 108000! “'6‘ 66 100 37 30 35 6 1 3230 100 30 2730 2, 25 108 22 30 20 . ,, 1730 10815 72 ., 1230 . 16° 72 27 6 61 , 440221301: C? 2: 44 2230 2 1 1 1 1 .1. I . . , ,7 , 2 6 ,7 ._ , 6 , 6 . 2 6 ,2 . , __ , . 2 7 2 . 2 2 72 2 D1637 7 L 7 2 , , , . _ , 7 . , 7 601239 7 7&258 2 ', 2 7 7 I 1 V I - 2. I I '7 I. ‘6 3 , L ,1 6 ‘1 ' " W7 , D1873 2 i Y293Q 7' I . . . , 7- 2 1 _ ' 2 7 7 I Y121 5“” - . 2. 1 2 7 ' Q D1857 “23$ 2 Y122 Y403 . D1 709 D1904 k ‘ D1591 D1872© 2_ ' ’ 7 f7 2 MIU‘PF“ 0 , f "T C 7 y416 ’ _ Y399 . 22 . 66 22 7NM37627 , . 7 Y412 . Y294 6 Y381 6? AC 2. q; 7 7 7 ' D1711 1 2 Y95 7i ' . ‘ 2 D- 815 . 67 . 6 ,- 2 Y119 k ‘ NM37638 AC 2. , _ Y295 Y29o Y322 Y148 ( 7 . \ ’ .7 * Y291 Y \ . W600 . 6 D1143 Y292 147 7 \ 2 2 44§Y301 ‘ 91879 7 2 Y120 \66 \ D1141 q 7 \\ Y79 D1710 ‘Y423 IO 01649 m W\ 01650 D1740 ' D1568 ' 2 D1870 J y424 O D1739 P 6% ' D1260 ' - D-1848 (é. . '.Y319 2 . C3 ~D1264 D1869 DiBGGg D1875 . 2, ‘ 2 Y205 — C9. 2 2 2 7 \ \ 2 , . 2 D1146 2 D ’ GR9 ‘ ‘ " ' " A ., .— —— 1 " V \ 2 2 D1938 7 I \C D1142 2 % 17410 7 Y397 Y203 GR4 Y324 NM37662 01900 172 91 - Y - 1 6, _ O O , D 6 2 2 EC 393 _ 16, 7 ' . 31901 ‘ o / Y419 ‘ /' \ 2 NM37656 6 2 , M 2 Y202 Y201 ,Y270Q 6 ~6 _ - - {£122 GR1\___. _..._..___.._/ \6 \2 72 \ D1182 ’ Y4” 2 ' \ T Y320 2 2 -2 6 \ 019233 Y156 Y4oo Y395 “64 2 Y358 ) D1780 D1935 7 7 7 ., Y359 Y8 9 1 D193:*1 D1145“ EXPLANATION 2 2 - 22 . . . . 2 1 2 . 1 2 2 - , _ 2 2 , 2 , 2 , .2 D1570 . -. 2 2 ,2 Y426 D1259 Y4 - / . i , ; 2, _ 7 2 7 2 7 I 2 I 7 2 ,$ P Y152 Y152N Y296\\ I 02 I Y394 2 I . 7 _ 20' Measured sections—Letters indicate acronyms for measured sections ,91913 o . . _ , 6 26 2 . , . 6, , .6 6,6 66. 62 , . .2 . , 6 , . 2 6 .6 , _ .2 2 6 22 , 2 ”D1876 _ _ 2 HYZBZ 49 \\ y302 C5 \\ 2 \ Y96 ‘6 . (table 16). Dashed where location is uncertain 6 , . ,6 2 76 67 6 26 2 2 . . , 7 6 6 2 , 6 6 . 2 7 ‘ 7 ,7 .2 . 2 ' , 6 ‘7 66 " 7' 6 ‘ 6 6 7 ‘ Y325. ' D15 9 D1548 2 ' 6 ' , ,6 6 1 [”9on 66 766 “3de «351$? D1959 6 Y206‘fi . ' . RB— RB’ Bown sections ‘ M 7 2 7 7 ~ ' ’ ‘ 7 7 _. ‘ _ 6 .2 2 7 ‘: 2 7 2 . -. 7 . 2 _2 , 7 _ ‘7 2 . 4 EA 7 - 7 _ ' 7 ' Y277 Y278 7- 2 x, \q ~Y4o1 76 Y406 113642127407 2 , , 1 2 I . . 22,01,932 .- V 7, 7 - 7 2 ' 2 2 ' ' 22 : 2 ‘ 2 .7 -- - , Y , . 2 2 ,2 2 " , " I 7, , - _ ,7 , \ -2 2 f - 2 . ,, , . -7 ,. bfio?9?4% D1488 - 2 . , 2 6 2 ygoo ' 2, 1 Y304 Y207 2 1 7 2 66 2 6 1 77 2 . 2 EC—— EC schanker-ng sections . 7. , 2 6 62 2 2 6,6 7 . 6 . 6 ‘.7 2 7 7 7 67 67 7 7 77 2 2 . 2 , . .-. 6 ' 26 _. 26 3 2 . 7 7 6713216551 E 903Q 2 , “ ‘ . 2 \ Y396 '5 6m 7, 7 7 _ , Y284%1 I . 2 \ I I institution that established the looality. D, US. Geological Survey; DPC, . D1792 2 2 666626 6 . .6 2 6 . 66 . 62 3., ,6 . 6 , 6 2 2 ., . 62 2, _-7. 6 _ 2 2, , , 2 . 26 . C, Y27196EG - 01806 6 \\ 6 2 I “4‘ AC/*_Y1463:\K16363 66 6 , , -, 6 2 22 7 , . 2 2,- . 7,2 2 2 2 , . _ 72 i , 2 2 2 _ , 261m D1929 D1926 , EC k \\ QD-1807 EC. Y145 Eff/60% 6 7. 2 _ M7 h‘ M fPl t1 . U iversityofW 0min 'YYale . 2, ,7 ' ‘ I ‘2 ' .2 7 2 ' 7 - , 2 2 '9 9-1803 . 7 7 22 2 ' ’7 - .. .2 2, 7 ‘ 7 , , ‘ 7‘ ‘7 _ Y233 9 0193‘ 2/' Y344 T ”‘ “K g I ‘ E 'c 19a" useum20 aeonoog6y1W, r}. y 9' ’ 7 ”426722 2, - 2 . .6 _ 6 . ,6 , 2 , 6 ., 2 6. , _ . 6 . . , 2 ,2 . ’, , 7 6 D-1816 Y374 , Y337 3 , 6 6 Peabody Museum: SW, Scott Wlng localities . . . a 2 , ” 2 g I 6‘ , ‘01553 7 7 2‘ ' L ' 7 ' ' ' ‘. D1514 1 . 2 6 2' '7 7 6' 2 ‘, V , i ‘ _ Y299 WWW/1, ’ I , 2 Y369 2 % D1194 7 6 Stratigraphic posmon of locality from base of Willwood Formation 7‘ YZMQ I. <5 N L 2 , 7' I I ‘7 fl V, 2} I ' ' 7 2' F I I. I ’ I I, 4 ’ H 2. D1964 D1930 A\ \ I I 7 6 6 i ‘ ’7 4 I 11 I 7 Unknown stratigraphic level ., 2 . 2 2 a 2 7 , 2 . . 7 " 2 72 .2 Y82‘ 7 7 - ’ ’ " '. 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' 77 ‘ ~ 7 ' 2 Y224Q§£77 7 7 67 2 2 ”248" 3‘ W , O 7 01884 x \ 7 D1262 7 ’ ‘ \ ”7 \ Y90 2 \ . 6 ‘— Y375 2 (/ \ .1 ' Y98«2 D119564. ’ 66L‘Y94 -\ \ Y108.»"\Y2‘3 Y212 v388 Q 227 27\ /. -2\ 2 c0 \2—— ‘ Y212 D-1827 .2 \ Y373 .Y372 ( Y390 2 NM37650 — -— — — —\ D- I 7 ‘ g \— 7 I 1820 EC 7 2 Y91 Y208 2. 2 . 1 \ 7 2 -2 \._.-27 2 2 EC 22 _ 2 ' 2 2 ‘ 2 ‘ 2 NM37641® T 7 7 ‘ 0 4M 7 2 ’ 2 7NM37640® \ EC" Y3‘3‘o 7 17356! J L/— 1,366 EC 217377 Y305 I ' V v—mQfi‘ D1178 I ,0 _ , 22 . 7 2 ’ Yam—66, 7 , 2011910 2 - Y‘—7"“'J Y362 __\ , SFEL'm/A NM37560 G9 US. National Museum fossil-plant locality— Showing number 0-1804 /% y9'2’ NM876456 ‘5‘ NM376473 - ” — 17'30" .0 2 2 91936 2 2 7 7' o 7 Y268 2 " 7 I . 27: 7 ‘ ~ Y251 7 ‘7: 77 ” 2D1877“ _2 2 77 7, .7 72 2 2 _ 7 7 2 2 7 7 7' f 22 .. 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' 2, 2 2 8‘ my _. 6 .-, 2 .2, 1 D1531 7 2 2 . 22. _ . , 2 . , 2 .,- -2 2 , , 0 D16 4907 . .2 66 ,2 6 .2 ._ 22 2 .6 2 2~ 2 7.. , I 7 >1 , 77 _ 2 2 77 , ‘22 D1347 NM37667 72 NM37668 7 f - 7 ' 7 ’ ' ' 7 ‘ 2 - 7‘" 7 7 7 4' 2‘” ' 7 7 \ 7 7 77 ‘D13781 . , 2 ’NM376757 , , 6 2 . 62 , 7 2 26_6 , - 2 7 . 7 .2 2 '2 _ . _ 2 2 2(01379 , NM37673 7 7’ - , 2 - 7 2 ' " ’ ' ' 7' ‘ - 7 7 7 '77 7 7 ' 7 ’ ' D1382 6 . 6 , 2, 7 7 2 7 7_ 2 , , ‘, :7' 7 ' ' ’ RSA D1198A‘ " SW881 $ SW8826 . Y166 . . ,. _ , 6,66 .7 , 2 . 2, .6 26 _ 13-1843 . . ,2 . 6 2 6 011666 6 Y4O 2 , , 6 . . 2 D1198B @Swee'z? I Q ‘ 2 . 7‘ 2 ,7 7, 2 __ ' 2. .7 .7 ‘ 7 7; ' 2_ 2 7 , 2. ’ 2 ' 2 I 22 _- 2 2, I ‘ I . D119“ ' NM37672 ®SW8828 ' V, 2' ’ - 2 J 77 7 , L ' "2 s.‘ ,7_. .,7 ‘7 2 ', ' 3 7 ‘01164 2 ‘ 62- " " 7 D4845 " ' , . , 2 2 , 2 7 ~ 7 ., , 2 2 7 , I 2 . I - D1934 2, 7 , 2: 2 R' 7. - 2 2 7 - 7 ' ' . 2 7 7 57. e2NM375-775 2 2- 7. ' F '7 2.. ,, .2 . $.17 ’2 fl ,. is?! 2 ,. , ' 2 " " 2' ,- , . ’ . 2. 2 . '2 ng .917?“ ,j 7 , 2 ,7 _ 6 ‘7 72 2 . 2 . 2 62 2 . .2 " - 27 ' 7 2 7 , ” - " 22 2' 2. 2 _ ’ , ‘_ ‘ " ' 22 2. . D-1846 ., , . _ 7 6,6 , .D1198H D1229 : D1331 I D1160 D1245 +. D1305‘ ’ D11980 D1198E S207 44°UU' INDEX OF UUADRANGLES SHOWN ON THIS PLATE D1198G :..,2 .. 7, ' . '2 I 2. 7 77 Y24 , .. I. f - Y45$ . 7 1 .- . '- 7 7 , , 7 2 , 2 2 7. -- 1 , D1198C 0' ‘ 7 , 2 H ' L 2 7 L: 0- ' (01244 Y188 o6 '7 2.6 ‘ 7‘ , . f L 7 . ' 2, , ’ '. ’ " UMRBO . i ' '7 .01168' ‘ ., 8D1641 7 7 . ' . HQ ‘Y57 . .1 .7 . 6 .7 D1398N , 02701-4727 ‘ ' ' . ” 2 2 7 2 2 22 D1398N., D1472 0 01642 ” ' ‘ O D1643 7, Q Y43. D1871 7 ' 7 ‘01687 9 . .’ 67 . ’ 2 SD D1688 DPCTZ 2 DPCI 1 UMRBTO . I ’0 I ' ' ‘ I ‘D1598 44°07 '7 44°07'30" 30 _D121727 D1222 D1157 D1511 CD1158 ’ D1506 D21219(P. D1504N .7. 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'77": _ ‘ _ . . 2 2 7 - 2 - 7 , 77 7 2 - 2 j7 72 7 77 7 _2 '2 72 222 77 ' 2 ,2-7'_D1,4_600 :7 D1736 ,6 72 6 27 6 72 .66 .6 _ 2 2 6 2 , 66 2, 6 _ , 0D17o1 , 1 2 2 . 2230,, 6 2,30" 7 ‘ - ' 2 2 ' ’ 2 7 , c901730 2 ' Q1313” 1. , ,1 2‘ 7| . ’ ' ‘1 100°22'30" 20' "7 17'30" 100°15' 1.31/2“ SCALE 1:41 [100 1 1/2 o 1 2 3M|LES 1—11—11—11—11—11——————1 1—-———-1 WYOMING 1 25 O 1 2 3 KILOMETERS ’ mom MEAN CONTOUR INTERVAL 20 FEET MAP LOCATION DECL’N‘T'ON' ‘9” NATIONAL GEODETIC VERTICAL DATUM 05 1323 TRUE NORTH FOSSIL VERTEBRATE AND PLANT LOCALITIES AND LINES OF MEASURED SECTIONS OF THE WILLWOOD FORMATION, SOUTH-CENTRAL BIGHORN BASIN, WYOMING By Thomas M. Bown, Kenneth D. Rose, Elwyn L. Simons, and Scott L. Wing 1994 ' 100°00' 4400' , , ,, 22 . , o . ,, 2 2 230 108°07’30" 35’ : 32'30” 108°3U' 27'30" 7‘ 12 30 11] 108 07 30 5 \ Mapping by T.M. Bown, 1980—92 US. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY wamu' swan". 7, 55' 107°52'30" 50' , 47'30" 107°45' 44°07'30" I . V , I _ . . I F 44°07'30" 001751 0-1808 Q, ' V y , , VW1s ’. 7 omeg‘wv. ‘ Wis ' ‘ ’ 5' —~ . s '5' \w130, ' D1485 i ’ Ownsé ';- Q 7 -~ , V ,, y D1227 308. ,- . 2'30" k ' 1 fl 2'30" 276“ m ..w36_ “ SL W80 , w37' ,., SL’ w30 Y139 ' n ws3 44°00' F W55 4 44000, i 1 ' I ' " 7Y37OA I ‘, ‘ W8 u, E ,’ I . .y BJ W1“ 1 ' ‘ W16 Ban/o H _ . “a, .. ,4 , ‘ ,quarry ‘ . y ‘ , 'W81 , _ "w55 W111 ‘ V W17 ‘ , fi 1 is “a W129H , _ ysoe “.43 D1228 W86 , __ _ Sl/‘ck’Creek . quarry W54 w W49 W441 V , z " w77- W33 ' t ((l 54 , ' Wadi Kra'us " ‘ ‘ ‘~ ' , 9 ‘ i , ‘ ~ ' quarry -. -, v . ‘ rw51 W25 5L ‘ v3433’; H y i 'W25 ' .. W2 7; _ \. WZOA W85 :_ z y ‘ ‘ ' \ W50 ~ Stoneheng-\ ‘ gW31‘ _ ‘ » quarry __ fl, ,._ _ .L ‘ fl . ' , : W32 ‘ xii/202‘ ‘ ' f ‘ OB m8, - , ,_ , F " ' ' ZIW2 7 01296 E ' - BJ \\ , 1W47 ’ W203} ‘ 9 kW4O 57,30” ~— 5730" ' '1‘ , (we L Y115 : , ' /Wl}05 55' T w 55, 43°52'30" 0 , ; I; H ' r WV" -: l '_ ' *2 ,- , ‘ 1, V F. ‘ I ,. I H .1, 4305230” 108 00 57 30 55' 107°52'30” 50' " ' H 47'30" 107°45' Mapping by T.M. Bown, 1980-92 131/2“ SCALE 1:41 000 1 1/2 0 1 2 3 MILES I E l—i i—I l—i I—I i—l i-——-——i I—_—a WYOMING g 1 .5 o 1 2 3 KILOMETERS g t—I I—i l—I i—i l—I i—-—-—I T—i ,_V7L MAP LOCATION CONTOUR INTERVAL 20 FEET NATIONAL GEODETIC VERTICAL DATUM OF 1929 APPROXIMATE MEAN DECLINATION,1994 FOSSIL VERTEBRATE LOCALITIES AND LINES OF MEASURED SECTIONS OF THE WILLWOOD FORMATION, SOUTHEAST BIGHORN BASIN, WYOMING By Thomas M. Bown, Kenneth D. Rose, Elwyn L. Simons, and Scott L. Wing 1994 BJ PROFESSIONAL PAPER 1540 PLATE 2 6P E 775’ Pg; V. ){Lg 5:) F /q7le, ‘2 OK («on EXPLANATION BJ I Measured sections—Letters indicate acronyms for measured sections (table 16) D1 2 96 Fossil vertebrate locality— Showing locality number; letter prefix indicates % institution that established the locality. D, US. Geological Survey; W, University of Wyoming; Y, Yale Peabody Museum Stratigraphic position of locality from base of Willwood Formation Unknown stratigraphic level 0—99 m 100-199 in ‘9 :1, § 3% s s x s §é°§ §$°§ {N '3' ’\ ’\ ‘0 a s <3 ‘Q % “6 % CS3? § $33“ § Q Q“ 9 w‘ q? x ‘8‘ \a INDEX OF [IUADRANGLES SHOWN ON PLATE Mantle Origin and Flow Sorting of Megacryst—Xenolith Inclusions in Mafic Dikes of Black Canyon, Arizona U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1541 ”N \ itgzii4i994 ) U.S. DEPOSITORY MAY 2 5 199'. 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Maps Only Maps may be purchased over the counter at the U.S. Geologi- cal Survey offices: 0 FAIRBANKS, Alaska—New Federal Building, 101 Twelfth Ave. 0 ROLLA, Missouri—1400 Independence Rd. 0 STENNIS SPACE CENTER, Mississippi—Bldg. 3101 Mantle Origin and Flow Sorting of Megacryst-Xenolith Inclusions in Mafic Dikes of Black Canyon, Arizona By Jane E. Nielson and John K. Nakata U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1541 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994 US. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Robert M. Hirsch, Acting Director For sale by US. Geological Survey, Map Distribution Box 25286, MS 306, Federal Center Denver, CO 80225 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the US. Government. Text and illustrations edited by James W. Hendley II Library of Congress Cataloging-in-Publication Data Nielson, Jane E. Mantle origin and flow sorting of megacryst-xenolith inclusions in mafic dikes of Black Canyon, Arizona I by Jane E. Nielson and John K. Nakata. p. cm.——(U.S. Geological Survey professional paper ; 1541) Includes bibliographical references. Supt. of Docs. no.: I9.l6:1541 1. Basalt—Inclusions—Black Canyon (Ariz. and Nev.) 2. Geology, Stratigraphic—Miocene. Pliocene. 4. Geology—Arizona. I.Na.kata, John K. II. Title. III. Series. QE462.B3N54 1994 552'.26'0979159—dc20 3. Geologx Stratigraphic— 93-23011 CIP Cover—Segment of north-trending dike array in Black Canyon, Arizona. Tabular dike segment crosses fanglomerate ridge. At north end (left), dike incorporated a mass of the host fanglomerate and developed a bulbous swelling. Wilson Ridge in background. QMPPPE‘ ._.,_. t".°.‘°9°>' CONTENTS Abstract ........................................................................................................................ 1 Introduction ................................................................................................................. 1 Acknowledgments ....................................................................................................... 3 Geologic relations in Black Canyon ........................................................................... 3 Extrusive and intrusive megacryst—bearing rocks ....................................................... 5 Vent area ............................................................................................................. 5 Tuff breccia deposits ................................................................................ 5 Intrusions .................................................................................................. 5 Magnetic expression of the vent area ...................................................... 6 Observations on the dike arrays .......................................................................... 6 Geologic relations and structures ............................................................. 6 Internal features ........................................................................................ 9 Structure-parallel joints .................................................................. 11 Cooling joints ................................................................................. 13 Inclusion suite ................................................................................. 13 Inclusion orientation and foliation ................................................. 13 Inclusion distribution patterns ........................................................ 14 Relation of inclusions and bulbous swellings ................................ 15 Composition of dikes and inclusions .......................................................................... 16 Petrography and composition of dikes ............................................................... 16 Compositions of mafic inclusions ...................................................................... 18 Olivine ...................................................................................................... 19 Pyroxene ................................................................................................... 19 Amphibole ................................................................................................ 23 Other minerals .......................................................................................... 25 Discussion .................................................................................................................... 25 Formation of the Black Canyon vent area ........................................................... 25 Structures and intrusive process of the dike arrays ............................................. 26 Origin of the mafic-ultramafic inclusion suite and host magma .......................... 27 Origin of zoning and inclusion distribution patterns .......................................... 28 Zoning ...................................................................................................... 28 Inclusion concentrations and size sorting ................................................ 28 Summary ...................................................................................................................... 30 References cited .......................................................................................................... 30 FIGURES Map showing outcrops of dikes in Black Canyon .................................................................................................... 2 Maps of vent area ...................................................................................................................................................... 2 Photograph showing bulbous dike in fanglomerate at north end of vent area ......................................................... 5 Photograph showing longitudinal section and flow joints parallel to dike tip, location 11 ..................................... 8 Diagram showing idealized dike ............................................................................................................................... 8 Photographs showing features of bulbous swellings ................................................................................................ 9 Photographs showing fanglomerate incorporation by Black Canyon dikes ............................................................. 10 Photograph showing dike with irregular distribution of massive and fissile joints ................................................. 11 Diagrammatic representation of dike exposures (X, Y, Z) at location 13, US. Highway 93 ................................. 11 Photograph showing flow banding in marginal zone of dike ................................................................................ 12 Photographs showing distance and close up views of dike segment at location 13 ............................................... 12 III 12. 13. 14. 15. 16. 17. PPNQMFS‘P?‘ CONTENTS Photographs showing static cooling joints ................................................................................................................ 13 Inclusion orientation, distribution, and abundance in dike at location 13 ................................................................ 15 Photograph showing fanglomerate in dike matrix of the contact zone .................................................................... 16 Quadrilateral compositions of pyroxene minerals ..................................................................................................... 19 Amphibole compositional variations ......................................................................................................................... 24 Amphibole (kaersutite) compositional variations in dike at location 13 ............................................................... 25 TABLES Characteristics of Black Canyon dikes ...................................................................................................................... 4 Features of zoned dikes ............................................................................................................................................. 7 Compositions of dike matrix ..................................................................................................................................... 17 Compositions of clinopyroxene ................................................................................................................................. 33 Compositions of orthopyroxene ................................................................................................................................. 36 Compositions of amphibole (kaersutite) .................................................................................................................... 37 Compositions of amphibole (pargasite) in xenoliths of Black Canyon dikes ........................................................ 20 Published compositions of Black Canyon kaersutite megacrysts ........................................................................... 22 Compositions of phlogopite and olivine .................................................................................................................... 23 Mantle Origin and Flow Sorting of Megacryst-Xenolith Inclusions in Mafic Dikes of Black Canyon, Arizona By Jane E. Nielson and John K. Nakata ABSTRACT Three arrays of inclusion-bearing alkali basalt dikes, 1 to 1.5 km in length, crop out in Miocene and Pliocene fanglomerate in Black Canyon, near the Colorado River, northwest Arizona. Erroneously called camptonite dikes, the best known exposures are in a series of roadcuts about 16 km south of Hoover Dam. The origin of axial concentra- tions of inclusions in these dikes has long been debated. The north-trending dike arrays consist of at least 16 short seg- ments, which are 61 to 366 m in length. Five of these segments pinch out at the north or south end, or both; where the tips of dike segments overlap, they may be deflected in opposite directions. These stress-related deflections show that the segments of each array were emplaced concurrently. A vent area of related tuff breccia and multiple intru— sions crops out at the south end of the 'dike arrays. The dikes, related tuff breccia, and a possible small lava flow all contain inclusions. Although the most distinctive inclusions are mafic to ultramafic mineral fragments (megacrysts) and xenoliths, the largest and most common inclusions are silicic igneous and metamorphic rocks from disaggregated masses of fanglomerate wall rock. Compositions of the suite of mafic megacrysts indicate derivation from the man- tle; thus they are xenocrysts. The alkali olivine basalt com- position inferred for the juvenile magma of Black Canyon dikes and eruptive units is consistent with these inclusion compositions. The dominant mantle-derived megacrysts are black kaersutite (Ti-homblende) cleavage fragments with ubiqui- tous reaction textures. Less common xenocrysts are black pyroxene grains and polygranular olivine clusters. Small xenoliths of spinel peridotite and pyroxenite—including amphibole- and mica-bearing types—are present but un- common; one peridotite contains a kaersutite veinlet with compositions similar to most analyzed kaersutite mega- crysts. Systematic analyses of kaersutite grains from the dike segment with the best-exposed inclusion concentration show no compositional variations that can be related to grain size, shape, textural relations, or position. Mineral Manuscript approved for publication May 12, 1993 compositions and textural relations indicate that the mafic xenolith-megacryst (xenocryst) assemblage in the Black Canyon dikes most likely was derived from an area of up— per mantle composed of peridotite with veins of pyroxenite and pods of coarse crystalline amphibole. Partial melting of this type of assemblage could have produced the dike mag- ma, but the observed reaction textures and isotopic disequi- librium between megacrysts and the dike matrix indicate that the suite of inclusions does not represent the actual parent material. ’ Our detailed observations indicate that most internal structures in the dikes are concordant with the axial planes of the dike segments and are related to flow processes of magma in conduits. These structures include: alternating zones of massive or fissile matrix (containing longitudinal joints), rare flow banding, and the boundaries of matrix structure zones, as well as orientations of the long dimen- sions of vesicles and of mineral and rock inclusions. One roadcut through a dike segment exhibits four to five regu- larly-altemating matrix structure zones in combination with a large volume of size-sorted inclusions. Only three dike segments contain more than 10 per— cent inclusions. In all these segments the largest volume of inclusions—of both mantle and near-surface origin—is concentrated in the axial zones; the largest inclusions and the greatest size range of inclusions are found in the cen- tral zone of the dike. The presence of fanglomerate clasts in these axial inclusion concentrations demonstrates that inter-grain pressures effectively moved inclusions toward the center of the dike conduits. Therefore, axial concentra- tions of mantle xenolith-xenocryst inclusions are found in the dikes where the flowing magma contained a relatively large volume of particles. The axial inclusion concentra- tions and size sorting of inclusions were most likely pro- duced by flow sorting and not by multiple injections of magma or progressive crystallization phenomena, which have been proposed previously. INTRODUCTION Alkali olivine basalt dikes and dike-fed tuff breccia crop out in an area of approximately 1.5 kmz, near U.S. 2 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA Highway 93, in the Black Canyon of the Colorado River, "4‘37'35' northwest Arizona. The best-known dike exposure is a A roadcut located 16 km south of Hoover Dam and the tuff breccia is found in a small eruptive center, located at the south end of dike outcrops (figs. 1 and 2). The dikes were 1 14°37'36' 1 14°37'30' C / /> if? Z\Aba:gon§d ['0 cu / \Location 13 d -\ Area of figure 28 CONTOUR INTERVAL 40 FEET Figure 1. Index map of study area, in northwestern Arizona. Dikes are shown in heavy black lines; numbered locations are described in table 1 and text. Heavy dashed line represents a jeep trail. Topo- graphic base from US. Geological Survey Ringbolt Rapids, Arizo- na—Nevada quadrangle map, l:24,000 scale, photorevised 1973. Figure 2. A, Map showing geology of vent area and southem- most dikes of southern Black Canyon array (location shown in fig. 1). B, Map showing the magnetic expression of the vent area, superimposed on outcrops of intrusions (location shown in fig. 2.4). Light shading shows main region of domed magnetic anom- aly; darker shading is the highest peak on the magnetic anomaly. EXPLANATION Alluvium (Quaternary) Tufiiirgddiokifirfiaryk Tull breccia (Tertiary) D Fanglomerate (Tertiary) ..... Q00 / Contour of altitude Dike Tertia Magnetic contours, dotted ( ry) —/ 400 / where inferred. Hachurs indicate closed low 0 100 METERS 0 100 200 300FEET CONTOUR INTERVAL 40 FEET MAGNETIC CONTOUR INTERVAL 400 nanoTeslas GEOLOGIC RELATIONS IN BLACK CANYON 3 emplaced in fanglomerate of Miocene and Pliocene age, which contains clasts derived from older metamorphic rocks and granite of the adjacent mountain ranges. Roadcuts expose a dike segment with conspicuous concentrations of kaersutite megacrysts and rock frag- ments; inward from the contacts the kaersutite grains in— crease in abundance and are larger in size. These concentrations were called “zoning” by Campbell and Schenk (1950), who interpreted the dike as a carnptonite magma that had crystallized in place. They hypothesized that volatile components of the magma had been concen- trated in the axial zone of the dike, allowing crystallization of coarse kaersutite grains, and that smaller crystals formed in the dike margin, owing to the smaller propor- tion of volatiles in the magma near dike contacts. Howev— er, rock fragments also are larger in the dike axial zone, and xenoliths of altered peridotite, probably of mantle ori- gin, have been identified in the inclusion suite (Wilshire, Schwarzman, and Trask, 1971). Compositions of kaersutite and pyroxene megacrysts from the roadcut exposures sug- gested that these minerals also were derived from a mantle source (Best, 1974; Irving, 1977; Basu, 1978; Boettcher and O'Neil, 1980; Foland and others, 1980; Garcia and others, 1980). Our detailed study of structures, textures, and inclu- sion content and distributions in all the exposed dike seg- ments verifies the mantle origin of the mafic megacrysts and xenoliths. Thus, the kaersutites did not crystallize in place. Moreover, the distribution of inclusions by size are more complex than Campbell and Schenk (1950) indicat- ed, and we conclude that neither inclusion concentrations nor the size distribution in various dike segments could have originated as those authors proposed. We also found that longitudinal zones, defined by alternations of massive matrix and dike—parallel fissile joints, are ubiquitous and that only two other exposed dike segments of the Black Canyon arrays contain inclusion concentrations similar to those in the well-known highway roadcuts. Therefore, the “zoning” observed in the highway roadcut is a coincidence of features that occur in various combinations throughout the exposures of dikes in Black Canyon. ACKNOWLEDGMENTS We especially thank Howard Wilshire who originally suggested that “zoning” in the Black Canyon dikes was due to flow sorting, and Myron Best whose early encour- agement kept us going. W.A. Duffield and EL Smith pro- vided careful and constructive reviews that led to substantial improvements in the manuscript. Determina- tions of oxygen and carbon isotopic compositions were done by L.D. White, through the courtesy of Ivan Barnes and JR. O'Neil. Whole-rock major-element compositions were analyzed by J. Baker, A.J. Bartel, K.C. Stewart, J.E. Taggart, and IS. Wahlberg. Volatile elements were deter- mined by P.R. Klock, G. Mason, H.M. Neiman, S. MacPherson, and C. Stone. Dennis Sorg prepared the leached rock powders for analysis. Between 1981 and 1985, field support was provided by Jay Noller, Tova Dia- mond, and Cynthia Ardito. Modeling of natural remanent magnetization (NRM) was suggested by Bob Simpson, who provided the mag- netic susceptibility bridge for those measurements; Ray Wells guided us in collection of oriented samples for NRM determinations, and those measurements were per- formed by Vicki Pease. Andrew Griscom provided a mag- netometer for traverses of the vent area. Todd Fitzgibbon, Linnea Larsen, and Ruby Harper helped with data and word processing. Various parts of the study were prompted by observations of features in the Black Canyon dikes, communicated orally or in reviews by Steve Bergman, Ray Binns, Dave Eggler, Mike Garcia, and Frank Spera. GEOLOGIC RELATIONS IN BLACK CANYON The Black Canyon dikes comprise three distinct arrays of discontinuously exposed dike segments. Two subparal- lel arrays, l and 1.5 km long, trend close to due north (fig. 1). Exposed dike segments in each array are from 61 to 366 m long (table 1). A third, more dispersed array with a northeasterly trend is 1 km long and comprises dike seg- ments 60 to 160 m long (fig. 1). This third set of dikes trends into related eruptive deposits and intrusions at the south end of the study area (fig. 2). The Black Canyon dikes intrude gently west-dipping Miocene and Pliocene fanglomerate deposits of the Muddy Creek Formation. The fanglomerate forms an alluvial apron along the west flank of north-trending mountain ranges, from which clasts of Precambrian gneiss and gran- ite were derived. Volcanic rocks of early to middle Mi- ocene age underlie fanglomerate west of the dike arrays; these rocks are mostly andesite and dacite with subordi- nate basalt and include dacite airfall and ash-flow tuff (Anderson and others, 1972; Anderson, 1978; El. Smith, written commun., 1988). Mesa—capping flows of aphyric basalt locally overlie the fanglomerate and Precambrian rocks (Anderson and others, 1972). The dikes have K-Ar ages of 4 to 5 Ma (Anderson and others, 1972), and ages of 3.7 to 5.8 Ma are reported for massive mesa-capping basalts (Anderson and others, 1972). The megacryst-bearing dikes are distinctly different in composition and appearance from the bulk of approxi- mately coeval basalt flows (Campbell and Schenk, 1950). Thus, the megacryst—bearing dikes probably were not feed- ers for these mesa-capping flows. MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA Table 1. Characteristics of Black Canyon dikes. lec segment Description Attitude Width (“‘01 Length Cements (see fig- 1) Strike Dip Min. Max. (m) 1 Short segment, N20°E 79°W 80 150 61 Tabular, with horizontal cooling joints. outcrops 900 m Matrix fissile in axis. Sparse inclusions, north of highway. kaersutite, olivine predominate. 2 Crops out on N16°E 90° 91 370 213 South end tabular, no zoning. Bulbous fanglomerate ridge, swelling at north end, adjacent to tabular east of jeep trail; 2 segment with 5 massive to fissile zones. segments with about Abundant inclusions; fanglomerate clasts 70—m gap between predominate, kaersutite less abundant. exposures. 3 to 4 Sinuous, offset from N02°W to 90° 0 1,110 275 Predominantly tabular, 3 interior zones. north end of N35°E Mass of fanglomerate inclusions at contact segment 2. Segment near south end. Sparse inclusions, all in axis 3 is south end, 4 near north end; kaersutite predominates. No north end, of dike. size sorting. Bulbous swelling at north end near dike tip. 5 to 6 Northemmost N10°E 71°E 0 115 275 Bulbous swelling predominant in outcrop. exposure of eastern Two asymmetric zones, sparse inclusions; array. West contact predominantly kaersutite. No size sorting. is not exposed. 7 Northemmost N02°E to 90° 0 100 183 Tabular, resembles segment 1. Tip exposed exposure of western N15°E at north end, near small dam in wash. array. 7A to 8 Relatively straight N10°E 90° 0 180 152 Tabular, massive contact, fissile axis zones. segment, some Sparse inclusions; kaersutite predominant. unexposed parts. No size sorting. Tip exposed at south end. 8 to 9 Relatively long and N20°E 90° 110 280 366 Tabular, resembles segments 7A to 8. Forms straight segment. large and small dams across 2 washes. 10 to 11A Straight segment, N 90° 0 100 150 Tabular, massive contact, fissile inner zone, but tip at south end and massive axial zone. No size sorting. deflected sharply to northwest. 11A to 11 Sinuous segment. N10°E to 76°W 0 240 244 Tabular, 2 asymmetric zones. Small bulbous Parabolic tips at N11°W swelling near north end. Sparse inclusions, both ends. no size sorting. Forms large dam in wash. 11 to 118 Sinuous segment. N05°E to 90° 0 255 245 Tabular, no distinct zones or size sorting; At north end is well N10°W sparse kaersutite inclusions. Parabolic exposed parabolic joints concentric to contact in tip exposed at tip. north end. 12 Two short segments N25°E 90° 60 100 200 Tabular and massive. No zones; sparse in large wash inclusions, predominantly kaersutite. between highway and Station 1. 13 Cross section N25°E 78°E 115 160 244 Tabular, 5 alternating zones, massive to exposed in US. fissile zones. Inclusion concentrations, Highway 93 marked size sorting. Highest inclusion roadcuts. abundances observed; kaersutite predominant. lAll widths measured perpendicular to the local axial plane of the dike. EXTRUSIVE AND INTRUSIVE MEGACRYST—BEARING ROCKS 5 EXTRUSIVE AND INTRUSIVE MEGACRYST-BEARING ROCKS VENT AREA The vent area exposes pyroclastic tuff breccia and ir- regularly-shaped intrusions (fig. 2A). The apparent subsur- face extent of intrusions is defined by a magnetic survey, described below. Although the area appears very complex, the essential relations can be simply summarized: (1) N0 exposures show interstratification of pyroclastic rocks and fanglomerate; and (2) outcrop relations and magnetic anomalies indicate that the contact between the fanglomer- ate and the complex of related volcanic and intrusive rocks is steep near the southernmost boundary. This con- tact defines the margin of the eruptive vent. Dikes intrude both tuff breccia and fanglomerate in the northern part of the vent area. In the southern part of the vent area a unit of mixed rocks most likely consists of tuff breccia and intrusions, although a part of the exposure may be an eroded lava flow remnant (fig. 2A). Irregular blocks of jointed aphyric basalt are found locally, and these may be accidental inclusions derived from older Mi- ocene lava. However, the most massive dike in the vent area, which intrudes the contact between tuff breccia and fanglomerate, grades from holocrystalline and inclusion bearing to massive and aphyric. Most other outcrops of aphyric basalt are poorly exposed, and their relation to in- trusions of the vent area remains unclear. TUFF BRECCIA DEPOSITS The pyroclastic deposits are buff—colored or red to red- brown, massive to bedded mafic tuff breccia; layering is crude and localized in the southwestern part of the vent area (fig. 2A). Matrix of the bedded tuff breccia is mostly clay and arkosic sand that probably derives from fanglom- erate. The matrix also includes small grains of kaersutite, olivine, and vesicular lava. Clasts include gneiss and gran- ite from the fanglomerate, kaersutite megacrysts as much as 1.5 cm across, and irregular masses of vesicular lava as much as 20 cm across. Some beds contain flattened masses of clay, which may be accretionary lapilli. In the southern part of the vent area, tuff breccia layers and interleaved sills dip 25° to the east. The continuity of dips in all other units suggests that the bedded tuff probably was tilted by the upwelling intrusive magma. The bedded tuff breccia locally is friable, but near intrusive contacts it is metamorphosed to a tough, flinty rock. Massive light-colored tuff breccia that resembles vent agglomerate forms a small outcrop in the northern part of the vent area. It is composed of angular scoria fragments and has a lower content of mafic megacrysts, clay, and sand than the bedded tuff breccia. Contact relations between the massive and bedded breccia deposits are unexposed. INTRUSIONS Mafic intrusions that contain kaersutite megacrysts oc- cur throughout the vent area. In the south part of the vent area, several dikes intrude the contact between ejecta and fanglomerate on the west side (fig. 2A); oval pieces of massive aphyric basalt 0.5 to 1 m across are found in these intrusions. The matrix of the fanglomerate is red- dened at distances as much as 70 cm from the contacts with these dikes. The most prominent of the dikes strikes N. 25° E. to N. 10° E. and has dips that vary from moder— ate to steep (as much as 78° southeast). This tabular dike contains columnar cooling joints that are perpendicular to the dike walls; because of the vertical to subhorizontal change in the dike orientation, the columnar joints also vary from subhorizontal to subvertical. A few meters north of the northernmost outcrop of tuff breccia, several dikes intrude fanglomerate; a cross section of the largest of these dikes is exposed in a wash. The chilled contact between the dike and the fanglomerate is irregular, and the dike itself has a bulbous shape that is roughly oval in cross section (fig. 3). The internal struc- ture is complex, with zones of chilled magma next to masses of partly disaggregated fanglomerate. Gradational between the areas of chilled magma and fanglomerate is pépérite-like breccia of magma and sandy matrix from the fanglomerate. Figure 3. Bulbous intrusion in fanglomerate at north end of both vent area and outcrop; scale given by seated figure in light hat (at base). Along the top of the fanglomerate ridge, the dike ap- pears tabular. ' 6 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA MAGNETIC EXPRESSION OF THE VENT AREA A ground-level magnetic survey was made of the vent area to determine the extent and probable shape of the in- trusions. Traverses to measure the vertical component of the magnetic field were made with a fluxgate magnetome- ter, from a baseline oriented N. 70° W., located 50 m south of the southernmost dike exposure. Approximately north- south lines of traverse were established at 32—m spacings along the baseline. Measurements were made at 50-ft (16 m) intervals, resulting in a rectangular grid of data points over an area 500x400 m. The magnetic background was determined to be 250 gammas, from the average readings made over fanglomerate along the baseline; values are be- lieved accurate to 110 gammas (1 gamma=1 nanoTesla). Data were corrected for diurnal drift by readings taken at baseline station 1 at the beginning and end of each traverse. Magnetic susceptibilities of the dikes were measured in the field using a hand-held susceptibility meter. Selected samples also were measured in the laboratory with a sus- ceptibility bridge. The natural remanent magnetization (NRM) of the samples was measured in the laboratory on oriented hand samples. The NRM direction has normal po- larity, and for five of the nine samples it points in the di- rection of the present-day field. Magnetic susceptibilities (measured in the cgs system) for all samples range from 2.6X10'3 to 17X10'3. Seven of the nine samples have sus- ceptibilities from 2.6x10‘3 to 4.76X10‘3, with a median value of 3.5x10‘3. A domed magnetic anomaly (average readings be- tween 650 and 1,050 gammas; fig. 23), with steep margin- al gradients, was recorded in the northern part of the vent area; sharp anomalies peak at 2800 garnrnas (light and heavy shaded areas, fig. 2B). The shape of this anomaly indicates that exposures are connected to an intrusive body or multiple intrusive bodies beneath the vent area; the steep marginal gradients indicate that the intrusive mass is relatively shallow. Another area of high anomalous values (1,200 to 1,600 gammas) was detected in the southern and southwestern part of the vent area (light shaded area, fig. 2B). This southern anomaly is coincident with the out- crops of mixed tuff breccia and intrusions (mixed rocks unit, fig. 2A). The essential features of the measured magnetic field in the vent area are represented well by a two-dimensional model of a uniformly magnetized body at shallow depth. To model the amplitude of the observed anomaly, magne- tization values of 5x10“3 were required; these are the highest measurements on seven of nine surface exposures. The sharp peaks and valleys of the anomaly can be ex- plained by assuming irregularities in the upper boundary of the body. We also considered an alternative model of a body that consists of a variably magnetized intrusion or complex of intrusions, which could explain the essential features of the anomaly equally as well. Bodies 50 and 200 m in thickness were tested in the model of a uniformly magnetized body; solutions for each body thickness match the essential features of the anoma- ly. Thus, the data provide few constraints on depth or shape of the base of the magnetic intrusive mass. On the south and west margins of the vent area, the 400—gamma magnetic contour bounds the two-dimensional model body. Steep magnetic gradients at these margins are explained well by assuming nearly vertical contacts, which may correspond either to faults or steep intrusive contacts. However, the east and north boundaries of the vent area are modeled best by contacts with relatively shallow out- ward dips. For a model body with steep contacts, a well- defined magnetic polarization low is expected north of the vent area. The absence of this polarization low supports the idea that the magnetic body has a northern contact with a shallow north dip. This simple model of a single, uniformly magnetized body explains the anomaly. However, we prefer the alterna- tive model of many variably magnetized intrusions because it is consistent with field observations, which indicate that the magnetic body is a composite of intrusions. Because the NRM of dikes in the vent area and the present-day field have the same direction of magnetization, the high average magnetization used to model the amplitude of the observed anomaly can be justified as an effect of additive magnetiza- tions from several individual intrusions. OBSERVATIONS ON THE DIKE ARRAYS GEOLOGIC RELATIONS AND STRUCTURES Three discontinuous arrays of offset dike segments crop out north and northeast of the vent area in Black Canyon (fig. 1). The southernmost array has predominant- ly N. 25° E. strikes, and the two northernmost arrays have predominantly N. 0° E. to N. 10° E. trends and steep dips (75° to 85°) to the east (table 1). Some of the north-trend- ing dike segments are sinuous, with local strikes up to N. 10° W. (fig. 1). Only one dike segment (between locations 11 and 11A, fig. 1) strikes northwest along the entire length of exposure. All other Miocene dikes in the study area, including mafic and silicic varieties, have northerly orientations (Anderson, 1978). The contacts between dikes and fanglomerate are sharp, and all dikes have distinct chilled margins (table 2). The fanglomerate shows slight but distinct reddening as much as 300 cm from the contacts, owing to the thermal effects of dike emplacement. Clasts and sandy matrix that clearly came from incorporation of fanglomerate wall rocks are found locally in the dikes. No faults are apparent in the fanglomerate deposits; however, numerous north-trending high-angle normal faults occur in older Miocene rocks, which are exposed 5 to 10 km Table 2. Features of zoned dikes. [—, no data; n.d., data not determined] EXTRUSIVE AND INTRUSIVE MEGACRYST-BEARING ROCKS Dike segment Zone Width Inclusion Inclusion size (mm) Matrix Matrix Comments (see fig- 1) (cm) abundancel Max. Min. texture structure 2 1 1-2 Sparse to — — Glassy Massive Symmetrical chilled margin. barren 2 2—5 Sparse - — Glassy to very Massive Inner chill zone. fine grained 3 15-25 Abundant 0.5-—30 n.d. Fine grained Sparsely Zones symmetrical to axis; "braided" fissile matrix structure. Kaersutite, olivine inclusions predominate. 4 110— Very 5—70 ?—50 Indeterminate Massive Axis contains granite, gneiss clasts 130 abundant to 70 mm. Less abundant kaersutite to 50 mm. 3 1 10—20 Abundant 0.1—25 n.d. Glassy, Massive Chilled contact. vesicular 2 70 Sparse O.8~20 n.d.—2 Very fine Sparsely Symmetrical to axis. grained fissile 3 140 Abundant 0.1-70 n.d. Very fine Variably Axial zone varies irregularly from grained to fine fissile massive to fissile. grained 4 1 10—25 Sparse 0.5—20 n.d. Glassy to very Massive Chilled contact. Rare flow banding fine grained parallel to contact. 2 56—145 Sparse 0.5—25 n.d. Fine grained Variably Symmetrical to axis, varies in width. fissile 3 25—50 Sparse to 03-25 n.d. Fine grained Fissile Inclusions concentrated in axial moderately zone. abundant 5 to 6 1 ?—20 Sparse 0.2—20 n.d. —— Massive West half of dike; contact not exposed. 2 95 Sparse 1.0—50 n.d. — Fissile East half of dike. 10 to 11 1 20—43 Sparse ?—20 n.d. — Massive Contact and chilled margin. 2 24—41 Barren n.d. n.d. — Fissile 3 87—100 Sparse 1.5—60 n.d. — Massive Zone absent north of location 11A. 13X,Y, Z 1 3—1 3 2 0.5—5 0.1—2 Glassy, Massive Symmetrical contact, in all vesicular exposures. 2 7—18 5—6 05—20 0.1—4 Very fine Sparsely Symmetrical in all exposures. grained, fissile Contact of zones 1—2 gradational. vesicular 3 18—40 25—30 05—40 0.1—6 Fine grained, Highly Symmetrical to axis in Y, Z; occurs vesicular fissile W side of axial zone of exposure X. 4 20—40 13—15 05—40 0.1-6 Fine grained, Massive Symmetrical in exposure Z; absent amygdaloidal in Y; occurs only E side of axis in exposure X. 5 15—40 13—40 05—72 2—12 Fine grained, Highly Axial zone always present; amygdaloidal fissile gradational to zones 3 and (or) 4. ‘Qualitative estimates, except for location 13, for which numbers are mode percents (field mode); see figure 13C. 8 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA west of US. Highway 93 (Anderson, 1978). The Black Canyon dike and fault trends also are parallel to those of nearby mountain ranges and thus probably are parallel to unexposed range-front faults. Miocene extension in an east— west direction is well documented to the west of Black Canyon in the nearby Eldorado Mountains of Nevada and to the south of Black Canyon in the Colorado River trough (Anderson, 1971, 1978;Anderson and others, 1972; Howard and John, 1987; Faulds and others, 1990). Thus, Black Can- yon dike arrays are oriented nearly perpendicular to the direction of Miocene extension and parallel to the direction of least horizontal stress at the time of dike emplacement. Most dike segments crop: out continuously (fig. 1) and are best exposed on the lower slopes of dissected alluvial fans, although some outcrops can be followed across inter- fluves. Gaps along strike occur on ridges where dike crests have not been exposed by erosion. Most of the large open areas between dike segments are washes with alluvial fill and may be due either to the level of exposure or the ab- sence of an intrusion in those areas. Dikes that cross narrow washes commonly form sediment dams (table 1; Campbell and Schenk, 1950). With notable exceptions, dikes typically are tabular and range in width (“thickness” as defined by Delaney and Pollard, 1981) from 80 to 370 cm (table 1). Widths de— crease abruptly near the parabolic tips where dike seg- ments pinch out. Few tips are seen in outcrop; the best exposed tip is at location 113 (table 1; figs. 1 and 4). At locations 2, 4, between 5 and 6, and at 11 the otherwise tabular dike segments display bulbous swellings (“protru- sions” of Campbell and Schenk, 1950; “buds” of Delaney and Pollard, 1981) that are up to 1,110 cm wide (table 1; figs. 5 and 6A, B). Bulbous swellings occur both in the middle and near ends of tabular segments. Magnetic anomalies of the thin vertical Black Canyon dikes are observed only when the magnetometer is directly Figure 4. Longitudinal section of dike tip at location 11 (fig. 1), viewed from above. Internal part- ings are concentric to the shape of the contact (arrow); pencil (p) is about 10 cm long. Propagation direction Flow direction Bulbous swelling (Bud) Figure 5. Idealized dike (from Delaney and Pollard, 1981) based on study of northeastern dike at Shiprock, New Mexico, which is exposed by erosion to deeper levels than the dikes in Black Can- yon. For example, features such as cusps at the join of the main dike and uncoalesced segments are not exposed in the Black Canyon dike arrays. Parentheses denote terms of Delaney and Pollard (1981) not used in this report. EXTRUSIVE AND INTRUSIVE MEGACRYST—BEARING ROCKS 9 Figure 6. i A, Dike segments be- tween locations 2 and 4 (fig. 1) (north is to left); location 2 is the bulbous structure at upper right; lo- cation 3 marks site of deflected southern tip of a tabular dike with bulbous structure at location 4 (de- scribed in tables 1 and 2) (telephoto view, from a distance of about 0.5 km). V B, Curved fissile joints in bulbous structure at location 5; scale shown by figure (and shad- ow) at left edge of photograph. over an outcrop. Dikes commonly show magnetic-polarity reversals along the length of outcrop, which we ascribe to lightning strikes. Magnetic susceptibility measurements on samples of dikes north of Highway 93 suggest that they have one-half to one-third the bulk magnetization of intru— sions in the vent area. We found no magnetic anomalies to indicate the presence of multiple dikes or large intrusive masses in the subsurface north of the vent area. Dike segments in Black Canyon are offset, and the ends of some offset segments overlap. These relations are best exposed in the western array (segments between locations 7 and 118, fig. 1). The cause of offsets between dike exposures was discussed by Campbell and Schenk (1950), and a dike with similar structure at Shiprock, New Mexico, has been studied in detail by Delaney and Pollard (1981; fig. 5). The tips of adjacent offset and overlapped segments commonly are deflected away from each other, and some tips have different strikes from the overall strike of the dike segment. At location 11, the parabolic tips of two dikes are within a few meters of each other; the segment north of location 11 and its tip both have northwest strikes. However, the segment south of location 11 has a northerly strike on average, but its tip is deflected to the northeast (fig. 1). The north tip of the dike segment between locations 10 and 11A is deflected to the northeast from the main north trend of the segment such that the tip trends toward the overlapped south tip of the dike segment between locations 8 and 9 (fig. 1). The two dike tips are separated by 200 m. In contrast, two segments with overall due north trends pinch out at location 11A, where the overlapping tips are offset 7.6 In; both these tips have northwest trends. Deflection of the tips probably reflects local stress fields present during intrusion of the dike segments, which are branches of a main intrusion at deeper levels (Delaney and Pollard, 1981; fig. 5). Only one tabular dike is offset in the middle of its exposed length (about 10 m south of location 8), possibly as a result of late Miocene faulting. However, the dike has no relief above the ground surface, and the displacement is so small (one dike width) that unexposed dike geometry, such as two dike tips connected by a small bulbous swelling, could produce the apparent offset (Delaney and Pollard, 1981). INTERNAL FEATURES With the exception of the dike segment at location 13 (fig. 1), which is exposed in roadcuts, the internal charac- teristics of most dikes are seen in longitudinal section 10 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA Figure 7. Fanglomerate incor- poration in Black Canyon dike segments. k A, Breccia of fan- glomerate and dike matrix in margin of dike at location 2 (fig. 1) adjacent to bulbous structure; contact of dike and fanglomerate wall rocks is close to the left edge of photograph (arrow); hammer lies across a mass of fanglomer- ate matrix and clasts; below ham- mer are two lozenge-shaped masses of quenched basalt ((1); dark spots are anhedral kaersutite megacrysts. V B, Detail of fan- glomerate-basalt breccia; lower edge of photograph, light-col- ored fanglomerate clasts in dark- er matrix of baked sandstone; top of photograph, mixed fanglom- erate and basalt with large irregu- lar kaersutite megacrysts. (eroded dike crests); thus, variations along strike can be examined more easily than variations with depth. All the dikes have chilled contact zones. Massive matrix of the contact zones was originally glassy but now is devitrified and mostly altered to clay minerals; the axial parts of dikes more than 100 cm wide have coarser matrix tex- tures. The marginal and internal matrix of all dikes is vari- ably vesicular and locally amygdaloidal, and vesicles locally are flattened parallel to the dike axial plane. Interior chilled zones are rare and usually occur adja- cent to masses of included fanglomerate (fig. 7A, B); at one site we observed an internal chilled zone that is paral- lel to the longitudinal contact and appears unrelated to fanglomerate incorporation. However, the inclusions in this exposure are predominantly centimeter-sized granitic clasts, probably from disaggregated fanglomerate. The thinnest tabular segments (for example, locations 1 and 12; table 1) and narrow parts of, dikes near segment tips are predominantly massive in structure and have very fine grained to fine-grained matrix texture. Matrix plagio- clase laths generally are oriented subparallel to each other in a microscopic pilotaxitic texture that is most apparent adjacent to megacryst grains. Both tabular dike segments and bulbous swellings lo- cally exhibit a variety of joints that probably formed at different stages of dike emplacement or cooling and that interact to form complex patterns. Although some dikes have only massive matrix structure (table 1), the interiors of most dikes contain variably spaced joints that are ori- ented parallel or subparallel to the axial plane. When, as is common, the joints are closely spaced (1 cm or less), we refer to this matrix structure as “fissile” (tables 1 and 2). Many dikes also exhibit columnar cooling joints, which are perpendicular to the dike walls. Bulbous swellings have particularly complex internal joint patterns, including irregularly alternating fissile to massive matrix structure and columnar cooling joints. Ori- entations of joints in the bulbous structures range from horizontal to vertical. Three-dimensional exposures at lo- cation 5 (fig. 1) show that the joints that create fissile structure define curved internal surfaces (fig. 6B). EXTRUSIVE AND INTRUSIVE MEGACRYST—BEARING ROCKS ll STRUCTURE-PARALLEL JOINTS Zones of massive or fissile matrix structure, formed by closely spaced joints, alternate across the width of many dikes and may vary irregularly along the outcrop length of tabular dike segments. The joint patterns in these segments locally resemble currents in flowing streams (fig. 8). In most exposures, zone margins are parallel or subparallel to axial planes of the dikes; locally the zones may be sym- metrical to the axial plane, but arrangements can change to asymmetrical in a short distance along strike (table 2; fig. 9). Near location 4, we observed flow banding in glassy matrix at the contact between the chilled margin and the next zone inward (zone 2), which contains fissile joints (table 2; fig. 10). We believe that the fissile jointing is in- herited from flow banding, which is rarely preserved in the devitrified matrix. In the dike tip at location 11 (table 1), fissile joint structure parallels the parabolic shape of the tip (fig. 4); this relation is the only one in which fissility lies at a high angle to the axial plane and supports an origin of these t. . Figure 8. Dike having irregularly interspersed massive and fissile matrix zones with stream-flow appearance; view of longitudinal section from above. Width of area depicted is about 100 cm. joints as shear planes in late-stage flow patterns of the in- truding magma. A few tabular dike segments have three to five regu- larly alternating massive or fissile zones, but such regular zonations continue along strike for only a few meters. Zones merge gradationally; therefore, recorded zone widths (table 2) are measurements based on arbitrary, but consistently applied, boundary criteria. Zones are num- bered for convenience in this discussion: zone 1 is always the chilled contact, and zones 3, 4, or 5 may be axial. The dike segment between locations 3 and 4 contains three zones that all vary in character along strike (table 2). Near location 3, the dike has a massive contact zone (1), a massive to fissile inner zone (2), and a variably fissile axial zone (3). Near the north end (location 4), zone 2 is variably Figure 9. Block diagram of roadcut sections across dike seg- ment at location 13 (fig. 1), showing the gradational variations of structural zones between exposures X, Y, Z (also see table 2 and fig. 11A, B). Pattern of ovals and dots denotes fanglomerate country rock. Numbered zones correspond to descriptions in ta- ble 2. Dike chilled margin (zone 1) is unpattemed, massive zones 2 and 4 are shown in gray and black stipple, respectively. Lined patterns represent finely fissile zones—narrow pattern depicts zone 3, and wide pattern is coarsely fissile zone 5. 12 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA fissile and the axial zone is entirely fissile. The dike seg- ment near location 2 contains a fissile axial zone (3), which lies between the dike's central zone (zone 4) and a fine- grained zone (2) inboard of the chilled contact. This fissile axial zone meanders longitudinally in a braided—stream fashion. The single dike segment at location 13 is exposed by two parallel roadcuts that trend nearly perpendicular to strike of the dike; no other segments have comparable ver- tical or lateral exposure (figs. 1, 9, 11A, B). The roadcut sections are labeled X, Y, and Z, from southwest to north- east (figs. 1 and 9); exposures Z and Y are opposite faces of the same roadcut (fig. 9). This dike segment contains as many as five massive and variably fissile zones that range from 3 to 40 cm in width (table 2). Zones of the dike segment at location 13 vary in width, occurrence, and arrangement between exposures. In exposure Z all the matrix zones are present and arranged symmetrically around the coarsely fissile dike axis (zone 5). However, the massive internal zone (4) is absent in exposure Y (table 2; fig. 9). In exposure X, all zones are present but are arranged asymmetrically—the fissile zone (3) occurs only on the west, and the massive zone (4) only on the east, side of the dike axis. Different asymmetrical arrangements of zones are observed in other dike seg- ments. For example, in the tabular part of the segment be- Figure 10. Photograph of flow banding in margin of dike at location 4 (fig. 1). Pencil (10 cm length) defines vertical orientation. Long dimension of kaersutite mega- cryst (left of pencil) is oriented parallel to banding and dike wall. To right (east) of pencil the matrix contains closely spaced fissile joints. Figure 11. Photographs of dike segment at location 13. A, Exposures of dike seen from the south side of US. High- way 93. Exposure X is on the modern highway and expo- sure Z can be seen in old roadcut beyond; exposure Y faces Z in old roadcut (see fig. 9). B, Detail of exposure 2 showing chilled margins and internal zones (table 2). EXTRUSIVE AND INTRUSIVE MEGACRYST-BEARING ROCKS l3 tween locations 5 and 6 and also between locations 10 and 11A (fig. 1), a fissile zone 95 cm wide forms the east side, whereas the west side of the dike is massive in structure. COOLING JOINTS Columnar cooling joints are common within the dikes. The columns are generally observed on vertical dike walls as polygons 20 to 50 cm across (fig. 12A). However, in the dike segment at location 1, interior horizontal to sub- horizontal joints with smaller polygonal dimensions occur at the contact between chilled margin and the axial zone. At locations 7, 9, and 11 (fig. 1) small-scale vertical co- lumnar joints occur in the exposed (and eroded) dike crest Figure 12. Static cooling joints in Black Canyon dike segments. A, Horizontal cooling joints, expressed as polygons on dike wall at location 1 (fig. 1). B, Dike at location 7 (fig. 1) showing verti- cal polygonal cooling joints (photograph is oriented nearly paral~ lel to strike of dike). (fig. 123), suggesting that the top of this outcrop is within a few centimeters of the original upper contact of the dike. INCLUSION SUITE All segments of Black Canyon dikes, as well as intru- sions in the vent area, contain irregular inclusions of shiny black kaersutite. Other minerals observed or reported as inclusions are altered (rarely fresh) olivine, black clinopy- roxene, magnetite, milky plagioclase, alkali feldspar (sani- dine and anorthoclase; Foland and others, 1980), and quartz. Although usually called “megacrysts,” measured kaersutite and pyroxene grains range in size from less than 0.1 mm to as much as 100 mm. Kaersutite grains normally display cleavage shapes, al- though many large grains have embayed, irregular outlines (fig. 7B). Relic deformation textures identify large, unal- tered olivine grains as xenocrysts rather than phenocrysts. Pyroxenes have oval or circular shapes, although a few grains that we analyzed appear euhedral. Melt and reaction textures are ubiquitous. Plagioclase and quartz grains have spongy margins, probably owing to incipient melting, and many contain cavities with glassy margins, indicating a more advanced stage of melting in the host magma. Locally, large and small kaersutite and clinopyroxene grains have reaction rims, and some kaersu- tite grains appear to be largely fused. Fused areas in kaer- sutite grains are altered to fine-grained opaque material, and some enclose small birefringent patches of unfused amphibole. Large amphibole grains commonly show melt- induced fragmentation—grain margins are serrated, and grain splinters, although surrounded by matrix, lie along— side and in optical continuity with the parent grains. Xenoliths of the inclusion assemblage comprise a maf- ic and ultramafic suite of altered wehrlite and dunite (tin- terstitial pargasite), spinel lherzolite with rare unaltered diopside, and pyroxenite, including magnetite— and kaersu- tite-bearing pyroxenite (AJ. Irving, written commun., 1982). Evidence of a mantle origin for this mafic-ultramaf- ic suite is presented and discussed in following sections. Felsic rock types among the inclusions are granite, pegmatite, aplite, and various kinds of gneiss. The felsic rocks and some felsic mineral inclusions, such as quartz and possibly K-feldspar, might be derived from lower crustal levels traversed by the magma conduits. However, the felsic inclusions are similar to the mixed gneiss and granite clast types found in the host fanglomerate. Because partly disaggregated fanglomerate masses are observed commonly in the dike exposures, we believe that the fan- glomerate is the most probable source of felsic inclusions. INCLUSION ORIENTATION AND FOLIATION Some dike segments with abundant mineral and rock inclusions have a foliation that is defined by the preferred l4 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA orientation of matrix plagioclase laths, equant sections of tabular inclusions, and long dimensions of flattened vesi- cles. In tabular dikes this foliation is generally parallel to the axial plane of the dike segment and thus is generally parallel to the planes of fissile joints. Vesicles are rare in fissile zones. In the plane of foliation, plagioclase laths do not define a consistent lineation but generally are oriented tangential to the boundaries of inclusions and vesicles. Most inclusions, both megacrysts and xenoliths, are tabular. In the dike segment at location 13, the shortest triaxial dimension of inclusion grains is about half of the longest dimension and is oriented approximately perpen- dicular to both the dike axial plane and the foliation. Re- gardless of the dike segment dip direction (fig. 13A), long dimensions of inclusions are parallel or subparallel to the dip of the dike axial plane. This alignment of inclusion long axes is very prominent in every zone, except the chilled contact zones. Observed inclusion shapes are near- ly equant in the plane of foliation and do not form a mea- surable lineation. In the dike segment at location 13, all features that parallel the axial plane, including fissile joints, boundaries between fissile and massive matrix, inclusion concentra- tions, flattening of vesicles, and orientation of the longest dimensions of both matrix minerals and inclusions (table 2) are superimposed, perhaps coincidentally. INCLUSION DISTRIBUTION PATTERNS Most of the dike segments contain sparse inclusions with maximum dimensions between 0.5 mm and 100 mm; grains of all sizes are randomly distributed within the two or three most commonly observed patterns of dike struc- ture zonation (table 2, and above). However, three of the dikes that contain a large number of matrix structure zones also contain abundant inclusions that are sorted symmetri- cally by size with respect to the dike's axial zone. This symmetrical size sorting is observed in dike segments near location 2, in the segment between locations 3 and 4, and in the roadcut sections at location 13 (table 2). In each of these locations, the greatest volume, as well as the largest size of inclusions, is concentrated in axial zones. Because roadcut sections at location 13 (fig. 1) provid- ed the best exposure of any dike segment, detailed, quanti- tative measurements of inclusion abundance, mode, size, and shape, were made only at this location. Inclusion abun- dances for location 13 are listed in table 2 as minimum and maximum mode percent for the three roadcut sections. Abundances listed for other dike segments (table 2) are qualitative estimates, recorded as barren (no inclusions seen), sparse (up to 5 mode percent), abundant (5 to 15 mode percent), and very abundant (greater than 15 mode percent). Inclusion abundances, types, sizes, and size rang- es in table 2 are referred to the structural zones as a matter of convenience and should not be regarded as implying a genetic connection. In the dike segment near location 2, granite and gneiss clasts (fanglomerate derived) are the most abundant inclu- sions (table 2) and are concentrated in the dike axis (roughly corresponding to zone 4) and the adjacent fissile zone 3. No inclusions were observed in the chilled contact zone, and zone 2 contains only a few small inclusions. Lo- calized between sparsely fissile zone 3 and the axial zone is a pépérite-like breccia, which is composed largely of fanglomerate clasts and lumps of sandy matrix but which also includes anhedral kaersutite megacrysts as much as 30 mm across, olivine grains 10 to 25 mm across, and clasts of nonvesicular dike matrix (fig. 7A, B). Inclusion concentrations and sizes vary along the strike of the dike segment between locations 3 and 4. Near location 3, abundant inclusions occupy both contact and axial zones. A few meters to the north of location 3, inclu- sions are concentrated only in the axial zone, and the mar- ginal zone is nearly barren. Near location 4, however, inclusions are of lower abundance in all zones, although the axial zone contains a slightly larger volume of inclu- sions than the other zones (table 2). Close to location 3, inclusions are as much as 70 mm across in the axial zone, and the other zones contain particles less than 25 mm across. Near location 4, inclusions of all sizes are distrib- uted across all the zones. In the roadcut exposures at location 13 (figs. 1, 9, 11A, B), each of the zones contains a range of inclusion sizes. Inclusions are small and sparse in the two outermost zones (:10 mm in zone 1, <20 mm in zone 2; fig. 133). Zones 3, 4, and 5 have moderate to high inclusion concen- trations, which vary within the zones, but abundances are greatest in zone 3 (table 2; fig. 118). The size of the larg- est inclusions and size ranges of inclusions both increase progressively toward the axial zone (5) (table 2; fig. 133). Although the symmetry of fissile zone 3 and massive zone 4 vary between the three exposures and zone 4 is not present in exposure Y, the symmetrical distribution of in- clusion sizes does not change between exposures (table 2; fig. 13B). The field mode (fig. 13C) shows that kaersutite is the main mineral inclusion at location 13. Olivine is the next most abundant inclusion but is very subordinate to kaersu- tite. Variations in megacryst/matrix proportions shown in figure 13C (circle with dot) are due entirely to variations in the abundance of kaersutite grains, because other compo- nents are either minor or have nearly constant abundance across the dike. These minor constituents are pyroxene, magnetite, plagioclase, alkali feldspar (sanidine and anor- thoclase; Poland and others, 1980), and quartz (also see Irving, 1977; Garcia and others, 1980). Lithic fragments of granite, gneiss and peridotite also are present in the dike segment at location 13. Like the mineral constituents, the largest rock fragments also are found in zone 5. EXTRUSIVE AND INTRUSIVE MEGACRYST—BEARING ROCKS 15 RELATION OF INCLUSIONS AND BULBOUS SWELLINGS Bulbous swellings in dike segments commonly are as- sociated with high inclusion abundances—particularly near partially incorporated fanglomerate pods. The relation be- tween incorporated fanglomerate and bulbous swellings is exhibited at locations 2, 4, south of location 11 (fig. 1), and in the vent area intrusion pictured in figure 3. The bulbous swelling at location 2 (fig. 7) is continuous with a tabular dike segment that contains gneiss and granite A Exposure X Figure 13. Inclusion orientation, size distribu- tion, and abundance in dike segment at location 13, exposures X, Y, Z. A, Rose diagram show- ing dips of inclusion long dimensions (mea- sured on vertical surfaces perpendicular to strike); total of 787 grains. B, Distribution of long and short inclusion dimensions (plotted with respect to structural zones); same data set as 13A. C, Field mode of mineral and lithic fragments (total of 8,500 grains); for each ex- 20 Zone L1 80 80 2‘ NUMBER OF INCLUSIONS 4O 20 10 20 3040 so so 70 '4 202428 3236 40 40‘ 20 30 1o LONG DIMENSION (mm) SHORT DIMENSION (mm) W E 0.6 — O 0.4 r O N [19 [> O i> O 8 FGM PERCENTAGE MODE ‘5 I 8 I-<>-I 0 at ong.0 DOD [3th 123454321 ZONE ..L O I posure, modes were counted on two traverses approximately perpendicular to strike of dike; mineral symbols are positioned at average value for six traverses; bars show range of values for all traverses (if greater than size of symbol); mineral symbols: circle with dot, ratio of inclusions to matrix counts given as a percentage; diamond, kaersutite; filled circle, olivine; square, feldspar grains; open circle, clinopyroxene; triangle, ultramafic xenoliths. 16 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA clasts concentrated in the axis and contains a marginal breccia of mixed fanglomerate and chilled matrix. At loca- tion 4, the dike contact zone contains masses of fanglom- crate (fig. 14). Near location 11, the intersection between the tabular part of the dike and a small bulbous swelling (table 1) is very sharp. The tabular part contains a small volume of mixed gneiss clasts, which probably were de- rived from fanglomerate. Only the large bulbous swelling near location 5 shows no clear relation to incorporation of fanglomerate wall rocks. COMPOSITION OF DIKES AND INCLUSIONS PETROGRAPHY AND COMPOSITION OF DIKES The holocrystalline, aphyric matrix of the Black Can- yon dikes comprises plagioclase-l—altered olivine+altered Ti-augite+magnetite. Samples taken from each structural zone at location 13 have plagioclase laths that range in size from less than 0.1 mm long in the chilled contact zone (zone 1) to 0.5 mm long in the axial zone. Grains of matrix olivine are equant and have a size range similar to the plagioclase, whereas Ti-augite and magnetite grains are smaller than 0.1 mm throughout the dike. Carbonate alteration pervades the matrix; in addition to calcite, patches of analcite, zeolite, and clay minerals are com- mon. Many amygdules and cracks are filled with calcite and analcite. Major-element analyses and calculated norms in table 3A represent three samples (DS-l, -6, and -12) from the axes Figure 14. Mass of fanglomerate (outline) engulfed by dike matrix near dike contact at location 4 (fig. 1). Daypack in lower part of photograph is about 0.5 m in height. of thin, massive dike segments with no visible inclusions (dike locations 1, 6, and 12, fig. 1) and one sample (DS-Y2) from the massive zone 2 of exposure Y at location 13 (table 2), which is relatively barren of inclusions. The average bulk compositions of these matrix samples (table 3) are obscured by alteration and the possible presence of microscopic inclu- sions; also, the original magma compositions may have var- ied. Samples DS-l, -12, and -Y2 were analyzed untreated (R) and after leaching (L) with dilute HCl to assess the effect of alteration (table 3A). Analyses of matrix from Campbell and Schenk (1950) (08, table 3A), Alibert and others (1986) (A-M-A, table 3A), and Daley and DePaolo (1992) (D-D, table 3A) are included for comparison. Sample D-D was collected at location 13, and it is likely that the GS sample was also collected at that site, either from exposure Y or Z of the old roadcut. The dike sampled by Alibert and others ( 1986) was described as aphanitic and containing rounded kaersutite megacrysts (of unspecified dimensions); it proba- bly is not from the segment exposed in roadcuts at location 13. Normative minerals were calculated for the all samples using program PETCAL (table 3A). Comparison between analyses of leached and untreated dike matrix and examination of the normative minerals in table 3 suggest that the compositions of samples DS-lR, —12R, -Y2R, and -6 are closest to the composition of the Black Canyon juvenile dike magma—probably alkali oliv- ine basalt. The unleached compositions of all four samples have normative olivine; three of them (DS-lR, -12R, -6, as well as A—M-A and D-D) also show nepheline in the norm and thus are alkalic in composition. These compositions agree with the alkalic compositions of matrix clinopyroxene grains, which are difficult to analyze owing to widespread Table 3. Compositions of dike matrix. COMPOSITION OF DIKES AND INCLUSIONS [Analyses by X-ray fluorescence, unless otherwise indicated; AJ. Bartel, .l.S. Wahlberg, LE. Taggart, J. Baker, K.C. Stewart, analysts. R, raw. or untreated dike matrix; L, matrix leached in dilute l-lCl prior to analysis (preparations of treated samples by D. Sorg); —. mineral not present in the norm] A. Whole-rock major-element analyses. Sample DS-l DS-12 DS-Y2 lasts 05 A_M_A‘ 13.135 R (2) L R (2) L R (2) L R Analyses (weight percent oxide) SiOz ---- 45.0 49.6 44.9 48.5 43.1 47.7 45.6 43.79 46.16 44.30 A1203 -- 15.6 14.5 15.6 14.9 15.2 14.9 15.4 17.84 15.71 14.95 FeOl 4.59 5.18 5.23 5.60 3.88 4.27 5.82 3.95 — 6.55 fie/2032 - 5.05 5.14 4.21 4.38 5.39 6.06 3.73 4.20 10.07 1.82 MgO 5.1 5.0 5.0 5.3 5.5 4.8 5.3 9.45 4.62 3.86 CaO --—- 9.1 7.1 9.6 6.9 9.7 7.0 9.1 10.44 8.20 8.44 Nazo 4.0 3.3 3.2 2.9 2.6 2.4 3.2 5.30 4.51 3.23 K20 2.8 2.4 2.8 2.5 1.9 1.8 3.1 1.96 3.22 2.87 Ti02 2.9 3.3 2.9 3.2 2.8 3.3 3.0 2.48 2.93 2.89 P205 0.80 0.32 0.79 0.39 0.76 0.22 0.82 0.54 0.92 0.76 MnO 0.16 0.16 0.16 0.15 0.15 0.15 0.16 0.04 0.17 0.15 I-120+ --- 1.36 1.76 2.80 2.65 2.64 3.06 2.48 3.93 1120' 0.63 1.32 0.47 1.30 2.05 3.15 0.83 2.72 (LI 3.21) (L1 9.1) C02 1.98 0.03 1.87 0.01 3.00 0.09 1.50 2.99 Total - 99.07 99.11 99.53 98.68 98.67 98.90 100.04 99.96 99.67 98.81 Normative minerals (weight percent)6 Ap ------ 1.95 0.77 1.94 0.95 1.93 0.55 1.99 1.25 2.21 1.96 11 -------- 5.79 6.53 5.83 6.41 5.84 6.76 5.98 4.71 0.38 6.11 Mt ------ 7.27 7.76 6.47 6.71 5.36 5.06 5.68 5.67 — 294 0r ------- 17.40 14.77 17.53 15.60 12.34 11.49 19.23 11.58 19.71 18.88 Ab ------ 18.42 29.08 18.42 25.91 24.18 21.93 18.379 2.77 27.33 21.67 An ------ 17.18 18.39 21.12 21.38 26.59 26.53 19.426 19.10 13.58 19.83 Di ------- 19.30 12.56 18.83 9.51 16.23 7.33 17.77 22.70 9.70 17.32 Hy ------ — 7.26 — 11.2 0.04 9.51 — 0.69 — — 01 ------- 3.09 — 4.30 — 5.25 — 6.08 9.12 5.20 6.53 Ne ------ 9.30 — 5.56 —— —- — 5.45 — 6.61 4.74 Q ------- -— 2.86 —— 2.31 — 7.78 —- — — — Hm ----- 0.30 — — 2.22 3.05 — 0.29 10.43 —- lGravimetric determination for samples DS-l, DS-l2, DS-Y2. and DS-6, HM. Neiman, G. Mason, P.R. Klock, C. Stone. S. MacPherson, analysts. (2) 17 designates average of two detemtinations for unleached (R) samples. Calculation of value for sample D-D given in Daley and DePaolo (1992) 2For samples DS-l , DS-12, DS-Y2, FezO3 value calculated: FeO gravimetric determination subtracted from total Fe determined by X-ray spectrography. For sample A-M-A total Fe is given as Fe203. 3Analysis from Campbell and Schenk (1950); all oxides by gravimetric determination. 4Analysis from Alibert and others (1986); authors also report minor and trace element compositions, including rare earth elements. LI, loss on ignition. 5Analysis TID-l from Daley and DePaolo (1992); note that isotopic composition reported under this sample number was determined on an amphibole megacryst (E. Daley, oral commun., 1993). Total given here omits Cr203 (0.012 weight percent). LI, loss on ignition. 6All norms calculated with program PETCAL. written by Richard Koch, U.S. Geological Survey. alteration (table 4; analytical technique described in table caption). The clinopyroxene grains are augite with high tita- nium and iron contents (Ti02, 3.4 to 4.7 percent) and Mg- ratios [Mg/(Mg+2Fe)] between 0.71 and 0.76. Unleached samples are rich in CaO (9.1 to 9.7 per— cent) and samples for which volatiles were determined are also rich in C02 (1.9 to 3.0 percent), whereas both these components are reduced significantly in the leached equiv- alents. Also, A1203 and Na20 contents are reduced as much as 1 percent by leaching. A11 leached samples con- tain normative hypersthene+quartz and thus appear to be subalkaline. Whether leached or unleached, samples of dike matrix from location 13 (Y2R, Y2L, C-S and DD) all contain normative hypersthene. 18 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA Table 3. Compositions of dike matrix—Continued. B. Stable isotope compositions of carbonate in dikes, inclusions, and fanglomerate wallrocks. Sample No. BC-Cl BC-C2 BC-C3 BC-C4 BC-C5 BC-C6 BC-C7 513d ........ -3.97 -1.74 -5.62 0 +1.45 +0.61 +0.11 81802 ........ +3473 +3146 +3858 0 +2259 +20.79 +22.78 Yield (pct) -- 62.4 83.3 69.8 0 85.1 91.3 1.0 ‘ Analyses by L.D. White, courtesy of IR. Barnes. 2 Analyses courtesy of JR. O'Neill. Samples: Cl—Fanglomerate 20 m from nearest dike. C4—Kaersutite megacryst. C2—Amygdule in dike axis (exposure Z). C3—Partly assimilated fanglomerate mass in dike. We suggest that the subalkaline compositions reflect either removal of important constituents by the leaching or—in the case of location 13—unavoidable contamina- tion by the ubiquitous inclusions, particularly by silicic components. Because the compositions of leached samples change from alkalic character toward compositions incom- patible with the modal mineralogy, we suggest that most of the CaO in matrix carbonate was derived from the dike minerals by reaction with near surface waters and was not added by alteration after intrusion. Therefore, removal of carbonate by leaching samples before analysis produces false matrix compositions. The isotopic compositions of carbon and oxygen in the matrix carbonate (table 33) usually resemble values typical of sedimentary rocks (813C of +1.45 to —l.74; 51 O of +20.79 to +3858). One carbonate sample from a partly disaggregated clump of fanglomerate within the dike segment near location 2 (fig. 1) produced a 813C of —5.62, which resembles some values of carbonatite and di- amond but also overlaps values reported from sedimentary rocks. We suggest that this dike segment is now in equilib- rium with ground water isotopic compositions as a result of isotopic exchange during late-stage alteration at the time of crystallization or during later weathering, or both. If any of the carbonate originally had a mantle origin, as suggested by MD. Garcia (written commun., 1984), it cannot now be discerned. Basu (1978) determined 87Sr/“Sr of 070399100008 for a leached sample of dike matrix, and Alibert and others (1986) obtained a similar value of 0.703789i-.000038; these values resemble Sr—isotopic ratios of most alkali basalts. Foland and others (1980) found a value of 0.70456 for untreated whole rock and a value of 0.70316 for the same rock after leaching with HCl; the Sr—isotopic composition of the soluble fraction resembled that of CaCO3 from amygdules. Foland and others (1980) concluded that these results are consistent with derivation of carbonate from CS—Tuff breccia. C6, C7—Amygdules in massive dike, vent area. crustal sources, consistent with the near-surface characteris- tics of stable isotopes that we report. COMPOSITIONS OF MAFIC INCLUSIONS Ultramafic and mafic xenoliths and megacrysts of mantle origin are uncommon, but most are found in mafic alkalic intrusions or ejecta (Ross and others, 1954). We detemlined compositions of mafic megacrysts and miner- als from mafic and ultramafic inclusions in the Black Can- yon dikes to determine whether the mafic-ultramafic suite derives from the same or a variety of mantle regions. All analyzed megacrysts but one are kaersutite or cli- nopyroxene grains, and most are from the roadcut at loca- tion 13. Samples from a few other dikes were included for comparison. Most of the clinopyroxene samples are black, glassy, and have irregular shapes. We did not observe any orthopyroxene megacrysts and none are reported in the lit- erature. Two small kaersutite grains (matrix size) were ana- lyzed for comparison with larger grains. From an intrusion in the vent area, we found one olivine megacryst that was fresh enough to analyze. To test the hypothesis of E]. Spera (written commun., 1984) that some of the kaersutite particles could be phe- nocrysts of the dike magma, we also sought amphibole grains that could be identified as euhedral (having regular outlines, uncontrolled by cleavage). We found five candi- date euhedral grains during several traverses of every dike segment in the three Black Canyon dike arrays; three of these inclusions proved to be amphibole (EG, table 6) and two are augites. In numerous thin sections, we saw no compositionally zoned amphibole grains, such as those mentioned by E]. Spera (written commun. 1984). Mafic to ultramafic xenoliths found in the Black Can- yon dikes represent a variety of rock types and have vari- ous textural relations: COMPOSITION OF DIKES AND INCLUSIONS 19 1. Altered lherzolite xenoliths are light-green granular masses containing relatively fresh chrome-diopside and brown orthopyroxene (tables 4, 5, and 7; see also Irving, 1977; Garcia and others, 1980). Some of the lherzolites contain interstitial kaersutite, and we observed two com- posite lherzolites with thin kaersutite veins. One analyzed sample (BC-2—21, tables 5 and 6) contains a 1- to S-mm- wide vein of orthopyroxene-kkaersutite. 2. Red-brown altered olivine clusters (wehrlitic xeno- liths) are altered olivine grains poikilitically enclosed by black Ti-clinopyroxeneiamphibole (possibly “pargasite wehrlite” of Irving, 1977). Analyses of clinopyroxene and amphibole from wehrlitic xenoliths are in tables 4 and 7, respectively. 3. Al-augite pyroxenites are granular masses that may also contain orthopyroxene and intergrown kaersutite (Irv- ing, oral commun., 1982). We found small pyroxenite xe- noliths but were unable to collect or analyze them. 4. Kaersutite grains poikilitically enclose biotite and apatite grains (KPA, tables 6 and 9), in clusters that could represent xenoliths or glomerophenocrysts. KPA aggre— gates have been reported as glomerophenocrysts from oth- er xenolith and megacryst localities (for example, Irving, 1974); such intergrowths are a well-known association in veins and (or) pods in both alpine peridotites (Conquéré, 1970; Spray, 1982; Mukasa and others, 1991) and perido- tite xenoliths in basalts (Wilshire and Trask, 1971; Best, 1974, 1975; Wilshire and others, 1980). Complete analyses of kaersutites from the dike seg— ment at location 13 have been published previously (table 8) by Campbell and Schenk (1950), Garcia and others (1980), and Boettcher and O'Neill (1980). Irving (1977), Basu (1978), and Poland and others (1980) published par- tial analyses of a wide range of megacrysts. OLHHNE The granular olivine cluster analyzed (table 9) lacks strain lamellae and probably is a recrystallized megacryst. Because of the widespread alteration, ours is the only oliv- ine analyzed from the Black Canyon dikes. The forsterite content of this sample (F079; CaO, 0.35 percent) is near the middle of the range (F070 to F084) reported for olivine megacrysts from alkalic lavas in the western United States and worldwide (Binns and others, 1970; Wilkinson, 1975; Fodor, 1978). However, chemical compositions of xeno- cryst and phenocryst olivines may be indistinguishable; for example, Wilkinson (1975) reported an alkalic sill that con- tains an olivine xenocryst with F0779 to F0839, Ti-augite- bearing peridotite nodules with olivine compositions of F0764 to F0859, and groundmass olivine of F0773 to F086. PYROXENE Peridotite xenoliths of the inclusion suite contain both diopsidic and augitic clinopyroxenes, whereas all clinopy- roxene megacrysts are Ti—augites (table 4). In the pyroxene quadrilateral (fig. 15), clinopyroxenes from lherzolite xe- noliths in the Black Canyon dikes are diopside to subcal- cic diopside. Compositions of poikilitic clinopyroxene grains in wehrlitic xenoliths overlap the megacryst compo- sitions, and both the poikilitic grains and the clinopyrox- ene megacrysts have trends from diopside toward Fe- enriched augite (fig. 15; table 4). The distinction between lherzolite and wehrlite cli- nopyroxene compositions persists for important nonquadri- lateral components (table 4). Diopsides from lherzolite are chrome-rich (0.46 to 1.1 percent Cr203) and low in Ti and Al (0.31 to 0.71 percent TiOz; 4.3 to 6.1 percent A1203). Poikilitic clinopyroxene grains have low chrome contents (0.13 to 0.16 percent Cr203) but high Ti and A1 contents (Ti02, 0.71 to 2.0 percent; A1203, 4.5 to 8.1 percent). In contrast, chrome contents of clinopyroxene megacrysts are moderate (0.30 to 0.57 percent Cr203), and ranges of Ti and A1 values are relatively restricted (TiOZ, 1.7 to 2.0 percent; A1203, 7.2 to 8.0 percent). The large composition- al range of Ti and Al in poikilitic clinopyroxenes fills the gap between the compositions of megacrysts and grains in lherzolite. Roden and Shimizu (1989) reported an even larger range in Ti02 content (1.9 to 4.4 percent) for clinopyrox- ene grains from xenoliths with refractory compositions (Group I) collected from Black Canyon (“Hoover Dam”) En Figure 15. Quadrilateral components of pyroxene minerals in the Black Canyon dikes (calculated values of Wollastonite (W0), Ferrosilite (Fs), and Enstatite (En); data from tables 4 and 5); shaded area shows location of plot volume between En and Di (Diopside) in pyroxene composition triangle. 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[n.d., not determined; —, not calculated] Sample No. as1 30-2-242 13 13492433 1064343 l-lD-l‘ HD-2“ HD-34 Analyses (weight percent oxide) 41.46 40.3 40.46 40.55 40.36 40.1 39.5 40.2 14.24 14.3 13.77 14.59 14.35 14.2 14.1 14.1 3.32 n.d. n.d. n.d. n.d. n.d. n.d. n.d. 5.70 n.d. n.d. n.d. n.d. n.d. n.d. n.d. 8.69 8.3 8.98 8.63 8.69 7.9 9.7 8.3 13.68 14.0 13.00 13.74 13.58 14.3 13.2 14.0 11.62 11.0 11.32 11.03 10.93 11.4 11.5 11.5 2.29 2.6 2.51 2.53 2.47 2.5 2.6 2.6 1.72 2.0 1.95 1.96 2.00 1.9 1.9 1.9 5.70 5.7 5.73 5.78 5.49 5.7 5.5 5.6 0.08 0.1 n.d. 0.14 n.d. 0.14 0.16 0.13 n.d. 0.1 n.d. n.d. n.d. 0.19 0.03 0.03 99.81 98.4 97.85 99.03 97.96 98.33 98.19 98.36 Mg ratio: Mg/(Mg+SFe) .74 .75 .72 .74 .74 .76 .71 .75 Amphibole structural formula—23 oxygens 5.93 5.86 5.94 2.07 2.14 2.06 0.33 0.32 0.33 2.40 2.46 2.39 1.04 1.01 1.10 2.92 3.04 2.84 0.10 0.01 — 0.61 0.62 0.63 — 0.01 — 1.78 1.71 1.78 0.64 0.73 0.72 0.31 0.37 0.36 A A R 5.87 5.90 5.84 5.82 5.86 2.13 2.10 2.16 2.18 2.14 0.36 0.38 0.27 0.26 0.28 2.49 2.48 2.43 2.44 2.42 1.04 1.06 0.96 1.19 1.01 2.96 2.96 3.10 2.90 3.04 0.02 — 0.02 0.02 0.02 0.63 0.60 0.62 0.61 0.61 — — 0.02 0.00 0.00 1.71 1.71 1.78 1.81 1.80 0.71 0.70 0.70 0.74 0.73 0.36 0.37 0.35 0.36 0.35 A A A R R 1Campbell and Schenk (1950): wet-chemical analysis of kaersutite megacryst. Data are presented as anhydrous and Peon” calculated for comparison with microprobe analyses. Total calculated using values for FeO and Fe203. 2 Boettcher and O'Neill (1980): microprobe analysis of kaersutite megacryst. 3Garcia and others (1980): microprobe analyses of three kaersutite megacrysts. 4AJ. Irving (1982) written commun.: microprobe analyses of kaersutite megacrysts. 5 Total Fe expressed as FeO. 6Total A1 values for comparison with those in tables 6—7 and plotted in figure 16A; these data are not plotted. 7Analysis accepted (A) or rejected (R) by Papike and others (1969) screen for amphibole probe analyses. All "R" analyses listed were rejected on the basis of one criterion and are indistinguishable from "A" analyses. dikes. These values are mostly higher than the highest Ti02 compositions found by us, either for clinopyroxene megacrysts or clinopyroxene in xenoliths. Roden and Shimizu (1989) also show high contents of strontium and rare earth elements (REE) in clinopyroxenes with REE patterns that are variably enriched or depleted in light rare earth elements (LREE) compared to heavy rare earth ele- ments (HREE). All clinopyroxenes in table 4 have compositions char- acteristic of high-pressure origin, notably high values of Ca-Tschermak's molecule: 15 to 19 percent in diopsides, 13 to 24 percent in poikilitic grains of wehrlite, and 16 to 27 percent in megacrysts. The poikilitic clinopyroxenes have compositions intermediate between Cr—diopside and augite megacrysts (table 4). Orthopyroxene compositions show less variation (ta- ble 5; fig. 15) than'clinopyroxene. Orthopyroxene grains intergrown with kaersutite in the vein of lherzolite xeno- lith BC-2—21 are slightly richer in [Fe and poorer in Cr than grains from other lherzolite xenoliths. Ti02 contents of orthopyroxenes in the three lherzolite samples (table 5) range from 0.08 to 0.37 percent, and orthopyroxene in the vein of sample BC-2—21 (table 5) has a Ti02 content with— in this range (0.17 percent). COMPOSITION OF DIKES AND INCLUSIONS 'Ihble 9. Compositions of phlogopite and olivine. [n.d., not detemiined] 23 Olivine Phlogopite grains (P) intergrown with kaersustite and apatite in kaersutite-phlogopite-apatite cluster megacryst (KPA) (0M) Sample No. KPA-Pl KPA-P2 KPA-P3 KPA-P4 KPA-PS KPA-P6 KPA-P7 OM Analyses (weight percent oxide) 35.3 35.1 35.3 35.1 35.0 35.0 35.0 38.9 15.7 15.8 15.6 15.8 15.8 15.6 15.6 n.d. 16.3 16.3 16.3 16.5 16.4 16.3 16.2 19.4 11.4 11.4 11.4 11.4 11.3 11.3 11.3 41.5 0.15 0.15 0.14 0.14 0.16 0.15 0.13 0.32 0.78 0.82 0.77 0.77 0.77 0.76 0.76 n.d. 8.6 8.7 8.6 8.7 8.7 8.6 8.6 n.d. 9.8 9.7 9.7 9.8 9.8 9.8 9.9 n.d. 0.15 0.14 0.14 0.14 0.14 0.14 0.13 0.24 0.031 0.031 0.033 0.025 0.032 0.026 0.030 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.12 0.004 0.000 0.001 0.001 0.001 0.001 0.002 n.d. 98.22 98.14 97.98 98.38 98.10 97.68 97.65 100.48 Mg ratio: Mg/(Mg+SFe) .56 .56 .56 .55 .55 .55 .55 2F079 Na20/1( 20 ---- .089 .094 .090 .088 .088 .088 .088 n.d. tural ts'tgfiiculae 22 oxygens 4 oxygens 5.2 5.2 5.2 5.1 5.1 5.2 5.2 1.0 2.7 2.7 2.7 2.7 2.7 2.7 2.7 n.d. 2.0 2.0 2.0 2.0 2.0 2.0 2.0 0.42 2.5 2.5 2.5 2.5 2.5 2.5 2.5 1.6 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.005 n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.002 1.1 1.1 1.1 1.1 1.1 1.1 1.1 n.d. 0.004 0.004 0.004 0.003 0.004 0.003 0.003 n.d. 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.008 0.22 0.23 0.22 0.22 0.22 0.22 0.22 n.d. 1.6 1.6 1.6 1.6 1.6 1.6 1.6 n.d. 0.001 0.000 0.000 0.000 0.000 0.000 0.001 n.d. lTotal Fe expressed as FeO. 2i=o=Mg ratio x 100. Total aluminum ions. AMPHIBOLE M.F. Roden (written commun., 1992) has found a much smaller range of Ti02 (0.06 to 0.21 percent) and A1203 values for orthopyroxene grains in analyses of Black Canyon xenoliths than we report (we found 3.2 to 5.0 percent A1203 in the three samples, whereas Roden found 4.4 to 5.6 percent A1203). We also found higher val- ues of MgO (as much as 33.4 percent, compared to 32.8 found by Roden). For other oxides, Roden's orthopyroxene data have larger ranges that completely overlap the values reported in table 5. However, compared to either set of xenolith data, orthopyroxene grains in the kaersutite vein of xenolith BC-2-21 are higher in FeO (7.0 percent). We analyzed 76 amphibole samples from xenoliths and megacrysts (table 6) with an electron microprobe. To avoid bias in favor of large or small grains or of position relative to the dike walls, hand samples were taken at measured inter- vals from exposures X, Y, and 2 (location 13). Whole or parts of 58 megacrysts were selected randomly from these samples for the analyses. In polished thin sections made from samples of zones 3, 4, and 5, all mafic mineral grains were traversed with the electron beam to test the possibility of compositional zoning. All analyzed amphiboles were homogeneous. 24 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA Interstitial amphiboles in peridotite xenoliths (table 7) are pargasite (low Ti-values and high Mg ratios). All other amphibole samples from xenoliths, including those in the KPA cluster (fig. 16A and B; table 6), are kaersutite (defi- nition of Leake, 1978) with at least 0.5 Ti atoms per for- mula unit. Black Canyon amphibole megacrysts form a chemically coherent group (figs. 16A through C). Compo- sitions from samples of apparently euhedral megacrysts and those of matrix-size grains in thin sections (AM7, luv-W A ®® v no”. % 'l'i ATOMS p a. l 0 I l l l 2.2 2.4 2.6 2.8 TOTAL Al ATOMS 9' o | 1102 (WEIGHT PERCENT) s 2: - I l 2? .3 O 4&5 O a: | O O O O P A | ._ u. g .0 0203mm PERCENT) I O O 0 1 J 1 1 I IV 1 V 12.5 13.0 13.5 14.0 14.5 15.0 15.5 A1203 (WEIGHT PERCENT) Figure 16. Amphibole compositional variations. A, plot of struc- tural Al and Ti (after Best, 1974, 1975). B, Mg-ratio and T102. C, variations of Cr203 and A1203. Symbols: inverted triangle, megacrysts, including supposedly euhedral grains and matrix- sized grains; circle with x, fused grain (altered megacryst); filled diamond, kaersutite in wehrlitic xenoliths; large open circle, kaersutite in kaersutite-phlogopite-apatite (KPA) aggregate; small filled dot, vein; upright triangle, lherzolite xenoliths. table 6) are well within the compositional range of plotted parameters for all amphibole megacrysts. Similar data plotted by Best (1974) show that amphi- bole megacryst compositions worldwide have Ti values of 0.3 to 0.7 atoms per formula unit and Al values from 1.9 to 2.8 atoms per formula unit (fig. 16A). Compositions of megacrysts from Grand Canyon localities alone occupy nearly the entire range of amphibole megacryst Ti values (Best, 1974). By comparison, all but three Black Canyon kaersutite analyses fall into a restricted compositional range: Ti from 0.61 to 0.67 and Al from 2.4 to 2.6 atoms per formula unit (fig. 16A). Kaersutite grains from the vein of xenolith BC-2—21 (table 6; small dots, fig. 16A through C) have compositions indistinguishable from most am- phibole megacrysts. Figure 163 displays Mg ratio plotted against Ti02 content (as weight percent) for all analyzed Black Canyon amphibole samples. Of the 61 megacryst compositions plotted, most are anhedral grains or cleavage fragments; however, three were selected because they appeared to be euhedral (table 6; fig. 163). All megacryst samples but one have Mg ratios between 0.64 and 0.76. Ti02 values for most megacrysts are bracketed between 5.5 and 6.0, al- though analyses of Black Canyon megacrysts from the lit- erature range to as much as 6.3 TiOZ (table 8). Three megacryst samples plotted in figure 163 have T102 values much lower than the dominant range (4.8 to 5.0) and markedly high contents of Fe. Two of these low-Ti megacrysts (circle with x, figs. 16A through C) are parts of a single fused grain; thus, the Mg ratios of 0.67 and 0.68, and Ti02 values of about 4.0 weight percent probably represent compositions that were altered by reaction in the magma. The other megacryst with low contents of Ti and Mg is from the contact zone; it has very high A1203 and also may have undergone partial melting, dissolution, or reaction. Amphibole grains intergrown with phlogopite and ap- atite (KPA, table 6; large open circles, figs. 16A through C) have Ti values and contents of A1203 and Cr203 simi— lar to megacrysts, but are distinguished by markedly low Mg ratios (0.55 to 0.56) compared to megacrysts. There- fore, the KPA grains do not resemble interstitial pargasite from lherzolite xenoliths (filled diamonds, figure 16A through C), which have high Cr203 and A1203 relative to megacrysts. Megacrysts vary more widely than other amphiboles in A1203 content (14.3 to 15.7; fig. 16C), at low values of Cr203 (0.20 to less than 0.01). The alumina contents of poikilitic amphibole in wehrlitic xenoliths are lower and more restricted than megacrysts, but the Cr203 values vary from slightly higher than megacrysts (0.23) to ones higher than lherzolite amphiboles (0.99). Figure 17 shows the compositions of amphibole mega- crysts plotted against position in the dike segment at loca- tion 13 (table 1). The average compositions of three anhedral and two euhedral kaersutite grains from other DISCUSSION 25 dikes of the swarm are included for comparison. The megacrysts are essentially uniform in Al and Cr across the zones of the dike, and all other compositional variations show no correlation with position in the dike. One small amphibole grain in the contact zone is markedly different from the bulk of megacrysts in A1 and Ti values and Mg ratio. However, other zones contain am- phiboles with similar low Mg ratios—all these grains are fused and probably were altered by reaction with the mag- ma, as discussed above. Other than this grain, Ti- and Al- values show little variation across the width of the dike. Chrome contents and Mg ratios vary most widely in zones 3 and 4, probably owing to the larger number of analyzed grains, which reflects the greater abundance of grains in these zones (fig. 133). Basu (1978) determined K, Rb, Sr, and Ba contents and Sr—isotopic ratios for a Black Canyon kaersutite mega- cryst and part of the surrounding dike matrix. The potassi- um content determined by Basu (1978) (1.6 weight percent K20) is within the range of microprobe determina- tions in our study (range 1.3 to 2.0 weight percent K20) for megacrystal and xenolithic kaersutites. A kaersutite megacryst from Black Canyon analyzed by Irving and Frey (1984) is relatively enriched in LREE compared to HREE and has a chondrite-norrnalized LREE/HREE value West ‘ East 16‘v ! A1203 6? I —l # I .0 no I 0203 _o m .0 .. WEIGHT PERCENT OXIDE T102 Acum‘lo 0.75 .o 3' Mg-RATIO Mg/Mg+2Fe 1 2 3,4 5 13.4 21 _o 8 20 cm Figure 17. Variations of amphibole (kaersutite) compositions plot— ted against distance across the width of the dike at location 13 for exposures X, Y, 2; compared to amphibole megacrysts from other Black Canyon dikes and grains that appeared euhedral. Symbols: inverted triangles, kaersutite megacrysts from location 13; squares, megacrysts from other dikes; circles, euhedral grains. Abscissa location of symbols for other dikes is not significant. of about 3.0. Sr—isotopic ratios for two Black Canyon kaersutite megacrysts are 0.70275i0.00005 (Basu, 1978) and 0.70273 (Foland and others, 1980). These values from different laboratories are in remarkable agreement and are comparable to the ratios of mantle-derived kaersutites worldwide (Basu, 1978). An amphibole analyzed by Daley and DePaolo (1992) has a eNd value of +6.4 and Sr-isoto- pic ratio of 0.70293, which is slightly higher than those of the megacrysts analyzed by Basu (1978) and Foland and others (1980), but much lower than values for dike matrix. OTHER MINERALS Seven analyzed phlogopite flakes (table 9) in the KPA cluster (table 6) have constant TiOz contents of 9.8 weight percent and Mg ratios between 0.39 and 0.55. Thus, all the mica compositions lie within the range reported by Irving (1977) and are similar to those from secondary phlogo- pites in peridotites (Boettcher and O'Neil, 1980). Although we did not analyze feldspars, some may be of high-pres- sure origin; for example, Irving (1977) analyzed titano- magnetite and sodic plagioclase (oligoclase—andesine) megacrysts from the dike segment at location 13. Foland and others (1980) reported anorthoclase megacrysts that have a range of 87Sr/86Sr between 0.70298 and 0.70396. The higher isotopic ratio of strontium is similar to that de— termined by Foland (1980) for Black Canyon dike matrix (see above); thus, the anorthoclase could have crystallized from the dike magma under high pressure conditions. DISCUSSION FORMATION OF THE BLACK CANYON VENT AREA Geologic and magnetic mapping indicate that an erup- tive center formed at the south end of the Black Canyon dike arrays. Lava flows are absent or are of relatively small volume in the vent area; also, fragments of scoria- ceous basalt are rare, and no cinder horizons are interbed- ded either in fanglomerate or tuff breccia. These observations imply that the volume of magma was too small or conduit pressures were too low to sustain lava fountaining. Many lines of evidence, such as the mixtures of fan- glomerate and rapidly chilled, fragmented magma in the tuff breccia, accretionary lapilli in layered tuff breccia, and pépérite zones in the tuff breccia adjacent to some dikes indicate a wet depositional environment. Therefore, the tuff breccia may be the product of one or more phreatomagmatic eruptions, caused by basaltic magma in- trusions into a relatively watery part of the fanglomerate deposit. However, no maar—bed deposits are preserved in 26 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA the vent area; therefore, the eruptions were not especially violent. The tuff breccia, fanglomerate, and tuff-fanglomerate contacts are intruded by dikes and sills; thus, intrusion con- tinued after eruption of the tuff breccia, emplacing multiple intrusions or a large intrusive mass that our magnetic sur- vey indicates must be present at depth. Our field observa- tions show that several distinct dikes with a range of magnetic susceptibilities crop out at the surface; therefore, we conclude that the magnetic source in the vent area con- sists of many intrusions with variable magnetizations. Multiple injections of alkalic magma into a small area of venting characterize the process of diatreme formation (Dawson, 1967). Diatremes are very deeply rooted struc- tures with complex internal relations produced by violent eruptions, which are driven by high pressures from deep crustal or upper mantle levels. In the Black Canyon vent area, features such as accretionary lapilli in layered tuff breccia and the steep contacts between eruptive—intrusive units and the country rock in the southern part of the area support a possible origin of the vent area as a protodiatreme. The composition of the dikes and the presence of mantle xenoliths support derivation of the dike magmas from the mantle, but no features of deposits or their con- tacts at the Black Canyon vent area indicate that eruptions were driven by the extremely high pressure of a deep—seat- ed source. Instead, as noted above, we see evidence for a relatively few phreatomagmatic eruptions in the vent area. If the dikes were injected directly from mantle levels, some deficiency—either of magma volume or pressure, or both—limited intrusive and eruptive events. We conclude that the vent area formed from explosive interaction be tween intrusive magma and water-bearing sediments near the surface. The abundance of volatiles in the host rock may have localized or even initiated eruptive activity. STRUCTURES AND INTRUSIV E PROCESS OF THE DIKE ARRAYS North of the vent area, the localized magnetic expres- sions of the dikes indicate that they are not underlain by larger magmatic masses. No eruptive deposits crop out in association with the dike arrays, nor have we seen any de- posits interbedded in fanglomerate. The marked relief of dike exposures in washes, gaps in outcrops of continuous dike segments on ridge tops, the common presence of fan- glomerate wall-rock inclusions and of vertical joints relat- ed to an upper cooling surface suggest that the present erosional surface is close to the upper contacts of the dike segments. The northeastern dike at Shiprock, New Mexico, stud- ied in detail by Delaney and Pollard (1981), provides a good model for interpreting the outcrop pattern of Black Canyon dike segments. Deflection of dike tips between offset segments and bulbous swellings are observed at both localities. Delaney and Pollard (1981) showed that tip deflections are produced by mutually interfering stress fields localized around the intrusive tips. These stress fields interact because the dike segments were all intruded virtually simultaneously and do not each represent dis- crete, independent conduits connected to a magma source in the deep crust or upper mantle. In the idealized dike depicted by Delaney and Pollard (1981; fig. 5), each segment is a sheetlike extension that merges downward into a main dike. The main dike grows by sending out these smaller extensions (or “fingers”— Baer and Reches, 1987) into the country rocks above or ahead of the main magma conduit. If the pressure and sup- ply of magma are maintained, the magma extensions may coalesce by dilation of the country rocks, and this causes the conduit to grow laterally and upward (Delaney and Pollard, 1981). If the uppermost extensions never coa- lesce, the cooled dike consists of a main tabular sheet of crystallized magma with subordinate sheets projecting from many sites (fig. 5). Like the bulbous swellings of the Black Canyon dikes, “buds” (Delaney and Pollard, 1981) at Shiprock are locat— ed at sites where brecciated country rock is seen in the dike. According to Delaney and Pollard (1981), the dike formed buds by abrasion erosion and brecciation of wall rocks during intrusion, a process that allowed the magma conduit to increase in width. Delaney and Pollard (1980) also suggested that plugs related to the northeastern Shiprock dike probably originated as bulbous swellings or buds, which enlarged enough to become volcanic vents. Buds also might be sites of dike branching (Delaney and Pollard, 1981). Using the model of Delaney and Pollard (1981), the Black Canyon dikes probably constitute as few as three different intrusive sheets. Dike segments between locations 1 and 6 (fig. 1) are related to a main northeastern dike, segments between locations 7 and 118 are upper parts of a northwestern dike, and segments at locations 12 and 13 and south of Highway 93 are all extensions from the third dike. Other than in the vent area discussed above, the Black Canyon dikes have no observable branches or vents, prob- ably because all exposures are so close to the preerosional surface. Bulbous swellings clearly formed from the incor- poration of easily eroded fanglomerate masses by dike magma (fig. 14). With only one exception, all internal chilled zones are adjacent to pods of incorporated fan- glomerate. If bulbous swellings initiate plugs, which are eruptive vents, as concluded by Delaney and Pollard (1981), the evidence of that relation remains unexposed beneath the vent area. Although the magnetic anomaly over the vent area could be caused by a plug, we prefer to interpret the source of the anomaly as many smaller intru- sions of variable magnetization, because this relation is observed in outcrops. DISCUSSION 27 Our study found no definitive evidence of the likely sequence of intrusive and eruptive events. Campbell and Schenk (1950) suggested that the Black Canyon vent area formed after injection of the dike swarm, but the evidence does not preclude the possibility that intrusions and phre- atic eruptions formed the vent area first, after which intru- sion shifted to the north. Measurement of directional indicators of dike propa- gation is limited by the degree of exposure (Delaney and Pollard, 1981). Features such as “cusps” (fig. 5; Delaney and Pollard, 1981), or grooves in wallrock at the dike con- tacts (Baer and Reches, 1987) may be used to determine propagation direction for a swarm. However, features such as cusps must be exposed below the level of the magmatic extensions to be reliable, and the wall rocks must be cohe- sive enough to preserve measurable striations. None of these requirements is fulfilled at Black Canyon. If inclusion concentrations and the symmetrical ar- rangement of inclusion sizes in the Black Canyon dikes are due to flow sorting (see below), the longitudinal coales- cence of disaggregated fanglomerate into the conduit axis of the dike segment at location 3 can be interpreted to sup- port a south to north flow of magma in that dike segment. The limited value of this speculation is further constrained by the lack of exposure. Propagation directions may also be inferred from farming of the dike system (Baer and Reches, 1987), but this inference is statistically based and requires a larger number of exposed dike segments and arrays than we can find in the Black Canyon area. ORIGIN OF THE MAFIC-ULTRAMAFIC INCLUSION SUITE AND HOST MAGMA Principal features that support a deep origin for mafic inclusions in the Black Canyon dikes include (1) the pres- ence of kaersutite megacrysts in association with magne- sian peridotite xenoliths, including kaersutite-bearing types; (2) intergrowths of kaersutite and aluminous clino— pyroxene; (3) the overwhelming abundance of cleavage or irregular anhedral shapes among the kaersutite crystals; and (4) melting or fragmentation of kaersutite megacrysts in the host basalt. The absence of correlation between megacryst compositional variations and positions of the analyzed samples in the dike at location 13 shows further that crystallization differentiation did not occur in'place. The compositions of mafic megacrysts in the Black Canyon dikes, especially of kaersutite and associated py- roxene, are comparable with those reported for high-pres- sure megacryst suites worldwide (Wilshire and Trask, 1971; Best, 1974; Irving, 1974, 1977). The association of kaersutite and Fe-rich aluminous pyroxene with peridotite and Al-augite-bearing xenoliths in the Black Canyon dikes and tuff breccia is common at xenolith-megacryst locali- ties elsewhere in the world (for example, Wilshire and Binns, 1961; Best, 1970, 1974; Irving, 1974; Wilkinson, 1975; Wilshire and Shervais, 1975; Wass, 1979; Wilshire and others, 1980). The presence of this association in the Black Canyon suite further supports the idea of a common origin for the mafic megacrysts and xenoliths (Wilshire and Trask, 1971; Best, 1974; 1975; Irving, 1980; Wilshire and others, 1988). Kaersutite and kindred high-pressure mafic minerals in basaltic lavas may form either from crystallization in the host magma at high pressure (“high-pressure pheno- crysts”—Binns, 1969; Green and Hibberson, 1970; Binns and others, 1970; Wilkinson, 1975; Wass, 1979) or may be accidental inclusions from the fragmentation of polycrystal- line aggregates (dikes or veins) already present in the man- tle (Best, 1970; Wilshire and Trask, 1971; Irving, 1974). The shapes, reaction textures, and compositions of the maf- ic megacrysts, as well as the isotopic disequilibrium be- tween kaersutites and dike rock at the Black Canyon locality (Basu, 1978; Foland and others, 1980), indicate that these amphiboles are not cognate to the magma and thus are xenocrysts. Clinopyroxene megacrysts are of low abundance in the inclusion suite compared to kaersutites, and the composi- tional variation between Clinopyroxenes of the megacryst suite and poikilitic grains in wehrlitic xenoliths is not as well delineated. Because Clinopyroxene megacrysts have compositions that overlap the poikilitic grains in peridotite, they could have a common origin. Therefore, Clinopyrox— ene megacrysts might be either xenocrysts or high-pressure phenocrysts. Campbell and Schenk (1950) classified the dikes as camptonite because they assumed that the large kaersutite grains crystallized in place. According to S¢renson (1974), camptonite is an intrusive alkali gabbro containing cognate sodic amphiboles, titanaugite, and biotiteiolivine. Howev— er, the Black Canyon dikes do not fit these criteria because the amphiboles are neither sodic nor cognate. We prefer to classify the dikes by the compositions of matrix and the main matrix minerals, Ti-augite and olivine. These miner- als, the norms of unleached rocks, and the isotopic compo- sition of matrix samples are all characteristic of alkali olivine basalt. Therefore, alkali olivine basalt probably is the best petrologic designation for the dike rocks. Mantle xenoliths of the inclusion suite, as well as the isotopic composition of the matrix (Basu, 1978; Foland and others, 1980) indicate a mantle origin for the Black Canyon alkali olivine basalt magma. Numerous studies (for exam- ple, Frey and Green, 1974; Hutchison and others, 1975; Wass and others, 1980; Boettcher and O‘Neil, 1980) have shown that alkali basalts cannot be produced by the melting of anhydrous peridotites with compositions similar to the most common xenolith types in suites from either kimber- lite or basalt. At least one precursory event must add the incompatible elements—such as Na, K, and Ti and minor elements such as U, Th, and LREE—to parental mantle 28 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA peridotite in order for it to produce basaltic magma from partial melting. Geochemical studies of xenoliths show that magnesian mantle peridotites can become enriched in incompatible trace elements by metasomatism and remain relatively re- fractory in major-element composition (for example, Kempton, 1987; McDonough and Frey, 1989). Composite xenoliths of peridotite in contact with kaersutite— or biotite- rich rocks, Al-augite pyroxenite, and hybrids of these litho- logic types have been shown to be mafic intrusions in peri- dotite (Wilshire and Shervais, 1975; Irving, 1980; Wilshire and others, 1980; Menzies and others, 1985; Nielson and others, 1993). These intrusions represent mantle magmas that locally metasomatized peridotite wall rock, enriching it in incompatible elements, before generation of the xenolith host basalt. Xenolith—megacryst suites, including composite xenoliths and megacrysts with compositions similar to those of minerals in mantle intrusions, are found (1) in Arizona at the north rim of the Grand Canyon (Best, 1974, 1975) and in the San Carlos and Four Corners areas (Wilshire and others, 1988), (2) in New Mexico at Kil- boume Hole (Wilshire, Schwarzman, and Trask, 1971; Irv- ing, 1980; Roden and others, 1988), and (3) in California at Dish Hill, Deadman Lake (Wilshire and Trask, 1971; Wilshire and others, 1980; Nielson and others, 1993), and the Cima volcanic field (Wilshire and others, 1991). Although the most abundant high-pressure inclusions in the Black Canyon dikes are amphibole xenocrysts and relatively minor peridotite xenoliths, the origin of mega- crysts from a source within mantle peridotite is shown by (1) olivine-rich xenoliths that contain interstitial amphibole, (2) a composite sample with a thin kaersutite vein, and (3) reports of amphibole-bearing pyroxenites (A.J. Irving, writ- ten commun., 1983). Clinopyroxene compositions from Group I Black Canyon xenoliths have widely variable con- tents of incompatible elements, including the LREE (Roden and Shimizu, 1989). Such wide variations can occur in re- gions where LREE-enriched magma intruded and locally metasomatized refractOry peridotite (Wass and others, 1980; Reisberg and Zindler, 1986; O'Reilly and Griffin, 1988; Nielson and others, 1993). The kaersutite xenocryst analyzed by Irving and Frey (1984) is relatively enriched in LREE and could represent a metasomatizing melt. There- fore, the mafic-ultramafic suite of inclusions in Black Can- yon dikes could be derived from a mantle source analogous to ones rich in 'pyroxenite xenoliths, such as Lunar Crater, Nevada (Bergman and others, 1981). We conclude that the physical and chemical evidence strongly suggests that the xenocryst-xenolith suite in Black Canyon dikes probably came from a region of peridotite that had been invaded locally by a large volume of hydrous alkali basalt magma. The magma crystallized to form a dense complex of kaersutite-rich pyroxenites and horn- blendite dikes and veins (O'Reilly and Griffin, 1988; Griffin and others, 1988; Nielson and others, 1993). Similar to out- crops of homblendite rock types in the peridotite massif at Lherz, France (Conquéré, 1970). Coarse-grained dikes probably were broken up by the later dike magma, thus producing the large kaersutite xenocrysts that are found in the Black Canyon dikes. ORIGIN OF ZONING AND INCLUSION DISTRIBUTION PATTERNS ZONING Our observations of all the dikes in Black Canyon ar- rays show that the “zoning” described by Campbell and Schenk (1950) is a rare combination of features that are all present coincidentally in the dike segment at location 13 and are all oriented parallel or nearly parallel to the longi- tudinal contacts and axial planes of dikes. These features include alternating fissile and massive matrix-structure zones that change in position and symmetry along strike, elongation of tabular vesicles, and preferred orientation of tabular matrix grains and inclusions. Flow banding (fig. 10), chilled internal zones, and incorporated fanglomerate masses are the only notable internal features of the Black Canyon dikes that are not seen in the exposures at location 13. The dike segment at location 13 also contains abun- dant inclusions (including rare clasts from the fanglomer- ate) that are concentrated in the dike axial zone and are sorted symmetrically, by size, about the axis. We believe that the alternations of matrix fissility and the alignments of tabular vesicles and xenocrysts are the preserved patterns of magma flow during intrusion. Platy or elongate rock fragments, bubbles, and crystals being carried in the magma were oriented within the longitudinal flow planes. The constant matrix grain size across the dike segment at location 13 suggests that all internal zones cooled at the same rate after the magma had stagnated. Shear planes present in the last stage of intrusion became flow banding or longitudinal joint planes as the rate of flow decreased and cooling began. Three or more symmetrical, regularly alternating zones are rarely observed in the Black Canyon dikes; these zones probably represent stable laminar-flow regimes that persisted only locally within individual dike segments. Enlargement of the magma conduit by erosion of fanglom- erate wall rock promoted development of turbulent-flow vortices. Bulbous swellings grew at the sites of erosion. When the vortices cooled, they were preserved as curved joint planes. INCLUSION CONCENTRATIONS AND SIZE SORTING Campbell and Schenk's (1950) hypothesis and other similar hypotheses about the origin of the supposed zoning in the dike segment at location 13 are all based on the DISCUSSION 29 distribution and size sorting of inclusions. The interpreta- tion of Campbell and Schenk (1950) that the kaersutites crystallized in place is clearly refuted by the composition- al data summarized above. An alternative idea is that the zones at location 13 formed from multiple injections of magma into established dike conduits (F.J. Spera, written commun., 1984), but this hypothesis is not substantiated by the structural and textural relations we recorded in all other Black Canyon dike segments. Black Canyon dike segments contain axial inclusion concentrations only where inclusions are abundant. Seg- ments with relatively few inclusions show no particular distribution of particles or particle sizes with respect to structural zones. All exposed dike tips and most chilled margins are relatively barren of inclusions. The original dike crests are either eroded or unexposed, but they proba- bly were wedge shaped, like dike tips. At location 13, kaersutite grains are the most numerous inclusions, but the three other segments with axial inclusion concentrations have populations in which fanglomerate clasts predomi- nate. These relations, as well as Delaney and Pollard's (1981) study of the northeastern Shiprock dike, lead us to conclude that masses of fanglomerate country rocks were eroded by the intruding magma and incorporated into the Black Canyon dikes through the large surface area at the vertical dike/fanglomerate contact walls. To form axial concentrations, fanglomerate inclusions must have tra- versed the relatively barren dike margins after the masses became disaggregated. Bulbous swellings formed at the sites of fanglomerate erosion and incorporation. The common presence of fan- glomerate masses in tabular dike segments near bulbous swellings, such as at locations 2 and 11A (figs. 1, 6A, B), show that incorporated clasts may be swept from the en- larging magma conduit into an adjacent tabular dike seg- ment. Regularly alternating matrix structure zones are observed in three tabular dike segments that contain a large volume of inclusions (tables 1, 2). Measurements at location 13 show that the smallest particle sizes are present in all zones internal to the dike contacts, whereas the size of the largest inclusions increases from the dike contacts to the axis, forming a log-normal distribution. This particle distribution implies a stable configuration of the flow regime in this dike segment. The regular alterna- tion of fissility suggests further that the flow regime was laminar. We speculate that large volumes of inclusions may produce, or help stabilize, local laminar-flow regimes. Size-sorted inclusion concentrations (the “zoning” de- scribed by Campbell and Schenk, 1950) also occur only in dike segments with abundant inclusions (table 2). At loca- tion 13, both near—surface fanglomerate clasts and kaersu- tite xenocrysts from the mantle were concentrated in the axial zones, and the largest inclusion sizes are found in the innermost axial zone. Therefore, whether or not the dikes represent multiple injections of magma, the process that concentrated and sorted the inclusions must be related to a mechanical process in the magma conduits and not to melting or extraction of magma in the mantle. We con- clude that the characteristics of the axial concentrations and size sorting of inclusions in the Black Canyon dikes resemble flow-sorting phenomena. Evidence for efficient flow-sorting processes in the Black Canyon dikes is seen at location 2 (figs. 1, 7B). The breccia at this locality probably formed when a mass of friable fanglomerate was incorporated into the contact zone at a level not far below the modern surface. At the present level of exposure, this partly disaggregated mass of wall rock, including clasts, sandy matrix, and chilled fragments of dike matrix, lies between the contact and dike axial zones. These clasts must have migrated from the contact zone toward the dike axis as they were carried both laterally and upward by the flowing magma. At loca- tion 3, fragments of partly disaggregated fanglomerate are found in the dike margin, but a short distance to the north they are concentrated into the dike axial zone. This south to north change from marginal incorporation to axial in- clusion concentration may show that the magma in this dike segment was moving northward. Flow sorting (Drever and Johnston, 1958), both of phenocrysts in magmatic bodies and of exotic fragments in brecciated intrusive bodies, is a widely reported phe- nomenon. For example, Baragar (1960) noted that axial concentrations of the largest fragment sizes characterize fi- bers of wood pulp in slurries. A similar phenomenon, sort- ing of noncognate fragments in intrusions, was reported by Reynolds (1954) for subvolcanic breccia at several Irish localities; by Wilshire (1961) for sedimentary fragments in a dike near Sydney, Australia; and by Wilshire, Offield, and Howard (1971) for coarse particles in nonfluid intru- sive impact breccia at the Sierra Madera structure, Texas. Quasiscale—model experiments by Bhattacharji and Smith (1964) and Bhattacharji (1967) demonstrated that particles are sorted toward the axial parts of a conduit by flowing magmalike fluids. Concentrations of olivine in the centers of basaltic dikes and slightly below the central zones of sills were ascribed to flow sorting by Bowen (1928, p. 145), Drever and Johnston (1958, 1967), Baragar (1960), Simkin (1967), and Gibb (1968). Bébien and Gagny (1979) re- ported that all phenocryst species (olivine+pyroxene+pla— gioclase) and even early formed matrix minerals are sorted into the central zones of dikes at a Greek ophiolite com- plex. These examples show that sorting is a common pro- cess in flowing magmas. However, current models for phenocryst concentration tend to favor accretionary crys- tallization, rather than flow sorting or flow differentiation, because accretion models allow the dike to be interpreted as a time profile (Platten and Watterson, 1987). Komar (1972, 1976) attributed the inward migration of particles in natural conduits to grain-dispersive pressures. 30 MANTLE ORIGIN AND FLOW SORTING OF INCLUSIONS IN DIKES OF BLACK CANYON, ARIZONA He also demonstrated that such pressures are larger than those related either to velocity gradients in the host fluid, to wall effects, or Magnus-type forces. Grain-dispersive pres- sure is due to grain-fluid or grain-grain interactions, de- pending on the parameters of the system. These pressures become important when a fluid contains more than 8 per- cent particles (Komar, 1972). The effect of dispersive pres- sures may also depend upon particle size. These characteristics fit our observation that axial inclusion con- centrations and size sorting are only seen where inclusions are abundant (greater than 10 percent) and where axial and near axial concentrations contain inclusion sizes of at least 20 mm (table 2). Axial concentrations of mantle xenocrysts may be pro- duced by sorting pressure anywhere between the mantle source region and the present erosional surface, but the concentrations of fanglomerate inclusions in Black Canyon dikes must form between the depositional base of the fan- glomerate and the surface. This distance is unknown for the Black Canyon area, but the fanglomerate unit is as much as several hundred meters thick elsewhere (I. Lucchitta, oral commun., 1992). Therefore, long distances of vertical flow are not required to produce size sorting of abundant inclu- sions with an appropriate range of grain size. Delaney and Pollard's (1981) model of dike growth im- plies that the sorting in Black Canyon dikes may take place over an even shorter vertical distance, depending upon the level at which individual dike segments formed as off- shoots from the main dike. If the segments connect with the main dike above the base of fanglomerate deposits, this would imply that sorting processes are extremely efficient. SUNIMARY The Black Canyon dikes are alkali olivine basalt intru- sions and related ejecta; the content of mafic and ultrama- fic inclusions indicates derivation of the dike magma from the mantle. Substantial textural and isotopic disequilibrium between the host dike matrix and kaersutite megacrysts shows that the amphiboles could not have crystallized from the host magma, either in the crust or upper mantle, and thus are xenocrysts. Identification of the kaersutite-Pclinopyroxene inclu- sions as xenocrysts requires reinterpreting the petrologic classification and petrogenesis of the Black Canyon dikes. Kaersutite grains that accompany orthopyroxene in a vein in a lherzolite xenolith have compositions identical to the bulk of the xenocrysts, and amphiboles with variable mag- nesian compositions are found as interstitial grains in al- tered wehrlitic xenoliths. Thus, the mafic-ultramafic inclusion suite may represent a mantle region of peridotite that was intruded and metasomatized by hydrous basaltic magmas some time before the generation of melts that formed the Black Canyon dikes. The mafic megacrysts were coarse veins and dikes that crystallized in this older magmatic episode. Most feldspathic and silicic minerals and lithic inclusions in the dikes apparently come from fanglomerate host rocks of the dike swarm, although anor- thoclase and some plagioclase grains probably derive from deep crustal levels. Zoning in the Black Canyon dikes is commonly de- fined by irregular and, less commonly, regular alternations of massive and fissile matrix structure that resemble flow patterns in streams. These zones are joint patterns inherit- ed from shear planes and boundaries between magmatic flow regimes in the dike conduits. The joints and other features related to flow generally are parallel to the axial plane of the dike and may occur individually or in combi- nation. The more regular symmetrical or asymmetrical tex- tural zones are rare, and they probably represent local stable-flow regimes that formed and persisted over very short distances. The rare axial concentration and size sorting of inclu- sions affects both mantle— and near-surface-derived inclu- sions from Miocene and Pliocene fanglomerate wall rocks in the best exposed dike (location 13; fig. 1) and other Black Canyon dikes. The log—normal distribution of the largest inclusion sizes in the dike segment at location 13 indicates that mantle— and crustal—derived fragments were carried in a stable laminar-flow regime. Most inclusion con- centration filaments are parallel to other flow-generated structures; the filaments are present only where inclusions are abundant and where maximum particle sizes reach 20 mm or greater and, except at location 13, the most common inclusions are fanglomerate clasts. Thus, the most likely origin for the size distributions and concentration of inclu~ sions is from flow sorting of particles in magma in the dike conduit and is unrelated to deep-seated magmatic processes or repeated injections of magma into near—surface conduits. 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L., 1988, Mantle metasomatism beneath western Victoria, Australia I; metasomatic processes in Cr—diopside lherzolites: Geochimica et Cosmochimica Ac- ta, v. 52, p. 433-449. Papike, J.J., Ross, Malcolm, and Clark, J.R., 1969, Crystal—chem- ical characterization of clinoamphiboles based on five new structure refinements: Mineralogical Society of America Special Paper 2, p. 117-136. Platten, I.M., and Watterson, J ., 1987, Magma flow and crystalli- zation in dyke fissures, in Halls, l-l.C., and Fahn'g, W.F., Mafic dyke swarms: Geological Society of Canada Special Paper 34, p. 65-73. Reisberg, Laurie, and Zindler, Allen, 1986, Extreme isotopic variations in the upper mantle; evidence from Ronda: Earth and Planetary Science Letters, v. 81, p. 29-45. Reynolds, D.L., 1954, Fluidization as a geological process, and its bearing on the problem of intrusive granites: American Journal of Science, v. 252, p. 577-614. 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Spray, J.G., 1982, Mafic segregations in ophiolite mantle se- quences: Nature, v. 299, p. 524-528. Wass, S.Y., 1979, Multiple origins of clinopyroxenes in alkali ba- saltic rocks: Lithos, v. 12, p. 115-132. Wass, S.Y., Henderson, Paul, and Elliot, C.J., 1980, Chemical het- erogeneity and metasomatism in the upper mantle; evidence from rare earth and other elements in apatite-rich xenoliths in basaltic rocks from eastern Australia: Philosophical Transac- tions of the Royal Society of London, v. A297, p. 333-346. Wilkinson, J.EG., 1975, Ultramafic inclusions and high pressure megacrysts from a nephelinite sill, Nandewar Mountains, northeastern New South Wales, and their bearing on the ori- gin of certain ultramafic inclusions in alkaline volcanic rocks: Contributions to Mineralogy and Petrology, v. 51, p. 235-262. Wilshire, H.G., 1961, Layered diatremes near Sydney, New South Wales: Journal of Geology, v. 69, p. 473-484. Wilshire, H.G., and Binns, R.A., 1961, Basic and ultrabasic xe- noliths from volcanic rocks of New South Wales: Journal of Petrology, v. 2, p. 185-208. Wilshire, H.G., McGuire, A.V., Noller, J.S., and Tum'n, B.D., 1991, Petrology of lower crustal and upper mantle xenoliths from the Cima volcanic field, California: Journal of Petrolo- gy, v. 32, p. 169-200. Wilshire, H.G., Meyer, GE, Nakata, J.K., Calk, L.C., Shervais, J.W., Nielson, J.E. and Schwarzman, EC, 1988, Mafic and ultramafic xenoliths from volcanic rocks of the western United States: US. Geological Survey Professional Paper 1443, 179 p. Wilshire, H.G., Offield, T.W., and Howard, K.A., 1971, Impact breccias in carbonate rocks, Sierra Madera, Texas: Geologi- cal Society of America Bulletin, v. 82, p. 1009-1018. Wilshire, H.G., Pike, J.E.N., Meyer, GE, and Schwarzman, EC, 1980, Amphibole-rich veins in lherzolite xenoliths, Dish Hill and Deadman Lake, California: American Journal of Science, Jackson Volume, v. 280-A, p. 576-593. Wilshire, H.G., Schwarzman, EC, and Trask, N.J., 1971, Distri- bution of ultramafic xenoliths at 12 North American sites: NASA Interagency Report Astrogeology v. 42, p. 53-57. Wilshire, H.G., and Shervais, J.W., 1975, Al-augite and Cr-diop- side ultramafic xenoliths in basaltic rocks from western United States: Physics and Chemistry of the Earth, v. 9, p. 257-272. Wilshire, H.G., and Trask, N.J., 1971, Structural and textural re- lationships of amphibole and phlogopite in peridotite inclu- sions, Dish Hill, California: American Mineralogist, v. 56, p. 240-255. 33, TABLES 4—6 < < y. < < < M. < < < < < < < :25. 3...... 2.8 $8 8.2 3...: 2.8 $8 :..8 8.8 8.8 8.8 3.8 $2 8.... no.” ....... a .26 8.... 3.5. 8.3. m. .3 3.3 :8 8.3. 8.3. 3.5 3.3 8...... 8.8 «an 8...... .5 No.0 3...: 8.: «no S... 8.: 8.: m3 :2 Sn 8.: 3... 8... 8.3 2.9. on... 8.3. E... 2.2. .3... 8.3 8.3 8.5. 8.2. 3.8 3.8 3.8 25... m8... 8.... 8.... 8.... m8... m8... 8.... m8... m8... 2...... 8.... $8. 3...... m8... m8... 2.8 8:. 3:... E... 58 at... 8:. 8w... .8... was .8... 3.... So... so... .8... So... So... me... cs... 8.... ms... 8...... es... .8... .8... 88... m8... $8. So... So... 82. Re... So... So... So... o8... So... as... 8. .c 5o... 83. 3o... 3.... «8... So... a... v8... .2... .3. .u... .o... Be... So... 8a... 9.8 $3 88 no; 88 83 $3 $3 m2... 9...... 8.... m. S «8... .8... a... 2. .o 8.... a: .o .33 8.... 8.... 8.... 8.... 8.... 8:... .8... m8... :8... 8.... 2.... 8.... 8...... 8.... 8o... 8.... 8...... 8.... go... So... 8.... 3...... 8o... 8... 8... 2... S... w... 8... 2... S... 8... 8... 8.0 8... a... 8... F. 8.. 3... m... S. E... x... m... 8.. E... n: 8.. 8.. 3... 5—58 155932 0:23.; 8. 8. .w. 5. .m. 8. .w. .w. 8. 8. 8. E. E. eh .omwaéus. nova. 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' STENNIS SPACE CENTER, Mississippi—Bldg. 3101 101 Twelfth Allostratigraphy of the U.S. Middle Atlantic Continental Margin — Characteristics , Distribution, and Depositional History of Principal Unconformity-Bounded Upper Cretaceous and Cenozoic Sedimentary Units By C. Wylie Poag and Lauck W. Ward U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1542 Descriptions, maps, and names for 12 alloformations and designations of their ofishore stratotype sections and onshore supplementary reference sections UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON I 1993 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY ROBERT M. HIRSCH, Acting Director For sale by U.S. Geological Survey, Map Distribution Box 25286, MS 306, Federal Center Denver, CO 80225 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Library of Congress Cataloging in Publication Data Poag, C. Wylie. Allostratigraphy of the U.S. Middle Atlantic continental margin—Characteristics, dis- tribution, and depositional history of principal unconformity-bounded Upper Cretaceous and Cenozoic sedimentary units / by C. Wylie Poag and Lauck W. Ward. p. cm. — (U.S. Geological Survey professional paper ; 1542) Includes bibliographical references. 1. Geology, Stratigraphic—Cretaceous. 2. Geology, Stratigraphic—Cenozoic. 3. Geology—Mid-Atlantic Bight. 4. Mid-Atlantic Bight. 1. Ward, Lauck W. 11. Title. 111. Series. QE688.P62 1993 551 .7’7’0975 —d020 93—268 10 CIP H CONTENTS Abstract ........................................................................................... 1 Introduction ...................................................................................... 1 Previous Work ............................................................................ 4 Scope of this Report ..................................................................... 7 Acknowledgments ........................................................................ 7 Principles of Allostratigraphy ................................................................. 7 Data used in this Study ........................................................................ 10 Boreholes and Seismic Data ............................................................ 10 A Key Allostratigraphic Stratotype: DSDP Site 612 ............................... 10 Sixtwelve Alloformation ....................................................................... 15 Accomac Canyon Alloformation ............................................................. 24 Island Beach Alloformation ................................................................... 28 Carteret Alloformation ......................................................................... 32 Lindenkohl Alloformation ..................................................................... 37 Baltimore Canyon Alloformation ............................................................ 41 Babylon Alloformation ........................................................................ 45 Berkeley Alloformation ........................................................................ 47 Phoenix Canyon Alloformation .............................................................. 51 Mey Alloformation ............................................................................. 55 Toms Canyon Alloformation ................................................................. 60 Hudson Canyon Alloformation ............................................................... 64 Principal Conclusions .......................................................................... 67 Allostratigraphic Relations between Seismostratigraphic Sequences and Borehole Strata ................................................................... 67 Proximate Causes of Unconformities .................................................. 68 Depositional Regimes and Sediment Provenance and Dispersal .................. 71 Implications Regarding the Exxon Sequence-Stratigraphy Model ................ 72 Intrinsic Advantages of Allostratigraphy ............................................. 72 References Cited ................................................................................ 73 FIGURES Map showing location of principal geologic and physiographic features of study area ................................ 2 New Jersey Transect, a diagrammatic cross section from the New Jersey Coastal Plain to the northern Hatteras basin ....................................................................................................................... 3 Map showing location of selected boreholes and tracklines along which multichannel seismic-reflection profiles were collected in the study area ....................................................................................... 5 Map showing location of tracklines along which seismic—reflection profiles were collected and selected boreholes in vicinity of DSDP Site 612 ........................................................................................ 6 Summary chart showing geographic and stratigraphic distribution of alloformations proposed herein .............. 8 Stratigraphic section at DSDP Site 612 and extrapolation along dip segments of multichannel seismic- reflection profile 25 and single-channel seismic-reflection profile 69 ..................................................... l2 Stratigraphic section at DSDP Site 612 and extrapolation along strike segment of single-channel seismic— reflection profile 89 ................................................................................................................ 15 Stratigraphic section at COST B—3 well and extrapolation along dip segment of multichannel seismic- reflection profile 218 .............................................................................................................. 16 Photograph of unconformity separating Sixtwelve Alloformation from Accomac Canyon Alloformation at DSDP Site 612 ...................................................................................................................... 17 III IV 10. 11. 12—14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26, 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37, 38. 39. 40. 41. CONTENTS Isochron map of Sixtwelve Alloformation ................................................................................ Correlation chart comparing stratigraphic positions of alloformations and previously published depositional units of offshore segment of US. Middle Atlantic margin ............................................................ Stratigraphic columns showing onshore supplementary reference sections for— 12. Lower part of Sixtwelve Alloformation and its lower bounding unconformity ............................... 13. Nearly complete exposure of Sixtwelve Alloformation ........................................................... 14. Upper part of Sixtwelve Alloformation, lower part of Accomac Canyon Alloformation, and unconformity that separates them ..................................................................................... Stratigraphic section at DSDP Site 603 and extrapolation along dip segment 77 of multichannel seismic— reflection profile Conrad 21 ................................................................................................. Stratigraphic section at DSDP Site 105 and extrapolation along dip segment 77 of multichannel seismic- reflection profile Conrad 21 ................................................................................................. Stratigraphic section at DSDP Site 605 and extrapolation along dip segment of single-channel seismic- reflection profile 75 ........................................................................................................... Photograph of unconformity separating Accomac Canyon Alloformation from Island Beach Alloformation at DSDP Site 605 ............................................................................................................. Stratigraphic column showing onshore supplementary reference section for upper part of Accomac Canyon Alloformation, lower part of Island Beach Alloformation, and unconformity that separates them... Photograph of unconformity separating Island Beach Alloformation and Carteret Alloformation at DSDP Site 605 ......................................................................................................................... Stratigraphic column showing onshore supplementary reference section for upper part of Island Beach Alloformation and its upper bounding unconformity .................................................................... Photograph of unconformity separating Carteret Alloformation from Lindenkohl Alloformation at DSDP Site 612 ......................................................................................................................... Stratigraphic columns showing onshore supplementary reference sections for— 26. Lower part of Carteret Alloformation and its lower bounding unconformity ................................. 27. Upper part of Carteret Alloformation, lower part of Lindenkohl Alloformation, and unconformity that separates them ..................................................................................................... Stratigraphic section at DSDP Site 613 and extrapolation along dip segment of single- -channel seismic- reflection profile 105 ......................................................................................................... Photograph of unconformity separating Lindenkohl Alloformation from Baltimore Canyon Alloformation at DSDP Site 612 ............................................................................................................. Isochron map of Lindenkohl Alloformation .............................................................................. Stratigraphic column showing onshore supplementary reference section for upper part of Lindenkohl Alloformation, upper part of Babylon Alloformation, and unconformity that separates them ................... Photograph of unconformity separating Baltimore Canyon Alloformation from Mey Alloformation at DSDP Site 612 ................................................................................................................. Isochron map of Baltimore Canyon Alloformation ...................................................................... Stratigraphic column for part of the Exmore corehole showing Baltimore Canyon Alloformation and its upper bounding unconformity ........................................................................................... Isochron map of Babylon Alloformation .................................................................................. Isochron map of Berkeley Alloformation ................................................................................. Stratigraphic columns showing onshore supplementary reference sections for— 37. Berkeley Alloformation ................................................................................................ 38. Upper part of Berkeley Alloformation, lower part of Phoenix Canyon Alloformation, and unconformity that separates them ..................................................................................... Isochron map of Phoenix Canyon Alloformation ........................................................................ Stratigraphic column showing onshore supplementary reference section for upper part of Phoenix Canyon Alloformation and its upper bounding unconformity ......................................................... Photograph of unconformity separating Mey Alloformation from Toms Canyon Alloformation at DSDP Site 604 ................................................................................................................. 19 CONTENTS 42. Stratigraphic section at DSDP Site 604 and extrapolation along strike segment of single—channel seismic- reflection profile 170 ......................................................................................................... 43. Isochron map of Mey Alloformation ....................................................................................... 44, 45. Stratigraphic columns showing onshore supplementary reference sections for— 44. Lower part of Mey Alloformation and its lower bounding unconformity ..................................... 45. Upper part of Mey Alloformation, lower part of Toms Canyon Alloformation, and unconformity that separates them ........................................................................................................... 46, 47. Photographs of unconformity separating Toms Canyon Alloformation from Hudson Canyon Alloformation at— 46. DSDP Site 612 ........................................................................................................... 47. DSDP Site 613 ........................................................................................................... 48. Isochron map of Toms Canyon Alloformation ........................................................................... 49. Stratigraphic column showing onshore supplementary reference section for upper part of Toms Canyon Alloformation and its upper bounding unconformity .................................................................... 50. Isochron map of Hudson Canyon Alloformation ........................................................................ 51. Schematic summary of important geologic, paleoclimatic, and paleoceanographic events affecting U.S. Middle Atlantic margin during last 84 my. .............................................................................. TABLES 1. Locations and primary references for key boreholes used in this study .................................................... 2. Primary references for seismic-survey tracklines and seismic-reflection profiles used in this study .................. 3. Stratotypes and typical profiles of the 12 alloformations proposed in this report ........................................ CONVERSION FACTORS Multiply By To obtain Length centimeter (cm) 0.3937 inch meter (m) 3.281 foot kilometer (km) 0.6214 mile 0.5400 nautical mile Area square kilometer (kmz) 0.3861 square mile 57 58 59 60 61 61 63 64 66 69 11 14 14 Allostratigraphy of the U.S. Middle Atlantic Continental Margin—Characteristics, Distribution, and Depositional History of Principal Unconformity-Bounded Upper Cretaceous and Cenozoic Sedimentary Units By C. Wylie Poag1 and Lauck W. Ward2 ABSTRACT Publication of Volumes 93 and 95 (“The New Jersey Transect”) of the Deep Sea Drilling Project’s Initial Reports completed a major phase of geological and geophysical research along the middle segment of the U.S. Atlantic continental margin. Relying heavily on data from these and related published records, we have integrated outcrop, borehole, and seismic-reflection data from this large area (~500,000 kmz) to define the regional allostratigraphic framework for Upper Cretaceous and Cenozoic sedimentary rocks. The framework consists of 12 alloforrnations, which record the Late Cretaceous and Cenozoic depositional history of the contiguous Baltimore Canyon trough (includ- ing its onshore margin) and Hatteras basin (northern part). We propose stratotype sections for each alloformation and present a regional allostratigraphic reference section, which crosses these basins from the inner edge of the coastal plain to the inner edge of the abyssal plain. Selected supplemen- tary reference sections on the coastal plain allow observa- tion of the alloforrnations and their bounding unconformi— ties in outcrop. Our analyses show that sediment supply and its initial dispersal on the middle segment of the U.S. Atlantic margin have been governed, in large part, by hinterland tectonism and subsequently have been modified by paleoclimate, sea—level changes, and oceanic current systems. Notable events in the Late Cretaceous to Holocene sedimentary evolution of this margin include (1) development of continental-rise depocenters in the northern part of the Hatteras basin during the Late Cretaceous; (2) the appear- Manuscript approved for publication June 3, 1993. 1 U.S. Geological Survey, Woods Hole, MA 02543. 2 Virginia Museum of Natural History, Martinsville, VA 24112. ance of a dual shelf-edge system, a marked decline in siliciclastic sediment accumulation rates, and widespread acceleration of carbonate production during high sea levels of the Paleogene; (3) rapid deposition and progradation of thick tenigenous delta complexes and development of abyssal depocenters during the middle Miocene to Quater- nary interval; and (4) deep incision of the shelf edge by submarine canyons, especially during the Pleistocene. Massive downslope gravity flows have dominated both the depositional and erosional history of the middle segment of the U.S. Atlantic Continental Slope and Rise during most of the last 84 million years. The importance of periodic widespread erosion is recorded by well-documented uncon— formities, many of which can be traced from coastal—plain outcrops to coreholes on the continental slope and lower continental rise. These unconformities form the boundaries of the 12 allostratigraphic units we formally propose herein. Seven of the unconformities correlate with supercycle boundaries (sequence boundaries) that characterize the Exxon sequence—stratigraphy model. INTRODUCTION Seismic surveys and exploratory drilling have estab- lished the presence off the U.S. Middle Atlantic States of a deep, elongate, sedimentary basin named the Baltimore Canyon trough (Maher, 1965; figs. 1 and 2). Kingston and others (1983) and Emery and Uchupi (1984) classified this feature as a margin sag basin. The Baltimore Canyon trough underlies the coastal plain and the continental shelf and slope for 600 km between Long Island (Long Island platform) and Cape Hatteras (Carolina platform) (fig. 1; Schlee, 1981; Poag, 1985a). The maximum thickness of sedimentary rocks in the trough is about 18 km under the 2 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN 82° 80° 78° 76° 74° ‘ I I I I I I I I 72° 70° 68°W T I —O 200 400 KILOMETERS I 1 l - 46°N - , uniformity - 44° CANADA (:3 j - 42° — — - — CAPE COD V '44 K) ‘ 40° B K) a \ ’\ Q V. \I '1 38° ’\ V ‘ 36° 1 1 1 J 1 I I 1 n I 1 I J Figure 1. Principal geologic and physiographic features of the study area and the Northeastern United States. Rivers: C, Connecticut River; D, Delaware River; H, Hudson River; J, James River; P, Potomac River; S, Susquehanna River; SK, Schuylkill River. Other features: Ches Bay, Chesapeake Bay; Del Bay, Delaware Bay; LI, Long Island; MV, Martha’s Vineyard; NT, Nantucket Island. New Jersey Shelf. 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ZED | ON wk Emsmsojq 539 up 5.95% M 3 |I«...%IIo||I| fidJ$uMII 20.2210 3.. w I 3 a. S) o 4 ago 5|szme 5.: q 383 M 0— I. 1:553: 5%.: “HM I 3 l O— m<5>>>>> Baku HEW II 59: .wmIfi. m2) m $1? :5“ HI m 52s; , . d Ivm m i o 1 55m I. § I Ema H z w I m m5: 3 I | : a _ O . 3&6 k3 hfifluxwfimofi ozguguqx? 5:5 mm I _ |. I: I:I w .Eguxnvim 551.... 2925. 20.82.... wt: 3 0 £5.13 Ema: . I : | : I : | . .. . . . . K mzuooqox O 8 o z Noam 22 $0.3m m9 mow vow m6 mom m6 m m m “3 PRINCIPLES OF ALLOSTRATIGRAPHY 9 includes such discontinuities as diagenetic boundaries or soil horizons. Thus, all unconformity-bounded units are allostratigraphic units, though not all allostratigraphic units are unconformity-bounded units. The basic allostratigraphic unit is the alloformation; allomembers and allogroups are finer and coarser divisions, respectively. Four years later, the International Subcommission on Stratigraphic Classification (1987, p. 233) noted the North American Stratigraphic Code’s terminology but curiously declined to comment on it; instead, the Subcommission recommended a different series of names, centered around synthem, proposed on p. 236 and defined on p. 233 as “a body of rock bounded above and below by specifically designated, significant, and demonstrable discontinuities in the stratigraphic succession (angular unconformities, dis- conforrnities, etc.), preferably of regional or interregional extent.” Synthems may be divided into subsynthems or grouped as supersynthems. Because the allostratigraphic terminology was pro- posed specifically for sedimentary strata, and because it was published first, and because the U.S. Geological Survey recommends following the North American Stratigraphic Code, we have adopted this system. The characteristics of the alloformations we propose are those recommended by the North American Stratigraphic Code (p. 865—867): (1) Physical, chemical, and paleontological characteristics may vary horizontally and vertically throughout the units; (2) Boundaries of the allostratigraphic units are laterally traceable discontinuities; (3) The units are mappable at the scale practiced in the study area; (4) Inferred time spans are not used to define the allostratigraphic units, but most units have characteristic time spans within the study area; (5) The allostratigraphic units can be extended from their strato- types by tracing the boundary discontinuities and by tracing the deposits between the discontinuities; and (6) Names of the proposed allostratigraphic units are derived from per- manent natural or artificial geographic features in the study area. Relatively few named geographic features are present in the offshore region (principally submarine canyons), and so we have used, in one instance, the name of a Deep Sea Drilling Project site. We concede that the concept of a widespread (200,000—500,000 kmz) allostratigraphic unit bounded everywhere by unconformities is somewhat idealistic and probably is not applicable in its purest sense. That is, there are places where the contacts between successive allostrati- graphic units become conformable, especially in the Hatteras basin. But even where conformable, the allostrati- graphic boundaries are marked by significant discontinui- ties, whose acoustic impedance contrasts cause distinct, traceable seismic reflections. In its explanation of allostratigraphic units, the North American Stratigraphic Code contains what appears to be a serious contradiction, or ambiguity. Article 58(e) appears to prohibit the use of formal allostratigraphic nomenclature in areas where lithostratigraphic units have been formalized. Yet the example illustrated in the code’s Fig. 7 (p. 866) implies that formations and allostratigraphic units can be recognized in identical rocks at the same locality. If article 58(e) were adhered to, we would be required to erect artificial vertical cutoffs between offshore alloformations and equivalent onshore formations, as if their mutual presence would defy some stratigraphic principle. We argue that such cutoffs are indefensible, both conceptually and in the field. As a conceptual argument, we cite the relation between lithostratigraphic units and bio- stratigraphic units. It is normal for these two types of units to overlap or embrace one another in the field. But the code recognizes the individuality of each type of unit, even though the upper and (or) lower boundaries of the units might coincide. Both types of unit are recognized because each type is defined by separate, easily distinguished criteria. So too, are lithostratigraphic and allostratigraphic units defined by separate, easily distinguished criteria. From the perspective of field relations, we contend that the unconformities that bound the alloformations offshore do not stop at the coastline, but extend across much of the coastal plain and may be observed in outcrop. Some authors, in fact (for example, Vail and others, 1977b; Haq and others, 1987), would go so far as to claim that these unconformities are globally distributed. Moreover, the stratigraphic and geographic relations between the allo— stratigraphic and lithostratigraphic units are complex. For example, for every alloforrnation proposed herein, the designated unconformable boundaries encompass more than one formal onshore formation. Each formation has its own separate distribution pattern and correlates with its encom— passing alloforrnation at a different stratigraphic level. We believe that to erect artificial cutoffs between offshore alloformations and onshore formations implies paradoxically that the two types of units are inherently the same; that the presence of one excludes the other. This practice is scientifically unacceptable. Our viewpoint coin- cides, rather, with that of the International Subcommission on Stratigraphic Classification (1987), which specifies that (p. 234): Unconformity-bounded units may include any number of other kinds of stratigraphic units (lithostratigraphic, biostratigraphic, chronostratigraphic, magnetostratigraphic, and so on), from a few to scores, both in vertical and/or lateral succession. . . . The beds they contain may range widely in age, from a substage or chronozone to one or more systems. In certain cases, in a certain locality, or even over a certain area, a rock body bounded by unconformities may have an over-all uniform lithology or may represent a single biostratigraphic unit. The unconformity- bounded unit will then be essentially equivalent to a given lithostratigraphic or biostratigraphic unit. Thus, we recognize the presence of the formalized allofor- mations onshore and have recommended onshore supple- mentary reference sections where the alloformations and 10 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN their bounding unconformities may be observed and studied. In extending the proposed allostratigraphic units to the coastal plain, we are cognizant that interpretations of lithologic, biostratigraphic, and chronostratigraphic rela- tions vary, and sometimes conflict, from State to State. We have not attempted to resolve these conflicts, but have tried to accommodate as many viewpoints as possible in our synthesis. DATA USED IN THIS STUDY BOREHOLES AND SEISMIC DATA We agree with AD. Miall (1984, p. 3) that “Strati- graphic units ideally should be established on the basis of a basin-wide perspective. . . .” The stratigraphic data avail- able to us from the U.S. Middle Atlantic continental margin provide just such a perspective. Key boreholes used in this study are listed in table 1 and are plotted in figures 3 and 4. We used lithologic, microfossil, and geophysical-log analyses of these bore- holes to document the allostratigraphic framework along the New Jersey Transect. The results also provided a positive test of the coarse (second-order) framework of the Exxon sequence-stratigraphy model (Vail and others, 1977b; Vail and Mitchum, 1979; Vail and others, 1984; Haq and others, 1987, 1988; Van Wagoner and others, 1988). The model postulates that nine Upper Cretaceous and Cenozoic depo- sitional supersequences are separated by widespread (major or global) unconformities. The stratigraphic positions of the unconformities are fixed by microfossil biozonation and then correlated with a paleomagnetic and radiometric time scale. Coring on the continental slope and upper rise sampled supersequences UZA—3 through TB3 of Haq and others (1987) and found erosional unconformities or slump zones (biostratigraphic and (or) lithic discontinuities) at all supersequence contacts (fig. 5). Geophysical logging at Sites 612 and 613 (Poag, Watts, and others, 1987) showed that physical discontinuities correlate with impedance con- trasts on seismic-reflection profiles and sonic velocity changes in the boreholes, confirming that seismostrati- graphic sequence analysis is applicable in the study area. Thus, a reliable basis in ground truth was established for extrapolating the allostratigraphic framework across the Baltimore Canyon trough and the Hatteras basin along the grid of seismic—reflection profiles (table 2). The close correspondence of these alloformations and supersequences (fig. 5) refutes the claim of Thorne and Watts (1984) that seismic—sequence analysis is useless in predicting the strat- igraphic succession of continental shelves and slopes. A multichannel seismic-reflection grid (fig. 3; table 2) provides the principal network from which isochron maps were constructed for the 12 allostratigraphic units (equiva- lent, in part, to the depositional sequences of Poag, 1987, and Poag and Mountain, 1987; see also Poag, 1992). Poag and Sevon (1989) published simplified versions of these maps. An additional 15 high-resolution, single-channel profiles provide more detailed stratigraphic and thickness data in the vicinity of the updip DSDP boreholes (fig. 4, Sites 604, 605, 612, 613; Poag and Mountain, 1987). These isochron maps help to demonstrate the chief attributes of depositional style and fabric and the regional aspects of depositional history. In particular, the maps indicate the location of principal depocenters and allow calculation of sediment volumes and net accumulation rates. Generalized sets of isopach maps (isochrons converted to depth), most of which combine several of the proposed alloformations, have been published by Tucholke and Mountain (1979, 1986), Schlee (1981), Emery and Uchupi (1984), Ewing and Rabinowitz (1984), Mountain and Tucholke (1985), Schlee and Hinz (1987), and McMaster and others (1989). The general stratigraphic relations and depositional charac- teristics of the mapped alloformations have been tabulated and discussed by Poag (1987, 1992). A KEY ALLOSTRATIGRAPHIC STRATOTYPE: DSDP SITE 612 The most landward DSDP drilling on the U.S. Middle Atlantic margin was carried out on the lower continental slope at Site 612 (figs. 2—7). Its position, ~O.7 km northwest of the intersection of USGS multichannel seismic profiles 25 and 34 (figs. 3 and 4), affords an excellent correlation with most of the Upper Cretaceous and Ceno- zoic sedimentary sequences previously identified on the continental shelf and upper continental slope (Schlee, 1981; Poag and Schlee, 1984; Poag, 1985a, 1992; Poag, Watts, and others, 1987) and those of the continental rise (Van Hinte, Wise, and others, 1987; McMaster and others, 1989; Locker and Laine, 1992). Site 612 is located in 1,404 m of water, 5 km updip of a broad submarine outcrop of middle Eocene biosiliceous chalk and limestone (Hollister, Ewing, and others, 1972; Robb and others, 1983). The hole is the stratigraphic link between the COST B—3 well (12 km north on the upper continental slope (figs. 2—5) and Site 605 (17 km southeast on the uppermost continental rise). Hole 612 was continuously cored to 675.3 In below the sea floor and was logged; core recovery was 86 percent complete. Nine of the 12 proposed alloformations are represented in Hole 612 (figs. 4—7; see Poag, 1987, and Poag and Low, 1987, for further details of allostratigraphic units and unconform— ities documented at Site 612). For these reasons, we chose Site 612 as the stratotype for 6 of the 12 alloformations we propose herein (table 3). The oldest alloformation continuously cored at DSDP Site 612 is of Campanian age and is the oldest unit we discuss. Eleven pre—Campanian allostratigraphic units Table 1. DATA USED IN THIS STUDY Locations and primary references for key boreholes used in this study. 11 [Boreholes plotted in figures 3 and 4. ACGS-4 was named for the Atlantic County Girl Scout Council Camp 4. AMCOR, Atlantic Margin Coring Project; ASP, Atlantic Slope Project; COST, Continental Offshore Stratigraphic Test; DSDP, Deep Sea Drilling Project] Borehole name llggtgllgggflvz’) Location (1:: (1 Primary reference ACGS—4 corehole 39°29’ Atlantic County, N.J. (fig. 3) 1984 Owens and others, 1988. 74°46’ AMCOR corehole 6021 38°57.92’ Outer Continental Shelf 135 km 1976 Hathaway and others, 1979. 72°49.20’ southeast of Atlantic City, N.J. (fig. 4). Anchor—Dickinson 38°57’ Cape May County, N.J. (fig. 3) 1963 Poag, 1985a. No. 1 well. 74°57’ ASP borehole 14 38°48’ Lower continental slope 150 km 1967 Poag, 1985a. 72°50’ southeast of Atlantic City, N.J. (fig. 4). ASP borehole 15 38°46’ Lower continental slope 150 km 1967 Poag, 1985a. 72°48’ southeast of Atlantic City, N.J. (fig. 4). COST B—2 well 39°22.5’ Outer Continental Shelf 146 km east 1976 Poag, 1985a. 72°44’ of Atlantic City, N.J. (fig. 3). COST B—3 well 38°55’ Upper continental slope 150 km 1979 Poag, 1985a. 72°46.4’ southeast of Atlantic City, N.J. (figs. 3, 4). Dover Air Force Base well 39°7.60’ Kent County, Del. (fig. 3) 1970 Benson and others, 1985. 75°28.98’ DSDP Site 105 34°53.72’ Lower continental rise 575 km east 1970 Hollister, Ewing, and others, 1972. 69°10.40’ of Cape Hatteras, N.C. (fig. 3). DSDP Site 106 36°26.01’ Lower continental rise 555 km 1970 Hollister, Ewing, and others, 1972. 69°27.69’ northeast of Cape Hatteras, N .C. (fig. 3). DSDP Site 107 38°39.59’ Upper continental rise 180 km southeast 1970 Hollister, Ewing, and others, 1972. 72°28.52’ of Atlantic City, N.J. (fig. 4). DSDP Site 108 38°48.27’ Upper continental rise 160 km southeast 1970 Hollister, Ewing, and others, 1972. 72°39.21’ of Atlantic City, N.J. (fig. 4). DSDP Site 603 35°29.66’ Lower continental rise 500 km east 1983 Van Hinte, Wise, and others, 1987. 70°01.70’ of Cape Hatteras, N.C. (fig. 3). DSDP Site 604 38°42.79’ Upper continental rise 170 km southeast 1983 Van Hinte, Wise, and others, 1987. 72°32.95’ of Atlantic City, N.J. (fig. 4). DSDP Site 605 38°44.5’ Upper continental rise 165 km southeast 1983 Van Hinte, Wise, and others, 1987. 72°36.6’ of Atlantic City, N.J. (fig. 4). DSDP Site 612 38°49.21’ Lower continental slope 150 km 1983 Poag, Watts, and others, 1987. 72°46.43' southeast of Atlantic City, N.J. (fig. 4). DSDP Site 613 38°46.25’ Upper continental rise 165 km southeast 1983 Poag, Watts, and others, 1987. 72°30.43’ of Atlantic City, N.J. (fig. 4). Exmore corehole 37°35.13’ Accomack County, Va. (fig. 3) 1986 Powars and others, 1992. 75°49.15’ Haynesville corehole 37°57.22’ Richmond County, Va. (fig. 3) 1985 Mixon, 1989. 76°40.43’ Island Beach No. 1 39°48’ Ocean County, N.J. (fig. 3) 1962 Poag, 1985a. borehole. 74°06’ Kiptopeke corehole 37°08.11' Northampton County, Va. (fig. 3) 1989 Powars and others, 1992. 75°57.13’ Lewes, De1., borehole 38°43.98’ Sussex County, De]. (fig. 3) 1986 Benson, 1990a. 75°10.22’ Newport News, Va., 37°12.22’ York County, Va. (fig. 3) 1990 Poag, unpub. data, 1993. corehole. 76°34.23’ Ohio Oil-Hammond 38°18.75’ Wicomico County, Md. (fig. 3) 1944 Anderson and others, 1948. No. 1 well. 75°29.50’ Shell 272—1 well 38°42.10’ Middle continental shelf 120 km 1978 Poag, 1985a. 73°32.50’ southeast of Atlantic City, N.J. (fig. 3). 12 TWO -WAY TRAVELTIME (SECONDS) NW LINE 25 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN SE n 30|oo 34'00 hr? ' w? ' .4" VERTICAL EXAGGERATION X5 .7) KILOMETERS l I L I EXPLANATION (Includes lithologies shown in related figures) CONGLOMERATE BASALT @ DIATOM ooze E LIMESTONE MUD OR MUDSTONE CLAY 0R CLAYSTONE CALCAREOUS CLAY OR CLAYSTONE RADIOLARIAN OOZE PORCELLANITE NANNOFOSSIL OOZE SAND OR SANDSTONE E NANNOFOSSIL CHALK PEBBLES OR GRAVEL E NANNOFOSSlL-FORAMINIFER CHALK DSDP SITE 6I2 (D ® HUDSON CANYON HOLOCENE AND ALLOFORMATION PLEISTOCENE PLIOCENE TOM 3 CA NYO N ALLO FORMATION MESSINIAN TORTONIAN MEY ALLOFORMATI ON LOWER ALLOMEMBER LINDENKOHL AL LOFORMATION MIDDLE EOCEN E CARTERET ALLOFORMATIO N LOWER EOCENE NE MIDDLE ACCOMAC CANYON $ng __ _ ALLOFORMATION MAASTRWHTIAN SIXTWELVE ALLOFORMATION CAMPANIAN IV‘? UNCONFORMITY—QUERIED WHERE UNCERTAIN -‘BOUNDING UNCONFORMITY IN SEISMIC- REFLECTION PROFILE—DASHED WHERE APPROXIMATELY LOCATED % FAULT—HALF ARROWS SHOW DIRECTION OF RELATIVE MOVEMENT '? UNCERTAIN I00 200 DEPTH (METERS) DATA USED IN THIS STUDY NW 22'30 hr 23'00 hr CROSS 89 DSDP 6|2 N, - :3? ALLOFORM ~-.‘.—':.;. 3:93,. __~..~o TWO-WAY TRAVELTIME (SECONDS) 3 I t 1- .» . . a ...I IIIIIIII VERTICAL EXAGGERATION XI2 0L i’) KILOMETERS 1 l (_T Figure 6. Stratigraphic section at DSDP Site 612 and extrapolation along seismic-reflection profiles 25 and 69 (see fig. 4 for profile locations). Site 612, located on profile 69, but 0.2 km northeast of profile 25, is stratotype for Sixtwelve, Accomac Canyon, Carteret, Lindenkohl, Baltimore Canyon (lower and upper allomembers), and Toms Canyon Allofor- mations. Column 1 shows allostratigraphic nomenclature pro- posed herein; column 2 indicates chronostratigraphic position of strata; column 3 shows simplified lithology; column 4 shows position of coring gaps (black rectangles); column 5 shows numbered lithologic units used by Poag, Watts, and others (1987). Intersecting seismic profiles are indicated by arrows (for example, Cross 89). A, Dip segment of multichan- SE 13 DSDP SITE 6I2 (D (9 HUDSON CANYON HOLOCENE AND ALLOFORMATION PLEISTOCENE TOMS CANYON ALLOFORMATION PLIOCENE MESSINIAN TORTONIAN MEY IOO ALLOFORMATION UPPER LOWER ALLOMEMBER EOCENE 200 LINDENKOHL ALLOFORMATION MIDDLE EOCENE 300 DEPTH (METERS) CARTERET ALLOFORMATION LOWER EOCENE 500 a art“ N LOWER —— ALLOFORMAT'ON MAASTRICHTIAN MIDDLE AND SIXTWELVE ALLOFORMATION CAMPANIAN nel seismic-reflection profile 25. Profile 25 is typical profile for Sixtwelve, Accomac Canyon, and Island Beach Alloformations; that is, it shows typical seismic expression of these alloformations. Shotpoints along top of profile provide correlation with navigation tracklines. B, Dip segment of single-channel seismic-reflection profile 69, which is typical profile for the Carteret, Lindenkohl, Baltimore Canyon, and Toms Canyon Alloformations. Hour designations along top of profile (for example, 2230 hr) provide correlation with navigation tracklines. Note that Phoenix Canyon Alloformation thickens dramatically to northwest but has been truncated by erosion before reaching Site 612. A thin section of Babylon Alloformation is also truncated by local channel just updip from Site 612. 14 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN Table 2. Primary references for seismic-survey tracklines and seismic-reflection profiles used in this study. [Seismic-reflection profiles: Mcs, multichannel; Scs, single channel. USGS, U.S. Geological Survey] Trackline and profile no. Figure Type of Trackline and profile no. . (this report) (this report) profile (primary reference) anary reference Collected by 68, 69, 75, 77, 89, 100, 4 Scs Same numbers Robb and others, 1981; USGS. 101, 102, 105, 170, Poag and Mountain, 171, 172, 173, 176, 1987. 178, 183 2, 3, 5, 6, 8b, 8c, 9, 3 Mcs Same numbers prefaced Sheridan and others, USGS. 10, 11, 12, 13, 14, 15, by USGS. 1988, and references 16, 17, 21, 22, 23, 24, therein. 25,* 26, 27, 28, 29, 30, 34,* 35,* 36, 37 201, 202, 203, 204, 3 Mcs Same numbers prefaced Poag and Mountain, USGS and Bundesanstalt 205, 206, 207, 214, by 79—. 1987. fiir Geowissenschaften 215, 216, 217, 218,* und Rohstoffe (BGR). 219,* 220, 221 70, 71, 72, 73, 74, 75, 3 Mcs Same numbers prefaced Poag and Mountain, Lamont—Doherty Geolog- 76, 77 by Conrad 21—. 1987. ical Observatory. 1, 2, 3, 4, 5, 6, 7, 31, 3T Mcs Same numbers prefaced Poag and Mountain, Woods Hole Oceano— 32, 33, 34, 35, 36 by Knorr 80—. 1987. graphic Institution. CP3—B 4 Scs CP3—B Poag and Mountain, Deep Sea Drilling 1987. Project, Leg 95. * Trackline also shown on figure 4. 1‘ Trackline numbers on figure 3 are prefixed by Knorr 80; tracklines are shown in lower right corner. Table 3. Stratotypes and typical profiles of the 12 alloformations proposed in this report. [Stratotypes are plotted in figures 3 and 4. DSDP, Deep Sea Drilling Project; COST, Continental Offshore Stratigraphic Test] Alloformation Age Stratotype Typical profile Hudson Canyon Toms Canyon Mey Phoenix Canyon Berkeley Babylon Baltimore Canyon Lindenkohl Carteret Island Beach Accomac Canyon Sixtwelve Quaternary Pliocene (Tabianian and Piacenzian) Late Miocene (Tortonian and Messinian) Middle Miocene (Langhian and Serravalian) Early Miocene (Aquitanian and Burdigalian) Late Oligocene (Chattian) Late Eocene (Priabonian) and late early Oligocene (Rupelian). Middle Eocene (Lutetian and Bartonian) Early Eocene (Ypresian) Paleocene (Danian and Thanetian) Late Cretaceous (Maastrichtian) Late Cretaceous (Campanian) DSDP Site 613 DSDP Site 612 DSDP Site 603 DSDP Site 603 COST B—3 well COST B—3 well DSDP Site 612 DSDP Site 612 DSDP Site 612 DSDP Site 605 DSDP Site 612 DSDP Site 612 105 (fig. 28). 69 (fig. 6B). Conrad 21, segment 77 (fig. 15). Conrad 21, segment 77 (fig. 15). 218 (fig. 8). 218 (fig. 8). 69 (fig. 69 (fig. 69 (fig. 25 (fig. 25 (fig. 25 (fig. 6B). 6B). 68). 6A). 6A) . 6A). SIXTWELVE ALLOFORMATION 15 NW |830hr ' CROSS 69 DSDP 8|2 CARTE RET CANYON 2.2 TWO-WAY TRAVELTIME (SECONDS) .N A | Le-.;v~.-.§-.I¥;.r..-+E;:L-.._r 0 3 KILOMETERS Figure 7. Stratigraphic section at DSDP Site 612 and extrapo- lation along strike segment of single-channel seismic-reflection profile 89 (see fig. 4 for profile location). Note local erosional channel penetrated by Hole 612. As a result, Babylon, Berkeley, (eight drilled at Sites 603 and 105) have been discussed by Poag (1987, 1991, 1992), but data are presently inadequate to formalize an allostratigraphic nomenclature for them. SIXTWELVE ALLOFORMATION DEFINITION We propose the name Sixtwelve Alloformation (figs. 5—7) for unconformity-bounded, outcropping and subsur— face beds on the exposed coastal plain (Salisbury embay- ment), the submerged continental shelf and slope (Balti— more Canyon trough), and the continental rise (Hatteras basin) of the Middle Atlantic States (Virginia, Maryland, Delaware, New Jersey), southern New England (Connect- icut, Rhode Island, Massachusetts), and New York (fig. 1). The alloformation is bounded above and below by uncon- formities correlative with those bounding the Campanian (Upper Cretaceous strata) in this region. The Sixtwelve Alloformation is named after its stratotype, DSDP Site 612, SE leloom DSDP SITE 6l2 (D © HUDSON CANYON HOLOCENE AND u L .. ALLOFORMATION PLEISTOCENE ‘ TOMS CANYON PLIOCENE ,,,,, ALLOFORMATION ; . MESSINIAN TORTONIAN IOO UPPER LOWER ALLOMEMBER EOCENE 200 LINDENKOHL ALLOFORMATION MIDDLE EOCENE DEPTH (METERS) LOWER EOCENE CARTERET ALLOFORMATION ACCOMAC MIDDLE CANYON AND ALLOFORMATION LOWER ._ _ MAASTR ICHTIAN SIXTWELVE ALLO FOR MATION CAMPAN'AN i7; and Phoenix Canyon Alloformations are missing at corehole. Baltimore Canyon Alloformation appears to crop out in walls of Carteret Canyon. See figure 6 for explanation of geology, profile reference points, and columns 1—5. on the lower continental slope, 150 km southeast of Atlantic City, N.J., at lat 38°49.21’ N., long 72°46.43' W. (figs. 3 and 4). At the stratotype, the alloformation is approximately 200 m thick and consists of gray to black chalk and mudstone (figs. 6 and 7). BOUNDING UNCONFORMITIES The lower bounding unconformity has not yet been cored offshore, but it was drilled at the COST B—3 site, and its seismic expression can be seen on USGS multichannel seismic-reflection profile 25, which passes 0.2 km south— west of the stratotype (fig. 6A). This unconformity is also expressed on profile 218 (fig. 8), which passes ~10 km north of the stratotype and through the COST B—3 site (fig. 4). On profiles 25 and 218, the unconformity truncates reflections within the underlying Santonian depositional unit; reflections in the lower part of the Sixtwelve Allofor- mation onlap the lower unconformity. The lower uncon- formity can be traced widely in the northern part of the 16 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN IOOO 1040 IOSO “20 | | l l N o I TWO-WAY TRAVELTIME (SECONDS) 9‘ o is” m ‘ 4.0?‘171 NEH»? l§ VERTICAL EXAGGERATION X2 0 5 KILOMETERS |_|_|__._J Figure 8. Stratigraphic section at COST B—3 well and extrapo- lation along a dip segment of multichannel seismic-reflection profile 218 (see fig. 4 for profile location). COST B—3 well is stratotype for Babylon and Berkeley Alloformations; profile 218 is typical profile for these units. Stratigraphic column derived Hatteras basin and the Baltimore Canyon trough, including parts of the Salisbury embayment, where it generally is above Upper Cretaceous beds of the Santonian Stage. The upper bounding unconformity of the Sixtwelve Alloformation (figs. 6A and 9) has been cored at the stratotype, 639.6 m below the sea floor (8 cm below the top of section 3, core 69 (fig. 6A; see Poag and Low, 1987). The unconformity appears as a concave scour surface that separates Campanian dark-gray to black, fissile, finely glauconitic, pyritic, laminated mudstone and chalk (below) from Maastrichtian light-gray, coarsely glauconitic, pyritic, marly, foraminifer- and nannofossil—bearing chalk (above). Horizontal burrows filled with light-gray Maastrichtian sediment extend as deep as 10 cm below the unconformity. The upper unconformity can be traced widely in the northern part of the Hatteras basin and the Baltimore Canyon trough, including the Salisbury embayment, where it is generally overlain by strata of Maastrichtian, Paleo- cene, or Eocene age. On seismic-reflection profiles, the bounding uncon- formities of the Sixtwelve Alloformation can be traced throughout the offshore region by means of truncated, onlapping, and downlapping reflections at the contacts SE IIIGO COST B-3 CD ® HUDSON CANYON ”OLOCDENE ;T" AN ...... PLEISTOCENE _— " ALLOFORMATION PLIOCENE MEY UPPER ALLOFORMATION MIOCENE MIDDLE ~~~~ MIOCENE PHOENIX CANYON ALLOFORMATION BABY LON UPPER ALLOFORMATION OL IGOCENE DEPTH (METERS) UPPER ( EOCENE LINDENKOHL ALLOFORMATION MIDDLE EOCENE CARTERET ALLOFORMATION LOWER EOCENE MAASTRJCHTIAN -~ —: CAMPANIAN -'—'-- SANTONIAN' I principally from analysis of rotary cuttings; only a few scattered cores were taken (see Scholle, 1980). Shotpoints indicated at top of profile. See figure 6 for explanation of geology, profile reference points, and columns 1—3. (Poag and Schlee, 1984; Poag, 1985a,b, 1987, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Sixtwelve Alloformation extends in the subsurface from DSDP Site 603, on the lower continental rise, to ~50 km landward of the Dover Air Force Base well, ~700 km updip in the Salisbury embayment (fig. 10; Benson and others, 1985). Along depositional strike, it extends ~750 km from the Long Island platform (Cape Cod) to the Carolina platform (Cape Hatteras). The alloformation is generally thinner than 100 m in the Salisbury embayment and in the southern part of the Baltimore Canyon trough; it thickens gradually seaward to about 350 m at the Campa— nian shelf edge off Delaware. Its thickness on the shelf is maximum (~500 m) in a small shelf-edge delta southeast of Cape Cod. The main depocenters, however, occupy the upper continental rise and slope aprons along the base of the Long Island platform, which contain gravity-flow deposits as thick as 1,200 m (Poag and Sevon, 1989; Poag, 1992). SIXTWELVE ALLOFORMATION 17 S ACCOMAC CANYON ALLOFORMATION middle Maastrichtian CENTIMETERS Burrow SIXTWELVE ALLOFORMATION upper Companion Figure 9. Unconformity separating Sixtwelve Alloformation from Accomac Canyon Alloformation at DSDP Site 612. Uncon- formity is 639.6 m below sea floor and is 8 cm below top of section 3, core 69 (Poag and Low, 1987). Hiatus is approximately 1 m.y. Several large submarine fans contain as much as 250 m of deep-sea sediments on the lower continental rise. In the outer part of the Baltimore Canyon trough and in the Hatteras basin, the Sixtwelve Alloformation is equiva- lent to the lower part of seismic unit D1 of Schlee and others (1985); the lower part of seismic unit C of Schlee and Hinz (1987), and the Maastrichtian seismic unit of Mountain and Tucholke (1985) (fig. 11). The Sixtwelve Alloformation thins to less than 100 m in the deepest parts of the Hatteras basin, where it is equivalent to the lower part of the deep-sea Plantagenet Formation (fig. 11). In the coastal plain of New Jersey, Delaware, and Maryland, the Sixtwelve Alloformation encompasses the Merchantville Formation, Woodbury Clay, Englishtown Formation, Matawan Group, Marshalltown Formation, Wenonah Formation, and Mount Laurel Sand, all of which can be seen at numerous outcropping sections in those States. The lower bounding unconformity of this allofor— mation (separating the Merchantville Formation (Campani- an) from the underlying Magothy Formation (Santonian)) can be seen at Cliffwood Beach on Raritan Bay, N.J. (fig. 10), as described by Owens and others (1977, p. 98). We have selected this section as the onshore supplementary reference section for the lower part of the Sixtwelve Alloformation and its lower bounding unconformity (fig. 12). The other lithostratigraphic units encompassed by the Sixtwelve Alloformation can be seen in a series of outcrops also described by Owens and others (1977), but no single exposure exhibits all of the included formations. We have selected the relatively complete section at Elk Neck State Park, Md. (fig. 10; Owens and others, 1977, p. 109), as the onshore supplementary reference section for the nearly complete Sixtwelve Alloformation (fig. 13). At this expo- sure, the Campanian Merchantville Formation overlies deltaic deposits of the Santonian Potomac Group and is overlain, in turn, by the Englishtown Formation, Marshall- town Formation, and Mount Laurel Sand. The upper bounding unconformity of the Sixtwelve Alloformation can be seen at Irish Hill, near Runnemede, Camden County, NJ. (figs. 10 and 14), another of the exposures described by Owens and others (1977, p. 107). At Irish Hill, the upper bounding unconformity separates the Campanian Mount Laurel Sand from the Maastrichtian Navesink Formation (which constitutes the lower part of the Accomac Canyon Alloformation, as defined herein). THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS Relatively thin strata (<100 m) of the Sixtwelve Alloformation on the coastal plain of New Jersey, Dela- ware, and Maryland thicken seaward and to the northeast across the broad (~250-km-wide), gently sloping, Campa- nian shelf. The alloformation reaches ~500 m thickness on the outer shelf southeast of Cape Cod and >1,200 m in the slope apron south of New England (fig. 10; see Poag and Sevon, 1989; Poag, 1992). The buried Campanian shelf break is almost directly beneath the Holocene shelf break and is associated along the Middle Atlantic States with a pair of parallel regional growth faults, the Gemini fault system of Poag (1987; fig. 2), which rims the outer margin of the Baltimore Canyon trough (fig. 1). On the inner part of the Campanian shelf, at the Island Beach No. 1 borehole (fig. 10; Poag, 1985a), a 165-m section of the Sixtwelve Alloformation includes dark-greenish-gray to black, calcar- eous, fossiliferous, lignitic, pyritic, micaceous clay and silty clay of the Marshalltown Formation, which are topped by calcareous, glauconitic, clayey, quartzose sand and glauconitic clay interbeds of the Wenonah Formation and Mount Laurel Sand (Petters, 1976). Diverse and abundant microfaunas indicate deposition in middle to outer sublit— 18 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN 78° 76° 7'4° 42°N SIXTWELVE ALLOFORMATION o IOO o 50 \ W“ Mmqlfif¥ \\‘\V \W J. / ’ rs“ M‘Q ~ \%¢§Ja‘s§§m\ Q‘Kw%§r \ . (eye) . t «4 - we; EXPLANATION Q Alloformation missing or too thin to identify on seismic - reflection profiles —-O.2—- Isochron—In seconds (two-way traveltime); contour interval of OJ sec represents approximately lOOm of thickness. Dashed where approximately located Trockline—For multichannel seismic-reflection profiles. See figure 3 for designations ----- 200 ,,,.... Bathymetry—ln meters Figure 10. Isochron map of Sixtwelve Alloformation showing Beach No. l borehole; other labeled boreholes identified in text. principal sediment dispersal routes (heavy arrows) and depocen- Onshore reference sections: 1, Cliffwood Beach, N.J.; 2, Elk ters. Ancient rivers: C, ancient Connecticut River; EM, unspeci- Neck State Park, Md.; 3, Irish Hill, NJ. See figure 3 for location fied ancient rivers in eastern Massachusetts; H, ancient Hudson of DSDP Sites 603 and 105 and Cape Hatteras. River. Boreholes: DA, Dover Air Force Base well; IB, Island 19 .maougwmmow “Eségoumwomou 3865 A553 wmom How 5:38 E $8255 $285 .monfibnaaooas cabana €02 8m mm Ea .mm 6% dorm—880 Enema 5m com: 85958 :ouoocoubgwEm 8x £102 93 655 an d .=< Ear—8:: Pa 8:: wow—oi. ”oaafiioama v.5 was: cofiwfl domain—on 0.5983352? Emmom 5E SEE—son ogmfim h@582“ “.88 «o 95:58 @3388 £636 Ago: mach £933 :0 359a 8863 Fmom 058m: .2953 Hot mwfigon 5:38 :0 £385: 05on .595: 2323‘ 23:2 .m.D we Eofiwom 893cc we 3E: EcoEmomou 85:53 @253on can maouguowozm «o 3258 oEaEmusbm magmas Ego noufloboo .2 2%: SIXTWELVE ALLOFORMATION @ s 232328 steEm<<2 mauExa u om- zoF>2<§ m ©stgEm<§ “288 0 $32on m on- E35 9 z m? “238.5 E uzuoowjo l o 5 555 2:32 00. ZO_._.>>>>>\<<<<<<( H 0?: mzmooojo . 2923 - -mfioa 268;. _ No mzozzém M on mzmooi Ego; 52<<<<<<<<<_mo.._ mines. o 52<<<<<<<<<<§ | mm- _ wvwdmgw defim 3 ON. =< mm =< m|_ I . . ll x<<<<<>x<<<\<<<>Iom oz< 8mm: mz_m- I p— O 7 3 8 2 E —1 <1 2 Z I) o .._..+....,. EXPLANATION (For all figures showing onshore supplementary reference sections) FINE SAND 0R SILT El PEBBLES OR GRAVEL E MEDIUM TO COARSE SAND El COBBLES g SHALE,MUDSTONE, 0R CLAY — CONTACT CALCAREOUS BEDS w UNCONFORMITY Figure 12. Onshore supplementary reference section for lower part of Sixtwelve Alloformation and its lower bounding uncon— formity exposed at Cliffwood Beach, NJ. (modified from Owens and others, 1977, fig. 88). Subdivisions within Magothy Forma- tion are shown lithologically but are not labeled because they are not the focus of this report. See figure 10 for location. toral environments (100——200 m). If the paleoslope was uniform, then the Campanian shoreline was at least 50 km west of the present New Jersey outcrop, which contains microfaunas of 50~100 m paleodepth (Nyong and Olsson, 1984; Olsson and Nyong, 1984). On the outer shelf, the COST B—2 well (fig. 10; Poag, 1985a) penetrated 120 m of silty, calcareous sandstone and gray to black micaceous siltstone and claystone of the Zz .2 93 § 2 o>_ 32‘ E: I: <2 20 2x 0'5 gm 30-84 2 D—' 3 a _ I4 o : _rvvvvvvvv~ _ g MOUNT LAUREL SAND W. 25—3; M . - Eg a}; MARSHALLTOWN FORMATION LL . ‘ 33 *1. ) ENGLISHTOWN FORMATION _I _l < ' 13f k MERCHANTVILLE FORMATION 20 —rvvvv~./vvv~ . 5 I UNNAMED ALLOFORMATION POTOMAC GROUP 0 Figure 13. Onshore supplementary reference section for nearly complete exposure of Sixtwelve Alloformation at Elk Neck State Park, Md. (modified from Owens and others, 1977, fig. 95). See figure 10 for location and figure 12 for lithologic explanation. Sixtwelve Alloformation containing outer sublittoral to upper bathyal microfaunas (200—300 m paleodepth). The COST B—3 well, located near the Campanian shelf break, penetrated a Sixtwelve section comprising 95 m of dark- brown to gray, calcareous, silty mudstone containing rich microfaunal assemblages of upper bathyal origin (300—350 In paleodepth) (figs. 2 and 8). The Campanian shelf break is marked by a rapid seaward thickening of the Sixtwelve section as it crosses the Gemini fault system to form a lenticular slope apron (figs. SIXTWELVE ALLOFORMATION 21 AL LOFORMATION UNNAMED QUATERNARY UNIT 20- l ACCOMAC CANYON é HUDSON CANYON NAVESINK g FORMATION ALLOFORMATION MOUNT LAUREL SAND METERS 6 l ALLOFORMATION l MARSHALLTOWN EN FORMATION SIXTWE LVE ONAH FORMATION (’1 l W 0 Figure 14. Onshore supplementary reference section for upper part of Sixtwelve Alloformation, lower part of Accomac Canyon Alloformation, and unconformity that separates them exposed at Irish Hill, near Runnemede, Camden County, N .J . (modified from Owens and others, 1977, fig. 93). Subdivisions within units are shown lithologically but are not labeled because they are not the focus of this report. See figure 10 for location and figure 12 for lithologic explanation. 2 and 10). DSDP Site 612 (figs. 6 and 7) sampled 28 m of dark-gray to black chalk, shale, and mudstone, which constitutes approximately the upper one-seventh of the Sixtwelve slope apron (total thickness there is ~200 In). The dark, pyritiferous, organic-matter-rich shales near the base of the cored Sixtwelve section are evidence that an oxygen-minimum zone may have impinged upon the sea floor between Site 612 and the COST B—3 well during the late Campanian. Enrichment of the dinoflagellate assem- blage and the presence of a low-diversity assemblage of planktonic foraminifers may be further evidence of oxygen depletion (Poag, Watts, and others, 1987). Northeast of DSDP Site 612, the Sixtwelve slope apron forms a thick, elongate, double lens characterized by chaotic and onlapping seismic reflections; its maximum thickness there is ~1,200 m (fig. 10). Superimposed on the generally longslope-trending lenticular geometry of the Sixtwelve Alloformation is a series of downslope-trending, thickened pods, which alternate across the slope with thinner intervening swaths to produce a “ribbed” downslope fabric. Profiles that parallel the depositional strike (for example, profiles 34 and 35; fig. 3) show that the ribbing is produced both by erosion of deep channels in the upper surface of the alloformation (thinning) and by filling of channels cut into the underlying alloformation (thickening; Poag, 1987). Farther into the Hatteras basin (to the south- east), where the Sixtwelve Alloformation thins to 100 m or less, the principal component of the ribbed fabric is the filling of several broad channels (as wide as 17 km; fig. 10) and one ovate depression where the alloformation is >200 m thick. Southwest of DSDP Site 612, a different depositional pattern is seen. The Campanian shelf break is farther westward in this area, and the Sixtwelve slope apron is much thinner than that to the northeast (fig. 10). A period (or several periods) of erosion has removed a considerable amount of the Upper Cretaceous to lower Paleocene section over the crest of the buried Jurassic shelf-edge reef, producing an unconformity at which lower Eocene rocks lie directly on Santonian and older rocks. The Sixtwelve section seaward of this erosional scar, except for an elongate, >200-m-thick submarine fan, is relatively thin (~ 100 m). The strike profiles in this area clearly show that downslope channeling took place here as well. Evidence of Sixtwelve strata at the seaward end of the New Jersey Transect is scanty. At DSDP Site 603 (figs. 5 and 15), an unfossiliferous series of dark, reddish-gray and brown, terrigenous, silt-rich claystone and glauconite- and mica-rich quartz sand and sandstone (Accomac Canyon Alloformation(?) as defined herein; 34 In total thickness) separates upper Paleocene radiolarian-bearing claystone (Island Beach Alloformation as defined herein) from undif- ferentiated Cenomanian(?) to Campanian(?) terrigenous claystones. The undifferentiated claystones might contain Sixtwelve strata. At DSDP Site 105 (fig. 16), the Sixtwelve ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN 22 .vi 3828 BE .350m 8:80on @5on sac—cow O5 :oumquxo H8 0 Sign 8m .8382 mu: 3 Emfiwgbm 98 Eco»: 829:8 >325“? m mBBumaoo @988 28 8:588 95 Ammoo can .950 .980 .080 "mmoo 48¢ 68 835 85 wit 3 85% 895 86: 3089a :26m .509 E 2&on 3293 mm ARI EoEwomv i _ __ z<_m<_mmmm 1.: Iz<_z_oz<4<> 4 z<_>_xm._.:z02 H8 oabosbm fl moo 8mm A5382 0505 H8 m .ME 83 Ha 33:80 050E nouoomouéfimmow 6:32:58 «0 E :58me m6 waofi nouflomubxo was moo gm mama “a 8:03 oEmSwumbm .MH 95w?— _ wmumzofi m 0 3A 292E026 435% rt. t Emzomm (SONOOHS) SWINE/WEI AVM-OMJ. 23 SIXTWELVE ALLOFORMATION .VIH 255—8 65.. .959» 8.55%.— oEoE “QC—cow Mo savanna—axe H8 9 0.5mm 8m ANS» £550 USN .wfiBm ficfifiomv in 6.803%? 3 6838:: 8: 203 SE: BMOESE douuom Saagobdm-§€ufix0 E Euoxo 50m mm 39288 28 35 802 A53» £5502 Ea much» ”33 die—~05. 95 585535 but—Eon 3828 «8-5606 d .3238» QEOE By m .33» 83 K 25.59 058m cowoomouéwnflom Esau—SEE: we F EuEMom EU mac—a nowaommbxo USN we» 2% mama E .5508 ofimawagm . 6H Paw—rm _ mmm...m20.=x m 0 9x zoF < < F5593 000 I_I___I 2502936 22580 I I I <<<<<<<2>)\<2. _ _ _ zsozouxo 00m . ___ E _ 5255:; (SONOOEIS) 3WIl’IEIAVHi AVM— OMJ. <<<<<<<<<<2> 00¢ I I I G III|| 2<_.E< a IIII 8 I. I I 2<_2<_202mo H 11.11 2752;») is: as \l o M oom III|| owhmfimfiwfi»): >3..an§%» 5). o 5? m M I | Ifiwfifiwmf {KngW/sgogm .I II . 30 w I 5&3»??? I..I Emmsmsojq mused cow ..... mwmfinwrz 29:583.: I . .| 20>: o x_2mo:n_ UHF. 295.220.20.72 sz .5. 3 .. mzmoonm 2925 28 m0_ )>\<<<<<<<< mzmoopmai 55523: ”$264 $33 3 (<2. . uzm.o\<( mmwmmi «Ewing: _ _ _ I .. | E95 0 ..... ENE/fl? £030 50000 :5va © © @ 9 mm 32 m0_ ”.750 EDMD 24 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN Alloformation appears to be missing. The section presumed by Tucholke (1979, fig. 1, sheet 2) to represent Campanian deposits at Site 105 (and thus part of the Sixtwelve Alloformation as defined herein) is composed of multicol— ored (reddish-brown, yellow, orange, olive-green, black), silty, zeolitic, noncalcareous clays (Hollister, Ewing, and others, 1972). However, during and after the original analysis (Leg 11; Hollister, Ewing, and others, 1972), dinoflagellates and ichthyoliths of late Oligocene and undif- ferentiated Tertiary age were found in this section (cores 105—5 to 105—7; 241—268 m below the sea floor; Kaneps and others, 1981). Below this section, an undifferentiated Maastrichtian to Danian (ichthyolith—dated) section (268— 286 m below the sea floor) rests on Aptian to Cenomanian (dinoflagellate-dated) black clay (286-403 In). On multichannel seismic profiles crossing the outer Baltimore Canyon trough and the Hatteras basin, the Sixtwelve Alloformation comprises broad zones of moder- ately high amplitude, parallel to subparallel, continuous reflections that are inferred to represent relatively uniform deposits. The zones are interrupted, however, at irregular intervals, by chaotic or poorly defined reflections inferred to represent sediments deposited by downslope mass move- ment. The latter are particularly prevalent in the slope aprons (fig. 10). The persistence of the upper bounding unconformity of the Sixtwelve Alloformation in much of the present coastal plain and continental shelf, slope, and rise of the study area is evidence that it was caused, in large part, by a relative sea—level fall (Poag and Schlee, 1984; Poag, 1985a, 1987; Poag and Low, 1987). Olsson (1978) and Nyong and Olsson (1984) have noted that the basal part of the overlying Accomac Canyon Alloformation (Maastrichtian section; new allostratigraphic unit, herein described) beneath the New Jersey Coastal Plain was deposited during a sea- level low. Owens and Gohn (1985) have shown that regressive facies at the Sixtwelve-Accomac Canyon contact (Campanian-Maastrichtian boundary) can be traced from the Southeast Georgia embayment, located beneath the continental shelf and coastal plain of Georgia, to the Long Island platform. ACCOMAC CANYON ALLOFORMATION DEFINITION We propose the name Accomac Canyon Alloformation for unconformity-bounded, outcropping and subsurface beds on the exposed coastal plain (Salisbury embayment), the submerged continental shelf and slope (Baltimore Can- yon trough), and the continental rise (Hatteras basin) of the Middle Atlantic States (Virginia, Maryland, Delaware, New Jersey), southern New England (Connecticut, Rhode Island, Massachusetts), and New York (fig. 1). The allo- formation is bounded above and below by unconforrnities correlative with those bounding the Maastrichtian (Upper Cretaceous) strata in this region. The Accomac Canyon Alloformation is named after Accomac Canyon, which incises the present continental slope and shelf edge 160 km southwest of the alloforma- tion’s stratotype, DSDP Site 612 (figs. 3, 6, and 7). At the stratotype (lat 38°49.21’ N.; long 72°46.43’ W.), the alloformation is 80.2 m thick and consists of light— and dark-gray, marly, foraminifer- and nannofossil-bearing chalk containing occasional thin layers of lithified limestone. BOUNDING UNCONFORMITIES The lower bounding unconformity of the Accomac Canyon Alloformation has been cored at the stratotype, 639.6 m below the sea floor (8 cm below the top of section 3, core 69; figs. 6A, 7, and 9; see Poag and Low, 1987). The unconformity appears as a concave scour surface that separates Maastrichtian light-gray, coarsely glauconitic, pyritic, marly, foraminifer- and nannofossil-bearing chalk (above) from Campanian dark—gray to black, fissile, finely glauconitic, pyritic, laminated shale and chalk (below). Horizontal burrows filled with light-gray Maastrichtian sediment extend as deep as 10 cm below the unconformity. The lower unconformity can be traced widely in the northern part of the Hatteras basin and in the Baltimore Canyon trough, including the Salisbury embayment, where it generally is above Upper Cretaceous beds of the Six- twelve Alloformation. The upper bounding unconformity of the Accomac Canyon Alloformation was not cored (core was attempted, but not recovered) at the stratotype, but it was cored at DSDP Site 605, 17 km downdip from Site 612 (figs. 4 and 17). At DSDP Site 605, the unconformity is present at ~778.73 m below the sea floor, in a 30-cm-thick disturbed zone of broken core fragments, which obscures the contact (fig. 18; Poag, 1985b; Lang and Wise, 1987; Smit and Van Kempen, 1987). The unconformity separates Maastrichtian light-gray, argillaceous, foraminifer- and nannofossil- bearing limestone (below) from Paleocene light-blue-gray, slightly laminated, foraminifer—bearing mudstone (above). The upper unconformity can be traced widely in the northern part of the Hatteras basin and in the Baltimore Canyon trough, including the Salisbury embayment, and generally is overlain by strata of either Paleocene or Eocene age (fig. 6A). On seismic-reflection profiles, the bounding uncon- formities of the Accomac Canyon Alloformation can be traced throughout the offshore region by means of trun- cated, onlapping, and downlapping reflections at the con- tacts (Poag and Schlee, 1984; Poag, 1985a, 1987, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). ACCOMAC CANYON ALLOFORMATION 25 NW SE O4IOOhr 01|5hr CROSS 25 * CROSS 95 - . l DSD P CROSS I?! ,~- I. ~ 7,-- -. firm-H. flPIRsr COREL’ ’ ‘. (Top = l45m) 3.. TWO-WAY TRAVELTI ME (SECONDS) VERTICAL EX AGGERATION Xl2 0 ? KILOMETERS l l 1 Figure 17. Stratigraphic section at DSDP Site 605 and extrap- olation along dip segment of single-channel seismic—reflection profile 75 (see fig. 4 for profile location). Site 605 is stratotype for Island Beach Alloformation. Typical profile is multichannel DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Accomac Canyon Alloformation extends in the subsurface from DSDP Site 603 (on the lower continental rise) to ~45 km landward of the Dover Air Force Base well, ~700 km updip in the Salisbury embayment (fig. 19). Along depositional strike it extends 750 km from the Long Island platform (Cape Cod) to the Carolina platform (Cape Hatteras). The alloforrnation is generally thinner than 100 m in the Salisbury embayment and across the continental shelf of the Baltimore Canyon trough, where it appears to have \ \ W \W ACCOMAC CANYON DSDP SITE 605 ® ® ©©© WWW/\All —0 Z 85 UPPER HOngiIIEER AND é:— ALLWEMBER PLEISTOCENE 2E ’?w’?’v?w?w’?o IOO OU- _ 83 LOWER LOWER :_I ALLOMEMBER PLEISTOCENE I300 In in an outer shelf delta on the Long Island platform and to >500 min a shelf-edge depocenter seaward of Cape Charles, Va. Thickest depocenters are located along the base of the Long Island platform, where broad channels contain gravity-flow deposits as thick as 600 m. In the outer part of the Baltimore Canyon trough and in the Hatteras basin, the Accomac Canyon Alloformation is equivalent to a lower part of seismic unit D1 of Schlee and others (1985); the middle part of seismic unit C of Schlee and Hinz (1987); and the Eocene seismic unit of Mountain and Tucholke (1985) (fig. 11). In this part of the Hatteras 26 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN ‘1 t, '1 l I z 2: 1' S2 g-3O l— _ < i E _ m 1 E ., — C) c _ —‘ 8 -—l o _ < 2 U _ I:a_ L) _ <1 5 UH 3 00 2 c3 2: . . <1 3 —‘40 _J 9 » T‘ 1.1.1 05 E fizAP . m.. ' y E [— 2: u: c) --50 ACCOMAC CANYON ALLOFORMAHON upper Maastnchhan (disturbed zone) Figure 18. Unconforrnity separating Accomac Canyon Allofor- mation from Island Beach Alloforrnation at DSDP Site 605. Unconformity is 778.73 m below sea floor and is 43 cm below top of section 1, core 66 (Poag and Low, 1987). Hiatus is approxi- mately 0.5 m.y. basin, the Accomac Canyon Alloforrnation is equivalent to the upper part of the deep—sea Plantagenet Formation (fig. 1 1). In the coastal plain of New Jersey, Delaware, and Maryland, the Accomac Canyon Alloforrnation encom- passes the Navesink Formation, Redbank Sand, Tinton Sand, and Severn Formation, which can be seen at numer- ous outcropping sections in these States. No single coastal- plain exposure, however, exhibits all the lithostratigraphic units encompassed by the Accomac Canyon Alloforrnation. The lower bounding unconformity of the Accomac Canyon Alloforrnation may be seen at Irish Hill, near Runnemede, Camden County, NJ. (fig. 19), a section described by Owens and others (1977, p. 107). We have, therefore, selected the exposure at Irish Hill as the onshore supple- mentary reference section for the lower part of the allofor— mation and its lower bounding unconformity (fig. 14). At this exposure, the lower bounding unconformity separates the Campanian Mount Laurel Sand (upper part of Sixtwelve Alloforrnation) from the Maastrichtian Navesink Formation (lower part of Accomac Canyon Alloforrnation). The upper bounding unconformity (as well as the lower) of the Accomac Canyon Alloforrnation is exposed at Round Bay, on the Severn River, near Annapolis, Md. (fig. 19; Owens and others, 1977, p. 113). Thus, we have selected the Round Bay exposure as the supplementary reference section for the upper part of the Accomac Canyon Alloforrnation and its upper bounding unconformity (fig. 20). At Round Bay, the upper bounding unconformity separates the Maastrichtian Severn Formation (Accomac Canyon Alloforrnation) from the Paleocene Brightseat For- mation (lower part of the Island Beach Alloforrnation, as defined herein). THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS The distribution and depositional fabric of the Acco- mac Canyon Alloformation are similar to those of the Sixtwelve Alloforrnation, but the Accomac Canyon section is thicker throughout most of the northern Hatteras basin (fig. 19; see Poag and Sevon, 1989; Poag, 1992). A broad Maastrichtian shelf, like that of the Campanian, was cov- ered by a thin blanket of contemporaneous sediments (generally <100 m thick), but, in several broad patches, Accomac Canyon strata appear to be entirely missing due to subsequent erosion. The Maastrichtian shelf break had prograded southeastward about 10 km (along profile 25) relative to the Campanian shelf break (fig. 2). The ribbed (cut—and-fill) downslope fabric characteris- tic of the Sixtwelve Alloforrnation is also widely distributed within the Accomac Canyon slope aprons (fig. 19). This fabric is evidence of the continued dominance of downslope mass sediment dispersal. Even as far as 100 km downdip from Site 612, the middle-rise deposits are marked by broad (20-km-wide) southeast-trending erosional swaths and intervening linear thickenings (Poag, 1987). The persis- tence of terrigenous components at DSDP Sites 603 (fig. ACCOMAC CANYON ALLOFORMATION 27 78° 76° 74° I 72° l l ? l 7 \ ACCOMAC CANYON ALLOFORMATION NY ,/ \- —— 0 ICC 200 KILOMETERS ‘ t-——|‘——r‘l-—r’J——r’ 50 lOO NAUTICAL MILES ‘ -v «‘4 ° . ‘\v\\\\’\‘ 40 § \\\\ ‘ i i\: {1; t i ii ‘ WW Mv/idlmMKM! It», \‘ w t. .03 ()1 EV - ,4- TV- ‘ hi ““gfiz‘l’fi _‘r 5; ‘ m A] ,3‘iiif.\s_muii§lihilt$§q - *YM "NI ‘ \ . V J ‘15 CAP cruiizLEs r 41¢ ’ EXPLANATION §§ Alloformation missing or too thin to identify on seismic - reflection profiles —0.2—— lsochron—ln seconds (two-way traveltime); contour interval of 0.! sec represents approximately l00m of thickness. Dashed where approximately located Trackline—For multichannel seismic-reflection profiles. See figure 3 for designations ----- 200 mm Bathymetry—ln meters Figure 19. Isochron map of Accomac Canyon Alloformation showing principal sediment dispersal routes (heavy arrows) and Beach No. l borehole; other labeled boreholes identified in text. depocenters. Ancient rivers: C, ancient Connecticut River; EM, Onshore reference sections: 1, Irish Hill, N.J.; 2, Round Bay, Md. unspecified ancient rivers in eastern Massachusetts; J, ancient See figure 3 for location of DSDP Sites 603 and 105 and Cape James River; P, ancient Potomac River. Boreholes: AD, Anchor- Hatteras. Dickinson No. 1 well; DA, Dover Air Force Base well; 1B, Island 28 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN 2 5 9 it: ’2: 3“ 2 CE [I <0: O O 20— L. L. O 3' _‘ < m I — o <[ Lu I—Z co :9 ‘ I— : 2< <1 I: - 0 a E0 _ m“- _uvwvvvvv' 2 _ 9 i— <1: ‘ E U) 2 E IO 8 o — o — p— l— —' <3: Lu —1 z E _ < p): 2 u. - S 2 E < Lu _ 0 > $ 0 < ‘ E O o o 5— <3: ‘MV‘NVW (z) . Lu— 2' -5: $9 LuE BI— 33 «<1 _’-u_ F2 >_100 m in a narrow depocenter a few kilometers seaward of Cape May, N.J. The alloforrnation is missing (or too thin to identify on seismic—reflection profiles) beneath much of the continental shelf; it thickens to >200 min slope aprons off New Jersey and Long Island and reaches a maximum of >300 m in an elongate submarine fan seaward of Cape Henry, Va. (Poag and Sevon, 1989; Poag, 1992). In the outer part of the Baltimore Canyon trough and in the Hatteras basin, the Island Beach Alloformation is equivalent to the middle part of seismic unit D1 of Schlee and others (1985); the upper 30 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN 78° 76° 74° 72° 70°W 42° N l l \ l r l I ‘ \ , CAPE >9 ‘1 COD 1 \, ISLAND BEACH xi ALLOFORMATION fl — 0 I00 200 KILOMEl’ERS \‘ 0 so 100 NAUTICAL MILES f in / PA \I ‘ o-Q _ NJ 200m ; 400 D -:_ 6} 00 01 02 o.\ . 0.2 00 I 0.0 . " V ' x \ , 3 °\' . . WASHINGTON DC“; .2 CAPE °MAY .. ' A 6055' -o ' o. 0.2 \ 0.0 00 q, 0.1 \ 5 or E m 01 v 38° " 00 0.l 09 ...... “(90“3 603 I05 36° EXPLANATION Alloformation missing or too thin to identity on seismic-reflection profiles Isochron—in seconds (two-way traveltime); contour interval of OJ sec represents approximately too In of thickness. Dashed where approximately located Trackline—For multichannel seismic—reflection profiles. See figure 3 for designations ----- 200 ,,,.... Bathymetry—ln meters Figure 22. Isochron map of Island Beach Alloformation show- ing principal sediment dispersal routes (heavy arrows) and depo— centers. Ancient rivers: D, ancient Delaware River; S, ancient Susquehanna River. Boreholes: DA, Dover Air Force Base well; IB, Island Beach No. 1 borehole; other labeled boreholes identi- part of seismic unit C and the lower part of unit D1 of Schlee and Hinz (1987); and most of the lower Oligocene(?) seismic unit of Mountain and Tucholke (1985) (fig. 11). fied in text. Onshore reference sections: 1, Round Bay, Md.; 2, USGS loc. 26332 on Potomac River near Aquia Creek, Va. See figure 3 for location of DSDP Sites 603 and 105 and Cape Hatteras. The Island Beach Alloformation is quite thin (< 100 m) or missing beneath most of the rest of the continental rise. Where present in the northern part of the Hatteras basin, the ISLAND BEACH ALLOFORMATION 31 alloformation is equivalent to the lower part of the deep-sea Bermuda Rise Formation (fig. 11). In the coastal plain of New Jersey, Delaware, Mary- land, and Virginia, the Island Beach Alloformation encom- passes the Brightseat Formation, Hornerstown Sand, Aquia Formation, Vincentown Formation, and Marlboro Clay, which may be seen at numerous outcropping sections in those States. One of the best exposures of the lower bounding unconformity, which separates the Maastrichtian Severn Formation (Accomac Canyon Alloformation) from the Paleocene Brightseat Formation (Island Beach Allofor- mation), is at Round Bay, Md. (Owens and others, 1977, p. 113). This is the same outcrop selected above as the onshore supplementary reference section for the upper part of the Accomac Canyon Alloformation (fig. 20). We designate this exposure also as the onshore supplementary reference section for the lower part of the Island Beach Alloformation and its lower bounding unconformity. The upper part of the Island Beach Alloformation (Aquia Formation) is best exposed along the Potomac River in the vicinity of Aquia Creek, Stafford County, Va. We designate the exposure described by Ward (1985 , p. 62, loc. 3, USGS loc. 26332) as the supplementary reference section for the upper part of the Island Beach Alloformation and its upper bounding unconformity (figs. 22 and 23). At this locality, the upper bounding unconformity separates the Paleocene Marlboro Clay from the lower Eocene Nanjemoy Formation. The upper bounding unconformity of the allo- formation also may be seen at numerous other outcrops in southeastern Virginia, where the unconformity separates the overlying Nanjemoy Formation from either the Marlboro Clay, or where the Marlboro is absent, from the Aquia Formation. In the Island Beach No. l borehole, from which the name of this unit was taken, the Island Beach Alloformation consists of 47 m of light— to dark-greenish-gray, calcareous, glauconitic, lignitic, micaceous clay interbedded with olive- to greenish-gray, calcareous, lignitic, micaceous, pyritic, glauconitic sandy silt (Seaber and Vecchioli, 1963; Poag, 1985a). THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS The striking feature of the Island Beach Alloforrna— tion’s distribution pattern (fig. 22) is the unit’s widespread absence (or thinness) compared to the distribution of the underlying Sixtwelve and Accomac Canyon Alloforma- tions. The general pattern of a broad, thinly covered continental shelf, whose shelf break is marked by a thick- ened slope apron, persisted, however, during deposition of the Island Beach Alloformation. The position of the shelf break remained about the same as during Accomac Canyon deposition. On the inner to middle shelf, a thin (~ 100 m), Z 25 -’__gl {,4 COVERED m< 09 0:2 2,. “fig 3; 5.3.5 32‘, LL '. ‘ -°a‘ MARLBORO CLAY 0-0.23m WWW . . 20- 51 Z — Z (13. I5 9 92 l—LLJ' '2 <2 _ 2 2 , a: 0i ' (I: - U- U) Lu 0 Z _l <- l— .1 qt.- Lu — <1 50. 2 03:), <[<1 _ I D._ 0 55 IO— :13 _ D Z <[ — .1 <2 5- _ w. m m. co -' 2 Lu 2 >- _ <1 5 < I— _ < O 0,. E O Figure 23. Onshore supplementary reference section for upper part of Island Beach Alloformation and its upper bounding unconformity, exposed near Aquia Creek, along Potomac River, Stafford County, Va. (Ward, 1985, p. 62, Ice. 3, USGS 10c. 26332). Subdivisions within units are shown lithologically but are not labeled because they are not the focus of this report. See figure 12 for lithologic explanation and figure 22 for location. 32 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN elongate delta built out, extended a few broad lobes onto the outer shelf, and fed narrow slope aprons (~200 m thick). The Island Beach Alloformation gradually thins downdip to a featheredge before pinching out on the underlying surface of the Accomac Canyon Alloformation. Strata of the Island Beach Alloformation are missing from wide swaths on the outer shelf and upper slope northeast and southwest of New Jersey. A distinct subma- rine fan (200—300 m thick) developed in the Hatteras basin downdip from each of those erosional swaths. The thickness of the slope aprons and the obvious upslope origin of their sedimentary components (channel fill, as inferred from chaotic seismic reflections and from the terrigenous detritus cored at Site 605) are evidence that some of the updip erosion was contemporaneous with downdip deposition, which redistributed outer shelf sediments to the continental slope and rise. Elongate patches of thin or missing Island Beach deposits extend from the base of the slope aprons and appear to be additional erosional swaths created by down- slope channeling. At DSDP Site 603 (figs. 5 and 15), a 20-m section of the Island Beach Alloformation contains dark-greenish- gray, zeolitic, silt-bearing, radiolarian-rich claystone hav- ing minor amounts of quartz and mica. Obviously, long- distance dispersal of shelf—derived detritus continued in the northern Hatteras basin during the late Paleocene. Thin deposits of the Island Beach Alloformation beneath the continental shelf and at DSDP Site 603 contain chiefly late Paleocene fossils, indicating that erosion was dominant in the early Paleocene history of this region. At DSDP Site 605 (figs. 5 and 17), the Island Beach section is thicker and more complete, but a sharp intraformational contact between glauconitic silty strata and overlying argil- laceous nannofossil—bearing limestone (53 cm below the top of section 1, core 64; Van Hinte, Wise, and others, 1987) represents an important early Paleocene erosional event. This event may be used to divide the Island Beach Allofor- mation informally into an upper and a lower allomember. Approximately 14 m of multicolored zeolitic clay at DSDP Site 105 contains ichthyoliths of Maastrichtian to Danian age and might represent the Island Beach Allofor- mation (fig. 16). CARTERET ALLOFORMATION DEFINITION We propose the name Carteret Alloformation for unconformity-bounded outcropping and subsurface beds on the exposed coastal plain (Salisbury embayment), sub- merged continental shelf and slope (Baltimore Canyon trough), and continental rise (Hatteras basin) of the Middle Atlantic States (Virginia, Maryland, Delaware, New Jer- sey), southern New England (Connecticut, Rhode Island, Massachusetts), and New York (fig. 1). The alloforrnation is bounded above and below by unconforrnities correlative with those bounding the Ypresian (lower Eocene) strata in this region. The Carteret Alloformation is named after Carteret Canyon, which incises the present continental slope and shelf edge ~150 km southeast of Atlantic City, NJ. (fig. 3). The stratotype of the alloformation is DSDP Site 612 (figs. 6 and 7), on the lower continental slope, 2 km southwest of Carteret Canyon, at lat 38°49.2l’ N. , long 72°46.43’ W. At the stratotype, the Carteret Alloformation is 227.5 m thick and consists of light-greenish-gray to olive-gray porcellanite and porcelaneous, nannofossil- bearing chalk. BOUNDING UNCONFORMITIES The lower bounding unconformity of the Carteret Alloformation (fig. 21) has been cored at DSDP Site 605 (17 km downslope from Site 612), 563.83 m below the sea floor (33 cm below the top of section 5, core 44; see Poag, 1985b; Lang and Wise, 1987). The unconformity (fig. 17) separates lower Eocene light-green-gray, lightly burrowed, argillaceous, porcelaneous, foraminifer- and nannofossil- bearing limestone (above) from upper Paleocene dark-blue- gray, densely burrowed, marly, foraminifer- and nannofossil-bearing limestone (below). The contact lies in a 4-cm section disturbed by expansion cracks in the Paleo- cene sediments. The lower unconformity can be traced widely throughout the northern part of the Hatteras basin and the Baltimore Canyon trough, including the Salisbury embayment, and truncates upper Paleocene beds (Island Beach Alloformation), Upper Cretaceous beds (Accomac Canyon and Sixtwelve Alloformations), or older beds. The upper bounding unconformity of the Carteret Alloformation (fig. 24) has been cored at DSDP Site 612 (figs. 6 and 7), 331.90 m below the sea floor (80 cm below the top of section 3, core 37; see Poag and Low, 1987). The unconformity separates lower Eocene dark-yellowish- brown, horizontally burrowed, biosiliceous, foraminifer- and nannofossil-bearing chalk (below) from middle Eocene, light—greenish-gray, coarsely glauconitic, thinly laminated, biosiliceous, foraminifer— and nannofossil-bearing chalk containing clasts of dark-gray, Upper Cretaceous chalk (above). The upper bounding unconformity can be traced widely throughout the northern part of the Hatteras basin and the Baltimore Canyon trough, including the Salisbury embayment, and is generally overlain by middle Eocene beds of the Lindenkohl Alloformation (defined herein). On seismic-reflection profiles, the bounding uncon- formities of the Carteret Alloformation can be traced throughout the offshore region by means of truncated, onlapping, and downlapping reflections at the contacts (Poag and Schlee, 1984; Poag, 1985a,b, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). CARTERET ALLOFORMATION 33 LINDENKOHL ALLOFORMATION middle Eocene CENTIMETERS CARTERET ALLOFORMATION lower Eocene Figure 24. Unconformity separating Carteret Alloformation from Lindenkohl Alloformation at DSDP Site 612. Unconformity is 331.90 m below sea floor and is 80 cm below top of section 3, core 37 (Poag and Low, 1987). Hiatus is approximately 2 my DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Carteret Alloformation extends nearly continu- ously in the subsurface from DSDP Site 603 (and possibly Site 105) (on the lower continental rise) to ~30 km landward of the Dover Air Force Base well, ~700 km updip in the Salisbury embayment (fig. 25). Along depositional strike, the alloformation extends ~750 km along the outer shelf from the Long Island platform (Cape Cod) to the Carolina platform (Cape Hatteras). It is generally thinner than 100 m in the Baltimore Canyon trough, including the Salisbury embayment, and is missing from much of this area. Its distribution in the northern Hatteras basin is even more scattered; the unit principally forms an elongate series of slope aprons and two associated large submarine fans seaward of New Jersey and Long Island, where thickness reaches >200 m (see Poag and Sevon, 1989; Poag, 1992). In this area, the alloformation is correlative with the upper part of seismic unit D1 of Schlee and others (1985); the upper part of seismic unit D1 of Schlee and Hinz (1987); the uppermost part of the lower Oligocene(?) seismic unit and the lower part of the upper Oligocene(?) seismic unit of Mountain and Tucholke (1985); and the middle part of the deep-sea Bermuda Rise Formation (fig. 11). In the coastal plain of New Jersey, Delaware, Mary- land, and Virginia, the Carteret Alloformation encompasses the Nanjemoy and Manasquan Formations, which may be seen in numerous outcrops in those States. No single locality, however, exhibits both the upper and lower bound- ing unconformities of the Carteret Alloformation. We have selected Bull Bluff on the Potomac River, just downstream from Potomac Creek, Stafford County, Va. (fig. 25), as the supplementary reference section for the lower part of the alloformation and its lower bounding unconformity (Ward, 1985, p. 63, 10c. 11, USGS 10c. 26340). At Bull Bluff, the lower bounding unconformity separates the lower Eocene Nanjemoy Formation (Carteret Alloformation) from the Paleocene Marlboro Clay (Island Beach Alloformation; fig. 26). The upper bounding unconformity of the Carteret Alloformation has been cored in several places in the Virginia—New Jersey Coastal Plain, including the Haynes- ville corehole, Va. (Mixon, 1989). The only sections where this unconformity may be viewed in outcrop, however, are along the Pamunkey and James Rivers in Virginia; the best exposures are along the Pamunkey River in Hanover County. We have selected the Pamunkey River section described by Ward (1985, p. 73, 10c. 74, USGS 10c. 26403) as the onshore supplementary reference section for the upper part of the Carteret Alloformation and its upper bounding unconformity (figs. 25 and 27). At this locality, the upper bounding unconformity is an irregular, deeply burrowed surface that separates the lower Eocene Nanje- moy Formation (Carteret Alloformation) from the overlying middle Eocene Piney Point Formation (Lindenkohl Allofor- mation as designated herein). THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS The Carteret Alloformation was deposited under an elevated early Eocene sea level, which allowed several depocenters to develop on the continental shelf (figs. 2 and 25; see Poag and Sevon, 1989; Poag, 1992). Along the middle and outer shelf, the Carteret Alloformation is generally 100—250 In thick. A seaward—thickening slope apron is present seaward of New Jersey. Downslope cut— ting, filling, and slumping have produced a ribbed isochron 34 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN 7.80 l 716° 74° 72° I 700W 420N ‘\ ' ' l I ‘ W I II I I i ~I: ‘MA , iii-1'4. : fig? 5 c1- 1 RI; § :.-:- I CARTERET NY 3 , III, wfi ALLOFORMATION I ~J a O ICC 200 KILOMETERS I—H—H—r—g—r' O 50 IOO NAUTICAL MILES ////\\ / flfia .( \ L « W "§3®§f§~\g . \:\\ x} “\"W s as» M \ \\\\“ \, ‘t a A I% 02 \ ‘\\\‘§ 40° W‘§‘c ‘l/ \ ////4 EXPLANATION S Alloformation missing or too thin to identify ‘ on seismic-reflection profiles -—0.2—- lsochron—ln seconds (two-way traveltime); contour interval of OJ sec represents approximately IOOm of thickness. Dashed where approximately located Trackline—For multichannel seismic-reflection profiles. See figure 3 for designations ----- 200 m---- Bathymetry—In meters Figure 25. Isochron map of Carteret Alloformation showing principal sediment dispersal routes (heavy arrows) and depocen- ters. Ancient rivers: C, ancient Connecticut River; D, ancient Delaware River; H, ancient Hudson River. Boreholes: DA, Dover Air Force Base well; HA, Haynesville corehole; other labeled boreholes identified in text. Onshore reference sections: 1, Bull Bluff, Va.; 2, USGS 10c. 26403 on Pamunkey River, Va. See figure 3 for location of DSDP Sites 603 and 105 and Cape Hatteras. CARTERET ALLOFORMATION 35 4O 22 ‘99 z '— -§§ ES COVERED _xg [:2 —E“- ‘lo: m0 <0 35 <)--1 on. E: -mww 30- Z ' '2: <25 ‘ E :00 25- 0 :EE _ 3 0:2 _: E . _ _| - _ < o- w 622- c: - l— 20. LlJ 20_ Lu L|JE _ <2»)- <1 — 0-. O Figure 26. Onshore supplementary reference section for lower part of Carteret Alloformation and its lower bounding unconform- ity, exposed at Bull Bluff on Potomac River, just downstream from Potomac Creek, Stafford County, Va. (Ward, 1985, p. 63, Ice. 11, USGS 10c. 26340). Subdivisions within units are shown lithologically but are not labeled because they are not the focus of this report. See figure 12 for lithologic explanation and figure 25 for location. Z 49 ,_ COVERED II— 22 o< 59 3 a: mo ' g; 35 —_1 ES 42: o. . NAM/MM 5 _ z t; 933 5 " z |— CO 1 2’2 o LIJ L5 a: E U) _‘ E a: 4 LIJ _ < x ' l— ’_ >_ 8 - LIJ LIJ o '_ ' ES 2 ' m m uJ ulo' F— ”o a: gca. 3 2:3. ‘ COVERED 0 Figure 27. Onshore supplementary reference section for upper part of Carteret Alloformation, lower part of Lindenkohl Allofor- mation, and unconformity that separates them, exposed along Pamunkey River, Hanover County, Va. (Ward, 1985, p. 73, 100. 74, USGS loc. 26403). See figure 12 for lithologic explanation and figure 25 for location. 36 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN NW SE |4l45 hr |5|00hr I5I5hr | CROSSI7 DSDP 6|3 (0.2 km sw) {CROSS I02 TWO-WAY TRAVELTIME (SECONDS) LINEV Io :1 ~j = VERTICAL EXAGGERATION X|9 0 cl} KlLOMETERS l I 1 l DSDP SITE 6|3 _ . . O z Z HOLOCENE AND 9 E UPPER UPPER Z < ALLOMEMBER 5 2 PLEISTOCENE n: 5 E IOO U) 0 D _l D .1 I < LOWER LOWER ALLOMEMBER PLEISTOCENE 200 TOMS CANYON ALLOFORMATION PL'OCENE 27, 5 I— LU ALLOFgEYMATION MIOCENE E 300 a: '— 0. Lu 0 LINDENKOHL MIDDLE ALLOFORMATION EOCENE 400 PHOENIX CANYON ALLOFORMATION (MIDDLE ALLDMEMBER) 500 LOWER EOCENE CARTERET ALLOFORMATDN Figure 28. Stratigraphic section at DSDP Site 613 and extrapolation along dip segment of single—channel seismic-reflection profile 105 (see fig. 4 for profile location). Site 613 is stratotype for Hudson Canyon Alloformation; profile 105 is typical profile. See figure 6 for explanation of geology, profile reference points, and columns 1—5. pattern. The most distinctive component of the depositional fabric in the slope apron is a series of deep channels cut into the upper surface of the Carteret Alloformation. Farther downdip, most of the thickened pods are caused by filling of channels in the underlying Island Beach Alloformation. The borehole at DSDP Site 612 (figs. 6 and 7) was drilled through the thickest part of the Carteret slope apron, where it penetrated 227.5 m of bathyal, light-gray, biosili- ceous, nannofossil- and foraminifer-bearing chalk and lime- stone, which had been partly silicified during diagenesis by conversion of radiolarian skeletons to silica cements (Wilkens and others, 1987). Downdip at DSDP Sites 605 and 613 (figs. 17, 25, and 28), the Carteret Alloformation thins (214 m at 605; ~142 m at 613), but lithic and paleontologic characteristics are similar to those at Site 612. The depositional regime at Site 613, however, included slumping on the flank of an erosional channel. Broad erosional swaths flank two 200- m-thick submarine fans in the northern Hatteras basin. At DSDP Site 603 (fig. 15), the Carteret Alloformation is only 36 m thick and consists of multicolored radiolarian claystones; silica diagenesis is believed to have been retarded here by the enriched clay content (Van Hinte, Wise, and others, 1987). Calcareous microfossils are present in only trace amounts, probably as a result of deposition below the carbonate compensation depth. At DSDP Site 105, approximately 23 m of multicol- ored zeolitic clay contains ichthyoliths and dinoflagellates of undifferentiated Tertiary age and might represent the Carteret Alloformation (fig. 16). LINDENKOHL ALLOFORMATION 37 Onlap-fill and chaotic-fill facies are abundant in the lower part of the Carteret slope apron (DSDP Site 613; fig. 28). Updip at Sites 612 (figs. 6 and 7) and 605 (fig. 17), seismic reflections are chiefly subparallel and subcontinu- ous or they are lacking; such reflections indicate relatively uniform lithology. An erosional surface equivalent to that at the top of the Carteret Alloformation has been reported widely outside the western North Atlantic (Steele, 1976; McGowran, 1979; Quilty, 1980; Barr and Berggren, 1980; Loutit and Kennett, 1981; Berggren and Aubert, 1983; Aubry, 1985). At Site 612, nannofossil biozonation indicates that the erosional hiatus is about 2 my. long. LINDENKOHL ALLOFORMATION DEFINITION We propose the name Lindenkohl Alloformation for unconformity-bounded outcropping and subsurface beds on the exposed coastal plain (Salisbury embayment), the sub- merged continental shelf and slope (Baltimore Canyon trough), and the continental rise (Hatteras basin) of the Middle Atlantic States (Virginia, Maryland, Delaware, New Jersey), southern New England (Connecticut, Rhode Island, Massachusetts), and New York (fig. 1). The allo- formation is bounded above and below by unconforrnities correlative with those bounding the Lutetian and Bartonian (middle Eocene) strata in this region. The Lindenkohl Alloformation is named after Lindenkohl Canyon, which incises the present continental slope and shelf edge ~160 km southeast of Atlantic City, NJ. (fig. 3). The stratotype is DSDP Site 612 (figs. 6 and 7) on the lower continental slope, ~15 km northeast of Lindenkohl Canyon, at lat 38°49.21’ N., long 72°46.43’ W. At the stratotype, the alloformation is 150.6 m thick and consists of pervasively bioturbated, light-greenish-gray to grayish-yellow-green, biosiliceous, foraminifer— and nannofossil-bearing ooze and chalk or biosiliceous nannofossil-bearing ooze and chalk. BOUNDING UNCONFORMITIES The lower bounding unconformity of the Lindenkohl Alloformation (fig. 24) has been cored at DSDP Site 612 (figs. 6 and 7), 331.90 m below the sea floor (80 cm below the top of section 3, core 37; see Poag and Low, 1987). The unconformity separates middle Eocene light—greenish-gray, coarsely glauconitic, thinly laminated, biosiliceous, foraminifer- and nannofossil-bearing chalk (above) from lower Eocene dark-yellowish—brown, horizontally bur— rowed, biosiliceous, foraminifer- and nannofossil—bearing chalk (below). The lower unconformity can be traced widely throughout the northern part of the Hatteras basin 5 HO *5 Z_ (I) o l20 LINDENKOHL ALLOFORMATION S middle Eocene d Figure 29. Unconformity separating Lindenkohl Alloformation from Baltimore Canyon Alloformation at DSDP Site 612. Uncon- formity is 181.35 m below sea floor and is 119 cm below top of section 5, core 21 (Miller and others, 1991). Hiatus is approxi- mately 6 my. and the Baltimore Canyon trough, including the Salisbury embayment, and generally truncates beds of Paleocene (Island Beach Alloformation) or Late Cretaceous (Six- twelve and Accomac Canyon Alloformations) age. The upper bounding unconformity of the Lindenkohl Alloformation (fig. 29) has been cored at DSDP Site 612 (figs. 6 and 7), 181.35 In below the sea floor (119 cm below the top of section 5, core 21; Miller and others, 1991). The unconformity is an irregular scour surface that sepa- rates middle Eocene medium—gray, biosiliceous, sparsely burrowed, nannofossil-bearing ooze (below) from upper Eocene, dark-greenish-gray, glauconitic clayey sand (above) containing tektite fragments, microtektites, micro- krystites, coesite, stishovite, and shocked rock fragments and mineral grains (Cousin and Thein, 1987; Keller and others, 1987; Thein, 1987; Glass, 1989). The upper bound- ing unconformity can be traced widely throughout the northern part of the Hatteras basin and the Baltimore 38 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN Canyon trough, including the Salisbury embayment, and truncates beds of middle Eocene (Lindenkohl Alloforma- tion) to early Eocene (Carteret Alloformation) age. On seismic-reflection profiles, the bounding uncon- formities of the Lindenkohl Alloformation can be traced throughout the offshore region by means of truncated, onlapping, and downlapping reflections along the contacts (Poag and Schlee, 1984; Poag, 1985a,b, 1987, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Lindenkohl Alloformation extends in the subsur- face continuously from the middle part of the continental rise to ~25 km landward of the Dover Air Force Base well, ~400 km updip in the Salisbury embayment (fig. 30). Along depositional strike, the alloformation extends ~750 km from the Long Island platform (Cape Cod) to the Carolina platform (Cape Hatteras). The alloformation is generally thinner than 100 m in the Salisbury embayment and in the continental-shelf segment of the Baltimore Canyon trough, but it reaches a maximum shelf thickness of >400 m in a large mid-shelf delta off Delaware Bay. Several small slope aprons and submarine fans are present in the Hatteras basin, but most of the upper and middle continental rise contains a layer <100 m thick. In this region, the Lindenkohl Alloformation is equivalent to the uppermost part of seismic unit D1 of Schlee and others (1985); the lower part of seismic unit D2_1 of Schlee and Hinz (1987); the upper part of the upper Oligocene(?) seismic unit and the lower part of the lower and middle Miocene unit of Mountain and Tucholke (1985); the middle Eocene of Poag (1987); and the lower part of the Eocene- Oligocene to upper middle Miocene unit of McMaster and others (1989) (fig. 11). The alloformation is notable for its broad swath of outcrops along the base of the continental slope and a parallel downslope swath (5—20 km wide) where the alloformation is absent (fig. 30). The Lindenkohl Alloformation also appears to be missing in the southeastern comer of the study area, but where present in the Hatteras basin, it is correlative with the upper part of the deep—sea Bermuda Rise Formation and the lower part of the Blake Ridge Formation (fig. 11). In the coastal plain of New Jersey, Delaware, Mary- land, and Virginia, the Lindenkohl Alloformation encom- passes the Shark River and Piney Point Formations. The Lindenkohl Alloformation crops out only along the Pamun— key and James Rivers in Virginia, where it is represented by the Piney Point Formation. The Shark River is an equivalent in the subsurface of New Jersey (Olsson and Wise, 1987). No single Pamunkey River outcrop, however, exhibits the entire lithostratigraphic succession of the Lindenkohl Allo- formation. We have selected the Pamunkey River section described by Ward (1985, p. 73, 100. 74, USGS loc. 26403) as the onshore supplementary reference section for the lower part of the Lindenkohl Alloformation and its lower bounding unconformity (fig. 27). This is the same locality selected as the onshore supplementary reference section for the upper part of the Carteret Alloformation. The sediments of the Lindenkohl Alloformation are best represented, however, on the Pamunkey River at Horseshoe, Hanover County, Va. (Ward, 1985, p. 74, 10c. 83, USGS 100. 26412) (fig. 31). At this locality, the upper part of the alloformation is exposed along with the upper bounding unconformity. We have chosen this locality as the onshore supplementary reference section for the upper part of the Lindenkohl Alloformation and its upper bounding uncon- formity. The upper bounding unconformity here is a deeply burrowed erosional surface that separates the middle Eocene Piney Point Formation (Lindenkohl Alloformation) from the Old Church Formation (upper Oligocene; Babylon Alloformation as designated herein). THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS The middle Eocene was a time of considerable change in the depositional patterns in and near the Baltimore Canyon trough, as relative sea level reached maximum heights for the Cenozoic, and carbonate-enriched sediments of the Lindenkohl Alloformation are widespread. The most notable change is the development of a large (>400 m thick), elongate, middle-shelf delta complex (fig. 30; see Poag and Sevon, 1989; Poag, 1992). The front of this delta complex formed a second (“hinter”) shelf break, marked by a relatively thick, prograded wedge of sediments yielding clinoform reflections along the inshore segments of the dip profiles. The chief source of sediments for this delta appears to have been northwest of the Dover Air Force Base well (Benson and others, 1985). The Lindenkohl sediments presumably were dispersed by a precursor of the Susque- hanna River system (Poag and Sevon, 1989; Poag, 1992), which constructed a thick subaqueous delta complex (chiefly marine sediments where drilled). The preserved delta stretches for 250 km along the Maryland-New Jersey coast and resembles the subaqueous delta of the modern Amazon Shelf (Nittrouer and others, 1986). A secondary, more northerly sediment source, presumably the ancient Hudson River system (Poag and Sevon, 1989; Poag, 1992), built a smaller elongate, lobate delta complex seaward of what is now Long Island. From the hintershelf break (the delta front), the Lin- denkohl Alloformation thins significantly (to <100 m) seaward across a broad foreshelf, before thickening again in small slope aprons (200—500 m thick) that built out in the vicinity of the earlier Late Cretaceous and Paleocene shelf break (figs. 2 and 30). About 60 km southwest of DSDP LINDENKOHL ALLOFORMATION 39 78° 76° 740 I UNDENKOHL x-\ ALLOFORMAHON .»\~ / —— O IOO 200 KILOMETERS O 50 IOO NAUTICAL MILES Aan . V g egg CT \\ \ \ ‘ NV: ‘\ r H\640° ‘ v 'A “.z‘MAAAMArrflW“ ., t owgl‘KV-téne‘fl’ésv "\ "$13 fifiifififigmw it'fi“‘§‘“i ‘ ”3%,3) 3 ‘ _. . r ng , - 'YQ EXPLANATION §§ Alloformation missing or too thin to identify an seismic-reflection profiles -—O.2— Isochron—In seconds (two-way traveltime); contour interval of 0.! sec represents approximately lOOm of thickness. Dashed where approximately located Trackline—For multichannel seismic-reflection profiles. See figure 3 for designations ----- 200 m-"' Bathymetry—ln meters Figure 30. Isochron map of Lindenkohl Alloformation showing principal sediment dispersal routes (heavy arrows) and depocen— ters. Note two large deltas built out on middle continental shelf (hinter shelf); coalescing debris piles form slope aprons. Ancient rivers: H, ancient Hudson River; S, ancient Susquehanna River. Boreholes: AD, Anchor-Dickinson No. 1 well; DA, Dover Air Force Base well; IB, Island Beach No. l borehole; other labeled boreholes identified in text. Onshore reference sections: 1, USGS 100. 26403 on Pamunkey River, Va.; 2, USGS loc. 26412 on Pamunkey River at Horseshoe, Va. See figure 3 for location of DSDP Sites 603 and 105 and Cape Hatteras. 40 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN COVERED PHOENIX CANYON ALLOFORMATION CALVERT FORMATION E ALLOFORMATION E 3 gr CONCRETION BABYL OLD CHURCH ORMATION METERS 01 I PINEY POINT FORMATION LINDENKOHL ALLOFORMATION BED B OF WARD (l984) 0 Figure 31. Onshore supplementary reference section for upper part of Lindenkohl Alloformation, upper part of Babylon Allofor- mation, and unconformity that separates them, exposed at Horse- shoe, on Pamunkey River, Hanover County, Va. (Ward, 1985, p. 74, 10c. 83, USGS loc. 26412). Upper bounding unconformity of Babylon Alloformation also exposed at this locality. See figure 12 for lithologic explanation and figure 30 for location. Site 612, however, an elongate, narrow, erosional swath is present on the outer foreshelf, and another parallel swath was formed about 70 km northeast of Site 612 on the middle to lower continental slope. These erosional swaths appar- ently were scoured by turbidity currents and debris flows that radiated from the deltas. A downslope, ribbed, depo- sitional fabric is obvious along all the strike profiles southeast of the foreshelf edge, where numerous channels and lobate fans protrude onto the continental rise. Strata of the Lindenkohl Alloformation throughout the Baltimore Canyon trough and vicinity are characterized by an enrichment in calcium carbonate, which accumulated in a warm, moist, tropical, maritime climate (Wolfe, 1978; Frederiksen, 1984b). At updip locations in New Jersey, Lindenkohl strata include glauconitic sands and clays char- acterized by inner to middle sublittoral (10—50 In) micro- fossil assemblages (Charletta, 1980). Similar assemblages and lithologies characterize the Lindenkohl Alloformation in Virginia (Ward, 1984). The most carefully studied well in the updip axis of the subaqueous delta is the Dover Air Force Base well (fig. 30; Benson and others, 1985). There the Lindenkohl section consists of 37 m of silty sediments overlain by 74 m of glauconitic quartz sand. Calcareous clay becomes a more significant component in deeper water facies near the delta margin (for example, in the Anchor- Dickinson well). At the Island Beach No. 1 borehole, located 40 km shoreward from the edge of the middle Eocene hintershelf (figs. 2 and 30; Poag, 1985a), the Lindenkohl Alloforma- tion consists of 34 m of sandy, shelly, calcareous clay topped by a 9—m gypsiferous section. At the COST B—2 well, located between two delta lobes on the outer part of the gently sloping middle Eocene foreshelf (fig. 30; Poag, 1985a), the Lindenkohl Allofor- mation consists of 135 m of buff to light-gray, dense, argillaceous micrite containing bathyal (500—600 In) micro- fossil assemblages. Radiolarians are noticeably more abun- dant at this location than updip, and they increase even more at downdip sites. In contrast, at the Shell 272—1 well, located approximately on depositional strike with the B—2 well, but directly in front of the principal lobe of the southern delta, the Lindenkohl Alloformation consists mainly of mudstones (~50 m thick; Poag, 1985a). At the COST B—3 site (figs. 8 and 30), located on the middle Eocene continental slope, the Lindenkohl section consists of 90 m of light-gray to white calcareous claystone and fossiliferous limestone. Rich microfossil assemblages, including abundant radiolarians, indicate bathyal paleo— depths of ~1,000 m. Farther downslope at DSDP Site 612 (figs. 6 and 7), the Lindenkohl section thickens to 151.6 m and changes to light-greenish-gray, biosiliceous, nannofossil-bearing chalk; radiolarian and diatom abundances continue to increase, and terrigenous lithic components drop out. The upper 42 m of the section constitutes a soft ooze, but the BALTIMORE CANYON ALLOFORMATION 41 constituents are the same as those of the indurated lower section. The porcelaneous interval of the diagenetic front makes up the basal 8 m of the Lindenkohl Alloformation (Wilkens and others, 1987). The Lindenkohl Alloformation changes little in com— position downdip at DSDP Sites 605 and 613 (figs. 17 and 28), but it thickens gradually (to 145 and 173 m, respec- tively). Considerably thicker sections (300—400 m) are present in some of the slope-apron deposits (fig. 30). One notable lithologic change is the presence of a thin (2—5 cm) layer of unaltered rhyodacitic ash, 9 m above the base of the Lindenkohl Alloformation at DSDP Site 605 and 37 m above its base at Site 613. Von Rad and Kreuzer (1987) assumed that these ash layers were deposited simulta- neously, but the higher relative stratigraphic position and the 5-m.y. younger K-Ar age of ash at Site 613 are evidence that the two layers represent two different events. Schlee (1977), in fact, reported as many as nine different ash layers in the Eocene and Oligocene sections of JOIDES (Joint Oceanographic Institutions for Deep Earth Sampling) core- holes 3, 4, and 6 on the nearby continental margin of Florida. Presumably wind and (or) surface currents (such as the proto-Gulf Stream) transported the ash to the New Jersey margin from active centers of volcanism in the Caribbean Island Arc. No Lindenkohl strata were identified at DSDP Sites 603 and 105 (figs. 15 and 16). These results confirm the limited deep-sea distribution of the Lindenkohl Alloforma— tion, which pinches out (is truncated) about 200 km from the foreshelf edge. The seismic-reflection characteristics of the Linden- kohl Alloformation indicate that onlap-fill, slope—front fill, and chaotic-fill facies are abundant in the thickened slope aprons. Updip and downdip from these slope aprons, however, broad reflection-free intervals (on multichannel profiles) and parallel, subcontinuous, high-amplitude reflections (on single-channel profiles) are evidence for uniform, low-energy depositional environments. Coring confirmed the depositional environments deduced from seismic-reflection profiles. The Lindenkohl Alloformation is now exposed on the sea floor at the base of the continental slope (for example, between Sites 612 and 605; fig. 30; Robb and others, 1983; Hampson and Robb, 1984; Farre, 1985; Farre and Ryan, 1985, 1987; Poag, 1985a), where it was drilled during DSDP Leg 11 at Site 108 (Hollister, Ewing, and others, 1972). Farther seaward, at DSDP Sites 605, 613, and vicinity (figs. 17 and 28), the upper erosion surface of the Lindenkohl is onlapped by Tertiary and Quaternary sequences of the upper continental rise (Tucholke and Mountain, 1979, 1986', Mountain and Tucholke, 1985; Poag, 1985b), but its precise relation to the deep-sea erosion surface known as A11 is not yet determined (Poag, 1987). A significant positive deflection in the gamma—ray log at DSDP Site 612 is associated with the basal sand of the overlying Baltimore Canyon Alloformation; sparse to mod- erate amounts of glauconite and volcanic glass keep the gamma-ray values consistently higher in the Baltimore Canyon Alloformation section than in the Lindenkohl sec- tion. This gamma-ray characteristic is also seen on the COST B—3 well log (Poag, 1985b), which suggests a similar change in lithology at the Lindenkohl—Baltimore Canyon contact there. Sediments from the B—3 well have not yet been studied in detail (Pollack, 1980), but we can confirm that volcanic glass shards are present within the Baltimore Canyon Alloformation at this site. BALTIMORE CANYON ALLOFORMATION DEFINITION We propose the name Baltimore Canyon Alloforma- tion for unconformity-bounded subsurface beds of the exposed coastal plain (Salisbury embayment) and the sub- merged continental shelf and slope (Baltimore Canyon trough) of the Middle Atlantic States (Virginia, Maryland, Delaware, New Jersey), southern New England (Connect- icut, Rhode Island, Massachusetts), and New York (fig. 1). The alloformation is bounded above and below by uncon- formities correlative with those bounding the base of the Priabonian (upper Eocene) strata and the top of the Rupelian (lower Oligocene) strata in this region. The Baltimore Canyon Alloformation is named after the Baltimore Canyon trough, which underlies the coastal plain and continental shelf and slope of the Middle Atlantic States, southern New England, and New York (fig. 1). The stratotype of the Baltimore Canyon Alloformation is DSDP Site 612 (figs. 6 and 7), on the lower continental slope of the Baltimore Canyon trough, 150 km southeast of Atlantic City, N.J., at lat 38°49.21’ N., long 72°46.43’ W. (fig. 3). At the stratotype, the alloformation is 46 m thick and consists of light-greenish—gray to yellow-green, biosiliceous, perva- sively bioturbated, foraminifer- and nannofossil-bearing ooze and chalk. BOUNDING UNCONFORMITIES The lower bounding unconformity of the Baltimore Canyon Alloformation (fig. 29) has been cored at DSDP Site 612 (figs. 6 and 7), 181.35 m below the sea floor (119 cm below the top of section 5, core 21', Miller and others, 1991). The unconformity is an irregular scour surface that separates upper Eocene dark-greenish-gray, glauconitic clayey sand (above) containing tektite fragments, microtek- tites, microkrystites, coesite, stishovite, and shocked rock fragments and mineral grains from middle Eocene medium— gray, biosiliceous, sparsely burrowed, nannofossil-bearing 42 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN IIO MEY ALLOFORMATION upper Miocene CENTIMETERS W25m.y. K) BALTIMORE CANYON ALLOFORMATION lower Oligocene I20 Figure 32. Unconformity separating Baltimore Canyon Allofor- mation from Mey Alloformation at DSDP Site 612. Unconformity is 135.36 in below sea floor and is 116 cm below top of section 6, core 16 (Poag and Low, 1987). Hiatus is approximately 25 my. ooze (below). The lower bounding unconformity can be traced widely throughout the northern part of the Hatteras basin and the Baltimore Canyon trough, including the Salisbury embayment, where it truncates beds of middle Eocene (Lindenkohl Alloformation) and lower Eocene (Carteret Alloformation) age. The upper bounding unconformity of the Baltimore Canyon Alloformation (fig. 32) has been cored at DSDP Site 612 (figs. 6 and 7), 135.36 m below the sea floor (116 cm below the top of section 6, core 16; see Poag and Low, 1987). The unconformity is a sharply defined scour surface that separates lower Oligocene light-gray microfossil- bearing ooze (below) from upper Miocene dark-gray, well- sorted, coarse, glauconitic, quartzose, turbidite sand (above). The upper bounding unconformity can be traced widely throughout the northern part of the Hatteras basin and the Baltimore Canyon trough, including the Salisbury embayment, where it truncates beds of late Eocene (Balti- more Canyon Alloformation), middle Eocene (Lindenkohl Alloformation), and early Eocene (Carteret Alloformation) age. On seismic-reflection profiles, the bounding uncon- formities of the Baltimore Canyon Alloformation can be traced throughout the Baltimore Canyon trough by means of truncated, overlapping, and downlapping reflections along the contacts (Poag and Schlee, 1984; Poag, 1985a,b, 1987, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Baltimore Canyon Alloformation extends in the subsurface discontinuously from near DSDP Site 612 to landward of the Ohio Oil-Hammond No. 1 well in the Salisbury embayment, ~250 km updip (fig. 33). Along depositional strike, the alloformation extends discontinu- ously along the continental shelf and coastal plain ~450 km between the Long Island platform (northern tip of New Jersey) and the Carolina platform (Cape Hatteras). The principal depocenter is a small bilobate prism <200 m thick, centered about 60 km offshore from Cape May, NJ. The alloformation is missing or too thin to identify on seismic profiles of the rest of the offshore region, except for an elongate wedge (~170 km long) along the continental slope and upper rise (see Poag and Sevon, 1989; Poag, 1992). In this region, the Baltimore Canyon Alloformation is equivalent to the lower third of seismic unit D2 of Schlee and others (1985); the middle part of seismic unit D2_1 of Schlee and Hinz (1987); the middle part of the lower and middle Miocene seismic unit of Mountain and Tucholke ( 1985); the middle part of the Eocene-Oligocene to upper middle Miocene seismic unit of McMaster and others (1989); and the lower part of the deep-sea Blake Ridge Formation (fig. 11). The Baltimore Canyon Alloformation does not crop out in the coastal plain, but it is exposed along the base of the continental slope and in the walls of some submarine canyons. In the subsurface of the coastal plain, the Balti- more Canyon Alloformation encompasses the Chickahom- iny Formation and informally named sedimentary units in Virginia (Exmore and Delmarva beds of Powars and others, 1991, 1992; Poag and others, 1991; Poag, in press) and unnamed equivalents in Maryland and Delaware (Benson, 1990a). In southeastern New Jersey, it is represented by the ACGS Alpha unit and Mays Landing unit of Owens and others (1988), Poore and Bybell (1988), and Miller and others (1990). Because the Baltimore Canyon Alloformation does not crop out in the coastal plain, no exposure is available as a supplementary reference section. The upper bounding unconformity of the Baltimore Canyon Alloformation can be observed, however, in continuous cores taken from BALTIMORE CANYON ALLOFORMATION 43 78° 76° 74° 72° 70°W 42°N l l » l l ‘ i l i ' 7 ‘5) ‘1 l _ .lgfiMA . '. ’ CcAoPDE ? j lRI .1 :33: i NY ,‘ CT 1 £343" m i x . , ‘ ;» ' ,f BALTIMORE CANYON , , ,8 .4 ALLOFORMATION , . . a «- —— 0 [00 200 KILOMETERS ‘ |——-r‘—'—rJ——r—"_—I" 0 so lOO NAUTICAL MILES to L? W PA \ \ / \ / .NJ 2, ., mm 40° IB " zooom’u- of» B‘ \ .o J o.\ o: .‘oo 0° GEL 0°» _ S 6L2 1.600%" 38° 3,4000,” _‘ _ l a, ——————————————————— . CAPE .. . 603 - HATTERAS 3 3 , , " ‘ . t . l 36° EXPLANATION ———0.2— lsochron—ln seconds (two-way traveltime); contour interval of OJ sec represents approximately IOO m of thickness. Dashed where approximately located Trackline—For multichannel seismic-reflection profiles. See figure 3 for designations ----- zoo ,,,.... Bathymetry—ln meters Figure 33. Isochron map of Baltimore Canyon Alloformation DA, Dover Air Force Base well; E, Exmore corehole; IB, Island showing principal sediment dispersal route (heavy arrow) and Beach No. 1 borehole; K, Kiptopeke corehole; L, Lewes, Del., depocenters. Alloformation is missing or too thin to identify on borehole; OH, Ohio Oil-Hammond No. 1 well; other labeled seismic profiles (outside of 0.0 contour) throughout most of the boreholes identified in text. Onshore reference section is Exmore study area. Ancient river: S, ancient Susquehanna River. Bore- corehole. See figure 3 for location of DSDP Site 603 and Cape holes: AC, ACGS—4 corehole; AD, Anchor-Dickinson No. 1 well; Hatteras. 44 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN coreholes near Exmore and Kiptopeke on Cape Charles, Va. (the lower bounding unconformity was not recovered). At these sites (fig. 33), the upper bounding unconformity is a burrowed erosion surface between the lower Oligocene Delmarva beds (below) and the upper Oligocene Old Church Formation (above) (Babylon Alloformation of this report). We have chosen the Exmore corehole (table 1; Poag and others, 1992; Powars and others, 1992) as the onshore supplementary reference section for the Baltimore Canyon Alloformation and its upper bounding unconformity (fig. 34). THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS The Baltimore Canyon Alloformation is much more limited in its distribution than many of the other allostrati- graphic units (fig. 33; see Poag and Sevon, 1989; Poag, 1992). It has been sampled at DSDP Site 612 (figs. 6 and 7), the Anchor-Dickinson No. 1 well, the COST B—2 and B—3 wells (figs. 5 and 8), and ASP (Atlantic Slope Project) borehole 15 (Poag, 1978) and at a few additional boreholes in the Salisbury embayment (fig. 33, Ohio Oil-Hammond No. 1 well, Dover Air Force Base well, ACGS—4 corehole, Lewes, De1., borehole, Exmore corehole, Kiptopeke core- hole; Brown and others, 1972; Ward and Strickland, 1985; Benson, 1990a; Powars and others, 1992; Poag, in press). The alloformation does not crop out in the coastal plain and is missing in much of the subsurface of the Salisbury embayment. The alloformation is thin at most sites (45—65 m at COST B—2 and B—3 and DSDP 612) but thickens in the Anchor-Dickinson well to ~120 In (Poag, 1985a). In the subsurface of Virginia, the Baltimore Canyon Alloforma- tion is represented by the Exmore beds (upper Eocene), the Chickahominy Formation (upper Eocene), and the De]— marva beds (lower Oligocene), and it reaches a thickness as great as 100 m (Cushman and Cederstrom, 1945; RB. Mixon, written commun., 1989; Powars and others, 1991; Poag, in press). The combined thickness of the ACGS Alpha unit and the Mays Landing unit in New Jersey is ~55 In (Owens and others, 1988; Poore and Bybell, 1988; Miller and others, 1990). The alloformation is either missing or too thin to be traced on seismic profiles over much of the upper Eocene continental shelf (figs. 2 and 33). A long, narrow, prograded wedge of Baltimore Canyon strata appears to have created an inner shelf depocenter (~100—200 m thick) seaward of the Anchor-Dickinson and Island Beach wells (fig. 33). Sediments of the Baltimore Canyon Alloformation have not yet been positively identi- fied from the continental rise between DSDP Sites 612 and 603 (fig. 3). Where present in Virginia, the Baltimore Canyon Alloformation contains widely variable lithologies. The lower part (Exmore beds) is an unusual deposit of chaoti- fl CONTINUED 5; E; .. :g o: 320‘ 58 a: m_. -'o -' _l on. d , 325A 330- 335—- — E a —E. LLI 340- E I— _ a: “7—— DJ E _____ 2 ' <3 ___' _ Z _ _l ___‘_- _. - < 2 . I 345— 2 o ---- 1— _ I: ————— Lu — z 2 ‘7‘— O < m _____ ‘ 0 O . _J _ L'- __'__ =‘ 350— w _____ .. E g __:.__ _ 5 o “7,—- 4 g ———.— _. an x ___.__ 355— 2 ___'_ I . _ U _____ _‘ 360— — . 7-7.7" — m5 ‘_-':—-— 0:: -__.___.'_'_ 365- 2° .- — $23 "' L..__' “(gt-.mpr ‘ g3: .'.'.. - i; 22‘“--’.-" ._ ”3 ‘3‘7‘ 22' 370 - CONTINUED '-‘.~'—'§-‘ Figure 34. Stratigraphic column for part of the Exmore core- hole, drilled by the U.S. Geological Survey near Exmore, Acco- mack County, Va. , showing the Baltimore Canyon Alloformation and its upper bounding unconformity (modified from Powars and others, 1992, fig. 18.7). This section is designated as onshore supplementary reference section for Baltimore Canyon Alloforma- tion. Corehole recorded in feet; total depth is 1,396 ft (425.5 m). See figure 12 for lithologic explanation and figure 33 for location. BABYLON ALLOFORMATION 45 cally mixed sedimentary clasts (pebbles, cobbles, and boulders) ranging in age from Early Cretaceous to middle Eocene and enclosed in a glauconitic, sandy matrix of early late Eocene age (Powars and others, 1990, 1991, 1992; Poag and others, 1992; Poag, in press). Their chaotic nature, their content of shocked quartz and tektite(?) glass, and their biostratigraphic equivalence to the microtektite- bearing layer at DSDP Site 612 caused Poag and others (1991, 1992) to conclude that the Exmore beds represent an impact-wave deposit produced by a bolide impact nearby on the New Jersey Continental Shelf. The overlying Chicka- hominy Formation is mainly a deep-water silty clay (con- tains bathyal foraminifers; Poag and others, 1991); the succeeding Delmarva beds are much sandier and contain neritic foraminiferal assemblages (Powars and others, 1992; Poag, in press). In the subsurface of New Jersey, the ACGS Alpha unit consists mainly of brownish silty clay, medium to coarse glauconitic sand, olive-black silty clay, and medium glau- conitic quartz sand (Owens and others, 1988); the Mays Landing unit ranges from massive to laminated, fine, micaceous sand, to dark-greenish-gray, silty clay, to fine to medium glauconitic quartz sand. At the Anchor-Dickinson No. 1 well, the Baltimore Canyon Alloformation consists of mainly glauconitic sand, with minor amounts of silty clay and calcareous clay, containing neritic microfauna. At the Lewes, Del., borehole (Benson, 1990a), the alloformation is mainly a bathyal(?) glauconitic silt. At the COST B—2 and B—3 wells, the alloformation is mainly silty clay of outer neritic to bathyal origin. At DSDP Site 612 (figs. 6 and 7), the 45-m-thick Baltimore Canyon section is princi- pally light-greenish-gray, bathyal, biosiliceous, nannofossil- bearing ooze, similar to the softer upper strata of the Lindenkohl Alloformation, but a ~10-cm- thick zone at its base contains a small amount of glauconite, along with tektite glass, microtektites, microkrystites, and shocked quartz and rock fragments (Glass, 1989). The lower Oligo- cene part of the alloformation at Site 612 and at COST B—3 (as confirmed herein) contains trace amounts of volcanic glass shards. BABYLON ALLOFORMATION DEFINITION We propose the name Babylon Alloformation for unconformity-bounded beds on the submerged continental shelf and slope (Baltimore Canyon trough) and continental rise (Hatteras basin) of the Middle Atlantic States (Virginia, Maryland, Delaware, New Jersey), southern New England (Connecticut, Rhode Island, Massachusetts), and New York and equivalent outcropping and subsurface beds on the exposed coastal plain (Salisbury embayment) (fig. 1). The alloformation is bounded above and below by uncon- formities correlative with those bounding the Chattian (upper Oligocene) strata in this region. The Babylon Allo- formation is named after Babylon Canyon, which incises the present continental slope and shelf edge ~ 130 km south of the eastern tip of Long Island (fig. 3). The stratotype of the Babylon Alloformation is the COST B—3 well (fig. 8) on the upper continental slope, ~150 km southeast of Atlantic City, N.J., and ~97 km southwest of Babylon Canyon, at lat 38°55.0’ N., long 72°46.4’ W. (fig. 3). At the strato- type, the alloformation is 91 In thick and consists of light-olive-gray, glauconitic, microfossiliferous, calcareous clay. BOUNDING UNCONFORMITIES The bounding unconformities of the Babylon Allofor- mation were drilled, but not cored, at the stratotype. They can be discerned between shotpoints 840 and 1250 on seismic-reflection profile 218 (fig. 8), which crosses the stratotype COST B—3 well site. The lower bounding uncon- formity is present at 1.89 sec (two-way traveltime) where profile 218 crosses the COST B—3 site. The unconforrnity truncates reflections from the underlying upper Eocene section (Baltimore Canyon Alloformation). The upper bounding unconforrnity is present at 1.85 sec (two-way traveltime) where profile 218 crosses the COST B—3 site; the unconforrnity is downlapped by reflections from the overlying lower Miocene section (Berkeley Alloformation as designated herein; fig. 8). On other seismic-reflection profiles, the bounding unconformities of the Babylon Alloformation can be traced throughout the offshore region (where present) by means of truncated, onlapping, and downlapping reflections along the contacts (Poag and Schlee, 1984; Poag, 1985a,b, 1987, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Babylon Alloformation extends in the subsurface continuously from ~30 km east of the COST B—3 well to the Haynesville corehole in southeastern Virginia, and possibly to the Dover Air Force Base well (fig. 35). The Babylon Alloformation also appears to be present at one location, DSDP Site 105, on the lower continental rise (fig. 16). Along depositional strike, the alloformation extends continuously along the continental shelf from the Long Island platform (eastern tip of Long Island) ~550 km southwestward toward the Carolina platform (southeast of Chesapeake Bay) (fig. 1). The Babylon Alloformation is thinner than 100 m throughout its extent, except for an elongate outer shelf delta complex seaward of the Middle Atlantic States, where 46 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN 78° 76° 74° 42°N ‘ I J“ Aqv NY BABYLON _ ALLOFORMATION 0 I00 200 KILOMETERS O 50 I00 NAUTICAL MILES i a ‘x‘ CAPE ‘r‘HATTERAS I “Y p EXPLANATION S Alloformation missing or too thin to identify on seismic-reflection profiles—Pattern not shown for large areas outside 00 contour —O.2— Isochron—In seconds (two-way lraveltime); contour interval of OJ sec represents approximately IOOm of thickness. Dashed where approximately located Trackline—For multichannel seismic-reflection profiles. See figure 3 for designations ~~-~~200m---- Balhymetry—ln meters Figure 35. Isochron map of Babylon Alloforrnation showing Haynesville corehole; L, Lewes, De1., borehole; N, Newport principal sediment dispersal routes (heavy arrows) and depocen- News, Va., corehole; other labeled boreholes identified in text. ters. Ancient rivers: D, ancient Delaware River; H, ancient Onshore reference section: 1, USGS 10c. 26412 on Pamunkey Hudson River; S, ancient Susquehanna River. Boreholes: AC, River at Horseshoe, Va. See figure 3 for location of DSDP Site ACGS—4 corehole; DA, Dover Air Force Base well; HA, 105 and Cape Hatteras. BERKELEY ALLOFORMATION 47 its maximum thickness is ~300 m. Seismic profiles indicate that the alloformation is missing or too thin to identify throughout most of the Hatteras basin (see Poag and Sevon, 1989; Poag, 1992). Figure 11 shows how the Babylon Alloformation correlates with units described in other reports. The Babylon Alloformation is sparsely represented in the coastal plain, both in the subsurface and in outcrop. The best microfaunally documented sections are of the Old Church Formation cored near Haynesville and Newport News, Va., which contain moderately to well-developed late Oligocene foraminiferal assemblages (Zone P 22; Poag, 1989, and unpub. data, 1993). Outcropping sections of the Old Church Formation in southeastern Virginia (Pamunkey River outcrops) also have been assigned to the upper Oligocene (or lower Miocene; Edwards, 1984, 1989; Fre- deriksen, 1984a; Ward, 1984; Poag, 1989) on the basis of mollusks, dinoflagellates, sporomorphs, and planktonic foraminifers. Informally named beds in the subsurface of New Jersey (ACGS Beta unit of Owens and others, 1988; Poore and Bybell, 1988) may belong in the Babylon Alloforma- tion. Miller and others (1990) assigned this unit to the upper Oligocene on the basis of four divergent Sr—isotope dates (ranging from 34.5 Ma to 27.6 Ma; early to late Oligocene). Planktonic microfossils are virtually absent from this unit, and the predominant benthic foraminifers (Pseudononion pizzarensis and Caucasina elongata) are characteristic of Miocene strata in other coastal-plain localities (Gibson, 1983; Poag, 1989). Autochthonous late Oligocene foraminiferal assem— blages in rotary cuttings from the Lewes borehole (Benson, 1990a) represent the Babylon Alloformation in southeastern Delaware. In northeastern Delaware, an upper Oligocene foraminiferal assemblage possibly assignable to the Baby- lon Alloformation was reported from the Dover Air Force Base well (Benson and others, 1985). The depositional age of this assemblage is equivocal, however, because it is a mixture of Eocene, Oligocene, and Miocene taxa. We have chosen the type section of the Old Church Formation on the Pamunkey River at Horseshoe, Hanover County, Va. (Ward, 1985, p. 74, 10c. 83, USGS 10c. 26412), as the onshore supplementary reference section for the upper part of the Babylon Alloformation and its lower and upper bounding unconformities (fig. 31). At this reference section, 0.9 m of grayish-olive, clayey sand of the Old Church Formation (Babylon Alloformation) uncon- forrnably overlies the middle Eocene Piney Point Formation (Lindenkohl Alloformation) and is unconformably overlain by the middle Miocene part of the Calvert Formation (part of the Phoenix Canyon Alloformation as defined herein). Both the lower and upper bounding unconformities are deeply burrowed marine erosion surfaces. THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS The Babylon Alloformation, as presently known, is chiefly an upper Oligocene shelf deposit (fig. 35; see Poag and Sevon, 1989; Poag, 1992). Like the middle Eocene Lindenkohl Alloformation, the prograded strata of the Babylon Alloformation created a double shelf. Sediments of the hintershelf are thickest (~300 in) southeast of the present entrance of Delaware Bay. Principal sediment sources appear to have been the same as those that built the Lindenkohl hintershelf. Strata of the Babylon Alloformation extend downdip to within a few hundred meters of DSDP Site 612 before the section is truncated by erosion (figs. 5—7 and 35). The original edge of the Oligocene foreshelf appears to have been completely eroded in the study area, and its former position can only be grossly estimated to have been some— where near the edge of the middle Eocene foreshelf. It is possible that a thin deposit of Babylon strata is present in the northern Hatteras basin (Mountain and Tucholke, 1985; Poag, 1985a), but its presence is not obvious on seismic profiles, and it has not yet been identified by drilling. A thin sedimentary section probably belonging to the Babylon Alloformation was drilled near the outer end of the New Jersey Transect at DSDP Site 105 (fig. 16). There, a 4—m interval in core 105—5 contains noncalcareous, multi- colored, zeolitic clays and silts and an ichthyolith assem- blage of possibly late Oligocene age (Kaneps and others, 1981). BERKELEY ALLOFORMATION DEFINITION We propose the name Berkeley Alloformation for unconformity-bounded subsurface beds of the exposed coastal plain (Salisbury embayment), the submerged conti- nental shelf and slope (Baltimore Canyon trough), and continental rise (Hatteras basin) of the Middle Atlantic States (Virginia, Maryland, Delaware, New Jersey), south- ern New England (Connecticut, Rhode Island, Massachu- setts), and New York (fig. 1). The alloformation is bounded above and below by unconformities correlative with those bounding the Aquitanian and Burdigalian (lower Miocene) strata in this region. The Berkeley Alloformation is named after Berkeley Canyon, which incises the present continen- tal slope and shelf edge ~150 km southeast of Atlantic City, NJ. (fig. 3). The stratotype of the Berkeley Allofor- mation is the COST B—3 well (figs. 3 and 8), 2 km southwest of Berkeley Canyon at lat 38°55.0’ N., long 72°46.4’ W. At the stratotype, the alloformation is ~96 m thick and consists of glauconitic, micaceous, organic- 48 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN matter-rich, silty clay containing thin glauconitic sandstone beds. BOUNDING UNCONFORMITIES The bounding unconformities of the Berkeley Allofor- mation were drilled, but not cored, at the stratotype. The lower bounding unconforrnity is present at 1.85 sec (two- way traveltime) where seismic-reflection profile 218 crosses the stratotype COST B—3 well site (fig. 8, shotpoint 1080). Reflections at the base of the Berkeley Alloforma- tion onlap and downlap the underlying upper Oligocene surface (Babylon Alloformation). The upper bounding unconformity can be seen at 1.80 sec (two-way traveltime) where profile 218 crosses the stratotype COST B—3 well site. Reflections in the upper part of the alloformation are truncated along the unconforrnable contact. On other seismic-reflection profiles, the bounding unconforrnities of the Berkeley Alloformation can be traced throughout the offshore region by means of truncated, onlapping, and downlapping reflections along the contacts (Poag and Schlee, 1984; Poag, 1985a,b, 1987, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Berkeley Alloformation extends in the subsurface nearly continuously from the COST B—3 well to ~30 km northwest of the Dover Air Force Base well, ~300 km updip (fig. 36). Along depositional strike, it extends nearly continuously along the Outer Continental Shelf ~600 km from the Long Island platform (eastern tip of Long Island) to near Cape Hatteras. The alloformation is generally thinner than 100 m in the Salisbury embayment and the inner shelf part of the Baltimore Canyon trough, but it reaches a maximum of >500 m in an elongate delta complex on the middle shelf seaward of New Jersey. The alloformation is missing or too thin to be identified on seismic profiles throughout most of the Hatteras basin (Poag and Sevon, 1989; Poag, 1992), but, where present, it is equivalent to a portion of the upper part of seismic unit D2 of Schlee and others (1985); the upper part of seismic unit D21 of Schlee and Hinz (1987); the upper part of the lower and middle Miocene seismic unit of Mountain and Tucholke (1985); the upper part of the Eocene-Oligocene to upper middle Miocene seismic unit of McMaster and others (1989); and the middle part of the deep-sea Blake Ridge Formation (fig. 11). On the coastal plain of New Jersey, Delaware, Mary- land, and Virginia, the Berkeley Alloformation encom- passes an informally named lithostratigraphic unit (ACGS Beta unit of Owens and others, 1988) below the Calvert Formation, the lower part of the Calvert Formation in some localities, and probably most of the Kirkwood Formation. In Maryland, the Berkeley Alloformation encompasses the Fairhaven Member of the Calvert Formation, which crops out at numerous localities. The best exposures, however, are along the western shore of the Chesapeake Bay in Calvert County, Md. We have chosen the bluffs exposed at Fairhaven Bay, Anne Arundel County, type section for the Fairhaven Member (Shattuck, 1904, p. lxxxvi, sec. II), as the onshore supplementary reference section for the Berke- ley Alloformation (fig. 37). The lower bounding uncon- formity of the Berkeley Alloformation may be observed along a branch of Lyons Creek, Calvert County, Md., where it separates the Fairhaven Member of the Calvert Formation from strata of Eocene age (Shattuck, 1904, sec. 1). The top of the Berkeley Alloformation is not exposed at Fairhaven Bay but can be seen at the high bluffs south of Chesapeake Beach and north of Randle Cliff, also in Calvert County, Md. (Shattuck, 1904, p. lxxxvii, sec. IV; Ward, 1992, 10c. 26). There the upper bounding uncon- formity separates the lower Miocene Fairhaven Member from the middle Miocene Plum Point Marl Member of the Calvert Formation (fig. 38). The Plum Point Marl Member is encompassed by the Phoenix Canyon Alloformation as defined herein. THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS The Berkeley Alloformation is distributed in two widely separated swaths: one in the deep sea near DSDP Site 603, and the other on the continental shelf and coastal plain (see Poag and Sevon, 1989; Poag, 1992). The latter swath extends ~250 km from the shelf edge to ~40 km northwest of the Dover Air Force Base well in Delaware, and ~600 km along strike between the eastern end of Long Island and Cape Hatteras (fig. 36). During the early Miocene, the double-shelf physiog- raphy of the New Jersey margin was maintained (figs. 2 and 36), but the edge of the hintershelf prograded ~40—60 km to the southeast as the Baltimore Canyon trough entered a phase of accelerated terrigenous deposition (Poag and Sevon, 1989; Poag, 1992). The main source of elastic detritus of the Berkeley Alloformation appears to have been north and northwest of the study area (dispersed by the ancient Hudson, Delaware, and Susquehanna Rivers), as the thickest accumulation (>500 m) lies off central New Jersey. The Berkeley Alloformation is represented on the coastal plain by very silty and sandy paralic and inner sublittoral beds. On the inner part of the coastal plain, such as in the Dover Air Force Base well (figs. 5 and 36), the BERKELEY ALLOFORMATION 49 42°N 0 50 |00 NAUTICAL MILES _ EA‘\ WASHINGTON DC 78° . 76° 74° 72° 70°W I i 1“ T | l I S ,_ BERKELEY NY ALLOFORMATION /~.\ _ a IOO zoo KILOME‘I’ERS \‘ EXPLANATION --0.2-— Isochron—In seconds (two-way traveliime); contour interval of OJ sec represents approximately IOOm of thickness. Dashed where approximately located Trockiine—For multichannel seismic-reflection profiles. See figure 3 for designations ----- 200 m---- Bathymetry—ln meters Figure 36. Isochron map of Berkeley Alloformation showing principal sediment dispersal routes (heavy arrows) and depocen- ters. Alloformation is missing or too thin to identify on seismic profiles (outside the 0.0 contour) over most of continental slope and rise. Ancient rivers: D, ancient Delaware River; H, ancient Hudson River; S, ancient Susquehanna River. Boreholes: DA, alloformation becomes increasingly fine grained and enriched with diatoms. Besides its stratotype at the COST B—3 well, the best documentation of the Berkeley Allofor- Dover Air Force Base well; other labeled boreholes identified in text. Onshore reference sections: 1, Fairhaven Bay, Md.; 2, Lyons Creek, Md.; 3, high bluffs between Chesapeake Beach and Randle Cliff, Md. See figure 3 for location of DSDP Site 603 and Cape Hatteras. mation on the early Miocene foreshelf comes from the ASP l4 and 15 coreholes (figs. 4 and 36; Poag 1985a), where it consists of glauconitic, micaceous, silty clays. 50 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN |._ 22 — 00 Z >-— D _Z'— O>-' <[< LUCK 5<2' ZO‘ZLL 20:. Oo ZLIJ 8—: DE -3—1 g I1. 0: 3E: Lu an ”E 5.. 0 Figure 37. Onshore supplementary reference section for Berke- ley Alloformation, exposed at Fairhaven Bay, Anne Arundel County, Md. (Shattuck, 1904, see. II). See figure 12 for lithologic explanation and figure 36 for location. 20 O COVERED PHOENIX CANYON ALLOFORMATION FORMATION PLUM POINT MARL MEMBER BERKELEY ALLOFORMATION SCHOPTANK FORMATION S CALVERT BEACH MEMBER é CALVERT s BOSTON CLIFFS FAIRH V MEMBER DRUMCLIFF . AND ;_-.~_;;_-_.-_-; S'IZLEONARD .-.'-'-.-‘.-,'.'-. MEMBERS Figure 38. Onshore supplementary reference section for upper part of Berkeley Alloformation, lower part of Phoenix Canyon Alloformation, and unconformity that separates them, exposed south of Chesapeake Beach and north of Randle Cliff, Calvert County, Md. (Shattuck, 1904, sec. IV; Ward, 1992, 10c. 26). Subdivisions within units are shown lithologically but are not labeled because they are not the focus of this report. See figure 12 for lithologic explanation and figure 36 for location. PHOENIX CANYON ALLOFORMATION 51 At DSDP Site 603 (figs. 5 and 15), part of a 14-m section of gray, brown, and yellow, silty, sideritic, gas- emitting claystones may belong to the Berkeley Alloforma- tion. This claystone section contains early to middle Mio- cene ichthyoliths in an otherwise nonfossiliferous interval (Van Hinte, Wise, and others, 1987) resting on lower Eocene radiolarian-bearing claystones. Seismic extrapola— tion of this thin claystone section updip across the conti- nental rise shows that it pinches out ~400 km southeast of the base of the continental slope. PHOENIX CANYON ALLOFORMATION DEFINITION We propose the name Phoenix Canyon Alloformation for unconformity-bounded outcropping and subsurface beds on the exposed coastal plain (Salisbury Embayment) and the submerged continental shelf and slope (Baltimore Canyon trough) and continental rise (Hatteras basin) of the Middle Atlantic States (Virginia, Maryland, Delaware, New Jer- sey), southern New England (Connecticut, Rhode Island, Massachusetts), and New York (fig. 1). The alloformation is bounded above and below by unconformities correlative with those bounding the Langhian and Serravalian (middle Miocene) strata in this region. The Phoenix Canyon Allo- formation is named after Phoenix Canyon, which incises the present continental slope and shelf edge ~ 150 km southeast of Atlantic City, NJ. (fig. 3). The stratotype of the Phoenix Canyon Alloformation is DSDP Site 603 (fig. 15) on the lower continental rise, at lat 35°29.66’ N., long 70°01.70' W. At the stratotype, the alloformation is 258.9 m thick and consists of dark-greenish-gray, silty, micaceous, commonly sideritic, organic-matter-rich, turbiditic claystone. BOUNDING UNCONFORMITIES The lower bounding unconformity of the Phoenix Canyon Alloformation has been cored at DSDP Site 603 (Hole 603B; Poag, 1987). The unconformity occurs, how- ever, in a section whose stratification has been disrupted by the coring process, thus obscuring the precise position of the contact (Van Hinte, Wise, and others, 1987). The estimated position is at 928.37 m below the sea floor (1.37 m below the top of section 1, core 12). At this level, a 15-cm gap in the core separates dark-grayish—green clay- stone (below) from grayish-green, silt-rich, micaceous, quartzose claystone (above). On seismic profile Conrad 21 (segment 77, 1700 to 1800 hr), which crosses DSDP Site 603 (fig. 15), the lower bounding unconformity can be seen at 7.19 sec (two-way traveltime), where reflections in the lower part of the Phoenix Canyon Alloformation onlap the upper surface of the underlying lower Miocene beds (Berkeley Alloforma- tion). The upper bounding unconformity of the Phoenix Canyon Alloformation has been cored at DSDP Site 603 (Hole 603), ~669.4 m below the sea floor (top of section 1, core 39; fig. 15; see Poag, 1987; Van Hinte, Wise, and others, 1987). The unconformity separates dark—greenish- gray, mica-rich, silty claystone (below) from dark-greenish- gray, quartz—bearing, silty claystone (above) containing pyritized burrows and siderite nodules. Disturbance of stratification by the coring process obscures the unconform— able contact. On seismic profile Conrad 21 (segment 77, 1700 to 1800 hr), which crosses DSDP Site 603 (fig. 15), the upper bounding unconformity can be seen at 6.79 sec (two-way traveltime), where reflections from the upper part of the alloformation are truncated and onlapped by reflections of the overlying upper Miocene beds. On other seismic-reflection profiles, the bounding unconformities of the Phoenix Canyon Alloformation can be traced throughout the offshore region by means of truncated, onlapping, and downlapping reflections along the contacts (Poag and Schlee, 1984; Poag, 1985a,b, 1987, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Phoenix Canyon Alloformation extends continu- ously from seaward of DSDP Site 603 to ~20 km west of the Dover Air Force Base well, ~750 km updip (fig. 39). Along depositional strike, the alloformation extends contin- uously over the entire study area, ~900 km from the Long Island platform (Cape Cod) to the Carolina platform (Cape Hatteras). The Phoenix Canyon Alloformation is generally thin- ner than 100 m in the Salisbury embayment, but it thickens dramatically to >1 ,300 m in an enormous complex of deltas on the Miocene outer continental shelf. The alloformation has been eroded along much of the continental slope, but, in the northern Hatteras basin, it comprises large submarine fans and contourite drifts, which reach thicknesses of >1,600 m (McMaster and others, 1989; Poag and Sevon, 1989; Poag, 1992). In the outer part of the Baltimore Canyon trough and in the Hatteras basin, the Phoenix Canyon Alloformation is correlative with the uppermost part of seismic unit D2 of Schlee and others (1985); the uppermost part of seismic unit D21 and the lower half of seismic unit D 2.2 of Schlee and Hinz (1987); the uppermost part of the lower and middle Miocene seismic unit and the lower third of the upper Miocene(?) unit of Mountain and Tucholke (1985); the middle Miocene and “not known” 52 ALLOSTRATIGRAPHY OF THE US MIDDLE ATLANTIC CONTINENTAL MARGIN 78° 76° 74° 72° 70°W 42°N ’ I k I I ; I r ! II NCAPE I>J I I. » " ' . ,7 y con I) , .RI, ‘\ NY I CT PHOENIX CANYON x, I ALLOFORMAWON L”\\ o IOO 200 KILOME'I'ERS o 50 IOO NAUTICAL MILES ‘l _ Nu {(SI ‘- CI ‘40 ("7 "’ I ’) "a M " ' / WQKL MD 4%??{2/53- - "Qt-VIN ,1 /\ WASHINGTON DC 7 7 ‘ ‘ ‘4); \, \ I ’/ I 7..“ \1 l \ /"‘~ -.. \ I .. II L/ i 4’ , €Wflé‘» LIA , («ff Ir ma" ‘3: A -.«4II///,/é2g- . wEEEE. 25-2LL2E' 0:23: _l§H- - _| .CE‘ <5“? WARM (I) LL _ LL. ‘11 our m _ 22 Cu ‘52. O 20— w; W _ 2 . 91' _ l—g g: LIJ .1 0:: O LLO 2 a: ‘ 9 ‘2‘ 1— x0. l5-5. —1I— " <2 00' D. ‘ 2. D. _J. O D. Figure 40. Onshore supplementary reference section for upper part of Phoenix Canyon Alloformation and its upper bounding unconformity, exposed south of Parker Creek, Calvert County, Md. (Shattuck, 1904, sec. X; Ward, 1992, loc. 18). Subdivisions within units are shown lithologically but are not labeled because they are not the focus of this report. See figure 12 for lithologic explanation and figure 39 for location. 53 54 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN deposition in the Baltimore Canyon trough (see Poag and Sevon, 1989; Poag, 1992). Presumably, deep weathering of humic subtropical soils (Frederiksen, 1984b) and tectonic uplift of the central Appalachian Highlands (Hack, 1982; Poag and Sevon, 1989; Poag, 1992) contributed to this rapid accumulation. The main shelf depocenter of the middle Miocene, located off the present mouth of Delaware Bay, collected more than 1,300 In of terrigenous detritus assigned to the Phoenix Canyon Alloformation (figs. 2 and 39). The chief sources for these terrigenous strata appear to have been the Adirondacks and central Appalachian High- lands (Poag and Sevon, 1989; Poag, 1992). The Phoenix Canyon Alloformation of the continental shelf forms the bulk of Schlee’s (1981) prograded Unit G. Garrison (1970), writing before borehole data were available, speculated that this wedge prograded during the Oligocene. Several major pulses of seaward progradation took place during the middle Miocene, as shown by the presence of discrete sets of prograding reflections on the shelf segments of the dip profiles (Greenlee and Moore, 1988). The Phoenix Canyon Alloformation thins to the north- east and southwest and shoreward from the outer shelf depocenter, and its slope apron has been deeply incised by shelf-edge submarine canyons that developed during the Pleistocene (fig. 39). By the end of the middle Miocene, the hintershelf edge had moved seaward ~30—60 km from its early Miocene position and had formed the relatively steep slope face that is the foundation of today’s continental slope. At this time, therefore, the New Jersey margin was again characterized by a single shelf break (fig. 2). The Phoenix Canyon Alloformation has been truncated by erosion along much of the lower continental slope, where it borders the submarine outcrop belt of the Lindenkohl Alloformation (diagonal-line pattern on fig. 39). Presum- ably, Phoenix Canyon strata originally covered this belt and joined the upper rise prism as they presently do along the Long Island platform. Three unnamed allomembers can be distinguished within the Phoenix Canyon Alloformation (Poag, 1987). The older two allomembers can be traced with confidence all the way to Site 603 along seismic profile Conrad 21 (fig. 15), where microfossils document their middle Miocene age. The oldest allomember reaches DSDP Site 105 (fig. 16), but the middle allomember does not. The youngest allomember is limited to a small area southwest of the upper rise drill sites (DSDP Sites 604, 605, 613; figs. 4 and 39) and has not yet been sampled. In composite distribution, these three allomembers are thickest (1,000—1,600 m) in a submarine fan complex southwest of the shelf-edge depo- center (fig. 39); they thin northeastward in concert with the shelf sequences of the Phoenix Canyon Alloformation. They also thin basinward in the direction of DSDP Site 603, where a 258.9—m section was cored (fig. 15). The down- slope ribbed fabric, characteristic of older alloformations of the upper rise prism, was maintained and intensified during deposition of the Phoenix Canyon Alloformation, as turbid- ity currents and debris flows repeatedly cut and filled downslope channels and extended multilobed submarine fans across the continental rise (fig. 39). The Phoenix Canyon Alloformation is noted on the coastal plain for its content of quartzose, shelly, diatoma- ceous, sandy beds and gray-green clay (Owens and Minard, 1979; Ward and Strickland, 1985). Paleocurrent directions derived from extensive crossbedding in the fluviatile sands (Owens and Minard, 1979) indicate that a major middle Miocene drainage system (perhaps the ancient Schuylkill River) paralleled the present Delaware River southwestward across New Jersey and turned sharply eastward directly toward the principal outer shelf depocenter of the Phoenix Canyon Alloformation (fig. 39). In the Island Beach well (fig. 39), 100 m of glauco- nitic, micaceous, shelly, medium to coarse, quartzose sand and several beds of gray, micaceous, lignitic, silty clay represent the Phoenix Canyon Alloformation (Poag, 1985a). Most samples are barren of microfossils, but diatoms and a few middle Miocene radiolarians have been identified. Paralic and inner and middle sublittoral paleo- environments are inferred from the lithofacies and biofacies of these strata. At the COST B—2 well (Poag, 1985a, 1987), along the northeast margin of the depocenter, the Phoenix Canyon Alloformation thickens to 600 In. Here silty, micaceous, organic-matter-rich sands, sandy silts, and silty clays con- tain abundant diatoms. Foraminifers are sparse and poorly preserved, and radiolarians are few. Middle sublittoral paleoenvironments are inferred from these constituents. Three AMCOR coreholes (6009, 6010, 6011; Poag, 1985a) penetrated part of the Phoenix Canyon Alloformation within 100 km of the COST B—2 well, revealing similar lithofacies and microfaunal assemblages. At the COST B—3 well, the Phoenix Canyon section thins to 200 m on the lower part of the middle Miocene continental slope (fig. 8). Glauconitic, micaceous, organic- matter-rich, silty clays dominate this site and contain lower bathyal (1,000—1,500 m) microfossil assemblages; radiolar- ians and diatoms are especially abundant constituents. At nearby ASP borehole 14, 240 m of similar strata were cored, and an abbreviated 24—m section was sampled at ASP borehole 15 (Poag, 1985a). The Phoenix Canyon Allofor- mation has been completely removed from DSDP Site 612 (figs. 6 and 7) and Site 605 (fig. 17) by local downslope channeling, but seismic-reflection profiles show that the unit is present downdip from Site 613 (fig. 28), which occupies an interchannel ridge. Within the upper rise prism, seismic facies of the Phoenix Canyon Alloformation include onlap and chaotic fill, which are especially common near the base of the deep MEY ALLOFORMATION 55 downslope channels. Several mounded sedimentary sec- tions represent submarine fan deposits. At DSDP Site 603 (fig. 15), the Phoenix Canyon Alloformation stratotype consists of 258.9 m of dark- greenish-gray, silty, micaceous, commonly sideritic clay- stone and is the second thickest alloformation cored at Site 603. Foraminifers are sparse or missing throughout this section, but nannofossils are common, especially in the upper half of the section, and radiolarians are abundant in the lower two-thirds. Siliciclastic turbidites characterize this site, and the emission of gas from many of the cores results from relatively abundant terrigenous organic matter (as much as 1.32 percent total organic carbon). Phoenix Canyon strata of the continental shelf and slope also are enriched in organic matter (both marine and terrigenous). Poag (1985a) and Palmer (1986) concluded that upwelling combined with the accumulation of organic- matter-rich deltaic sediments created high biologic produc- tivity in the coastal waters in the middle Miocene (see also Snyder, 1982; Riggs, 1984), which accounts for the abun- dance of diatoms and radiolarians in the shelf sequences. The contact between the Phoenix Canyon Alloforma- tion and overlying upper Miocene sections has not been cored on the continental shelf, slope, and upper continental rise region off New Jersey, but seismic-reflection profiles (figs. 8, 15, and 17) indicate that it is a widespread erosional surface. The uppermost part of the Phoenix Canyon Alloformation is missing at the most complete stratigraphic sections in Virginia and Maryland (Ward and Strickland, 1985 ; Olsson and others, 1987). An even longer hiatus seems to be represented in the subsurface of New Jersey and parts of Delaware, where Pleistocene strata of the Hudson Canyon Alloformation rest on the upper surface of the Phoenix Canyon Formation in many places (Owens and Minard, 1979; Benson and others, 1985; Ward and Strickland, 1985). The paralic nature of many of the middle Miocene and younger formations of the coastal plain, however, reduces the accuracy of fossil dating techniques so that most age relations (and the duration of hiatuses) are imprecisely known. The most severe erosion on the upper surface of the Phoenix Canyon Alloformation took place on the continen- tal slope, as expressed by abrupt truncation of seismic reflections along all the dip profiles (for example, see figs. 8 and 28). Clearly, large volumes of sediment were removed from what is now the submarine outcrop belt of the Lindenkohl Alloformation (middle Eocene) and transferred to the upper rise wedge by downslope gravity flows. The Gemini fault system (fig. 2), which presumably periodically triggered downslope mass movement (Poag, 1987), appears to have become dormant during the late middle Miocene, as seismic reflections are offset along the fault traces only about halfway up through the thick Phoenix Canyon section (fig. 8). MEY ALLOFORMATION DEFINITION We propose the name Mey Alloformation for unconformity-bounded outcropping and subsurface beds on the exposed coastal plain (Salisbury embayment) and the submerged continental shelf and slope (Baltimore Canyon trough) and continental rise (Hatteras basin) of the Middle Atlantic States (Virginia, Maryland, Delaware, New Jer- sey), southern New England (Connecticut, Rhode Island, Massachusetts), and New York (fig. 1). The alloformation is bounded above and below by unconformities correlative with those bounding the Tortonian and Messinian (upper Miocene) strata in this region. The Mey Alloformation is named after Mey Canyon, which incises the present conti- nental slope and shelf edge ~ 150 km southeast of Atlantic City, NJ . (fig. 3). The stratotype of the Mey Alloformation is DSDP Site 603 (fig. 15), on the lower continental rise ~420 km southeast of Mey Canyon, at lat 35°29.66’ N., long 70°01.70' W. At the stratotype, the Mey Alloforma- tion is 341.8 m thick and consists of dark-greenish-gray, micaceous, quartzose, sideritic claystone. BOUNDING UNCONFORMITIES The lower bounding unconformity of the Mey Allofor- mation has been cored at Site 603 (fig. 15), ~669.4 m below the sea floor (top of section 1, core 39; Poag, 1987; Van Hinte, Wise, and others, 1987). The unconformity separates dark-greenish-gray, mica-rich, silty claystone (below) from dark-greenish-gray, quartz-bearing, silty clay- stone (above) containing pyritized burrows and siderite nodules. Disturbances of stratification by the coring process obscure the unconformable contact. The contact is excep- tionally well preserved, however, at DSDP Site 612 (fig. 32; see Poag and Low, 1987). There, dark-olive-gray, homogeneous mud of the Mey Alloformation is separated from light-gray microfossil-bearing ooze of the Baltimore Canyon Alloformation by a 5-cm section of dark-gray, well-sorted, coarse, quartzose, turbidite sand. The lower bounding unconformity can be seen on seismic profile Conrad 21 (segment 77), which crosses DSDP Site 603 (fig. 15). The unconformity is expressed between the 1700-hr and 1800—hr positions on this profile at 6.79 sec (two—way traveltime). Seismic reflections from the bottom part of the Mey Alloformation onlap and downlap the underlying unconformable surface of the Phoenix Can- yon Alloformation at this locality. The upper bounding unconformity of the Mey Allofor- mation has been cored at Site 603 (Hole 603C), ~327.6 In below the sea floor (core catcher of core 36; fig. 15; Poag, 1987; Van Hinte, Wise, and others, 1987). The unconform- ity separates dark-gray to greenish-gray, nannofossil-rich, 56 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN ' —30 Z _ Q l— _ <1 _ 2 m _ 0 LI. _ O , __1 g . — —l a) _ <[ o O — Z Z O Q. _ >_ 40 Z —. <1: 0 _ 0') _ E _ O |-— _ _ (I) 05 l E W - - ; _ m.y. l— _ Lu .E E «a A - e C _ O :1 W _ 2 Q _ |_ g _ CD _ 0: S O o _. LL 0 i O '_ ' — _l E _l a — <1: 8 _ 1:: 3’ —60 2 .. 'vvvv‘ — a 8 _ 8 8 _ gs E _ Figure 41. Unconformity separating Mey Alloformation from Toms Canyon Alloformation at DSDP Site 604. Unconforrnity is 238.97 In below sea floor and is 47 cm below the top of section 2, core 26 (Poag, 1985b). Hiatus is approximately 0.5—1.0 m.y. sideritic, pyrite-bearing claystone (below) from dark- greenish-gray quartz- and mica-bearing claystone (above). The upper bounding unconformity is more sharply expressed at DSDP Site 604 (figs. 41 and 42; see Poag and Low, 1987). At Site 604, the Mey Alloformation consists of brownish-gray conglomerates, which are separated by a sharp scour surface from dark-olive-green, biosiliceous, glauconitic claystone of the Toms Canyon Alloformation. The upper bounding unconformity may be seen between the 1700-hr and 1800-hr marks on seismic profile Conrad 21 (segment 77) at 6.36 sec (two-way traveltime), where it truncates reflectors in the top part of the Mey Alloformation (fig. 15). On other seismic-reflection profiles, the bounding unconformities of the Mey Alloformation can be traced throughout the offshore area by means of truncated, onlap- ping, and downlapping reflections along the contacts (Poag and Schlee, 1984; Poag, 1985a,b, 1987, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Mey Alloformation extends continuously in the subsurface from the vicinity of DSDP Site 603 to ~750 km updip in the Salisbury embayment (fig. 43), where it crops out in the coastal plain. Along depositional strike, it extends continuously ~900 km along the margin from the Long Island platform (Cape Cod) to the Carolina platform (Cape Hatteras). The Mey Alloformation is thinner than 100 In in most of the Salisbury embayment, but it reaches 100—300 In along the edge of the upper Miocene continental shelf (outer part of the Baltimore Canyon trough) between the present Cape Charles, Va., and Cape May, NJ. (Andres, 1986; Benson, 1990a), and thickens to as much as 300—500 m in several small shelf-edge depocenters. The alloformation is missing in a broad swath along most of the continental slope but reaches its maximum thickness of >800 m on the lower continental rise (Mountain and Tucholke, 1985; Poag and Sevon, 1989; Poag, 1992). In the northern Hatteras basin, the alloformation is equivalent to the lower third of seismic unit D3 of Schlee and others (1985); the upper half of seismic unit D2_2 of Schlee and Hinz (1987); the upper two- thirds of the upper Miocene(?) seismic unit of Mountain and Tucholke (1985); the upper Miocene seismic unit of Poag (1987); seismic sequence 4 of Tucholke and Laine (1982); the lower part of the middle transparent subunit and of the lentil subunit of the layered rise seismic unit of O’Leary (1988); the lower two-thirds of seismic unit SW of Danforth and Schwab (1990); seismic unit T2 of Locker and Laine (1992); and some of the upper part of the deep-sea Blake Ridge Formation (fig. 11). On the coastal plain of Virginia, Maryland, Delaware, and New Jersey, the Mey Alloformation encompasses the St. Marys Formation, Eastover Formation, and Manokin formation of Andres (1986); perhaps the Bethany formation of Andres (1986) and the lower part of the Beaverdam MEY ALLOFORMATION 57 NE SW weom Isoom lelsom DSDP 6 (0.3 km NW) CROSS I76 CROSS 25 3.2 ‘ 3.4— , TWO-WAY TRAVELTIME (SECONDS) I I . t‘. i I ~. I VERTICAL EXAGGERATION X|9 O 5 KILOMETERS |_J_._.L_;_L__J DSDP SITE 604 00/750 SECTION (D ® © @© 53 R HOLOCENE AND -_-~_~' Z: UPPER A MEMBER 3; LLO PLEISTOCENE 5% 75 gg '?w? '?W'?w’? ' '00 E A .. :4 LOWER LOWER ’— ALLOMEMBER PLEISTOCENE ..... § I "'_"_' ’i TOMS CANYON PLIOCENE .. .. 200 E ALLOFOR MATION MEY ALLOFORMATION UPPER MIOCENE ------ U/VCO/PED SEW/ON MEY UPPER ALLOFORMATION MIOCENE PHOENIX CANYON ALLOFORMATION IMIDD LE ALLOMEMBER) MIDDLE MIOCENE L I NDENKOHL ALLOFORMATION MIDDLE EOCENE CARTERET ALLOFORMATION LOWER EOCENE Figure 42. Stratigraphic section at DSDP Site 604 and extrapolation along strike segment of single-channel seismic—reflection profile 170 (see fig. 4 for profile location). Note deep channels cut into Carteret and Lindenkohl Alloformations. See figure 6 for explanation of geology, profile reference points, and columns 1—5. Formation (Groot and others, 1990); and, possibly, part of the Pensauken Formation. The St. Marys Formation con- sists of three members whose coastal-plain depocenters migrated progressively farther southward through late Mio- cene time (Ward, 1984; Ward and Strickland, 1985). The (lower) Conoy Member is confined mostly to southern Maryland. The (middle) Little Cove Point member of Ward (1984) is also present in southeastern Maryland, whereas the (upper) Windmill Point member of Ward (1984) extends from southern Maryland into northeastern Virginia. The Conoy Member can best be seen south of Flag Pond, Calvert County, Md. (Shattuck, 1904, p. xc, sec. XIV; Ward, 1992, 10c. 17). We have selected the Flag Pond exposure as the onshore supplementary reference section for the lower part of the Mey Alloformation and its lower bounding unconformity (fig. 44). There the lower bounding unconformity separates the middle Miocene Boston Cliffs Member of the Choptank Formation (upper part of Phoenix Canyon Alloformation) from the upper Miocene Conoy Member of the St. Marys Formation (lower part of Mey Alloformation). The Little Cove Point member of Ward (1984) is best exposed just south of Little Cove Point (Shattuck, 1904, p. xci, sec. XV). The Windmill Point member of Ward (1984) is exposed at Windmill Point on the St. Marys River, Md., but it is best seen across the river from Windmill Point, at Chancellor Point (Shattuck, 1907, p. 80, sec. 11; Ward, 1992, 10c. 13). The areal extent of the Eastover Formation includes the coastal plain of Virginia, the southeastern part of Maryland, and northeastern North Carolina. The coastal-plain depo- 58 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN 42°N 78° I 76° 74° 720 I _ 70°w ' -.' ' i ' i ’ ' " as I NY ,‘ MEY . ALLOFORMATION /\_\ — 0 I00 200 KILOMETERS \. 0 50 IOO NAUTICAL MILES [M91 fi \ Jil I NW \\\~\\\»~\\§\« \‘V‘v‘ “ I 4 as EXPLANATION 36° Alloformation missing or too thin to identify on seismic-reflection profiles —0.2-— Isochron—In seconds (two-way traveltime); contour interval of 0.! sec represents approximately lOOm of thickness. Dashed where approximately located Trackline—For multichannel seismic-reflection profiles. See figure 3 for designations ----- 200 m---- Bathymetry—ln meters Figure 43. Isochron map of Mey Alloformation showing prin- cipal sediment dispersal routes (heavy arrows) and depocenters. Ancient rivers: D, ancient Delaware River; H, ancient Hudson River; S, ancient Susquehanna River. Boreholes: E, Exmore center of the Eastover is in central Virginia, where the formation is 43 m thick in the Exmore corehole (Powars and others, 1992). The (lower) Claremont Manor Member of corehole; other labeled boreholes identified in text. CD, Chesa— peake drift. Onshore reference sections: 1, Flag Pond, Md.; 2, Claremont, Va. Other onshore exposure: C, Cobham Wharf, Va. See figure 3 for location of DSDP Site 603 and Cape Hatteras. the Eastover is well exposed in the Vicinity of Claremont, on the south bank of the James River, Surry County, Va. (Ward and Blackwelder, 1980, p. 15, 100. 42; Ward, 1992, MEY ALLOFORMATION 59 loc. 7). The (upper) Cobham Bay Member of the Eastover is also present at the Claremont locality but is best exposed in its type area at Cobham Wharf, Surry County, Va. (Ward and Blackwelder, 1980, p. 22, 100. 28). We have chosen the Claremont locality as the onshore supplementary refer- ence section for the upper part of the Mey Alloformation and its upper bounding unconformity (fig. 45). There the upper bounding unconformity separates the upper Miocene Cobham Bay Member of the Eastover Formation (upper part of the Mey Alloformation) from the lower Pliocene Sunken Meadow Member of the Yorktown Formation (lower part of the Toms Canyon Alloformation as defined herein). THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS The late Miocene was a time when deep-water depo- sition dominated the middle Atlantic margin, as the shelf break migrated still farther seaward than its middle Miocene position, and the principal depocenters were established on the continental rise (400-800 m thickness; figs. 2 and 43; see Poag and Sevon, 1989; Poag, 1992). Shelf deposition of the Mey Alloformation was relatively sparse (generally <100 111), except at the shelf edge. In the northern Hatteras basin, the main depocenter for Mey sediments shifted northeastward relative to that of the Phoenix Canyon Alloformation (fig. 43); maximum thick- ness (>800 m) accumulated on the middle continental rise. There vigorous longslope bottom currents swept the sedi- ments into the elongate, crescentic, contourite mound known as the Chesapeake drift (Tucholke and Laine, 1982; Mountain and Tucholke, 1985; Tucholke and Mountain, 1986; Poag and Sevon, 1989; Poag, 1992). The upper and middle continental rise are crossed by numerous, broad to narrow, downslope channels filled with chaotic seismic facies of the Mey Alloformation. At DSDP Site 604 on the upper rise (fig. 42), the upper part of the Mey channel fill yielded coarse conglomeratic sands con— taining large quartz pebbles, igneous and metamorphic clasts, and white chunks of reworked Eocene chalk (Poag, 1985b; Van Hinte, Wise and others, 1987). DSDP Site 613 (fig. 28) is located over a late Miocene interchannel ridge, where the Mey section is much thinner than at Site 604, but even there the strata of the Mey Alloformation are coarse to fine, glauconitic, quartzose sands and conglomeratic sands. Channel-fill deposits were recovered from the Mey Alloformation also at DSDP Site 612 (figs. 6 and 7). There the sediments are finer grained, chiefly dark-gray, mica- ceous mud, but chert pebbles, glauconitic quartz sand, and vertebrate fossils are also present. Sediments of the Mey Alloformation have not been documented from any other drill site on the New Jersey margin. Although several exploration wells and the COST B—2 and B—3 (fig. 8) wells 4 4o - ‘22 '3'- oo 2 _ >“— D 2'- o>_ _ _l—0:¢ 2—a }_ VWVNQN “J g 2 a > : I < E O 2 2" _ O Q " l— 2 <3- 2 500 m 02 2 w. 3 2 mo __j 0:0. <. _ 02' >- 5 . a TOMS CANYON ALLOFORMATION upper Pliocene 80 Figure 47. Unconformity separating Toms Canyon Alloforma- tion from Hudson Canyon Alloformation at DSDP Site 613. Unconformity is 186.6 m below sea floor and is 73 cm below top of section 3, core 11 (Poag, 1985b). Hiatus is <0.5 m.y. of section 3, core 5; Poag and Low, 1987). The unconform- ity is a concave scour surface that separates an upper Pliocene section of homogeneous, dark-gray mud from an upper Pleistocene section of coarse, dark-green to black, glauconitic sand, mixed with clasts of the underlying dark-gray mud. The upper bounding unconformity is expressed on seismic-reflection profile 69 (Poag, 1987) at 1.92 sec (two-way traveltime) where it crosses DSDP Site 612 (fig. 6). Reflections in the upper part of the Toms Canyon Alloformation are truncated by the upper bounding unconformity and are downlapped by reflections in the lower part of the overlying Pleistocene section (Hudson Canyon Alloformation as described herein). The upper bounding unconformity was also cored at DSDP Site 613 (fig. 47) at 186.6 m below the sea floor (73 cm below the top of section 3, core 11). At that location, a sharp lithologic change separates dusky-yellow-green, homogeneous, unbedded, diatomaceous, nannofossil- 62 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN bearing mud of the Toms Canyon Alloformation from overlying greenish-gray, calcareous, glauconitic mud of the Hudson Canyon Alloformation (as defined herein). On other seismic-reflection profiles, the bounding unconformities of the Toms Canyon Alloformation can be traced throughout the offshore area by means of truncated, onlapping, and downlapping reflections along the contacts (Poag and Schlee, 1984; Poag, 1985a,b, 1987, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Toms Canyon Alloformation extends continuously in the subsurface from DSDP Site 105 to the inner edge of the coastal plain in southeastern Virginia (~750 km updip), and to the middle of the coastal plain in Delaware (Groot and others, 1990), except for a swath (10—60 km wide, ~650 km long) along the continental slope, where the alloformation is missing (fig. 48). In the northern Hatteras basin, the alloformation forms the upper part of the Ches- apeake drift (Mountain and Tucholke, 1985). Along depo- sitional strike, the alloformation extends continuously ~900 km from the Long Island platform (Cape Cod) to the inner coastal plain of North Carolina. The Toms Canyon Alloformation is missing or is < 100 m thick on the northern half of the coastal plain and most of the continental shelf, except for a narrow wedge at the New Jersey shelf edge, which reaches ~400 In in thickness. Depocenters in the Hatteras basin, however, are 600—800 m thick (Poag and Sevon, 1989; Poag, 1992). In the northern Hatteras basin, the Toms Canyon Alloforma- tion is correlative with the middle third of seismic unit D3 of Schlee and others (1985); seismic unit D2.3 of Schlee and Hinz (1987); the lower half of the Pleistocene seismic unit of Mountain and Tucholke (1985); the lower two-thirds of seismic sequence 5 of Tucholke and Laine (1982); the upper part of the middle transparent subunit and of the lentil subunit of the layered rise seismic unit of O’Leary (1988); the upper third of seismic unit SW of Danforth and Schwab (1990); the lower half of seismic unit T3 of Locker and Laine (1992); and some of the upper part of the deep-sea Blake Ridge Formation (fig. 11). On the coastal plain of Virginia, the Toms Canyon Alloformation encompasses the Bacons Castle, Yorktown, and Chowan River Formations and the Moorings unit of Oaks and Coch (1973). Marginal—marine equivalents of these formations are also present in southeastern Maryland. In Delaware, the Toms Canyon Alloformation comprises the upper part of the Beaverdam Sand and the lower part of the Omar Formation and, perhaps, the lower part of the Beaverdam Sand and the Bethany formation of Andres (1986) (Groot and others, 1990). The Yorktown Formation consists of four members, which were deposited during three separate marine trans- gressions (Ward, 1984). The (lower) Sunken Meadow Member is exposed in numerous sections, but the best exposure is its type locality, just east of Claremont, Surry County, Va. (fig. 48; Ward and Blackwelder, 1980, p. 15, loc. 42; Ward, 1992, 10c. 7). We have chosen this locality as the onshore supplementary reference section for the lower part of the Toms Canyon Alloformation and its lower bounding unconformity (fig. 45). There the lower bounding unconformity separates the upper Miocene Cobham Bay Member of the Eastover Formation from the lower Pliocene Sunken Meadow Member of the Yorktown Formation. The Rushmere Member, Morgarts Beach Member, and Moore House Member of the Yorktown are excellently exposed in the bluffs of Burwell Bay, just east of Rushmere, Isle of Wight County, Va. (fig. 48; Ward and Blackwelder, 1980, p. 37, 10c. 61). The Chowan River Formation (containing two mem- bers) is present in southeastern Virginia but is best exposed in bluffs along the western bank of the Chowan River in Bertie County, NC, extending from Colerain Landing to Edenhouse Landing. We have chosen the outcrop at Cole- rain Landing, which exposes both members (Blackwelder, 1981, fig. 2), as the onshore supplementary reference section for the upper part of the Toms Canyon Alloforma- tion and its upper bounding unconformity. There the upper bounding unconformity separates the upper Pliocene Chowan River Formation (upper part of Toms Canyon Alloformation) from unnamed Quaternary strata that con- stitute part of the Hudson Canyon Alloformation, as defined herein (fig. 49). THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS During the Pliocene, shelf deposition was concentrated even farther seaward than during the late Miocene (fig. 48). Accumulation rates slowed (Poag and Sevon, 1989; Poag, 1992) and maritime climates cooled (Frederiksen, 1984b). The main depocenter for the Toms Canyon Alloformation (800—900 m) was in the northern Hatteras basin, while a narrow, relatively thin, prograded wedge (100—300 m) formed at the shelf break seaward of New Jersey. On the inner and middle continental shelf north of Cape Charles, Va., Toms Canyon strata are missing or are too thin to identify on most multichannel seismic profiles. About 210 km northeast of DSDP Site 612, the Toms Canyon section thickens to >600 m in an upper rise lobe, whose terrigenous source was the New England Appalachian Highlands (fig. 1) (Poag and Sevon, 1989; Poag, 1992). A second major depocenter on the continental rise (800—900 m thick) is present 150 km southwest of DSDP Site 612, indicating a detrital source to the northwest (fig. 1, central Appalachian Highlands). TOMS CANYON ALLOFORMATION 63 78° 76° . 74° 72° “(SW 42%; l I k I l I I .1 CAPE 1: . coo "I, I TOMS CANYON ALLOFORMATION EM — o ICC 200 KILOME/TERS \‘ o 50 I00 NAUTICAL MILES {a \___‘v 09 0- .. . . . orig". 0.3 . I , k 05 \‘ 0 0.6 C “2 w 0.5 _ I 0.5 o‘f’ 3-3 _ . ~‘ 0.5 '2 6| . ‘ .23»: 5.5000“ 604 0, .. ' V 07 m 020/ V I o- c; 38° . I 5v .‘ I§I ..,_ 9 f 6.5 . 9 32 ° . |06 ‘ 05 o: .' " ' " 603 388 I05 Hg'IILlEERAS “ 0% I' v I 9 “IS-’1 9- 36° EXPLANATION Alloformation missing or too thin to identify on seismic-reflection profiles —-0.2— lsochron—ln seconds (two-way traveltime); contour interval of OJ sec represents approximately IOOm of thickness. Dashed where approximately located Trockline—For multichannel seismic-reflection profiles. See figure 3 for designations ----- 200 m-~- Bathymetry—ln meters Figure 48. Isochron map of Toms Canyon Alloformation show— ing principal sediment dispersal routes (heavy arrows) and depo- centers. Ancient rivers: D, ancient Delaware River; EM, unspec- ified ancient rivers in eastern Massachusetts; H, ancient Hudson River; J, ancient James River; P, ancient Potomac River; S, ancient Susquehanna River. Labeled boreholes identified in text. CD, Chesapeake drift. Onshore reference sections: 1, Claremont, Va.; 2, Colerain Landing, N.C. Other onshore exposure: B, Burwell Bay, Va. See figure 3 for location of DSDP Sites 603, 388, and 105 and Cape Hatteras. 64 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN z E: <2 _23 3 mi: 0< —'2 —ln: 0 3 o out 23 OZ 82 5 =3 -: WNMM METERS COLERAIN BEACH MEMBER TOMS CANYON ALLOFORMATION CHOWAN RIVER FORMATION EDEN HOUSE MEMBER 0 Figure 49. Onshore supplementary reference section for upper part of Toms Canyon Alloformation and its upper bounding unconformity, exposed at Colerain Landing on Chowan River, Bertie County, NC. (Blackwelder, 1981, fig. 2). Subdivisions within the Eden House Member are shown lithologically but are not labeled because they are not the focus of this report. See figure 12 for lithologic explanation and figure 48 for location. No beds unequivocally assignable to the Toms Canyon Alloformation have been recognized in New Jersey or most of Maryland (Owens and Minard, 1979; Ward and Strick- land, 1985). In Delaware, however, the Toms Canyon Alloformation includes mainly medium to coarse sands and fine to very fine shelly sands of fluvial and estuarine origin (Groot and others, 1990). In Virginia, the Toms Canyon Alloformation contains shelly, phosphatic, and glauconitic sands of paralic to inner sublittoral origin, along with lagoonal clays and lag deposits of coarse sand, gravel, and cobbles (Blackwelder, 1981; Mixon and others, 1989). At DSDP Site 612 (figs. 6 and 7), the Toms Canyon Alloformation of the Pliocene continental slope consists of 51.14 m of channel-fill deposits, including dark-gray glau- conitic mud and distinctive interbeds of glauconitic sand. Samples were not recovered from the COST B—3 well (fig. 8) or the thin Toms Canyon section at the COST B—2 well. The Toms Canyon Alloformation was sampled in an upper rise setting at DSDP Sites 604 (fig. 42; 84 m thick) and 613 (fig. 28; 77 m thick), where dark-greenish-gray, glauconitic muds contain occasional layers of glauconitic sand and conglomeratic sand and intervals of biosiliceous, nannofossil-rich clay. Reworked Eocene microfossils also are common in the Toms Canyon sediments at these sites. Farther seaward, cores from DSDP Sites 105 (fig. 16), 106, 388, and 603 (fig. 15) sampled Toms Canyon strata from the flank of the Hatteras Ridge (Mountain and Tucholke, 1985). The most complete and thickest section of Toms Canyon deposits (298 m) was cored at Site 603C, where turbidites consist of greenish-gray, quartzose, mica- ceous muds, grading downward to micaceous, silty clay- stone. The downslope cut-and-fill fabric of the Toms Canyon Alloformation is seen along strike profiles, but channeling is not as extensive as in most older alloformations. Super- imposed on the cut-and-fill downslope fabric is a longslope fabric, created by contour-following bottom currents (Mountain and Tucholke, 1985). Seismic reflections from the upper rise sections of the Toms Canyon Alloformation are generally parallel and subcontinuous, except where chaotic channel-fill deposits are present. HUDSON CANYON ALLOFORMATION DEFINITION We propose the name Hudson Canyon Alloformation for unconformity-bounded outcropping and subsurface beds on the exposed coastal plain (Salisbury embayment), sub- merged continental shelf and slope (Baltimore Canyon trough), and continental rise (Hatteras basin) of the Middle Atlantic States (Virginia, Maryland, Delaware, New Jer- HUDSON CANYON ALLOFORMATION 65 sey), southern New England (Connecticut, Rhode Island, Massachusetts), and New York (fig. 1). The alloformation is bounded above and below by unconformities bounding the Quaternary strata in this region. The Hudson Canyon Alloformation is named after Hudson Canyon, which incises the present continental slope and shelf edge ~200 km southeast of New York City (fig. 3). The stratotype of the alloformation is DSDP Site 613 (fig. 28), ~50 km southwest of Hudson Canyon, at lat 38°46.25’ N., long 72°30.43’ W. At the stratotype, the alloformation is 186.6 m thick and consists of dark—greenish-gray, homogeneous, gas-emitting, organic-matter-rich, commonly diatomaceous mud and interbeds of quartzose, glauconitic sand and occasional zones of conglomerate. BOUNDING UNCONFORMITIES The lower bounding unconformity of the Hudson Canyon Alloformation (fig. 46) was cored at DSDP Site 612 (figs. 6 and 7) at 36.96 m below the sea floor (39 cm below the top of section 3, core 5; Poag and Low, 1987). There the unconformity is a concave scour surface that separates coarse, dark-green to black, glauconitic sand, mixed with clasts of dark-gray mud, of the Hudson Canyon Alloformation from underlying homogeneous, dark-gray mud of the Toms Canyon Alloformation. The lower bounding unconformity also was cored at DSDP Site 613 (fig. 47), 186.6 m below the sea floor (73 cm below the top of section 3, core 11; Poag, 1987). At Site 613, the unconformity is a sharp lithologic change that separates Pliocene dusky-yellow-green, homogeneous, unbedded, diatomaceous, nannofossil-bearing mud (below) from Quaternary greenish-gray, calcareous, glauconitic mud (above). The lower bounding unconformity is expressed on single-channel seismic-reflection profile 105 (fig. 28; Poag, 1987) at 3.35 sec (two-way traveltime) where the profile crosses the continental slope and rise (in a dip direction) 0.2 km northeast of DSDP Site 613. Reflections from the lower part of the Hudson Canyon Alloformation onlap the uncon- formity near Site 613. On other seismic-reflection profiles, the lower bound— ing unconformity of the Hudson Canyon Alloformation can be traced throughout the offshore area by means of truncat- ing, onlapping, and downlapping reflections along the contact (Poag and Schlee, 1984; Poag, l985a,b, 1987, 1992; Poag and Mountain, 1987; Poag and Sevon, 1989). The upper bounding unconformity of the Hudson Canyon Alloformation is the present sea floor, an irregular surface marked by numerous channels (valleys, canyons) and sediment mounds (fans, slumps, drifts; O’Leary, 1988; McMaster and others, 1989; Pratson and Laine, 1989; Poag, 1992; Locker and Laine, 1992). Older beds of Cretaceous to Pliocene age crop out at various places along this surface in the study area (Hampson and Robb, 1984). DISTRIBUTION AND STRATIGRAPHIC EQUIVALENTS The Hudson Canyon Alloformation extends from DSDP Site 105 nearly continuously to the inner edge of the coastal plain, ~750 km updip (fig. 50). Along depositional strike, it extends >900 km from the Long Island platform (Cape Cod) to the coastal plain of North Carolina. The Hudson Canyon Alloformation is generally <100 m thick over the coastal plain and continental shelf, but it is >700 m thick in three depocenters on the continental slope and rise of the northern Hatteras basin (Poag and Sevon, 1989; Poag, 1992). In the Hatteras basin, the alloformation is equivalent to the uppermost part of seismic unit D3 of Schlee and others (1985); seismic unit 132.4 of Schlee and Hinz (1987); the upper half of the Pleistocene seismic unit of Mountain and Tucholke (1985); the Quaternary seismic sequence of Poag (1987); the upper third of seismic sequence 5 of Tucholke and Laine (1982); the upper layered subunit of the layered rise seismic unit of O’Leary (1988); seismic units 1W—4W of Danforth and Schwab (1990); the upper half of seismic unit T3 of Locker and Laine (1992); and the uppermost part of the deep-sea Blake Ridge Formation (fig. 11). On the coastal plain of New Jersey, Delaware, Mary- land, and Virginia, the Hudson Canyon Alloformation encompasses a complex array of lithostratigraphic units, which have been given a host of formation names, including Bridgeton Formation, Pensauken Formation (part), Cape May Formation, Omar Formation, Joynes Neck Sand, Nassawadox Formation, Wachapreague Formation, Kent Island Formation, Windsor Formation, Charles City For- mation, Chuckatuck Formation, Shirley Formation, Nor- folk Formation, and Tabb Formation (Mixon, 1985; Mixon and others, 1989). These units contain a variety of upper alluvial, estuarine, and back-barrier deposits and include crossbedded sands, gravels, cobbles, silty sands, shelly sands, and organic-matter—rich sands. Good exposures of the units are sparse, except in borrow pits. One of the better natural exposures of this alloformation is on the left bank of the Rappahannock River, just downriver from the Virginia Route 3 bridge, Lancaster County, Va. There beds range from slightly brackish water sands containing Rangia, to more brackish shelly sands dominated by Crassostrea, to open-bay shelly sands containing a moderately diverse molluscan assemblage, and finally to fine clean sands of nearshore and beach origin. Mixon (1985) has described and illustrated additional good exposures of the Hudson Canyon Alloformation in the southern Delmarva Peninsula of Virginia and Maryland. 66 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN 78° 76° 74° 72° . 79°W 42°N I ' . _‘ ' : .1 ' _,‘-,-'v NY HUDSON CANYON - ALLO FORMATION 0 IOO 200 KlLOMETERS \Q 7 l——H—r-‘—fi—*—r‘ 0 so lOO NAUTICAL MILES \ w will? ”,9 ’40° W ‘ Vé‘é’v‘fiefi’ ‘ fiI/Q‘WEWNFV l‘p‘l‘ “‘1 \’ l4 .. EXPLANATION Q Alloformation missing or too thin to identify an seismic - reflection profiles ———o.2— Isochron—In seconds (two-way traveltime); contour interval of Oil sec represents approximately IOOm of thickness. Dashed where approximately located Trackline—For multichannel seismic-reflection profiles. See figure 3 for designations ----- 200 mu" Bathymetry—ln meters Figure 50. Isochron map of Hudson Canyon Alloformation River;S, ancient Susquehanna River. Labeled boreholes identified showing principal sediment dispersal routes (heavy arrows) and in text. HF, Hudson Fan; HR, Hatteras Ridge. Onshore reference depocenters. Ancient rivers: C, ancient Connecticut River; D, section: 1, Rappahannock River, Lancaster County, Va. See ancient Delaware River; EM, unspecified ancient rivers in eastern figure 3 for location of DSDP Site 603 and Cape Hatteras. Massachusetts; H, ancient Hudson River; P, ancient Potomac PRINCIPAL CONCLUSIONS 67 THICKNESS, LITHOLOGIES, AND PALEOENVIRONMENTS The Hudson Canyon Alloformation, like the Mey and Toms Canyon Alloformations, is relatively thin (<100 m) over the continental shelf, except for a 200- to 300-m-thick wedge of sediments on the outer shelf south of New England (figs. 2 and 50). Downslope erosional and depositional processes inten- sified during the sea-level fluctuations of the Pleistocene, and the locus of extensive cutting and filling shifted upslope by 20—40 km from its preceding Pliocene position on the upper rise. This intensification is manifest by deep incisions of the shelf edge and upper continental slope by submarine canyons, which channeled large volumes of terrigenous detritus to continental rise depocenters. Some of these canyons have been subsequently filled with as much as 700—800 In of terrigenous sediment. The Hudson Canyon Alloformation is unusually thin (10—25 m) or absent along the base of the continental slope seaward of New Jersey and Long Island, where the chalky limestones of the middle Eocene Lindenkohl Alloformation are extensively exposed. To the southwest (off Virginia, Maryland, Delaware) and northeast (off Massachusetts), however, elongate slope aprons are 400—700 m thick. Two principal submarine fan systems extend across the northern Hatteras basin. The largest and thickest fan system (600—700 m thick) is the Hudson Fan, which was fed mainly by sediments traversing Hudson Canyon. On the lower continental rise at the southeast corner of the study area, a 300-m-thick mound of sediment parallels the shelf edge and forms part of the current-built Hatteras Ridge (Mountain and Tucholke, 1985; McMaster and others, 1989; Locker and Laine, 1992). Quaternary gravels and paralic terrigenous strata of the Hudson Canyon Alloformation are known in the New Jersey Coastal Plain (Minard and Rhodehamel, 1969', Owens and Minard, 1979). Downdip on the upper conti— nental rise, sediments are characteristically dark—greenish- gray, homogeneous, gassy, organic-matter-rich, commonly diatomaceous muds, interbeds of quartzose, glauconitic sand, and occasional conglomeratic zones, as seen at Site 613 (figs. 28 and 47). The lithic and microfossil evidence (coarse sands, conglomerates, chunks of white Eocene chalk, displaced shelf-dwelling species) confirms the importance of downslope depositional processes (turbidity currents, debris flows) inferred from the sediment- distribution pattern of the isochron maps. At DSDP Site 603 (fig. 15), approximately 31 m of Hudson Canyon strata are draped over the Hatteras Ridge. There the sediments are mainly greenish-gray, nannofossil- rich clay and claystone, which emit hydrogen sulfide gas. At DSDP Site 106, drilled on the lower continental rise terrace (figs. 2 and 50), the ponded, turbiditic Hudson Canyon section is 360 m thick and consists of gray to brown terrigenous mud and glauconitic, quartzose sand interbeds. Mica, wood, and plant fragments are common in some sandy layers, and siliceous microfossils are especially notable in the lower part. Seismic-reflection profiles crossing the continental rise (fig. 16) show that the Hudson Canyon Alloformation can be divided into two distinct allomembers. Drilling at DSDP Site 105 proved that the lower allomember represents early Pleistocene deposition and the upper allomember represents late Pleistocene and Holocene deposition. On the upper rise prism, sediments of the lower allomember fill downslope- trending channels cut into the upper surface of the under- lying Toms Canyon Alloformation. The contact between the two Quaternary allomembers is, in contrast, a relatively smooth surface (Poag, 1987). The upper surface of the upper allomember (the present sea floor), generally displays a marked relief, created by differential downslope and alongslope erosion and deposition. Far downdip, however, ponding behind the Hatteras Ridge has smoothed the sea—floor topography. PRINCIPAL CONCLUSIONS ALLOSTRATIGRAPHIC RELATIONS BETWEEN SEISMOSTRATIGRAPHIC SEQUENCES AND BOREHOLE STRATA Direct correlations between unconformities seen on seismic-reflection profiles and unconformities identified in continuously cored and logged offshore sections are rare. DSDP Site 612 on the continental slope of New Jersey (figs. 6 and 7) is one of the best examples currently available. There stratigraphic changes on sonic logs and gamma-ray logs correspond closely to lithic and biostratigraphic dis- continuities and to unconformable seismic-sequence bound- aries. These relations firmly support the validity of seismo- stratigraphic interpretation methods proposed (but weakly documented) by Vail and others (1977a,b) and many subsequent authors, though Thome and Watts (1984) would disagree. Similar data from DSDP Site 613 (fig. 28) corroborate conclusions drawn from Site 612 (Poag, Watts, and others, 1987; Van Hinte, Wise, and others, 1987). In fact, the geologic record at all the other New Jersey Transect boreholes studied (DSDP Sites 105, 106, 603, 604, 605; figs. 15—17 and 42) also supports the sequence- stratigraphy model, although no geophysical logging was carried out at these sites. These results, along with new continuously cored and logged boreholes on the coastal plain (for example, Exmore and Kiptopeke coreholes, fig. 33), strengthen prior stratigraphic interpretations (for exam- ple, Schlee, 1981; Poag and Schlee, 1984; Poag, 1985a; Poag and Ward, 1987; Mixon, 1989) derived from borehole data collected on the coastal plain and continental shelf and from offshore seismic profiles. 68 ALLOSTRATIGRAPHY OF THE US. MIDDLE ATLANTIC CONTINENTAL MARGIN The location of the New Jersey Transect drill sites within a grid of single—channel and multichannel seismic- reflection profiles allows their bounding unconformities to be traced beneath most of the continental slope and rise and confirms their correlation with those of the adjacent shelf and other nearby shelf basins (Poag, 1982, 1985a, 1987, in press; Poag and Schlee, 1984; Popenoe, 1985; Poag and Sevon, 1989), of the coastal plain (Hazel and others, 1984; Kidwell, 1984; Owens and Gohn, 1985 ; Ward and Strick- land, 1985; Poag and Ward, 1987; Poag, 1989, 1992), and of the margins of several other continents (Steele, 1976; McGowran, 1979; Barr and Berggren, 1980; Quilty, 1980; Loutit and Kennett, 1981; von Rad and Exon, 1982; Ziegler, 1982; Riggs, 1984; Schlee, 1984; Seiglie and Baker, 1984; Seiglie and Moussa, 1984; Aubry, 1985; Poag and others, 1985). On the basis of these relations, we have proposed a formal allostratigraphic framework of 12 allo— formations for the US Middle Atlantic margin. PROXIMATE CAUSES OF UNCONFORMITIES On the coastal plain and continental shelf, distinct, burrowed scour surfaces overlain by basal marine conglom- erates, plus the absence of paralic lithofacies above the contacts (Darby, 1984; Ward and Krafft, 1984; Poag, in press), are evidence that allostratigraphic boundaries (unconformities) in the shallow marine environments were created largely in two steps; regressive subaerial erosion followed by transgressive submarine erosion and ravine- ment. On the continental slope and upper continental rise, the presence of sand layers, exotic clasts, and conglomer- atic zones immediately above scour surfaces, and of faults or contorted bedding within alloformations, indicates that erosion by downslope mass sediment displacement (turbid- ity currents, debris flows, slumps) was the chief agent in forming many of the allostratigraphic boundaries in deep marine environments. Outcrops, cores, and seismic profiles clearly indicate that the accumulation rates and dispersal patterns of successive downslope sediment gravity flows were highly variable. Equivalent variability in the depth of submarine erosion created longer hiatuses in some sections than in others. Gravity-flow deposits sandwiched between allostrati- graphic boundaries of the continental slope and rise of the Middle Atlantic States have equivalents elsewhere around the Atlantic basin, such as the opposing continental slope and rise off Ireland (Graciansky, Poag, and others, 1985a,b; Miller and others, 1987). Correlation of these deposits with paleobathymetric cycles derived from sites on the coastal plain and continental shelf (Poag and Schlee, 1984; Ward and Strickland, 1985; Olsson and Wise, 1987; Olsson and others, 1987; Poag and Ward, 1987; Miller and others, 1990) links these erosional episodes with relative sea-level falls and subsequent marine transgressions. The strati— graphic positions of five allostratigraphic boundaries of the US. Middle Atlantic continental margin (base of Linden- kohl, Baltimore Canyon, Babylon, Phoenix Canyon, and Mey Alloformations) correlate well with major Cenozoic supersequence boundaries (“global” unconformities) of the Haq and others (1987) version of the Exxon sequence- stratigraphy model (fig. 51); two boundaries (base of Toms Canyon and Hudson Canyon Alloformations) correlate better with the original version of the model (Vail and others, 1977b); four other boundaries (base of Accomac Canyon, Island Beach, Carteret, and Berkeley Alloforma- tions) do not fit either version of the model. Furthermore, Poag and Sevon (1989) and Poag (1992) have shown that many bathymetric shifts in the location of major Late Cretaceous and Cenozoic depocenters of the US. Middle Atlantic margin correspond to eustatic changes postulated by the model. Thus, we conclude that second-order relative sea-level changes have been major forcing mechanisms for many, but not all, deposition and erosion cycles on the U.S. Atlantic margin and its conjugate margins of the eastern North Atlantic. Relative sea—level change was a particularly effective control on depositional patterns during the Paleogene and early Neogene because siliciclastic accumulation rates were unusually low (Poag and Sevon, 1989; Poag, 1992). During the Late Cretaceous and middle Miocene, however, signif- icant uplift of terrigenous source terrains accelerated the supply of siliciclastic sediments to the offshore basins (fig. 51). This rapid accumulation modified the second-order effects of relative sea—level change and may have been responsible for the poor correlation of some allostrati- graphic boundaries with those of the Exxon sequence- stratigraphy model. The ultimate cause of any given relative sea—level change is the subject of heated debate (eustasy vs. tecton- ism). Systematic changes in paleoclimate, seawater temper- ature, and global ice volumes, inferred from extensive analyses of oxygen and carbon isotopes, provide independ- ent evidence that major eustatic changes have taken place during the Cenozoic. A clear link between widespread sublittoral and bathyal (and even abyssal) erosion, increased global ice volumes, cooler global climates, and lower sea levels has been established for the Cenozoic as far back as the late Eocene (Vail and others, 1977b; Frakes, 1979; Keller and Barron, 1983; Miller and Fairbanks, 1983; Keigwin and Keller, 1984; Poag and Schlee, 1984; Aubry, 1985; Miller and others, 1985, 1987, 1990; Poag, 1985a, 1987; Poag and others, 1987). The stratigraphic positions of major inflections in the oxygen-isotope curves (indicating increased ice volumes) correlate well with several of the principal allostratigraphic boundaries of the US. Middle Atlantic margin (fig. 51; Poag, 1987). Some authors have interpreted the oxygen-isotope record as an indication that significant global ice volumes were present even in the Late Cretaceous (Matthews and Poore, 1980; Matthews, 1984). 69 PRINCIPAL CONCLUSIONS .833 030300813 08300 A230 wsom .GwoC 0030002 000 030000.3Ilm3 08300 .833 00>0w 00m wnomlmfi 08300 .GmoC 030030m 00w. 0009353 3 000.8003 80008 0030 8 00830 0000030 00.38 00 A320 wow“ 80 300 00000800 R933 09% 000 waom 803 £300 00303000< 00m 63C 008008 000 000w3M 8000 £005 08000000800001: 08300 800000: 00003 000000 ”0008800000 00033 000200 0300 ”3me 330002 000 030003. .Gwos 0000m— 000 00> 00s 00000M|S 08300 0008800000 00003 00030 0:00 000 3000003 ”6me 00030 000 000wm00m Ammo: 0030002 080 030000hlm 80300 .AmwoC 00>0w 05 030$ 08:30 $30 2208 as a“: .380 530:: 0a 00> .0530 22% .3w300w 8300083 00 A53 £00m 800m 02.30080 @0883 0008030@ 000 max/IN. 08300 .0002 mEHIo 08300 80000 mEHIm 08300 A50: wwomlv 08300 0008080000 00003 00:30 0500 ”Emma: wmom A353 0030m 00m mmomlm 08300 0008800000 00033 00500 0300 A533 8080 000 can .333 300000005 000 =0>|N 08300 A303 306080 000 000M Amwoc 8080 000 000ww00m|_ 08300 ”030:8 00 88300 00% 000003000 000 830 00 008cm .6 083000 30000 00000000 0000080000330 00 800300 .005 000 80000—0! 00 030008000 .58 0w $3 M086 8308 00033‘ 3032 .m.D M00000? £005 0308800000200 000 6008300080 .E 2:000 mIqNa m _ _ mI_<:m am 00 8 25>; m _ 5.25:3 m M low vain mmm m w ”.3958 m _ a m me . m. H QEDImDm .7qu d w; W Z I ”WI. 0 w W #25128: e. 8. my _m 0 w m NW NW 3 M. II s M W mm _M m._ 2:06.592: w ON SI W. .H a s s 3 M _<._. am 53.. _M w_ 55m m I w >25? mm .II. N m N0 51% _W m m»: m low 0? llllllll 50.8 £0 E E n m mifizm z_1 :3 022858 02230055 .335 w 255.2 -845 N .V. m_ N_ _ _ O_ 0 m P Q m .V m N 70 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN On the other hand, Cloetingh (1986, 1988, and several related papers) has established therrnomechanical models to demonstrate that variations in external compression or tension (brought about by fluctuating intraplate stress) at the edge of passive-margin basins can produce the same types of onlap-offlap depositional patterns produced by eustasy. It is easy to envision allostratigraphic processes at work on a shallow continental shelf. But it is more difficult to understand how erosion on the continental slope and rise, which were covered by thousands of meters of water, could be induced by a relative sea-level fall. Several possible mechanisms have been suggested. Samthein and others (1982) suggested that internal waves and turbulence, caused by density differences at water-mass boundaries, could cause significant erosion where a boundary intersects that sea floor. Where such a boundary intersects the continental slope, it would be depressed or elevated in unison with sea-level change or other major changes in circulation, creating a broad erosional swath. Poag and others (1985) suggested that evidence of such a process could be found in the sedimentary and microfossil record of the Goban Spur. Stanley and others (1983) discussed similar relations for water-mass boundaries on the New Jersey margin. They showed that the mudline on the modern New Jersey margin (above which intermittent deposition and erosion take place) can range from 200 m to 1,000 m, depending on several variables. Beneath the shelf water mass (shoreline to the shelf break; 0—200 111), erosion takes place continually from the interplay of storms, fronts, tides, and internal waves. The upper few hundred to 1,000 m below the intersection of the shelf and slope water masses is a transitional zone in which sediments are periodically resus- pended by surface waves, tidal currents, wind-stress cur— rents, internal waves, and shear forces between major water masses and oceanic fronts. This alternation of deposition and resuspension triggers sediment flow down the middle and lower slope. A falling sea level would depress this transitional zone of erosion even farther down the slope. The benthic microfossil record along the New Jersey Transect shows that one or more hydrographic boundaries have separated DSDP Site 612 (mid-slope) from DSDP Sites 604, 605, and 613 (upper rise) during much of the Late Cretaceous and Cenozoic. Deep boundary currents (fig. 51), such as the Gulf Stream and the Western Boundary Undercurrent, also are effective agents for eroding the continental slope and rise (Tucholke and Mountain, 1979; Vail and others, 1980; Tucholke, 1981; Pinet and Popenoe, 1982; Ledbetter and Balsam, 1985; Mountain and Tucholke, 1985; Popenoe, 1985; McMaster and others, 1989). Geographic and bath- ymetric shifts of such currents, coincident with sea-level changes, have been demonstrated (for example, Tucholke and Laine, 1982; Ledbetter and Balsam, 1985; Popenoe, 1985). For example, the high-velocity core of the Western Boundary Undercurrent off New Jersey accelerated, moved shoreward by 150 km, and shoaled by 1,000 m (relative to its modern velocity and position) during the last Pleistocene glacial (Ledbetter and Balsam, 1985). Seismicity also may have accelerated erosion on the slope and rise in unison with sea-level falls. The outer shelf growth faults of the Gemini fault system (Poag, 1987) were active along the outer shelf and upper to middle continental slope of New Jersey from at least the Late Jurassic until well into the middle Miocene. Shelf-edge and upper slope depocenters have been associated with this fault system since the Campanian, and broad erosional swaths have paralleled it at varying positions since the Paleocene. Presumably, sea-level falls, which reduce the hydrostatic pressure, could thereby create excessive sedimentary pore pressures and trigger periodic movements along these faults, displacing large volumes of sediment from the shelf edge and slope to cut erosional swaths across the continental rise (Booth, 1979). Another mechanism that appears to have profoundly interrupted depositional processes in the study area, from coastal plain to continental rise, is the impact of an early late Eocene bolide that struck the outer continental shelf 40 km north of DSDP Site 612 (Poag and others, 1992). This event appears to have caused, directly or indirectly, much of the erosion that formed the lower bounding unconformity of the Baltimore Canyon Alloformation. Diverse parts of the unconformity could have been formed by at least four different processes related to the bolide. First, at the impact site, part of the unconformity was formed directly when the force of the collision deeply excavated the middle to early late Eocene sea floor and truncated beds of Late Cretaceous to late Eocene age. Second, at locations proximal to the excavation, such as DSDP Site 612, the impact triggered ejecta—bearing debris flows, which scoured the outer shelf and upper slope and truncated beds at least as old as middle Eocene. Third, seismic shock from the impact appears to have destabilized sediments over a large area of the conti- nental slope. This presumably resulted in massive debris flows, which eroded deep downslope-trending channels (seen on seismic profiles) and truncated Upper Cretaceous to upper Eocene beds on the lower continental slope and upper continental rise. Fourth, a gigantic tsunamilike wave train, generated by the bolide impact, widely scoured the late Eocene inner continental shelf and coastal plain. This superwave truncated beds ranging in age from Early Creta- ceous to late Eocene at the Exmore corehole and other sites in what now is southeastern Virginia. The presence of a broad, elongate outcrop of middle Eocene chalk of the Lindenkohl Alloformation along the base of the New Jersey Continental Slope has raised the question of whether downslope or alongslope erosion has dominated its excavation (Poag, 1987). Some authors have suggested that a repetitious two-step combination of erosive processes has taken place: (1) the lower slope was undercut by alongslope boundary currents (perhaps aided by subma- PRINCIPAL CONCLUSIONS 71 rine ground-water discharge (Robb, 1984)); (2) pervasive downslope mass wasting took place as the margin sought a new equilibrium profile (Farre, 1985; Mountain and Tucholke, 1985). Data from the New Jersey Transect give evidence of both processes. For example, chunks of middle Eocene chalk were incorporated into debris—flow deposits of the upper rise during the late Miocene (Mey Alloformation) and Quaternary (Hudson Canyon Alloformation) (sampled at DSDP Sites 604, 605, and 613). Thus, it is certain that downslope erosion has helped excavate the Lindenkohl Alloformation at least since the late Miocene. Furthermore, extensive systems of downslope-trending erosional chan- nels are present within each of the Upper Cretaceous and Cenozoic alloformations mapped on the upper continental rise. Thus, downslope erosion was significant in this region for at least the last 84 my. The presence of a marked shelf-edge declivity, coupled with the sedimentary record at DSDP Site 603 (Van Hinte, Wise, and others, 1987) and the regional depositional patterns mapped by Tucholke and Mountain (1979), Ewing and Rabinowitz (1984), Mountain and Tucholke (1985), Schlee and Hinz (1987), Poag and others (1990), McMaster and others (1989), Poag and Sevon (1989), and Poag (1992), attests to almost continu- ous passage of erosive turbidity currents and debris flows across the continental slope and rise since at least Bathonian time (Middle Jurassic; 165 Ma). Later, during the late Miocene and Quaternary, downslope deposition covered parts of the Lindenkohl outcrop belt, attesting to the preeminence of gravity-flow processes. As a final example, the Quaternary Hudson Canyon Alloformation has been truncated on both the updip and downdip edges of the Lindenkohl outcrop belt, forming a thin alongslope swath, several kilometers wide, which is interpreted to have resulted from late Quaternary, contour-following bottom currents. In combination, these relations are evidence that downslope sediment dispersal has nearly always been the principal agent of both deposition and erosion along the continental slope and upper rise off the Middle Atlantic States since sea-floor spreading began (~187 Ma). There is little doubt, however, that alongslope bound- ary currents and other vigorous bottom currents have modified downslope depositional patterns on the middle to lower rise since the middle Miocene, when elongate, mounded, contourite drift deposits began to build up (Tucholke and Mountain, 1979, 1986; Tucholke and Laine, 1982; Miller and Tucholke, 1983; Emery and Uchupi, 1984; Mountain and Tucholke, 1985; McMaster and others, 1989; Poag and Sevon, 1989; Poag, 1992; Locker and Laine, 1992). Off the Middle Atlantic States, however, in the bathyal transitional zone from continental slope to continental rise (ZOO—2,000 111 water depth), mass gravity flows appear to have dominated both deposition and erosion. A recent study of plate kinematics of the North Atlantic has provided an updated interpretation of plate motion changes (Klitgord and Schouten, 1986), which presumably would cause widespread, if not global, sea- level fluctuations (Hays and Pitman, 1973; Cloetingh, 1986). The timing of several of these plate motion shifts is nearly coincident with supersequence and alloformation boundaries of the study area (fig. 51) and thereby provides evidence that some preglacial sea-level cycles could have been caused by tectonism alone. DEPOSITIONAL REGIMES AND SEDIMENT PROVENANCE AND DISPERSAL Postrift sediment dispersal on the continental shelf, the continental slope, and the continental rise has involved a varied and complex series of processes (Poag, 1987, 1992; McMaster and others, 1989; Poag and Sevon, 1989; Locker and Laine, 1992). Processes such as delta progradation, downslope mass gravity flows, shallow surface currents (and associated gyres), deep boundary currents (and asso- ciated shear zones), shifting water-mass boundaries, storms, fronts, tides, and internal waves dominated differ- ent segments of the margin at different times in its deposi- tional history. These processes often interacted to augment or diminish each other, so that their relative effectiveness was inconstant, varying temporally and spatially. The continental slope, both now and in its earlier manifestations, has been a zone of transition between sublittoral (0—200 111) shelf processes and abyssal (>2,000 m) processes of the continental rise. Sediment dispersal routes and processes were complicated even more by the appearance of dual shelf breaks (resulting in hintershelves and foreshelves) during the early Eocene to middle Mio— cene, rapid progradation of massive, organic-matter-rich delta systems during the middle Miocene to Quaternary, and deep incision of shelf-edge submarine canyons, espe- cially during the Pleistocene. As the Cretaceous drew to a close and the deposits of the Sixtwelve and Accomac Canyon Alloformations accu- mulated, the position of the shelf edge off the Middle Atlantic States was still controlled in large part by the position of a buried Jurassic reef structure (Poag, 1987, 1991; Meyer, 1989; Poag and others, 1990). Erosional channels at the base of the Late Cretaceous continental slope provided numerous conduits for shelf- and slope- derived siliciclastic debris of the Sixtwelve and Accomac Canyon Alloformations to reach the continental rise (Poag, 1992). Concomitantly, relatively high sea levels allowed principally clay-sized particles to reach the outer part of the northern Hatteras basin, where they formed multicolored pelagic shales. The supply of siliciclastic components to the study area dwindled in the Maastrichtian, and the dominant offshore lithofacies of the Accomac Canyon Alloformation became calcareous sands, clays, chalks, and limestones. Chaotic seismic facies in Accomac Canyon channel-fill 72 ALLOSTRATIGRAPHY OF THE U.S. MIDDLE ATLANTIC CONTINENTAL MARGIN deposits are evidence, however, that some parts of the upper continental rise continued to receive considerable amounts of terrigenous gravity-flow detritus. A major shift in depositional regime took place in the Paleocene, as siliciclastic deposition rates diminished by two-thirds (fig. 51; Poag and Sevon, 1989; Poag, 1992) and carbonate accumulation dominated the continental shelf and deep-water sites above the carbonate compensation depth. Systems of downslope-trending channels continued to dis- tribute these carbonate-rich sediments onto the upper con- tinental rise into the early and middle Eocene, as indicated, for example, by an increase in the number of slumps and microfaults in the Carteret and Lindenkohl Alloformations at DSDP Site 613. During the middle Eocene, another significant shift in depositional regime occurred as a second shelf break (hintershelf; figs. 2, 30, and 51) developed 120 km land- ward of the buried Late Jurassic reef system, which still controlled the position of the seaward shelf edge (foreshelf). Thus, middle Eocene deposition of the Lindenkohl Allofor— mation was greatest on the hintershelf and just seaward of the foreshelf edge. The foreshelf was a bypass area of relatively thin, mainly carbonate, accumulation. Gravity— flow mechanisms continued to be important in dispersing sediments on the middle Eocene upper continental rise. The hintershelf edge prograded progressively seaward following the middle Eocene (figs. 2, 33, 35, 36, 39, 43, 48, 50, and 51), and terrigenous deposits dominated the margin depocenters again from the late Oligocene to the present (fig. 51). Siliciclastic progradation culminated in the middle Miocene with the development of a complex system of shelf-edge deltas that formed much of the Phoenix Canyon Alloformation. Terrigenous detritus was pumped across the foreshelf in huge volumes, until by the end of the middle Miocene, the major shelf depocenter was near the shelf break (figs. 2 and 39), giving the continental slope a modern aspect, with its relatively steep declivity. Having this major detrital source at the shelf edge signifi- cantly increased the volume of sediment reaching the continental rise, where these sediments were distributed by gravity-flow mechanisms through upper rise channels, onto the lower rise. Similar sedimentary processes dominated late Miocene through Pliocene deposition and formed the Mey and Toms Canyon Alloformations. But depocenters on the continental rise received the largest volumes of sediment, fed from smaller depocenters perched at the shelf break. On the middle and lower rise, contour-following bottom currents redistributed fine-grained hemipelagic sediments into elon- gate, mounded, contourite drift deposits. Continental—rise depocenters dominated margin accumulation in the Quater- nary as well, as the Hudson Canyon Alloformation was deposited (figs. 2 and 50). Sediment conduits across the continental slope became more localized, however, as large submarine canyons incised the shelf edge and created some channel systems that built large submarine fans on the lower rise. Punctuating these Late Cretaceous and Cenozoic dep- ositional episodes were periodic intervals of shelf and coastal-plain erosion (fig. 51), during which large volumes of sediment were redistributed to the continental slope and rise. IMPLICATIONS REGARDING THE EXXON SEQUENCE-STRATIGRAPHY MODEL Much of the observed allostratigraphic framework (stratigraphic position of unconformities) of the middle segment of the U.S. Atlantic margin fits the second-order (supersequence) cyclical framework of the Exxon sequence— stratigraphy model (Vail and others, 1977b; Vail and Mitchum, 1979; Vail and others, 1984; Haq and others, 1987, 1988; Van Wagoner and others, 1988). However, there are significant differences between the postulated distributions of seismic depositional sequences and the observed distribution of alloformations. The sequence- stratigraphy model postulates, for example, that during the Paleogene, four major lowstands occurred, during each of which a significant pulse of siliciclastic sediment should have reached the Hatteras basin. On the other hand, Poag and Sevon (1989) and Poag (1992) have shown that the Paleogene was characterized by the lowest sustained accu— mulation rates of the entire 187 my of postrift deposition on this margin. The sparsity of Paleocene and Eocene deposition can be attributed to development of a tropical rainforest in eastern North America (Wolfe, 1978). The presence of such heavy vegetation, according to Cecil’s (1990) model of depositional response to paleoclimate, would have minimized the availability and dispersal of siliciclastic sediment. Although the rainforest disappeared abruptly in the early Oligocene, approximately coincident with a postulated major lowstand (Wolfe, 1992), no thick Oligocene lowstand deposits have been identified anywhere in the study area. During the middle Eocene, depositional patterns were additionally complicated by development of a dual shelf system, in which the hintershelf was characterized by a prograded series of deposits (Lindenkohl Alloformation), whereas the broad foreshelf was a starved bypass region. Deposition increased significantly again seaward of the foreshelf edge, where biosilica—rich carbonate ooze accu- mulated in thicknesses as great as 200—300 m. INTRINSIC ADVANTAGES OF ALLOSTRATIGRAPHY Sequence stratigraphy, in the sense of Vail and others (1977a,b), offers a powerful methodology for organizing REFERENCES CITED 73 complex three-dimensional sedimentary geometries, litho- facies, and paleoenvironmental regimes into a comprehen- sive basinwide (or marginwide) depositional framework. The method has been widely adopted as a basic tool in exploring marine basins for natural resources, especially oil and gas (Payton, 1977; Berg and Woolverton, 1985; Shell Oil Company, 1987; Wilgus and others, 1988). Even though an intense controversy is raging over the mecha- nisms that control the formation of depositional sequences (tectonism vs. eustasy; see Cloetingh, 1988; Hallam, 1988; Haq and others, 1988; Hubbard, 1988; Kendall and Lerche, 1988; Galloway, 1989), the sequence concept is immensely popular and has been applied even to Paleozoic successions (Ross and Ross, 1987). Our experience in analyzing the stratigraphic record of the US Middle Atlantic margin convinces us that the application of sequence stratigraphy, as modified by allo- stratigraphic principles, provides significant advantages over traditional biostratigraphic, lithostratigraphic, and chronostratigraphic approaches. This advantage is particu— larly evident in geological frontiers, where regional synthe- sis requires one to establish genetic relations between disparate subsets of sedimentary rocks, which accumulated in widely divergent paleobathymetric (fluvial to abyssal) and paleophysiographic (coastal plain to abyssal plain) regimes. The allostratigraphic framework also is more applica- ble to the US. Middle Atlantic margin than the concept of “genetic stratigraphic sequences,” which Galloway (1989) has eloquently espoused for dominantly siliciclastic Ceno- zoic deposits of the northern Gulf of Mexico region. Galloway pointed out that his genetic stratigraphic sequences are a half-cycle out of phase with the depositional sequences of the Exxon sequence—stratigraphy model (and thus with the alloformations we propose), because Gallo- way’s sequence boundaries are marine flooding surfaces, not erosional unconformities. Marine flooding surfaces, where identifiable, should occur within (near the middle of) alloformations. The detailed geologic history of the US. Middle Atlantic margin (incorporating sediment supply, basin subsidence, source-terrain tectonism, paleoclimate, and paleoceanography) was sufficiently different from that of the Gulf of Mexico region that only a few basinwide flooding surfaces can be easily recognized in borehole and seismic data. We have been able to readily identify only two or three thin, widespread shale or carbonate units in the entire postrift succession of our study area that would qualify as Galloway’s sequence boundaries. The formal allostratigraphic nomenclature we have proposed is intended, first of all, to stabilize the strati- graphic terminology applied to deposits in the study area. Already as many as 10 different sets of descriptors have been applied to some of the seismic units recognizable there. Furthermore, we believe that the allostratigraphic nomenclature will clarify conceptual relations between genetically related deposits of the study area and will facilitate discussion and comparisons with sedimentary deposits of other basins. The allostratigraphic nomenclature is far more flexible in accommodating local and subregional perturbations (such as source-terrain tectonism, paleocli- mate change, basin subsidence, depocenter migration) than the familiar “global” sequence models characterized by awkward alphanumeric nomenclature, which is changed frequently and is applied inconsistently by different work- ers. Furthermore, the use of allostratigraphy precludes the subjective forcing of “anomalous” features to fit simplistic, stylized preconceptions inherent to the models. The inves- tigator is free to recognize the individuality of each basin. 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Ziegler, RA, 1982, Geological atlas of western and central Europe: Amsterdam, Elsevier, 130 p. 7 DAYS D m L The Dlatom Genus Actmacyclus 1n the Western Umted States; A L SULLLM 341% fifi'fifié‘flTflfiY LL 2 1 LL AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current-year issues of the monthly catalog “New Publications of the U.S. Geological Survey.” Prices of available U.S. Geological Survey publications re- leased prior to the current year are listed in the most recent annual “Price and Availability List.” Publications that may be listed in various U.S. Geological Survey catalogs (see back Inside cover) but not listed in the most recent annual “Price and Availability List” may no longer be available. 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Maps Only Maps may be purchased over the counter at the following U.S. Geological Survey offices: FAIRBANKS, Alaska—New Federal Bldg, 101 Twelfth Ave. ' ROLLA, Missouri—1400 Independence Rd. ' STENNIS SPACE CENTER, Mississippi—Bldg. 3101 The Diatom Genus Actinocyclus in the Western United States J. Platt Bradbury and William N. Krebs, Editors A. Actinocyclus (Bacillariophyta) Species from Lacustrine Miocene Deposits of the Western United States By J. Platt Bradbury and William N. Krebs B. Geologic Ranges of Lacustrine Actinocyclus Species, Western United States By William N. Krebs and J. Platt Bradbury U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543A—B UNITED STATES GOVERNMENT PRINTING OFFICE : 1995 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Robert M. Hirsch, Acting Director For sale by U.S. Geological Survey, Map Distribution Box 25286, MS 306, Federal Center Denver, CO 80225 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government Library of Congress Cataloging-in-Publication Data The Diatom genus Actinocyclus in the Western United States / J. Platt Bradbury and William N. Krebs, editors. p. cm.—(U.S. Geological Survey professional paper; 1543) Includes bibliographical references Contents: A. Acu‘nocyclus (Bacillariophyta) species from lacustrine Miocene deposits of the Western United States / by J. Platt Bradbury and William N. Krebs-— B. Geologic ranges of lacustrine Actinocyclus species, Westem United States / by William N. Krebs and J. Platt Bradbury. Supt. of Docs. no.: 119.16:P1543A&B. 1. Actinocyclus, Fossil—West (U.S.) 2. Paleobotany—Miocene. II. Krebs, William N. 111. Series. QE955.D53 1993 561’.93—dc20 93—35637 CIP CONTENTS [Letters designate the chapters] (A) Actinocyclus (Bacillariophyta) species from lacustrine Miocene deposits of the West- ern United States, by J. Platt Bradbury and William N. Krebs (B) Geologic ranges of lacustrine Actinocyclus species, Western United States, by William N. Krebs and J. Platt Bradbury k Actinocyclus (Bacillariophyta) Species from Lacustrine Miocene Deposits of the Western United States By J. Platt Bradbury and William N. Krebs THE DIATOM GENUS ACTINOC Y CLUS IN THE WESTERN UNITED STATES U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543—A UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995 V , 99°99‘99wa CONTENTS Abstract ........................... . ............................................................................................... 1 Introduction .................................................................................................................... 1 Acknowledgments .......................................................................................................... 1 Materials and methods ................................................................................................... 2 Choice of generic epithet ................................................................................................ 2 Key for separation of some nonmarine species of Actinocyclus .................................... 3 Systematic descriptions .................................................................................................. 4 Paleoecology of Miocene lacustrine Actinocyclus ......................................................... 13 References ...................................................................................................................... 14 Index ............................................................................................................................... 68 PLATES [Plates follow references] Actinocyclus acanthus ................................................................................................................................................. 21 Actinocyclus cedrus ..................................................................................................................................................... 23 Actinocyclus cedrus ..................................................................................................................................................... 25 Actinocyclus cedrus and Actinocyclus claviolus .......................................................................................................... 27 Actinocyclus claviolus and Actinocyclus cupreus ........................................................................................................ 29 Actinocyclus sp. cf. A cupreus and Actinocyclus ehrenbergii ..................................................................................... 31 Actinocyclus ehrenbergii and Actinocyclus grobunovii .............................................................................................. 33 Actinocyclus kanitzii, Actinocyclus krasskei, and Actinocyclus tubulosus .................................................................. 35 Actinocyclus krasskei and Actinocyclus motilis ........................................................................................................... 37 Actinocyclus motilis ..................................................................................................................................................... 39 Actinocyclus motilis and Actinocyclus nebulosus ........................................................................................................ 41 Actinocyclus nebulosus, Actinocyclus normam'i f. subsalsa, and Actinocyclus pinnulus ............................................ 43 Actinocyclus pinnulus, Actinocyclus sp. cf. A. pinnulus, and Actinocyclus theleus .................................................... 45 Actinocyclus theleus, Coscinodiscus (=Actinocyclus) variabilis, and Actinocyclus venenosus .................................. 47 Actinocyclus venenosus ............................................................................................................................................... 49 VII AC TINOC Y CLUS (BACILLARIOPHYTA) SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES By J. PLATT BRADBURY and WILLIAM N. KREBS ABSTRACT Species of the diatom genus Actinocyclus Ehrenberg were important constituents of lacustrine phytoplankton in the Western United States during much of the early and middle Miocene (19—10 Ma). Similar and (or) identical fos- sil Actinocyclus species are found elsewhere in the world, particularly in Eurasia, in Neogene lacustrine diatomaceous rocks. Ten new species of fossil lacustrine Actinocyclus (A acamhus, A. cedrus, A. claviolus, A. cupreus, A. motilis, A. nebulosus, A. pinnulus, A. theleus, A. venenosus, and Actinocyclus gorbunovii var. fossa) are described and a new name (A. krasskei) is proposed based on the study of samples from 115 localities in the Western United States that range in age from the early Miocene to Pleistocene. Seventy of these localities contain Actinocyclus. Diagnostic characteristics include degree and nature of fasciculation, size of pseudonodule, areolae density, disposition and shape of hyaline stripes on the valve disk and mantle, degree of undulation, diameter, presence and nature of mar- ginal tubular processes and spines, size and shape of areolae, and character of labiate processes. INTRODUCTION The diatom genus Actinocyclus characterized open- water lacustrine environments in the Western United States during much of the early and middle Miocene (19—10 Ma). Fossil localities containing Actinocyclus are found in diato- mites and diatomaceous shales deposited in paleolake sys- tems of Nevada, Idaho, California, Oregon, and Washington (Krebs and others, 1987). The forms of Actinocyclus found in these deposits resemble those from other parts of the world (for example, Bradbury and Krebs, 1982; Bradbury, 1984; Bradbury and others, 1985), particularly from Eurasia, where a number of distinct taxa have been described. Radio- metric dates associated with Actinocyclus occurrences in the United States suggest that some of the forms have biochron- ologic value. Preliminary information about the geologic distribution of related taxa in other parts of the world indi- cates that this group may have potential for use in a world- wide lacustrine diatom biochronology. This report describes and presents light and scanning electron microscope photographs of several distinctive Actinocyclus species from the Western United States. An artificial key based on characters observable in the light microscope assists separation of these morphologically vari- able taxa. The key includes a few European taxa, some of which also appear in the United States, and two modern nearshore marine species that can live in limnic environ- ments. One of these species, Actinocyclus normanii f. sub- salsa (pl. 12, figs. 2-5), lives today in the Great Lakes and has been recovered from late Holocene sediments of Lake Ontario (Stoermer and others, 1985). The appropriate morphological characters for taxo- nomic separation of Actinocyclus are still largely unknown. The variability of surface areolae patterns (for example, fas- ciculation), degree of undulation, and mantle characteristics is great in these centric diatoms, and may be environmentally controlled to some degree (Theriot and Stoermer, 1984). Study of smaller structures, such as labiate processes, exter- nal processes and pseudonodules, and their morphometric relationships may be required to understand the natural clas- sification of these diatoms. We do not resolve these ques- tions, but we do present guidelines for the consistent description and identification of Actinocyclus species appli- cable to biostratigraphy and paleoecology. ACKNOWLEDGMENTS We particularly acknowledge the efforts of Kathryn Dieterich-Rurup in securing scanning electron microscope photographs of the Actinocyclus species illustrated in the accompanying plates. Horst Lange-Bertalot photographed l 2 THE DIATOM GENUS ACT INOC YCLUS IN THE WESTERN UNITED STATES Krasske’s type material of Coscinodiscus (Actinocyclus) miocenicus and C. (=A.) variabilis. E.C. Theriot, Reimer Simonsen, Simone Servant-Vildary, and GK. Khursevich have all provided many helpful discussions and insights into the morphological variations and taxonomic-descriptive problems with Actinocyclus. Simone Servant-Vildary, Rainer Gersonde, S.W. Starratt, L.H. Burckle, and Fumio Akiba kindly supplied comparative material. J.A. Barron and Elisabeth Fourtanier reviewed the manuscript and provided many useful suggestions. We thank all these indi- viduals for their interest in this study. MATERIALS AND METHODS Diatornites, diatomaceous tuffs, and lacustrine shales have been sampled from outcrops and wells in the Western United States. The locality numbers referred to in the text refer to these sites whose age (if known) and locations are given in Appendix 1 and figure 2 of Krebs and Bradbury (Chapter B). To minimize contamination by water and airborne diatoms (Sovereign, 1963), outcrops were cleaned in the field to a depth of about 5 cm during sampling, and material representing 1—5 cm of stratigraphic thickness was removed and placed in air-tight plastic bags. About 1 cc of diatoma- ceous sediment, with all surfaces cleaned a second time, was disaggregated in distilled water and boiled in concentrated nitric acid. The samples, once rinsed of all traces of acid, were mounted in Hyrax (n=l.60). Observations for species descriptions were made with a compound microscope (LM) at appropriate magnifications. An aliquot of the diatom preparation was settled on a scanning electron microscope (SEM) stub and sputter- coated with gold/palladium. SEM photographs of selected specimens were taken with a JEOL 35 C scanning electron microscope. In general, internal surfaces of diatoms are bet- ter preserved than external surfaces (Bradbury, 1984), but where appropriate, SEM documentation of both sides of the diatom was made to illustrate external characteristics neces- sary for identification. Type and LM-figured specimens are located on designated 2.54x7.62 cm microscope slides by England Finder (E.F.) coordinates. CHOICE OF GENERIC EPITHET Coscinodiscus, Cestodiscus, Stephanodiscus, Pontodis- cus, and Actinocyclus have all been used as generic epithets for fossil lacustrine centric diatoms that possess a marginal ring of laterally expanded (fan-shaped) labiate processes and radial-fasciculate areolation (for example, Krasske, 1934; Lohman, 1957; Hajos, 1970; Temniskova-Topalova and others, 1981; Bradbury, 1984). The very close similarity of Pontodiscus and Cestodiscus (Radionova, 1987) suggests that some of these names might be synonymous. Bradbury (1984) confirmed the presence of a pseudo- nodule on Neogene lacustrine centric diatoms from Idaho and China supporting their inclusion in the genus Actinocy- clus (see also, Simonsen, 1975). Nevertheless, in some marine species of Actinocyclus, the pseudonodule is tiny and difficult to distinguish from a normal areola (Watkins and Fryxell, 1986), and Radionova (1987) maintained that Ces- todiscus may or may not have a pseudonodule. She distinguished this genus from Actinocyclus by the form of the labiate process (mushroom-shaped in Cestodiscus and nozzle-shaped in Actinocyclus) and by the character of the velum covering the areolae (star—shaped perforations in Cestodiscus and sieve-like openings in Actinocyclus) (Radi— onova, 1987). Marginal hyaline stripes of unadomed silica, positioned above and around the openings of the labiate pro— cesses characterize many Cestodiscus species (Radionova, 1987), but these structures are also present on diatoms referred to Actinocyclus (Simonsen, 1982). The choice of the generic epithet for these centric dia- toms clearly depends, upon whether expanded or restricted generic definitions are employed. SEM examination of rep- resentatives of type species may suggest the synonymy of some genera. Labiate process morphology in nonmarine diatoms of the family Hemidiscaceae is variable and easily altered by corrosion in fossil forms. Pseudonodules may be obscured by debris or overgrowths of silica and clay miner- als, further complicating the use of these structures for generic classification. At this time, there is no compelling reason to use the name Cestodiscus for these otherwise clearly Actinocyclus-like diatoms, and the latter name is retained for this study. Coscinodiscus appears to be genu- inely different (as shown by Radionova, 1987), although it is still not properly typified, and at least some Pontodiscus species have been incorporated into Actinocyclus (Khurse- vich and others, 1990). The species of Actinocyclus described in this report have been separated by more or less obvious, if variable, morphological differences. It can be argued (compare Mann, 1988) that each paleolake contained its own Actinocyclus species, particularly when such paleolake systems were tem- porally separated by hundreds of thousands or millions of years. Such great temporal and geographic separation with concomitant differences in climate, geology, hydrology, and ecology reduce the likelihood of potential biological interac- tion between individuals of Actinocyclus despite their morphological similarity. Nevertheless, the morphological units described here are moderately consistent and at least imply similar environmental controls on Actinocyclus that can be meaningful for biostratigraphic and paleoecologic ends. ACT INOCYCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES 3 KEY FOR SEPARATION OF SOME NONMARINE SPECIES OF ACTINOCYCLUS The following key organizes the characters of the non- marine species of Actinocyclus described in this report and a few others described elsewhere to facilitate their separation and identification. The species of Actinocyclus are quite variable, yet morphologically similar, and examination of a moderately large series of specimens is required to obtain an appreciation of the variation and a general sense of their structural characteristics. Even so, intermediate forms often occur that defy simple classification. Specimens at the very large and very small ends of the size spectrum may be diffi- cult to sort out with this key. A. Fasciculate: clearly defined sectors of areolae rows. B. Fascicles marked off only by radial rows of areolae. C. Pseudonodule large, conspicuous; areolae on marginal 1/3 of disk in more or less regular tan- gential rows; often in brackish water. Actinocy- clus ehrenbergii Ralfs, (pl. 6, fig. 3). C. Pseudonodule tiny, difficult or impossible to see in LM, especially in heavily silicified individu- als; areolae on marginal 1/3 of disk in undulat- ing, disorganized rows. Areolae within fas- cicles parallel. Actinocyclus nebulosus, (pl. 11, figs. 3, 4). C. Pseudonodule small, but generally visible in LM. Marginal areolae not in widely spaced undulat- ing rows. Areolae within fascicles subparallel/ subradial. Actinocyclus cupreus, (pl. 5, figs. 6, 7) B. Fascicles marked off by a combination of radial rows of areolae and (or) comparatively long, hyaline stripes originating at labiate process exit pore near disk/mantle juncture. C. Hyaline stripes extending about 1Is the distance toward the valve center and continuing in a radial row of areolae (see Frenguelli, 1928; Krasske, 1934). Coscinodiscus (=Acrin0cyclus) variabilis (sensu Krasske, 1934), (pl. 14, figs. 5,6). C. Fascicles marked off only by long hyaline stripes that extend nearly to the valve center (see Schaudema, 1983). Actinocyclus kam'tzii (Pant. and Grun.) Schauderna, (pl. 8, fig. 1). C. Fascicles marked off by pyriform or clove- shaped hyaline stripes with narrow, pointed ends that extend a short distance towards the valve center; the remaining fascicle boundary com- posed of a radial row of areolae. Actinocyclus claviolus, (pl. 5, figs. 1, 2). B. Fascicles marked off only by directional incongruity between adjacent sets of subparallel areolae rows. Hyaline stripes absent (see Hasle, 1977). Actin- ocyclus normanii (Juhl.—Dannf.) Hustedt, (pl. 12, figs. 2, 3). A. Nonfasciculate: no clear sectors or fascicles of areolae, or fascicles irregularly formed, difficult to define or highly variable on specimens of different size. Hya- line stripes mark location of labiate processes. B. >12 areolae/10 urn (usually 14—18). C. Marginal processes present, located on the exit pore of labiate process. D. Marginal processes conspicuous. E. Marginal processes narrow tubes with lateral, fin-like projections. Actinocyclus pinnulus, (pl. 13, fig. 1). E. Marginal processes are broad, irregularly forked tubes 1—2 pm long. Actinocyclus nordlingensis Schaudema, (not figured). E. Marginal process usually angled, unforked rather broad tubes, occasionally adorned with lateral spines. Actinocyclus acanthus, (pl. 1, fig. 3). D. Marginal processes inconspicuous. E. Marginal process is a low, small, shield- like bump or nipple; often difficult to observe, fine areolation, 13—18 areolae/ 10 pm, diameter typically <30 1.1m. Actin- ocyclus theleus, (pl. 14, fig. 1). E. Marginal processes slender, unorna- mented tubes on hyaline stripes. Actin- ocyclus tubulosus (pl. 8, fig.7) Khursevich (Khursevich and others, 1990). C. Marginal processes at labiate process exit pore absent. D. Diameter 20—70 pm, valve conspicuously undulate, weakly undulate, or flat, areolae generally 12—13/10 pm. Actinocyclus krasskei (Krasske), (pl. 8, figs. 2-8). E. Valve conspicuously undulate, often >50 pm in diameter. Actinocyclus krasskei (undulate form), (pl. 8, fig. 5). E. Valve flat or weakly undulate, diameter typically <50 1.1m. Actinocyclus krasskei (pl. 8, fig. 2). D. Diameter 30—70 pm, valve conspicuously undulate, areolae 14—18/10 pm. A “moat” surrounds the pseudonodule. Actinocyclus gorbunovii var. fossa, (pl. 7, fig. 3). B. <12 areolae/10 pm C. Areolae large (1+ um), closely packed, typically 7—10/10 um, polygonal in outline. 4 THE DIATOM GENUS ACT INOC YCLUS IN THE WESTERN UNITED STATES D. Conspicuous, generally pointed hyaline stripes enclosing exit pore and extending onto the valve disk. Actinocyclus venenosus, (pl. 15, fig. 1). D. Generally inconspicuous hyaline stripes that end near the valve/mantle juncture. Spines may or may not be present at disk/mantle junction. Actinocyclus cedrus (pl. 2, fig. 1) and A. cedrus spinose form (pl. 4, fig. 4). C. Areolae smaller, circular in outline and typically loosely packed. Marginal areolae rows sinuous and interdigitating. Actinocyclus mozilis, (pl. 9, figs. 4—6). SYSTEMATIC DESCRIPTIONS ACTINOCYCLUS ACANTHUS Bradbury & Krebs sp. nov. Plate 1, figures 1—9 Description.—Valve circular, shallowly concave with slightly raised margin. Diameter typically ranging from 30 to 100 um. Disk with round areolae arranged in non-fasciculate, radial rows; 9—14 areolae/10 pm. Valve center of larger specimens sometimes hyaline, containing only scattered areolae. Small, often obscure, radial, mar- ginal hyaline stripes at disk-mantle juncture mark positions of labiate processes and are adorned with stout, hollow tubules up to 2 pm in length that may bear terminal lateral spines. Tubule stems either rounded or angled (often trian- gular) in cross-section (pl. 1, fig. 7). Because of breakage, morphological characteristics of tubule ends seldom visi- ble. Valve mantle finely areolate (20/10 pm) and steeply sloping away from disk margin. Labiate processes short, narrow-stemmed, with broad, spade-shaped labiae. Pseud- onodule small, about 1 pm in diameter, and variably located between labiate processes near valve margin. Variability—The length of hyaline stripes appears to vary among individuals both within and between localities. In an unnamed unit at New Pass, Lander County, Nevada (10c. 42) and in the Esmeralda Formation (Miocene) at Cedar Mountain, Nye County, Nevada (loc. 74), the hyaline stripes are often very small and obscure (pl. 1, fig. 6). Specimens from the Bully Creek Formation (Miocene), Malheur County, Oregon (loc. 7) have longer hyaline stripes (2—3 pm or longer), as do occasional specimens from the Cedar Mountain section (Lohman, 1957). The hyaline central area is largest and best developed in specimens from the Cedar Mountain section, while in mate- rial from New Pass it is smaller or absent. Pseudonodule position also seems to vary. In New Pass and Cedar Moun- tain (Esmeralda Formation) specimens, it is small and closely adjacent to a labiate process, while in the Bully Creek Formation material, it is located about 1/3 the distance between two labiate processes. Because of their susceptibility to abrasion and corrosion, the external tubules of this species are often poorly preserved or incomplete. In material from New Pass, some appear to bifurcate or are adorned with short lateral spines or flanges, suggesting that the typically short, blunt tubes often seen in LM may be artifacts of preservation. Tubules vary in cross section, being either round, triangular, or elliptical, but it is not known how constant tubules are on a single specimen from our available material. The apiculate species of Actinocyclus from other local- ities are close to the type in appearance, but not identical. Detailed study, including morphometric analysis, may require splitting this apiculate Actinocyclus group into sev- eral species. Diagnosis.—Actinocyclus acamhus can be distin- guished from other lacustrine members of the genus by the presence of robust, often angled, hollow thom-like tubes on the hyaline stripes that mark the exit pores of labiate pro- cesses. A. gorbunovii is more finely areolate, and external tubules are absent. Actinocyclus nordlingensis Schaudema has forked tubes and is more finely areolate (14—20/ 10 um). Its labiate processes are narrow-stemmed but comparatively long (>2 ttm). The pseudonodule location in A. nordlingen- sis is located about 1/3 the distance between adjacent labiate processes (Schaudema, 1983). Carina-like spines may be present on Actinocyclus cedrus, but they are irregularly placed, apparently solid, and not necessarily located on the hyaline stripes. Actinocyclus tubulosus Khursevich is smaller (16—34 pm diameter), has more densely packed areolae (16—22/ 10 pm), and external tubes with a rounded cross section. A. cedrus has coarse, polygonal areolae. Actin- ocyclus pinnulus is similar to A. acanthus, but has distinctly finned tubules, is clearly fasciculate, and has long, narrow hyaline stripes. Types.—Holotype: Strew slide United States National Museum (USNM) #465534. specimen located at E.F. (England Finder) H46. Isotypes: Strew slides in the following institutions: Academy of Natural Sciences of Philadelphia (ANSP) A—G.C. #64465; US. Geological Survey, Denver (USGS—D) #14 VII 85—4; California Academy of Sci- ences (CAS) #21605]. Type Locality—Because the diatom is best preserved and most abundant in unnamed deposits near New Pass, Lander County, Nevada (loc. 42 = USGS Denver 14 VII 85—4), this site has been selected as the type locality. Remarks.—The specific epithet “acanthus” (L. thorn) refers to the presence of hollow, thom-like tubes at the labiate process exit pores. Actinocyclus acanthus has also been found in the Bully Creek Formation, Harper Basin, Malheur County, Oregon, and in the Esmeralda Formation near Cedar Mountain, Nye County, Nevada (10c. 74). Here the taxon was originally described by Lohman (1957) as Cestodiscus apiculatus nomen nudum. At the Cedar Mountain section, Actinocyclus acanthus is associated with species of Surirella, Anomoeo- neis, and Pinnularia (Lohman, 1957), whose modern ACT INOCY CLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES 5 relatives suggest deposition in moderately saline, alkaline water. At some levels in the New Pass locality, it is associ- ated with Chaetoceros, also suggesting saline water, but elsewhere at New Pass, and at Bully Creek, freshwater spe- cies of Aulacoseira dominate the samples. At Silvies Valley, Grant County, Oregon (10c. 75), Actinocyclus acanthus is associated with large numbers of F ragilaria sp. cf. F. vire- scens. Other diatoms present include Aulacoseira, Tetracy- clus, Tabellaria, Eunotia, and Achnanthes. Perhaps the morphological differences seen in Actinocyclus acanthus reflect salinity or other environmental characteristics. ACTINOCYCLUS CEDRUS Bradbury & Krebs sp. nov. Plate 2, figures 1—7; plate 3, figures 1—8; plate 4, figures 1-6 Description.—Valve circular, with slightly raised mar- gin. Diameter typically 50—100 mm, but ranging from 20 to >150 pm. Valve face shallowly concave to weakly concen- trically undulate with radial rows of large (1 pm diameter), polygonal-shaped areolae, ranging from 6—10/ 10 um. Vague fasciculation of valve disk caused by bundles of mutually parallel areolae rows that extend variable distances towards the valve center progressively truncating one another (pl. 3, fig. 2). Valve center typically densely packed with areolae. Small, generally short, hyaline stripes at valve mantle junc- tion barely extend over mantle to enclose large (1 pm diam- eter) exit pores of labiate processes. Labiate processes 3—5 pm tall, with narrow, round or oval stems and relatively broad, spade-shaped labiae. Disk/mantle margin often hya- line and irregularly areolate and (or) variably ornamented with solid, granule-, keel-, or spine-like protuberances. Man— tle variably high (10—15 pm), and nearly perpendicular to valve face plane, with vertical areolae rows, 16 areolae/ 10 pm. Pseudonodule small and variably located between labi- ate processes, generally closer to one. Variability—The disk/mantle juncture may or may not be hyaline and irregularly areolate, or ornamented with spine- or granule-like protuberances. Such ornamentation is more typical in specimens from the Turner Creek (Pit River) locality in Modoc County, California (loc. 17) (pl. 4, figs. 4—6), and less common at the type locality in Stewart Valley, Mineral County, Nevada (loc. 20). Areolae near the valve disk center are sometimes sparse and surrounded by hyaline silica. Fasciculation is more apparent in some speci- mens than others. For example, specimens from the Virginia Range, 16 km north of Virginia City, Storey County, Nevada (10c. 68), are not clearly fasciculate, although they conform to the species in other features. Size of the hyaline stripes varies to some degree among speci- mens from different sites and may represent temporal or environmental gradations within this species. Forms of this species from deposits correlated to the Aldrich Station For- mation (Miocene), Lyon County, Nevada (loc. 1), and from deposits near Drewsey, Harney County, Oregon (loc. 63), tend to be less fasciculate than the type and are typically spinose. The labiate processes are taller and thinner in spec- imens from Goose Creek, Baker County, Oregon (loc. 27). Diagnosis.———Actinocyclus cedrus is very similar to A. venenosus, another nonmarine, fossil Actinocyclus species with coarse, polygonal areolation on the valve face. Actin- ocyclus venenosus is characterized by generally longer and more prominent hyaline stripes that extend well onto the valve disk. A. cedrus tends to be more obviously, if irregu- larly, fasciculate than A. venenosus, and concentric undula- tion is usually poorly developed in A. cedrus. Types.—Holotype: Strew slide USNM #465535, speci- men located at E.F. L38/1. Isotypes: Strew slides ANSP A—G.C. #64466; CAS #216052; USGS—D #3121288—1(65). Type Localioz.—“Diatorr1ite Ridge” in Stewart Valley, northwest of Cedar Mountain, Mineral County, Nevada (10c. 20 = USGS Denver 31 1 88—1 [65]) has been selected as the type locality for Actinocyclus cedrus. The collection site is located at 38.62° N., 117.94°W., about 8 m below the top of a 40-m section of buff, thin-bedded to laminated diato- maceous shales, and about 28 m above a volcanic ash dated at 15.1 Ma (S.W. Starratt, written commun., 1986). The sec- tion has been assigned to the Esmeralda Formation. Remarks.—The specific epithet “cedrus” (L. cedar) refers to the type locality of this species near Cedar Moun- tain. The type material was collected by SW. Starratt and represents his sample DR—65. Lohman (1957) identified this diatom by the name Cesmdiscus cedarensis nomen nudum at a nearby locality on the southeast flank of Cedar Mountain. The same (or very similar) species is reported from the Otis Basin, Harney County, Oregon (VanLandingham, 1967) under the name Coscinodiscus subtilis. Associated diatoms at the type locality include fresh- water, benthic Fragilaria species, Ellerbeckia arenaria v. teres, Tetracyclus sp., and a dominance of planktonic Aula- coseira spp. ACTINOCYCLUS CIA VIOLUS Bradbury & Krebs sp. nov. Plate 4, figure 7; plate 5, figures 1—5 Description.—Valve circular, nearly flat with a slightly raised or depressed center. Diameter ranging between 17 and about 60 pm, typically about 27—30 pm. Areolae about 13—14/10 um, small, round and in subparal- lel to radial rows. Areolae rows grouped into fascicles set off by continuous rows of areolae originating from hyaline stripe of each labiate process and running to valve center. Valve center sometimes a small, irregular hyaline area. Hyaline stripes marking locations of labiate processes com- paratively long (3—7 pm), narrowed, or pointed proximally and expanded distally to form irregular, somewhat triangu— lar-, cross- or clove-shaped areas (pl. 5, figs. 1—3). External 6 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES expression of labiate process is a short, blunt, rather thick- walled tube with a narrow opening rising 1—2 pm above disk/mantle junction (pl. 5, fig. 3). Valve mantle steeply sloping away from disk, finely areolate (about 26/10 um) and fairly short. Labiate processes not observed, but pre- sumably with narrow, round stems. Pseudonodule of medium size (1—2 pm in diameter) and often easily visible between hyaline stripes (pl. 5, figs. 2, 4, 5). Variability.—Actinocyclus claviolus is known only from Jungle Point, Idaho County, Idaho (10c. 33). At this locality, large specimens have fascicles with radial areolae rows. Consequently, the radial row associated with the hya- line stripe is less distinctive. Small specimens have fascicles in which the areolae rows are parallel to the central areolae row or in irregular groups of subparallel rows. The hyaline stripes are irregular but always somewhat pyriform or cross- shaped. Larger specimens have proportionally longer stripes. The central hyaline area is typically irregular, but always small. Diagnosis.—Actinocyclus claviolus is morphologically similar to A. cupreus, but it can be distinguished by its thick, prominent hyaline stripes, generally smaller size, and the presence of thick external tubes over the labiate process pore. Like A. cupreus, A. claviolus is also morphologically close to Coscinodiscus (=Actin0cyclus) variabilis (sensu Krasske 1934) (pl. 14, figs. 5, 6), but that species does not have laterally expanded hyaline stripes and is more coarsely areolate than A. claviolus. In addition, the hyaline stripes of Coscinodiscus variabilis (sensu Krasske) are typically longer, extending to about 1/3 of the disk radius. Types.—Holotype: Strew slide USNM #465536, speci- men at E.F. R28/2. Isotypes: Strew slides ANSP A—G.C. #64467; USGS—D #5 XII 80—7; CAS #216053. Type Locality—The type locality of Actinocyclus cla- violus is an unnamed lacustrine deposit at Jungle Point, northwest of the town of Lowell, Idaho County, Idaho; SE1/4, SE1/4 sec. 15, T. 33 N., R. 6 E. (10c. 33 = USGS Denver 5 XII 80—7). The diatoms at this locality show some corrosion and breakage. Remarks.—The specific epithet “claviolus” (L. diminu- tive for nail or clove) refers to the small clove-like shape of the hyaline stripes of this species. Aulacoseira sp. cf. A. praeislandica is the dominant diatom associated with Acti- nocyclus claviolus. ACTINOCYCLUS CUPREUS Bradbury & Krebs sp. nov. Plate 5, figures 6—9 Description—Valve circular, shallowly concave with a broadly raised margin. Diameter typically around 50 pm and ranging between 20 and 76 um. Areolae round- polygonal, in roughly radial to parallel rows. Areolae rows grouped in broad fascicles set off by continuous rows of areolae originating from hyaline stripe of each labiate pro- cess and running to valve center. Areolae about 13/10 um, generally loosely packed near valve center. Comparatively long (2—5 pm), prominent hyaline stripes extend from exit pore of labiate processes over disk/mantle junction and onto disk. Valve mantle finely areolate (about 20/10 um) and gently sloping away from valve disk. Labiate processes with narrow, round stems and rather broad, spade-like labiae. Pseudonodule small, but usually clearly visible; located at a variable distance between labiate processes on disk-mantle junction. Variability—To date, Actinocyclus cupreus has been found at four localities in the Western United States. At Copper Kettle Canyon, Churchill County, Nevada (loc. 16), evident variability has been found in the degree of fascicu- lation. Small specimens, probably referable to this species, tend to be more coarsely areolate and do not clearly show the radial areolae rows running between the hyaline stripes and the valve center that separate the areolae fascicles. In large specimens, strong valve undulation may obscure the radial areolae rows that border fascicles. Between labiate processes, areolae rows become more radial than mutually parallel in small individuals. Hyaline stripes show some variation in length, with relatively longer stripes on larger specimens. At Juliaetta, Nez Perce County, Idaho (10c. 32), and at Jungle Point, Idaho County, Idaho (10c. 33), diatoms referable to A. cupreus are comparatively small and resem- ble A. claviolus and A. krasskei, respectively, although the distinctive fasciculation is evident. In the Miocene Hum— boldt Formation, Eureka County, Nevada (10c. 30), compar- atively large forms are present that closely resemble the Copper Kettle Canyon material. Diagnosis.—Actinocyclus cupreus is distinguished from A. ehrenbergii (which also has single, radial areolae rows between hyaline stripes and the valve center) by its inconspicuous small pseudonodule, finer areolation, and generally smaller size. See also diagnosis underA. nebulosus and A. claviolus. Actinocyclus cupreus is‘also similar to an Actinocyclus species identified as Coscinodiscus variabilis Frenguelli by Krasske (1934) from Miocene freshwater deposits near the town of Ruckers on the southeast margin of the Vogelsberg Range at the northern end of the Rhine graben in central Germany. The Ruckers material tends to have slightly coarser areolation (9—12 areolae/10 pm) than do specimens from Copper Kettle Canyon, and the hyaline stripes are longer, often extending to one half the valve radius. Also, C. variabilis appears to have an external extension associated with each pore of the labiate process, unlike A. cupreus. Pseudonodules are visible on well-preserved valves of the Ruckers material indicating their probable affiliation with Actinocyclus. Types.——Holotype: Strew slide USNM #465537, E.F. F46/4. ACT INOC YCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES 7 Isotypes: Strew slides ANSP A—G.C. #64468; USGS—D #15 XII 88—1F; CAS #216054. Type Locality—The type locality of Actinocyclus cupreus is an unnamed formation at Copper Kettle Canyon in the northern Stillwater Mountains, sec. 26, T. 24 N., R. 34 E., Churchill County, Nevada (loc. 16 = USGS Denver 15 XII 88-1F). Specimens of A. cupreus are uncommon and poorly preserved. Remarks.—The specific epithet “cupreus” (L. of copper) refers to the type locality in Copper Kettle Canyon. A similar, perhaps closely related species of Actinocyclus has been found in Miocene freshwater sediments now covered by the Sea of Japan in the region of Yamato Bank (pl. 6, figs. 1, 2) (Burckle and Akiba, 1978; Tsoy and others, 1985), and from Japan (Koizumi, 1988). Specimens from Yamato Bank have hyaline stripes that can be very long, in some cases extending more than halfway towards the valve center in large individuals. The valve disk of this diatom is flatter than in A. cupreus, and the parallel-rowed fascicula— tion pattern is more regular and distinct. Further studies may confirm that all these diatoms are closely related. Freshwater, planktonic species of Aulacoseira domi- nate the type material containing Actinocyclus cupreus; Pinnularia, Tetracyclus, and Fragilaria are present in smaller numbers. ACTINOCYCLUS EHRENBERGII Ralfs in Pritchard (1861) Plate 6, figures 3-9; plate 7, figures. 1, 2 Description.——Descriptions, figures, and diagnoses of Actinocyclus ehrenbergii from nearshore marine localities (such as in Hustedt, 1930) suffice to identify and separate this distinctive diatom from nonmarine species of Actinocy- clus. The chief characteristic is the large, well defined, annulate-operculate pseudonodule of A. ehrenbergii. In addition, marine examples of this species have numerous, close-spaced, short-stemmed labiate processes. In contrast, nonmarine Actinocyclus species appear to have small, non- annulate (but perhaps also operculate?) pseudonodules and typically few and wide-spaced labiate processes with rela- tively longer stems. Remarks.—Actinocyclus ehrenbergii (pl. 6, figs. 3—5) is present in upper Miocene continental deposits of the Quiburis Formation, Edgar Canyon, Pima County, Arizona (loc. 92), where it is associated with brackish-water diatoms, such as Hyaloa’iscus sp. cf. H. laevis, Melosira moniliformis, Diploneis interrupta, D. ovalis, Mastogloia braunii, M. elliptica, F rustulia interposita, species of Amphora, Nitzschia, Achnanthes, Navicula, and many others. Benthic alkaline-water diatoms, such as F ragilaria brevistriata, Denticula elegans, and Caloneis silicula, are also abundant and indicate a transitional brackish, perhaps estuarine (Blake, 1902), to freshwater environment. A. ehrenbergii is also present in the uppermost Miocene to lowermost Pliocene Furnace Creek Formation of Death Valley, Inyo County, California (loc. 113). ACTINOCYCLUS GORBUNOVII var. FOSSA Bradbury & Krebs var. nov. Plate 7, figures 3—8 Description—Valve face characterized by compara— tively small, round areolae (14—18/10 pm) arranged in a radial, generally non-fasciculate pattern. Valve diameter averages about 30 pm but varies between 15 and 48 um. Valve disks typically strongly undulate. Labiate processes with narrow, long stems and circular cross sections. Short (4 pm) hyaline stripes extend from external opening of labiate process at valve margin towards valve center. Pseudonodule comparatively distinct, located between labi- ate processes, and usually closer to one. A tiny, moat-like structure surrounds external opening of pseudonodule (pl. 7, figs. 5—6). In favorable cases, this structure can be seen by LM as a small ring of hyaline silica around pseudo- nodule pore. Variability.——Actinocyclus gorbunovii var. fossa is known from only one locality. Some variation in the degree of areolation is present in the center of the valve disk. In large individuals, areolae may be loosely scattered about the valve center. Large valves tend to be more conspicuously undulate than small valves. Not enough SEM observations have been made to determine the constancy of the moat-like structure surrounding the external opening of the pseudo- nodule. From light microscope observations, it appears to be better developed in some valves than in others. Diagnosis.—Actinocyclus gorbunovii var. fossa is distinguished from A. gorbunovii by the presence of a small moat-like structure of hyaline silicathat surrounds theextemal opening of the pseudonodule. This structure is not present in type material of Actinocyclus gorbunovii (G.K. Khursevich, written commun., 1990). The closely spaced areolae (14—18/ 101.1 m) and the strongly undulate valve disk, however, suggest a varietal affinity with Actinocyclus gorbunovii. Actinocyclus krasskei is generally more coarsely areolate (12—13/10 um, although finer forms are reported), smaller, and flatter than A. gorbunovii var. fossa. Nevertheless, considerable variation exists, and some over- lap is found in all these characters. Separation of these species is not likely to be consistent in mixed assemblages, and it may turn out that they all belong to the same variable taxon. Types.—Holotype: Strew slide USNM #465538, E.F. N33/1. Isotypes: Strew slides ANSP A—G.C. #64775; USGS—D #2 1X 87—3B; CAS #216081. Type locality—Actinocyclus gorbunovii var. fossa is common in the early middle Miocene leaf-bearing 8 THE DIATOM GEN US AC TINOC YCLUS IN THE WESTERN UNITED STATES diatomites at Forty-nine Camp, Washoe County, Nevada (10c. 69). Preservation is variable, and valves are often broken. Remarks.——The varietal epithet “fossa” (L. “ditch”) refers to the small ditch or moat surrounding the pseudonod- ule of this taxon. In the upper Cedarville Formation at Forty- nine Camp, Washoe County, Nevada, Actinocyclus gor- bunovii var. fossa is associated with abundant Aulacoseira sp. cf. A. islandica. Tetracyclus ellipticus, Ellerbeckia arenaria v. teres, and several other freshwater diatoms are present in smaller numbers. Bradbury (1984) suggested that Coscinodiscus gor- bunovii (Sheshukova-Poretzkaja and Moissejeva, 1964), belonged in the genus Actinocyclus according to its general morphology and the presence of a pseudonodule in a related species from the Poison Creek Formation (Miocene) in the Snake River Plain, Idaho. Khursevich and others (1990) formally transferred C. gorbunovii to Actinocyclus. The Poison Creek Formation taxon is now regarded as distinct from A. gorbunovii and has herein been described as Actin- ocyclus venenosus. In view of the biostratigraphic impor- tance of A. gorbunovii in Eurasia and of closely related taxa in the Western United States, it is appropriate to evaluate the original description of Coscinodiscus gorbunovii Shesh. and its varieties. The following description of Coscinodiscus gorbunovii represents an approximate translation from Russian (Sheshukova-Poretzkaja and Moissejeva, 1964). The origi— nal description includes two varieties, Coscinodiscus gorbunovii v. gorbunovii Shesh. and C. gorbunovii v. ethmo- discoidus Moiss. COSCINODISCUS GORBUNOVII SHESHUKOVA In Sheshukova-Poretzkaja & Moissejeva 1964, P. 94, pl. 2, figs. 1—5. Description—Cells of yellow-brown color, short cylindrical or disk—shaped, with or without intercalary bands, 30—70 urn in diameter, 2—20 pm tall. Valves con- centrically undulate with a single concave zone and con- cave center. Valve structure of small, dense areolae in radial rows, 12—18/10 um, not forming fascicles. Central area small, round or of irregular shape with one or several isolated areolae, or occasionally absent. Distinct undulat- ing rows of areolae occur at the valve margin, and a ring of 7—14 short, blunt spines (=tubules) from which short, radial, hyaline rays emanate towards the valve center. Valve mantle edge narrow, delicately crosshatched (23—24 striae/lO pm or not visible). Short-cylindrical cells have valves with clearly expressed mantles of moderate height (3—4 pm) and with small areolae in radial and obliquely intersecting rows, 23—24/ 10 um. COSCINODISCUS GORBUNOVII v. GORBUNOVII SHESHUKOVA In Sheshukova-Poretzkaja & Moissejeva 1964, P. 96, pl. 2, figs. 1—5. Description.—Frustules disk-shaped, height 2—3 um, without intercalary bands. Diameter of the valves 35—70 um. On the frustule, 13—18 rows of areolae/10 um, central zone present, marginal zone narrow, delicately crosshatched. Mantle not developed. COSCINODISCUS GORBUNOVII v. ETHMODISCOIDUS MOISSEJ EVA in Sheshukova-Poretzkaja & Moissejeva 1964, P. 96, pl. 3, figs. 1—7. Description.——Frustules short-cylindrical with small collar-shaped, structureless intercalary bands, 30—50 mm diameter, and up to 20 um high. 12 areolae rows/ 10 pm on the frustule, central zone absent, marginal zone inconspicu- ous. Mantle of the frustule 3—4 pm high with small areolae in radial and obliquely intersecting rows, 23-24/ 10 um. Variability and Comments on the Descriptions.———For the most part, the description of Coscinodiscus gorbunovii and varieties is straight forward. Some points however, require discussion and revision. 1. It is not quite clear what is meant by the undulating areolae rows on the valve margin. In direct translation this passage reads, “In the area by the edge are distinct concentric—undulating rows of the same kind of areolae and * * *”. Published figures of this species (Sheshukova- Poretzkaja and Moissejeva, 1964; Cheremisinova, 1968; Moissejeva, 1971; and Temniskova-Topalova and others, 1981) do not clearly illustrate what might be meant by this remark. It is possible that it refers to a wavy pattern of short, interdigitated, and truncated radial areolae rows sometimes visible near the margin of this diatom. Altema- tively, it could refer to a looser and somewhat undulate pattern of areolae distributed tangentially along the valve margin and visible in some specimens. The revised description of A. gorbunovii (Khursevich and others, 1990) does not mention this feature. Such patterns are evident on other freshwater Actinocyclus species, however, and are of unknown taxonomic significance. 2. The description of valve disk undulation sounds equiv- alent to the “shallowly concave” terminology used in this report. Both light and SEM photographs of Coscinodiscus gorbunovii from the literature show individuals that have raised central areas (truly “concentrically undulate”) (for example, Temniskova-Topalova and others, 1981 pl. 3, fig. 3) among specimens that are shallowly (or deeply) con— cave. This probably represents normal variation within the species. It appears that undulation consisting of a raised margin and center (for example, in Khursevich and others, 1990) characterizes larger individuals of this species. ACT INOC Y CLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES 9 3. The reference to the yellow-brown color of Coscino- discus gorbunovii is taken to be taxonomically important by Moissejeva (1971). The color of Coscinodiscus gor- bunovii or any other diatom for that matter, partly relates to the density of its structural elements, but also to its magni- fication, the refractive index of the mounting medium, and related optical properties that have nothing to do with the biological characters required for taxonomic separation (Bradbury, 1984). 4. The comment about the presence or absence of “inter- calary bands” probably reflects preservation and also seems irrelevant to the description of Coscinodiscus gorbunovii. 5. The “lack of mantle development” suggested for Cos- cinodiscus gorbunovii v. gorbunovii presumably means that the mantle of this species is short in comparison to that of Coscinodiscus gorbunovii v. ethmodiscoidus. 6. The presence of short, blunt spines associated with the hyaline rays is difficult to confirm by most illustrations of Coscinodiscus gorbunovii. Typically, no spines of any kind are shown, and the only figure that clearly illustrates spines (Temniskova-Topalova and others, 1981, pl. 3, fig. 3), shows a number of irregular, spine-like protrusions along the disk/mantle junction and without clear relation to the hyaline rays. The description of the spines in this case states that they are between the hyaline rays (Temniskova- Topalova and others, 1981). Such spine-like projections (see also Khursevich and others, 1990) may represent an ecotypical variant of this species. The description of the synonym, Pontodiscus gor- bunovii (Shesh.) Shesh. et Moiss. (Temniskova—Topalova and others, 1981), also indicates the presence of external tubules at the openings of the labiate processes, although these are not illustrated. Furthermore, Moissejeva in an oral communication to G.K. Khursevich (written commun., 1989) stated that the labiate processes of Coscinodiscus garbunovii were mistaken as short spines in the original description of this species. 7. Khursevich and others (1990) gave 16-18 areolae rows/10 m and 14-18 areolae/10 m (presumably along a radial row) for A. gorbunovii. According to Khursevich and others (1990), the coarser Coscinodiscus gorbunovii v. ethmodiscoidus is no longer considered a variety of A. gorbunovii. In this report, we follow the revised descrip- tion with regard to areolar density of A. gorbunovii. ACTINOCYCLUS KRASSKEI (KRASSKE) Bradbury & Krebs nom. nov. Plate 8, figures 2—6, 8—11; plate 9, figures 1—3 Syn. Coscinodiscus miocem'cus Krasske 1934, p. 23, figs. 5—7. A nomenclatural problem exists with Coscinodiscus miocem'cus Krasske. Unmounted type material of this taxon has not been found, precluding SEM investigations to precisely document micromorphological characters of this species. Nevertheless, pseudonodules can be seen by light microscopy in well-preserved specimens of type material (pl. 8, fig. 3). By this and other criteria (see Simonsen, 1982), Coscinodiscus miocenicus can be confidently transferred to Actinocyclus. Because the name Actinocyclus miocem'cus Jousé (Jousé, 1973) has preempted the logical new combina- tion, we propose that Actinocycl us krasskei be used to desig- nate this taxon. , Description (From Krasske, 1934)—Valve circular, rather flat, 11—47 pm in diameter. Large areolae in radial rows, at the margin about 13/10 um, organized in unclear fascicles. Secondary rows in clear spirals. Mantle oma— mented with delicate areolae organized in three self-crossing linear systems (quincunx), about 20 striae in 10 pm. Central area lacking. Small individuals show irregular areolation. Observations of the type material [Beuern (Vogels- berg) Hessen Kieselgur O. Miocene No. 3004 and 3005, No. 24/25] by LM indicate the presence of a comparatively distinct pseudonodule, located between short to medium- length, hyaline stripes that mark the position of narrow, long-stemmed labiate processes. In addition, concentrically undulate valve disks are common in the material. Areolae along radial rows are about 12—13/10 um in type material, although densities of 15—22/ 10 pm had been stated for this species (Moissejeva, 1971; Temniskova—Topalova and others, 1981). No external tubes are visible at the labiate process exit pores. Variability—As stated by Krasske (1934), small indi- viduals have irregular areolation. The shape of the valve disk varies from flat to concentrically undulate. In the Western United States, diatoms that otherwise conform to Actino- cyclus krasskei have somewhat undulate disks and diameters as large as 70 pm. The large, undulate forms of A. krasskei may actually be synonymous with Coscinodiscus gor- bunovii, although they tend to be coarser than most Asian examples of A. gorbunovii. Diagnosis—Moissejeva (1971) stated that the mar- ginal zone of Coscinodiscus gorbunovii is similar to that of Coscinodiscus miocenicus Krasske, but that C. gorbunovii is larger, yellow~brown, and concentrically undulate. Type material of Coscinodiscus miocenicus (light yellow or colorless) includes undulate valves whose diameter (11— 47 um; Krasske, 1934) overlaps with the lower end of the size range reported for Actinocyclus gorbunovii. The color of these diatoms is not taxonomically relevant, and in most other respects A. gorbunovii and A. krasskei are quite simi- lar. 1n the type material and in examples of A. krasskei from the Western United States, areolae density does not exceed 13/10 um along radial areolae rows. Remarks—The specific epithet of Actinocyclus krasskei acknowledges the original author of this taxon (Krasske, 1934). Krasske (1934) reported large quantities of freshwater Aulacoseira and F ragilaria species in association with 10 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES Coscinodiscus miocenicus. The identification of Stephano- discus astraea (Krasske, 1934) could not be confirmed by close re-inspection of the type material (Reimer Simonsen, written commun., 1984). Actinocyclus krasskei has been reported as Coscinodis- cus miocenicus from the Harper Basin, Malheur County, Oregon (Abbott and VanLandingham, 1972), and from the Squaw Creek Member of the Ellensburg Formation (Miocene) in Yakima County, Washington (VanLanding- ham, 1964). At both localities, fresh water Aulacoseira species are dominant. At Vinegar Creek, in the Mascall For- mation in Grant County, Oregon (10c. 88), and at Juliaetta, Nez Perce County, Idaho (10c. 32), undulate A. krasskei occur with coarsely structured Aulacoseira sp., possibly related to A. islandica or A. granulata. Flat forms of Actin- ocyclus krasskei are present in the Latah Formation (Miocene), Spokane County, Washington (10c. 77), and in unnamed Miocene units at Oviatt Creek, Clearwater County, Idaho (loc. 43), and Arrow Junction, Nez Perce County, Idaho (10c. 72). At these localities, Aulacoseira species related to A. distans and A. praeislandica dominate along with Ellerbeckia arenaria v. teres, Melosira undulata, and species of Eunotia, Tetracyclus, and Tabellaria. Some diatoms from Siberia, identified as Pontodiscus (=Coscinodiscus) miocenicus, have SEM illustrations of external tubules placed at the hyaline stripes (for example, Temniskova-Topalova and others, 1981, pl. 4, figs. 2, 3, and 8). Khursevich and others (1990) have renamed such diatoms Actinocyclus tubulosus, but this name probably should not be applied to Krasske’s (1934) material nor to forms in the Western United States without tubules. Never- theless, A. tubulosus is also present in the Squaw Creek Member (loc. 49). When the tubules of this diatom are miss- ing because of breakage or corrosion, it cannot be effectively separated from A. krasskei by light microscopy (like that of pl. 8, fig. 7). ACTINOCYCLUS MOTILIS Bradbury and Krebs sp. nov. Plate 9, figures 4—6; plate 10, figures. 1—12; plate 11, figure 1 Description—Valve circular, disk slightly concave to weakly concentrically undulate with broadly raised margin. Diameter 20—90 pm. Disk with spaced, round areolae in slightly sinuous radial rows (especially near margin). Areolae rows of variable length, interdigitating with one another near margin of disk. Areolae density of type material 11—13/ 10 um. Areolae near disk margin noticeably smaller and more crowded (to 16/10 um) than those closer to valve center (10/ 10 pm). Fasciculation not apparent. Valve center small and irregularly hyaline with loosely packed areolae. Hyaline rays at disk/mantle junction short, radial, and dis- tinct. Valve/mantle junction typically abrupt, with a steeply sloping mantle. Mantle finely areolate (about 18/10 pm) with vertical-quincunx arrangement. Pseudonodule very small (often not visible in LM), located between labiate pro- cesses, usually closer to one. Externally, pseudonodule appears on a slightly elevated platform or mound (pl. 11, fig. 1). Internally, it is represented by a small field of several irregular areolae or pores (pl. 10, figs. 4 and 6). Internal expression of pseudonodule on specimens of Actinocyclus morilis from Ellensburg Formation (Squaw Creek Member) is very difficult to differentiate from normal areolation pattern. Labiate processes have long, narrow, circular stems with narrow, flanged labiae. Variability—Some variability can be seen in the char- acter of the disk/mantle junction. Typically it is abrupt, but in some specimens it tends to become more gradual and gen- tly sloping. A stellate pattern, caused by the termination of areolae rows, is distinctive in large specimens of this species but absent in smaller ones. As with most species of Actino- cyclus, the hyaline central area is quite variable and some- times absent. Specimens from some localities have hyaline rays that are very small and obscure. Large specimens of Actinocyclus motilis appear to grade into A. cedrus at Goose Creek, Baker County, Oregon (loc. 27), and at the Ellens- burg Formation localities in Washington (locs. 49, 59). These forms have coarser, crowded, and somewhat polygo- nal areolation, especially near the valve center. Diagnosis.—Actinocyclus motilis is best distinguished by its sinuous, interdigitating rows of round, spaced areolae. This pattern is also visible in A. cedrus and A. venenosus, but the areolae in these species tend to be larger, uniformly crowded and polygonal. Labiate process labiae are also narrower in A. motilis. Nevertheless, large forms of A. moti- lis can be confused with the former taxa. The coarseness of areolation separates A. motilis from large forms of A. gorbunovii and A. krasskei. Types.—Holotype: Strew slide USNM #465539, E.F. Q39/2. Isotopes: Strew slides ANSP A.—G.C. #64469; USGS—D #23 I 81—10; CAS #216055. Type locality.—Ac!inoc_vclus motilis is abundant and well preserved in deposits of the Esmeralda Formation at the southeast end of Cedar Mountain, Mineral County, Nevada (loc. 22). This deposit (USGS Denver 23 I 81—10) is chosen as the type locality. Remarks—The specific epithet “motilis” (L. motion) refers to an apparent rotational movement of the valve when focusing through it in the light microscope, apparently caused by the sinuous nature of the marginal areolae rows. This species, called Cestodiscus mobilis Lohman (nomen nudum), was first recognized by Lohman (1957) from the Esmeralda Formation near Cedar Mountain, Nye County, Nevada, but here the species is rare, poorly preserved, and mixed with other forms of Actinocyclus. Similar but some— what coarser forms are extensively figured in VanLanding- ham (1964) under the name Coscinodiscus subtilis from the ACT INOCYCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES II Squaw Creek Member of the Ellensburg Formation in Yakima County, Washington. At the type locality, Actinocyclus motilis dominates the assemblage. Associated taxa include freshwater species of Aulacoseira, T etracyclus, Fragilaria, and occasional frag- ments of Actinocyclus cedrus. ACTINOCYCLUS NEBULOS US Bradbury & Krebs sp. nov. Plate 11, figures 2—8; plate 12, figure 1 Description—Valve circular, diameter 35—100 pm. Disk shallowly concave to slightly concentrically undulate and ornamented with fascicles of areolae. Areolae rows parallel to middle row of each fascicle. Fascicles separated by hyaline, costa-like rays enclosing a single row of wide- spaced areolae that run from disk margin to center. Areolae in fascicles irregularly spaced on distal third of valve and forming irregularly undulating rows tangential to valve cir- cumference. Areolae small and widely separated (9—12/10 um), and apparently with large and irregularly shaped inter- nal loculae, especially on distal third of disk. Central area of disk variable. Marginal hyaline stripes comparatively long (about 10 um) and with irregular edges. Stripes merge prox- imally into hyaline rays and corresponding radial rows of areolae marking fascicle. Disk/mantle junction sharp and mantle steep, finely areolate (16—20/10 pm) with vertical, slightly quincunx pattern. Labiate processes with broad, recurved flanges and comparatively narrow, circular stems. Pseudonodule small, generally close to labiate process. Variability—On some valves, the labiate process stems appear to be shorter and broader than the typical con- dition. The areolae, especially what are presumed to be their locules, are highly irregular in shape and apparently expanded internally so that the integrity of the areola disap- pears when focusing through the comparatively thin disk wall. This may be a partial artifact of preservation. The hya- line central area of the valve is highly variable, sometimes discrete and large, other times irregular or absent. Hyaline stripes, because of the irregularity of surrounding areolae, are also variable in shape, length, and clarity. Diagnosis.—Actinocyclus nebulosus is close to A. ehrenbergii in character of fasciculation, but it can be sepa- rated from that species by its small, obscure pseudonodule and the irregular, disorganized arrangement of areolae around the disk margin. A. cupreus is also similar but does not have disorganized areolae on the disk margin, and areolae rows within fascicles are not clearly parallel to the central areolae row. Types.——Holotype: Strew slide USNM #465540, E.F. K41. Isotypes: Strew slides ANSP A.—G.C. #64479; USGS—D #26 XII 86-2A; CAS #216056. Type Locality—We designate outcrops of the Esmer- alda Formation near Black Spring, Nye County, Nevada (loc. 93 = USGS Denver 26 Xll 86—2A), as the type locality of this species. Remarks.—The specific epithet “nebulosus” (L. cloudy or obscure) refers to the poorly defined marginal region of the valve apparently caused by irregular loculae beneath areoles. Smedman (1969) described and illustrated this species as Coscinodiscus nevadensis (nomen nudum) from an unnamed formation in Buffalo Canyon, southeast of East- gate, Churchill County, Nevada (Ice. 6), but she failed to designate a type specimen, slide, or a repository. The species is also common near the base of the Cedar Mountain section in Nye County, Nevada (Ice. 74), and was described and fig- ured (Lohman, 1957) as Cestodiscus fasciculatus Lohman (nomen nudum). Aulacoseira sp. cf. A. distans dominates in a sample containing abundant Actinocyclus nebulosus from near Buffalo Canyon, Nevada. Smedman (1969) listed several species of Melosira (Aulacoseira), Cymbella, Pinnularia, Navicula, and Gomphonema in the type assemblage. A. nebulosus is also present in the Mascall Formation near Aldrich Mountain, Grant County, Oregon (10c. 85), where it associates with freshwater Aulacoseira species related to A. distans, A. agassizii, and A. islandica. At the type locality, Actinocyclus nebulosus codomit‘lates with Aulacoseira spp. ACTINOCYCLUS PINNULUS Bradbury & Krebs sp. nov. Plate 12, figures 6, 7; plate 13, figures 1—5 Description.—Valve circular, with raised rim and shal— lowly concave center. Diameter ranging between 47 and’ 76 um, typically between 65 and 70 um. Disk with small, round areolae, about 13/10 pm. Near center of disk, areolae smaller and somewhat loosely packed. On disk margin, areolae larger, closely packed and slightly polygonal in shape. Areolae pattern obscurely fasciculate with two wedge-shaped fascicles of subparallel areolae rows between each pair of labiate processes. Intersection of adjacent sets of subparallel areolae rows evident near the disk margin and less so towards valve center. Valve center generally, but not necessarily, with loosely packed areolae forming irregular hyaline space. Disk/mantle juncture sharp, with mantle per- pendicular to disk plane. Mantle 8—10 pm high with tiny areolae in a quincunx pattern, about 18/10 um. Marginal, hyaline stripes narrow, about 5 1.1m long and extending from disk-mantle juncture onto valve disk. External tubules of labiate processes with a narrow stem, ornamented with two or more fin-like projections resembling pinnae or small leaf- lets attached parallel to tubule axis. Labiate processes long stemmed, with comparatively small, recurved and flexed 12 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES labiae. Pseudonodule small to medium, often obscurely vis- ible between two labiate processes. Variability.—Actinocyclus pinnulus is known only from three localities in the Western United States (locs. 81, 90, 91). Different collections of A. pinnulus from the Hole- in-the-Wall diatomite quarry (Miocene), Gooding County, Idaho (locs. 90, 91), show variations in the degree of central area development; in some populations the central areas are mostly absent or very small, while in others they are typi- cally large and irregular. The pseudonodule is larger and more visible in some specimens than others, and the fins on the external tubules of the labiate processes exhibit some variation apart from differences in preservation. Generally, each tubule has two opposite fins that lie in a plane tangential to the valve circumference. Rarely, individual tubules will have three or even four fins irregularly placed along the - tubule axis. Fasciculation and diameter of A. pinnulus appear comparatively uniform. At 986 m depth in the AMOCO Becharof No. 1 well, Alaska (loc. 112), a nonmarine species of Actinocyclus related to A. pinnulus is rare (pl. 13, fig. 6). It resembles A. pinnulus by the presence of flanged marginal apiculae and general pattern of fasciculation, although the areolae are smaller and less polygonal than in the species. It also differs from the species in having a sloping mantle with vertical (not a quincunx pattern) areolae rows. Diagnosis.—Actinocyclus pinnulus is closest to A. acanthus. A. acanthus does not, however, have tubules with fins, is non-fasciculate, and has only tiny, obscure hyaline stripes in contrast to A. pinnulus. A. nordlingensis has forked, not finned tubules, and Coscinodiscus (= Actinocy- clus) gorbunovii apparently lacks tubules. Types.~—Holotype: Strew slide USNM #465541, E.F. L34/2. Isotypes: Strew slides ANSP A—G.C. #64471; USGS—D #21 VI 88—1; CAS #216057. Type Locality—The type locality for Actinocyclus pin- nulus is the Hole-in-the-Wall diatomite quarry, NW 1/4 sec. 12, T. 4 S., R. 13 E., Gooding County, Idaho (Ice. 90), along the drainage of Clover Creek. Remarks.——The specific epithet “pinnulus” (L. small flu or pinna) refers to the fin-like projections on the external tubes of the labiate processes of this diatom. The species has also been collected from the same unit exposed in the NE 1/4 of sec. 19, T. 3 S., R. 13 E. (loc. 91 = USGS Denver 21 VI 88—1). Aulacoseira sp. cf. A. praeis- landica is the dominant associate of Actinocyclus pinnulus, and a species of Mesodictyon Theriot and Bradbury (Thalas- siosiraceae) is present in smaller numbers. Mesodictyon also \ occurs with A. pinnulus in the unnamed lacustrine beds at Durkee, Baker County, Oregon (10c. 81). ACTINOCYCLUS THELEUS Bradbury & Krebs sp. nov. Plate 13, figure 7; plate 14, figures 14 Description—Valve circular, concentrically undulate with broadly raised margin and shallowly raised or depressed center. Diameter 11-35 pm, typically around 20 um. Areolae small, round, loosely packed, about 13— 18/10 um and not forming clear fascicles. Areolae in valve center often scattered, but not always. Hyaline stripes inconspicuous, narrow, and extending onto disk edge. Exit pores of labiate processes with a low, shield-shaped or nipple-like protrusion rising about 1 pm above valve sur- face. Valve mantle perpendicular, with vertical rows of fine areolae, about 25/10 um. Labiate processes with nar- row, round stems and spade-shaped labiae with curved, slit-like openings. Pseudonodule generally small but prom— inent and variably located between labiate processes at valve-disk margin. Variability—The nipple-like protrusions at the exit pores of the labiate processes and associated hyaline stripes may be more or less prominent, perhaps as a result of preser- vation. At Emerald Creek, Benewah County, Idaho (10c. 21), degree of undulation and density of areolae vary consider- ably. Generally poor preservation of the species at Oviatt Creek, Clearwater County, Idaho (10c. 43), complicates comparison of these forms, but in general they appear flatter than the Emerald Creek forms, and with reduced shield-like processes. At Juliaetta, Nez Perce County, Idaho (loc. 32), and at the White Hills (Mascall Formation), Grant County, Oregon (10c. 87), A. thelelus tends to be coarser and more heavily silicified than at Emerald Creek. Perhaps the larger and coarser members of this complex merit separation. Diagnosis.—Actinocyclus theleus is characterized by the presence of nipple-like tubules external to the labiate processes and by its typically undulate shape and fine areola- tion. It can be distinguished from small forms of A. gor- bunovii and A. krasskei by the presence of the shield-like platforms that subtend the small external processes. The external processes of Actinocyclus acanthus are heavier, larger, and longer than those of A. theleus. Types.——-Holotype: Strew slide USNM #465542, E.F. M34/4. Isotypes: Strew slides ANSP A—G.C. #64472; USGS—D #5 XII 80—4; CAS #216058. Type Locality—Finely laminated lacustrine siltstone from the “Clarkia Lake deposits” of Miocene age from Emerald Creek, near Clarkia, Idaho (loc. 21 = USGS Denver 5 XII 80—4) represents the type locality of Actinocyclus theleus. The sample location is in the WW, NE 1/4, sec. 33, T. 43 N., R. l E., Benewah County, Idaho (= locality UIMM P—37, Smiley and Rember, 1985, at Emerald Creek; 10c. 21). ACTINOCYCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES I I3 Remarks.—The specific epithet “theleus” (G. nipple) refers to the character of the external tubes of the labiate processes. The species is figured as Actinocyclus sp. in Bradbury and others (1985), and at both Emerald Creek and at Oviatt Creek, Clearwater County, Idaho (loc. 43), it co—occurs with abundant Aulacoseira species related to A. Iirara and A. distans, and a large variety of benthic diatoms indicative of soft, fresh, humic-rich, slightly acid water. Actinocyclus theleus is not widely distributed, and it may be that this form is characteristic of softwater, slightly acid environ- ments. The coarser and larger forms at Juliaetta (10c. 32) and the White Hills (Mascall Formation), Grant County, Oregon (10c. 87) are associated with heavily silicified Aula- coseira sp. (cf. A. praeislandica) that may indicate more silicon-rich, eutrophic environments. ACTINOCYCLUS TUBULOS US Khursevich (Khursevich and others, 1990) Plate 8, figure 7 Remarks.—This small, fine Actinocyclus species with short external tubules of circular cross section occurs rarely in the Squaw Creek Member of the Ellensburg Formation in central Washington. Poorly preserved specimens (lacking external tubules) may be misidentified as Actinocyclus krasskei that is otherwise similar (for example, Temniskova- Topalova and others, 1981). The specimen figured (pl. 8, fig. 7), has external tubules that appear above the focal plane in light microscopy. The type locality is in western Siberia along the Tim River (Khursevich and others, 1990). ACTINOCYCLUS VENENOSUS Bradbury & Krebs sp. nov. Plate 14, figures 7, 8; plate 15, figures 1—6 Description.-——Valve circular, with broadly raised rim and shallowly concave to concentrically undulate valve disk. Diameter 35 to >160 pm, but typically around 70 to 100 pm in type material. Disk with coarse (about 1 pm diameter) polygonal areolae arranged in approximately radial rows, 6— 1. 10 in 10 pm. Areolae pattern non-fasciculate or vaguely fas- ciculate. In medium to large specimens, shorter areolae rows interspersed between longer rows terminate in narrow trian- gles ofhyaline silica at variable distances from valve margin. Valve center either tightly or loosely packed with areolae. Disk/mantle juncture often loosely and irregularly areolate and typically unomamented. Occasionally, closely spaced, keel-like spines present along the disk/mantle junction. Mar- ginal hyaline stripes prominent (often 2—3 pm in length) and proximally pointed or tapered. Stripes usually extend across valve mantle and onto valve disk. On mantle, marginal hya- line stripes enclose comparatively large and often elliptical exit pores of labiate processes. Labiate processes typically short, broad-stemmed, and with broad, recurved, crescentic, spade-like labium. Pseudonodule small, at disk/mantle junc- tion, and typically closer to one labiate process. Variability—Like other species of Actinocyclus, A. venenosus varies morphologically. The hyaline stripes are usually rather long and prominent but may be comparatively small; some variation is seen on single valves. They are generally easily seen at low magnifications. Typically, the disk/mantle junction is broad, and the mantle gently slopes away from the plane of the disk. In some specimens, how- ever, the junction is sharper and the mantle more steeply sloping. Labiate processes usually have short, elliptical stems and broad, recurved, crescent-shaped labiae, but occa- sionally, relatively taller, more circular-stemmed labiate processes occur. Fasciculation is occasionally evident. It is not certain whether these variations, which tend to co-occur (fasciculation, steep, sharp mantles, and sometimes longer labiate processes), represent intraspecific variation or char— acters of Actinocyclus cedrus. More fasciculate forms of this species occur in the Coal Valley Formation (Miocene), Lyon County, Nevada (loc. 15). Diagnosis.—Actinocyclus venenosus is best recognized by its prominent hyaline stripes, broad disk/mantle junction, gradually sloping mantle, radial, non-fasciculate areolation, and concentric undulation of the valve disk. It is closest to A. cedrus, and type material can usually be separated from this species that typically has a sharp disk/mantle junction, a steep, tall mantle, more evident and consistent fasciculation, and minute, blunt hyaline stripes. Nevertheless, intergrada- tions occur at other sites that frustrate simple separation, and broken valves may be impossible to identify. Actinocyclus cupreus is distinguished from A. vene- nosus by the presence in the former of continuous radial areolae rows that extend from each labiate process to the valve center. Actinocyclus cupreus is also somewhat more finely structured (13 rounded-polygonal areolae/10 um) and has labiate processes with comparatively long stems. Types.——Holotype: Strew slide USNM #465543, E.F. E39. Isotypes: Strew slides ANSP A—G.C. #64473; USGS—D #11 VI78—1A;CAS #216059. Type Locality—The type locality is at Reynolds Creek, Owyhee County, Idaho (NW1/4 sec. 2, T. 2 S., R. 3 W.) (loc. 44 = USGS Denver 11 VI 78—1A). Remarks.—The specific epithet “venenosus” (L. very poisonous) refers to its abundance in the Poison Creek For- mation of the Idaho Group, western Snake River Plain, Idaho. This species, labeled Actinocyclus sp. cf. A. gorbunovii from the Poison Creek Formation and from diatomaceous deposits in the Xian Feng Basin near Kunming, China is fig— ured in Bradbury (1984). Actinocyclus sp. (Khursevich and others, 1990) from the Primor region of western Siberia appears to be closely related to A. venenosus. Associated 14 THE DIATOM GENUS ACT INOC YCLUS IN THE WESTERN UNITED STATES diatoms at the type locality are dominated by Aulacoseira species. Navicula, Diploneis, Tetracyclus, Cymbella, Stau- roneis, and several other genera are present in smaller numbers. PALEOECOLOGY OF MIOCENE LACUSTRINE ACTINOCYCLUS Between 20 and 10 Ma, species of Actinocyclus were the dominant planktonic discoid diatoms of temperate lake systems in the Northern Hemisphere. With the clear excep- tion of Actinocyclus ehrenbergii, and possibly of A. acan- thus, the Actinocyclus species from Miocene lacustrine deposits in the Western United States are freshwater plank- tonic diatoms. Actinocyclus krasskei and A. theleus seem to have dominated in smaller, neutral to slightly acidic lake sys- tems (for example, Bradbury and others, 1985), while the larger and more coarsely structured forms, A. motilis, A. cedrus, and A. venenosus, appear to have been characteristic of larger, more eutrophic, slightly alkaline environments. Little is known about the limnology of the lakes inhab- ited by Actinocyclus. It is reasonable to assume that large Miocene lakes in the Western United States were warm monomictic; that is, circulating in the winter at temperatures above 4°C because Miocene climates were less seasonal and winters milder. By analogy to modern lake systems, Aula- coseira species would dominate the diatom plankton during times of circulation where turbulence could suspend the heavy cells and supply nutrients to the photic zone. Actinocy- clus normanii f. subsalsa is the only known extant Actinocy- clus species living in freshwater. Its ecology is not well known, although in Lake Ontario it prefers nutrient-enriched water and reaches maximum populations in late summer (Stoermer and others, 1974). In contrast, Aulacoseira island- ica blooms in late spring and early summer in Lake Ontario (Stoermer and others, 1974), during or shortly following spring circulation in less contaminated parts of the lake. The common association of Actinocyclus and Aula- coseira species in Miocene lakes suggests that perhaps the two diatoms occupied limnological niches similar to their counterparts in Laurentian Great Lakes. Nonetheless, extrapolation from the modern distribution of Actinocyclus normanii f. subsalsa may be compromised by the fact that this species has significant morphological differences com- pared to Miocene Actinocyclus species (for example, lack of hyaline stripes and apparently a structurally more compli- cated pseudonodule). REFERENCES Abbott, Jr., W.H., and VanLandingham. S.L., 1972, Micropaleon- tology and paleoecology of Miocene non-marine diatoms from the Harper District, Malheur County, Oregon: Nova Hedwigia, v. 13, p. 847—906. Blake, W.P., 1902, Arizona diatomites: Transactions of the Wis- consin Academy of Sciences, Arts, and Letters, v. XIV, pt. 1, p. 107—111. Bradbury, J.P., 1984, Fossil Actinocyclus species from freshwater Miocene deposits in China and the United States, in Mann, D. G. (ed.), Proceedings of the 7th International Diatom Sympo- sium, Philadelphia, 22—27 August, 1982: Koenigstein, Germany, Koeltz, p. 157—171. Bradbury, J.P., Dieterich, K.V., and Williams, J.L., 1985, Diatom flora of the Miocene lake beds near Clarkia in northern Idaho, in Smiley, C. J. (ed.), Late Cenozoic history of the Pacific Northwest: San Francisco, Califomia, Pacific Division of the American Association for the Advancement of Science, p. 33—59. Bradbury, J.P., and Krebs, W.N., 1982, Neogene and Quater— nary lacustrine diatoms of the western Snake River Basin, Idaho-Oregon, USA: Acta Geologica Academiae Scien- tiarum Hungaricae, v. 25, no. 1—2, p. 97—122. Burckle, L.H., and Akiba, Fumio, 1978, Implications of late Neo- gene fresh-water sediment in the Sea of Japan: Geology, v. 6, p. 123—127. . Cheremisinova, E.A., 1968, New data about the diatoms of the Neogene deposits of the Baikal area, in Fossil Diatoms of the USSR: Moscow. USSR, Academy of Science, Siberian Divi- sion, Institute of Geology and Geophysics. p. 71—74. Frenguelli, Joaquin, 1928, Diatomeas del Océano Atlantico frente 3 Mar del Plata (Repfiblica Argentina): Anales del Museo Na- cional de Historia Natural, Tomo XXXIV, p. 497—572. Hajos, Marta, 1970, Kieselgurvorkommen im Tertiiirbecken von Aflenz (Steiermark): Mitteilungen der Geologischen Gesell- schaft in Wien, v. 63, p. 149—159. Hasle, GR, 1977, Morphology and taxonomy of Actinocyclus nor- mam'i f. subsalsa (Bacillan’ophyceae): Phycologia, v. 16, no. 3, p. 321—328. Hustedt, Friedrich, 1930, Die Kieselalgen Deutschlands, Oster- reichs und der Schweiz unter Beriicksichtigung der iibrigen Lander Europas sowie der angrenzenden Meeresgebiete, in Ra- benhorst, L., Kryptogamen-Flora von Deutschland, Osterreich und der Schweiz: Leipzig, Akademische Verlagsgesellschaft m.b.H., Band VII, 920 p. Jousé, A.P., 1973, Diatoms in the Oligocene-Miocene biostrati- graphic zones of the tropical areas of the Pacific Ocean, in Simonsen, Reimer (ed.), Second symposium on recent and fos- sil marine diatoms: Beihefte zur Nova Hedwigia, Heft 45, p. 333—363. Khursevich, G.K., Moisseeva, A.I., Kozirenko, T.F., and Rubina, N.V., 1990, New taxa of the genus Actinocyclus (Bacillario- phyta) from the Neogene freshwater deposits of the USSR: Botanichcski Zhurnal v.75, no. 10, p. 1439—1442. Koizumi, Itaru, 1988, Early Miocene Proto-Japan sea: Journal of the Paleontological Society of Korea, v. 4, p. 6—20. Krasske, Georg, 1934, Die Diatomeenflora der hessischen Kiesel- gurlager: Sitzungsberichte der Heidelberger Akademie der Wissenschaften, Abhandlung 5, 26 p. Krebs, W.N., Bradbury, J.P., and Theriot, EC, 1987, Neogene and Quaternary lacustrine diatom biochronology, western USA: Palaios, v. 2, p. 505—513. Lohman, K.E., 1957, Cenozoic non-marine diatoms from the Great Basin: Pasadena, California Institute of Technology, Ph.D. dis- sertation, 190 p. ACT INOC YCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES 15 Mann, D.G., 1988, The nature of diatom species: analysis of sym- patric populations, in Round, F. E., Proceedings of the 9th International Diatom Symposium: Bristol, Biopress Ltd., p. 317—327. Moissejeva, A.I., 1971, Atlas of the Neogene diatom algae of the Primor region: Moscow, USSR, All Union Lenin Order of Scientific Investigation, Geological Institute, new series, v. 171, 152 p. Pritchard, A., 1861, A history of infusoira including the Desmidi- aceae and Diatomaceae British and foreign: London, 4th Edition, Whittaker and Co., 968 p. Radionova, ER, 1987, Diatom morphology of the genus Cesrodis- cus from lower middle Miocene deposits of the tropical zone of the Pacific Ocean: Academy of Sciences, USSR, Institute of Geology, Micropaleontology Edition, Issue 29, p. 141—154. Schaudema, Hedwig, 1983, Die Diatomeenflora aus den Miozéinen Seeablagerungen im Nordlinger Ries: Paleontographica, Abteilung B, Band 188, p. 83—193. Sheshukova—Poretzkaja, V.S., and Moissejeva, A.I., 1964, New and curious diatoms from the Neogene of western Siberia and the Far East: New Systematics of Lower Plants. Academy of Science, USSR, Botanical Institute, M—L, p. 92—103. Simonsen, R., 1975, On the pseudonodulus of the centric diatoms, or Hemidiscaceae reconsidered: Beihefte zur Nova Hedwigia, Heft 53, p. 83—94. 1982, Notes on the diatom genus Charcotia M. Peragallo: Bacillaria, v. 5, p. 101—116. Smedman, Gunilla, 1969, An investigation of the diatoms from four Tertiary lake bed deposits in westem Nevada: PaleoBios (Contributions from the University of Califomia Museum of Paleontology, Berkeley) no. 9, 16 p. Smiley, C.J., and Rember, W.C., 1985, Physical setting of the Miocene Clarkia fossil beds, nonhem Idaho, in Smiley, C.J. (ed.), Late Cenozoic history of the Pacific Northwest: San Francisco, California, Pacific Division of the American Asso- ciation for the Advancement of Science, p. 11—31. Sovereign, HE, 1963. New and rare diatoms from Oregon and Washington: Proceedings of the Califomia Academy of Sciences. 4th Series v. 31, no. 14 p. 349—368. Stoerrner, E.F., Bowman, M.M.. Kingston, J.C., and Schadel, A.L., 1974. Phytoplankton composition and abundance in Lake Ontario during IFYGL: Special report no. 53 of the Great Lakes Research Division, University of Michigan, 373 p. Stoenner. E.F., Wolin, J.A., Schelske, C.L., and Conley, D.J., 1985, Assessment of ecological changes during the recent history of Lake Ontario based on siliceous algal microfossils preserved in lake sediments: Journal of Phycology, v. 21, p. 257—276. Temniskova-Topalova, D.N., Kozyrenko, T.F., Moisseeva, A.I., and Sheshukova-Poret7kaya, VS, 1981. A new genus Ponto— discus (Bacillariophyta): Botaniska Zhumal (Leningrad), v. 66. p. 1308—1311. Theriot. EC, and Stoermer, ER, 1984, Principal component analysis of character variation in Stephanodiscus niagarae Ehercnb.: Morphological variation related to lake trophic status, in Mann, D.G., (ed.), Proceedings of the 7th Intema— tional Diatom Symposium, Philadelphia, 1982: Koenigstein, Germany, Koeltz, p. 97—1 11. Tsoy, I.B., Vashchenkova. N.G., Gorovaya, M.T., and Terekhov, Ye.P.. 1985, The finding of continental deposits on Yamato Rise. Sea of Japan: Tikhookeanskaya Geologiya (Pacific Geology), no. 3, p. 50—55. VanLandingham, S.L., 1964. Miocene non-marine diatoms from the Yakima region in south-central Washington: Beihefte zur Nova Hedwigia, Heft 14, 78 p. 1967, Paleoecology and microfloristics of Miocene diatomites from the Otis Basin-Juntura region of Hamey and Malheur Counties, Oregon: Beihefte zur Nova Hedwigia, Heft 26, 77 p. Watkins, T.F., and Fryxell. G.A., 1986, Generic consideration of Actinocyclus: consideration in light of three new species: Diatom Research, v. 1. p. 291—312. PLATES 1—15 Contact photographs of the plates in this report are available, at cost, from the U.S. Geological Survey Photographic Library Federal Center, Denver, Colorado 80225 PLATE 1 Figures 1—9. Actinocyclus acanthus Bradbury & Krebs, sp. nov. (p. 4). Scale bars in um. (18) 1. 7, 8. Unnamed Miocene unit, New Pass, Lander County, Nevada (10c. 42). Arrows mark marginal tubular processes at disk/mantle junction and concentric undulation of valve. Diameter 65 um. Slide USGS—D 14 VII 85—4 (2), ER 632/]. New Pass, Lander County, Nevada (loc. 42). Internal view showing pseudonodule (arrow). Diameter 55 um. Slide USGS—D l4 V1185—4(2), E.F. L45/3. Bully Creek Formation. Harper Basin, Malheur County, Oregon (loc. 7). Valve view of exterior surface showing obscure pseudonodule (arrow). Diameter 69 pm. Slide AMOCO: OM—29—1(+), E.F. K4/4. New Pass, Lander County, Nevada (10¢. 42). Internal views showing pseudonodule (arrows in figs. 4, 5) and labiate process (fig. 6). New Pass. Lander County, Nevada (10c. 42). Detail of marginal tubular processes. New Pass, Lander County, Nevada (10c. 42). Base of broken marginal tubular process. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 1 my. 3 , ACTINOCYCL US ACA NTHUS PLATE 2 Figures 1—7. Acrinocyclus cedrus Bradbury & Krebs, sp. nov. (p. 5). (20) 1. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada (Ice. 20). Note short, blunt hyaline stripe at the disk/mantle junction (arrow) and polygonal areolae. Diameter 53 ttm. Slide USGS—D 31 188—1 (65), HF. P41/1. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada (10¢. 20). Valve with hyaline rim. Diameter 56 um. Slide USGS—D 31 188—1 (65), ER L41/4. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada (10c. 20). Arrow marks pseudonodule. Diameter 45 pm. Slide USGS—D 31 188—1 (65), ER M32. Poison Creek Formation, Reynolds Creek, Owyhec County, Idaho (loc. 44). Detail of valve surface showing pseudonodule (arrow). Diameter 85 um. Slide AMOCO: IO—24—5(+), E.F. 09/2. Unnamed Miocene unit, southern Stillwater Mountains, Churchill County, Nevada (10c. 48). Detail of disk and mantle under different focus (a, mantle; b, disk center). Diameter is 67 um. Slide USGS—D 29 I 81—3B, E.F. N38 Juntura (‘2) Formation, Otis Creek, Hamey County. Oregon (10c. 34). Diameter 68 um. Slide USGS—D 14 VI 78—4B (3). BF. 034/4. Juntura (?) Formation, Otis Creek, Hamey County. Oregon (10c. 34). Large valve with triangular hyaline patches between rows of areolae producing stellate pattern. Diameter 157 um. Slide USGS—D 14 VI 78—4B (3), BF 032/1. U.S. GEOLOGICAL SURVEY ACTINOCYCLUS CEDRUS PROFESSIONAL PAPER 1543 PLATE 2 Q . l . ,. .0 3 '4”... n u”. ', 1.. M ,. ’ 1* t. 2-,! ‘3‘“ s at": «:2 wk 4*. Q I‘d? PLATE 3 Figures 1—8. Actinocyclus cedrus Bradbury & Krebs, sp. nov. (p. 5). Scale bars in mm. 1. 2, 3. 4, 5. 7, 8. (22) Unnamed Miocene unit, southern Stillwater Mountains, Churchill County, Nevada (10c. 48). Valve with hyaline rim. Diameter 49 um. Slide AMOCO: S.E. Carson Sink-low (-). E.F. Q4/3. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada (loc. 20). Valve exterior with hyaline rim and exit pores of labiate processes (arrows). Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada (loc. 20). Exit pores of labiate processes indicated by arrows. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada (10c. 20). Detail of valve margin and mantle. The arrow pinpoints an exit pore. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada (loc. 20). Overview of valve interior (fig. 7) and detail of disk/mantle junction showing labiate process and position of pseudonodule (arrow) (fig. 8). PROFESSIONAL PAPER 1543 PLATE 3 US, GEOLOGICAL SURVEY s. . o~" \o‘ ACTINOCYCLUS CEDRUS Figures 1—3. (24) PLATE 4 Actinocyclus cedrus Bradbury & Krebs, sp. nov. (p. 5). Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada (loc. 20). Scale bars in um. I. Overview of valve interior showing ring of labiate processes. Arrow marks location of pseudonodule. 2. Closeup of labiate processes. Internal view of pseudonodule (arrow). Acrinocyclus cedrus (spinose form) (p. 5). Unnamed Miocene unit, Turner Creek, Modoc County, California (loc. 17). Scale bars in pm. 4. Valve view; arrows highlight marginal spines. Diameter is 91 pm. Slide AMOCO: Pit River (+30). E.F. T72. Views of marginal spines. Actinocyclus claviolus Bradbury & Krebs. sp. nov. (p. 5). Unnamed middle Miocene unit, Jungle Point, Idaho County. Idaho (10c. 33). Note clove—shaped hyaline stripes on disk/mantle junction. Diameter 21 pm. Slide USGS—D 5 XII 80—7 (1). BR 837/ 1. USA GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 4 ACTINOCYCLUS CEDRUS AND ACTINOCYCLUS CLAVIOLUS PLATE 5 Figures 1—5. Actinocyclus claviolus Bradbury & Krebs. sp nov. (p. 5). Unnamed middle Miocene unit. Jungle Point. Idaho County, Idaho (Ice. 33). Scale bars in pm. 1. 2. 3. 4. 5. Valve view. Diameter 30 um. Slide USGS—D 5 XII 80—7 (3), BF. J33/2. Valve view. Arrow marks probable pseudonodule. Detail of marginal clove-shaped hyaline stripe. Valve interior showing position of pseudonodule (arrow). Internal view of pseudonodule (arrow) 6-9. Actinocyclus cupreus Bradbury& Krebs sp. nov. (p 6). 6. 9. (26) Unnamed lower‘Miocene unit Copper Kettle Canyon. Churchill County, Nevada (Ice. 16). Note the pattern of fasciculation and the simple hyaline marginal stripes that delimit each fascicle. Diameter 37 um. Slide AMOCO: NSD—6 (-), E.F. U9/ 1. Humboldt Formation, Eureka County. Nevada (loc. 30). Valve view. Diameter 43 um. Slide AMOCO: PC—3—79 (+). E.F. HIS/4. Unnamed middle Miocene unit. Juliaetta. Nez Perce County. Idaho (10c. 32). Valve view. Diameter 29 um. Slide USGS—D 5 X1] 80—3 (2), BF. K30/4. Juliaetta. Nez Perce County. Idaho (10c. 32). Valve view. Scale bar in pm. U‘S. GEOLOGICAL SURVEY PROFESSlONAL PAPER 1543 PLATE 5 ACTINOCYCLUS CLAVIOLUS AND ACTINOCYCLUS CUPREUS Figures 1, 2. 3—9. 6—9. (28) PLATE 6 Actinocyclus cf. A. cupreus (p. 7). Freshwater Miocene deposits, Yamato Bank, Sea of Japan. Valve views. Note the flat disk and long marginal hyaline stripes. 1. Core RC 12—394 (600 cm). Diameter 62 um. Slide AMOCO: RC12—394 600 cm (+), E.F. E33/4. 2. Core RC 12—394 (600 cm). Diameter 54 um. Slide AMOCO: RC12—394 600 cm (+). E.F. Vl0/2, Actinocyclus ehrenbergii Ralfs in Pritchard (p. 7). 3—5. Quiburis Formation, Edgar Canyon, Pima County. Arizona (loc. 92). Scale bars in pm. 3. Valve view showing large pseudonodule (arrow). Diameter 146 um. Slide USGS—D 19 IV 80—3A (2), BF. H36/3. 4. Internal detail of disk/mantle junction showing the closely spaced pores of labiate processes. Labiate processes are missing. 5. Closeup of lahiate process. Actinocyclus ehrenbergii Ralfs in Pritchard. Holocene marine sediment, Walvis Bay, Namibia. Scale bars in pm. 6. Overview of valve interior showing marginal ring of labiate processes. Closeup of labiate processes. Internal view of pseudonodule (arrow). PROFESSIONAL PAPER 1543 PLATE 6 US. GEOLOGICAL SURVEY ‘ a “f“ " WV.1§;'f*kf§*1?wtflaflrl¥*lv ~ .r » ..: s5 , , ":23; ' ol":5'o¢or:OQ 3' ‘ 12': ‘~ \ .2.” ".0. way: . 3.;{53 e . \ o" ‘ M . ...o;.r «'3N‘ i0“ .0 . . .: 9 ,. ”a”... ' ‘ c r .‘ ~e ”arm: 5.}? .“o a v u 5.. no, w. . ,ww,, , .aigvg P x” . _ 4‘ H“ ACTINOCYCLUS sp.cf. A. CUPREUS AND ACTINOCYCLUS EHRENBERGII PLATE 7 Figures 1, 2. Actinocyclus ehrenbergii Ralfs in Pritchard (p. 7). Holocene marine sediment, Walvis Bay. Namibia. Scale bars in pm. 1. 2. Internal view of corroded pseudonodule (arrow). External view of annulate pseudonodule (arrow) and exit pores of labiate processes. 3‘8. Actinocyclus gorbunovii (Sheshukova) var. fossa Bradbury & Krebs, var. nov. (p. 7). Cedarville Formation, Forty-nine Camp. Washoe County, Nevada (10c. 69). Scale bars in pm. 3. (30) Valve view; note the pseudonodule (arrow), the lack of marginal tubular processes, and the concentric undulation of valve. Diameter 35 pm. Slide USGS—D 2 IX 87—38 (1). E.F. P35. Overview of frustule showing steep mantle, concentric undulation, and position of pseudonodule (arrow). Detail of pseudonodule (arrow). View of disk/mantle junction and pseudonodule (arrow). Note the circular moat-like structure that surrounds the pseudonodule. Overview of valve interior showing labiate processes and pseudonodule (arrow). Interior closeup of disk/mantle junction with labiate process and pseudonodule (arrow). PROFESSIONAL PAPER 1543 PLATE 7 US. GEOLOGICAL SURVEY ACTINOCYCLUS EHRENBERGH AND ACTINOCYCLUS GROBUNOVH Figure (32) PLATE 8 1. Actinocyclus kanitzii (Pant. & Grun.) Schaudema (p. 3). Middle Miocene lacustrine and brackish water deposits, Szurdokpuspoki, Matra Mountains, Hungary. The fascicles are separated by hyaline stripes that run from the disk/mantle junction to the center of the disk. Diameter 74 um. Slide USGS—D 3 IX 80—1B. E.F. F43/3. 2—6, 8—11. Actinocyclus krasskei (Krasske) Bradbury & Krebs, nom. nov. (p. 9). 2. 9, 10. ll. “Kieselgur” (diatomite) deposits of Miocene? age in Vogelsberg Range, Beuem. Germany. Different focus showing detail of slightly undulate valve center (a) and margin (b). Diameter 31 um. Slide Krasske Collection. Natural History Museum, Kassel. Germany, Beuem #3004. Beuem, Germany. Valve view showing hyaline stripes and pseudonodule (arrow). Diameter 21 um. Slide Krasske Collection, Natural History Museum. Kassel, Germany. Beuern #3004. Beuem. Germany. View of undulate valve showing disk/mantle junction and areolae on mantle arranged in quincunx pattern. Diameter 40 ttm. Slide Krasske Collection. Natural History Museum. Kassel. Germany, Beuem #3004. Unnamed middle Miocene unit, Juliaetta, Nez Perce County, Idaho (100. 32). Valve view. Diameter 29 um. Slide USGS—D 5 XII 80—3 (2), E.F. D32/l. Unnamed Miocene? unit. Arrow Junction, Nez Perce County, Idaho (10c. 72). Valve view. Diameter 27 um. Slide AMOCO: USGS—DC#2289, E.F. H30/ 1. Juliaetta. Nez Perce County. Idaho (10c. 32). View of undulate valve. Diameter 40 um. Slide USGS—D 5 XII 80—3 (2). E.F. Q38. Squaw Creek Member, Ellensburg Formation. Yakima County, Washington (10c. 49). Interior of valve showing long-stemmed labiate processes and pseudonodule (arrow). Scale bars in um. Mascall Formation, Vinegar Creek. Grant County, Oregon (10c. 88). Interior of valve showing ring of long-stemmed labiate processes. Scale bars in pm. 7. Acrinocyclus tubulosus Khursevich. (p. 13). Squaw Creek Member, Ellensburg Formation, Yakima County. Washington (100.49). Valve view. Diameter 27 um. Slide USGS—D 26 II 79—2A (3), E.F. N47/4. PROFESSIONAL PAPER 1543 PLATE 8 .". . 0 JR: 1"“ «w; M‘ a» a u . .0:0.l' , ~ A‘ ' u 4 ,erw ACTINOCYCLUS KANITZII, ACTINOCYCLUS KRASSKEI, AND ACTINOCYCLUS TUBULOSUS PLATE 9 Figure 1. Flat forms of Actinocyclus krasskei (Krasske) Bradbury & Krebs, nom. nov. (p. 9). Mascall Formation. Vinegar Creek, Grant County, Oregon (10c. 88). Closeup of labiate process. Scale bars in mm. 2, 3. Undulate forms of Acrinacyclus krasskei (Krasske) Bradbury & Krebs, nom. nov. (p. 9). Squaw Creek Member, Ellensburg Formation, Yakima County. Washington (10c. 49). Scale bars in mm. 2. Closeup of labiate process. 3. Valve interior showing position of pseudonodule (arrow). 4—6. Actinocyclus motilis Bradbury & Krebs, sp. nov. (p. 10). 4. Esmeralda Formation, Cedar Mountain, Mineral County, Nevada (10c. 22). Note the truncation of sinuous rows of areolae by other rows. Diameter 23 pm. Slide USGS—D 23 I 81—10(1), E.F. L34/2. 5. Unnamed middle Miocene unit. Augusta Mountains. Churchill County, Nevada (loc. 4). Focus on valve margin (a) and center (h). Diameter 42 pm. Slide AMOCO: AMS—l—l(-), E.F. M34/2. 6. Unnamed middle Miocene unit. Goose Creek, Baker County. Oregon (10c. 27). Focus on valve margin (a) and center (b). Diameter 46 um. Slide USGS—D 10 VI 78-28 (3), BF. L24/4. (34) U.S. GEOLOGICAL SURVEY ‘3 i” . at} @- L 4* gggQ éfi‘fimwg _ :1 Q3153 , “fin: M fimé‘iflfim 133;: d" .. it E :*Q I ‘ xmfiiwa gfi‘figmmfi , g H 1‘, _ . 31%;} I _ 3 PROFESSIONAL PAPER 1543 PLATE 9 . " onuf‘ofiifl‘. i“! o...;..’.;..%1 ‘ viz-v): ACTINOCYCLUS KRASSKEI AND ACTINOCYCLUS MOTILIS Figure 1—12. 2—8. 7, 8. 9—12. (36) PLATE 10 Actinocyclus morilis Bradbury & Krebs. sp. nov. (p. 10). Scale bars in pm. 1. Squaw Creek Member, Ellensburg Formation. Yakima County, Washington (Ice. 49). Diameter 34 um. Slide USGS—D 27 1179—1, E.F. R31/4. Esmeralda Formation, Cedar Mountain. Mineral County. Nevada (loc. 22). 2. Valve view showing separation of valve from intercalary bands. Arrow marks probable pseudonodule. 3. Valve interior showing position of pseudonodule (arrow). ’ 4. Detail of pseudonodule (arrow) showing pore structure. 5. 6. Broken stumps of labiate processes. Arrow marks location of probable pseudonodule in figure 6. Closeups of long-stemmed labiate processes. Squaw Creek Member, Ellensburg Formation, Yakima County. Washington (10c. 49). 9. Exterior of valve showing concentric undulation and interdigitation of rows of areolae at the valve margin. Arrow marks probable pseudonodule. 10. Girdle view of frustule. 11. View of valve interior showing a marginal ring of long-stemmed labiate processes. 12. Closeup of labiate processes. U. S. GEOLOGICAL SURVEY ‘1.*pk?ma§sgamw~ yaw-kaawadm“ PROFESSIONAL PAPER 1543 PLATE 10 A.,< 33% i *2 *wa‘si « 6 a a »3 {l +w§§wwr *fiwaflfi gaspwwtv H ACTINOCYCLUS MOTILIS PLATE 11 Figure 1. Actinocyclus motilis Bradbury & Krebs, sp. nov. (p. 10). Squaw Creek Member, (38) Ellensburg Formation, Yakima County. Washington (10c. 49). Detail of valve disk/ mantle junction showing pseudonodule (arrow) and hyaline stripe with exit pore. Scale bar in mm. 2—8. Actinocyclus nebulosus Bradbury & Krebs. (p. 11). Scale bars in ttm. 2. Esmeralda Formation, Black Spring, Nye County. Nevada (10c. 93). Valve view. Diameter 67 um. Slide USGS-D 26 XII 86—2A (1), BF. H38/ 1. 3. Esmeralda Formation, Black Spring, Nye County, Nevada (10c. 93). Valve view. Diameter 77 um. Slide USGS—D 26 XII 86—2A (1), BF. 636/3. 4. Buffalo Canyon Formation. Buffalo Canyon, Churchill County. Nevada (Ice. 6). Valve view. Diameter 83 pm. Slide AMOCO: Buffalo Canyon, E.F. E6/4. 5. Esmeralda Formation, Cedar Mountain, Nye County, Nevada (10c. 74). Arrow marks probable pseudonodule. Diameter 67 um. AMOCO: USGS—DC #3394 (3). BF. M42/2. 6—8. Esmeralda Formation, Black Spring, Nye County. Nevada (loc. 93). Views of valve interior; arrow indicates position of pseudonodule. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 ‘. o n; ' v ‘ w m‘ ”w u . “aura"; ~ ‘. g: 35’ . , . .. .p. ~ . ,1' ‘:.. I: u-fi‘é‘fii :to o. .‘C' ' “I. v ’3.» w ‘ "“3“ “a": 7.2. :‘ K: ‘ § 3 4': “.3 is”. a»: . cu‘u.’ . 953:? ...;:':~. m. .2; ’ {a h. “I". «V . V '. ‘ . .. n '0 .‘ 9 J. .. m. gym...» «gag... . . mew» , . .. :‘3 yo, ACTINOCYCLUS MOTILIS AND ACTINOCYCLUS NEBULOSUS PLATE 1 1 PLATE 12 Figure 1. Actinocyclus nebulosus Bradbury & Krebs. sp. nov. (p. 1 1). Esmeralda Formation, Black Spring, Nye County, Nevada (loc. 93). Interior detail of mantle/disk junction showing short-stemmed broad labiate process and position of pseudonodule (arrow). Scale bar in um. 2—5. Actinocyclus normanii f. subsalsa (Juhl.-Dannf.) Hustedt. (p. 3). Holocene lake sediment, Saginaw Bay. Lake Huron. Michigan. Scale bars in pm. 2. Valve view. Diameter 33 um. Slide USGS—D 24 11 82—1 (1), BF. P31/1. 3. Valve view. Diameter 37 um. Slide USGS—D 24 II 82—1 (1), E.F. N39/1—2. 4, 5. Valve views. Arrows indicate position of pseudonodule. 6, 7. Actinocyclus pinnulus Bradbury & Krebs, sp. nov. (p. 11). Hole-in—the-Wall Diatomite, Gooding County, Idaho (loc. 90). 6. Valve view. Arrows indicate positions of marginal flanged tubular processes. Diameter 61 um. Slide USGS—D 2] VI 88—1 (1), BF. N29. 7. Valve view. Arrows highlight marginal hyaline stripes. Diameter 66 um. Slide USGS—D 21 VI 88—1 (1), ER P43. (40) US, GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 12 ACTINOCYCLUS NEBIULOSUS, ACTINOCYCLUS NORMANII f. SUBSALSA, AND ACTINOCYCLUS PINNULUS PLATE 13 Figures 1—5. Actinocyclus pinnulus Bradbury & Krebs, sp. nov. (p. 11). Hole-in-the-Wall Diatomite, quarry. Gooding County, Idaho (10c. 90). Scale bars in pm. 1. Valve view. Arrows highlight marginal flanged tubular processes. Diameter 66 um. Slide USGS—D 21 VI 88—1 (1), E.F. P43. 2, 3. Valve view. Arrows indicate the position of a marginal flanged tubular process 4. Overview of valve interior showing a ring of marginal short-stemmed labi- ate processes and the pseudonodule (arrow). 5. Closeup of labiate processes and the pseudonodule (arrow). 6. Actinocyclus sp. cf. A. pinnulus (p. 12). Amoco Becharof No. 1 well, depth 3220—3250 feet, Alaska Peninsula, Alaska (loc. 112). Focus on valve margin (a) and center (b). Arrow indicates the position of the pseudonodule. Diameter 40 um. Slide AMOCO: Becharof 3220—3250 ft. (-), E.F. V22/3. 7. Actinocyclus theleus Bradbury & Krebs. sp. nov. (p. 12). “Clarkia Lake deposits,” Emerald Creek. Benewah County, Idaho (10c. 21). Valve view; pseudonodule indicated by arrow. Diameter 25 um. Slide USGS—D 5 XII 80—4 (2), E.F. P28/2. (42) USA GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 13 ACTINOCYCLUS PI‘NNULUS, ACTINOCYCLUS sp.cf. A. PINNULUS, AND ACTINOCYCLUS THELEUS PLATE 14 Figures 1—4. Actinocyclus theleus Bradbury & Krebs, sp. nov. (p. 12). Scale bars in um. 1. Unnamed middle Miocene unit, Oviatt Creek, Clearwater County, Idaho (10c. 43). Valve view. Note arrow to the nipple-like marginal process(es) (mp). Pseudonodule is indicated by other arrow (pn). Diameter 34 pm. Slide USGS D 5 XII 80—1 (1), ER V39/1. 2. “Clarkia Lake deposits,” Emerald Creek, Benewah County, Idaho (Ice. 21). Valve view of exterior surface showing the pseudonodule (pn) and marginal process(es) (mp). 3. Emerald Creek, Benewah County, Idaho (10c. 21). Closeup of disk/mantle junction showing marginal process (mp) and pseudonodule (pn). 4. Emerald Creek, Benewah County, Idaho (loc. 21). Interior view with two labiate processes, and the pseudonodule (arrow). 5, 6. Coscinodiscus (= Actinocyclus) variabilis sensu Krasske. (p. 3). Unnamed Miocene? unit in the Vogelsberg Range, Ruckers. Germany. 5. Valve view. Diameter 37 pm. Slide Krasske Collection, Natural History Museum, Kassel, Germany, Ruckers #2996. 6. Focus on the valve disk (a) and mantle (b). Diameter 52 um. Slide Krasske Collection, Natural History Museum, Kassel, Germany, Ruckers #2996. 7, 8. Actinacyclus venenosus Bradbury & Krebs, sp. nov. (p. 13). Poison Creek Formation, Reynolds Creek, Owyhee County, Idaho (10c. 44). 7. Valve view showing long, pointed hyaline stripes. Diameter 71 um. Slide AMOCO: IO—23—2(+), E.F. 022/4. 8. Valve view of large specimen. Note the dash-like hyaline stripes. Diameter 125 pm. Slide AMOCO: IO—23—6(+), E.F. F35/4. (44) PROFESSIONAL PAPER 1543 PLATE 14 US. GEOLOGICAL SURVEY Mug; my " wag.“ 4w nwé *agfgW - 3r 9 '9 .0. "~ wh‘kfi‘r a. N t o W *1,“ 5% ~ 5:; ACTINOCYCLUS THELEUS, COSCINODISCUS (=ACTINOCYCLUS) VARIABILIS, AND ACTINOCYCLUS VENENOSUS PLATE 15 Figures 1—6. Actinocyclus venénosus Bradbury & Krebs, sp. nov. (p. 13). Scale bars in mm. 1. Poison Creek Formation, Reynolds Creek, Owyhee County, Idaho (10c. 44). Valve view showing polygonal areolae. concentric undulation of the valve face, and pointed marginal hyaline stripes. Diameter 66 um. Slide USGS—D 11 VI 78—1A (2), BF. G35. 2, 3. Idaho Group, Washington County, Idaho (10c. 31). View of exterior valve surface showing the exit pores of the labiate processes and marginal hyaline stripes. 4. Idaho Group, Washington County, Idaho (10c. 3]). Detail of valve disk/ mantle junction showing exit pores, hyaline stripes, and hyaline rim. 5. Idaho Group, Washington County, Idaho (10c. 31). View of interior surface. Note the ring of marginal short-stemmed, broadly flanged labiate processes. 6. Poison Creek Formation, Reynolds Creek, Owyhee County, Idaho (10c. 44). Closeup of labiate process. Arrow indicates the position of pseudonodule. (46) U.S. GEOLOGIC PROFESSIONAL PAPER 1543 PLATE 15 )7 , AL SURVEY y“, ACTINOCYCLUS VENENOSUS Geologic Ranges of Lacustrine Actinocyclus Species, Western United States By William N. Krebs and J. Platt Bradbury THE DIATOM GENUS AC TINOC Y CLUS IN THE WESTERN UNITED STATES U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543—B Preliminary geologic ranges of lacustrine species of the Western United States determined from radiometrically dated outcrops of diatomites and diatomaceous sediments from Nevada, California, Washington, Oregon, and Idaho UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995 CONTENTS Abstract .......................................................................................................................... 53 Introduction .................................................................................................................... 53 Materials and Methods ................................................................................................... 53 Results ............................................................................................................................ 54 Discussion ...................................................................................................................... 58 References ...................................................................................................................... 59 Appendix ........................................................................................................................ 63 Index ............................................................................................................................... 68 ILLUSTRATIONS Figure 1. Biochronology and general relative diversities of six lacustrine diatom genera, Western United States .......... 54 2. Location of sample sites .................................................................................................................................... 54 3. Preliminary range chart of obligate lacustrine Actinocyclus species, Western United States ........................... 56 51 GEOLOGIC RANGES OF LACUSTRINE AC TIN 0C Y CL US SPECIES, WESTERN UNITED STATES By William N. Krebs] and J. Platt Bradburyz ABSTRACT In the Western United States, twelve obligate fresh- water species of Actinocyclus Ehrenberg are restricted to the early and middle Miocene. Maximum diversity (11 species) was attained during the early middle Miocene, before the appearance of obligate lacustrine genera of the family Thalassiosiraceae. Three, possibly five, species of Actinocy- clus are restricted to the early middle Miocene; A. pinnulus is restricted to the late middle Miocene. Actinocyclus ehren- bergii Ralfs, a coastal marine species, has been found in latest Miocene to earliest Pliocene lake sediments, but because of its long geologic range in marine sediments and rarity in lacustrine rocks, it is probably not a useful biostrati- graphic indicator in continental deposits. Fossil lacustrine Actinocyclus spp. are found elsewhere in the world and may have geologic ranges that differ in detail, but which are gen- erally similar to those in the Western United States. INTRODUCTION Interest in lacustrine diatom biochronology has greatly increased in recent years (Servant-Vildary, 1978; Gasse, 1980; Rehakova, 1980; Bradbury and Krebs, 1982; Khursevich, 1982; Loginova, 1982; Loginova and others, 1984; Bradbury, 1984, 1986; Bradbury and others, 1985; VanLandingham, 1985; Fourtanier, 1987; Krebs and oth- ers, 1987; Theriot and Bradbury, 1987; Fourtanier and Gasse, 1988; Serieyssol, 1988). In the Western United States, lacustrine diatomaceous sediments are often inter- bedded with volcanic rock and are thus well suited for radiometric dating. Fossil microfloras can therefore be arranged geochronologically and key diatoms can be traced through time. In this manner, Krebs and others (1987) have documented the succession of several lacustrine diatom genera through the Neogene and Quaternary of the Western 1William N. Krebs, Amoco Production Co., 501 Westlake Park Blvd., Houston, Texas 77079 2]. Platt Bradbury, US. Geological Survey, MS 919 Box 25046, Denver Federal Center, Lakewood, Colorado 80225 United States (fig. 1). The purpose of this study is to present the geologic ranges of species belonging to one of these genera, Actinocyclus. These ranges will, of course, change as additional data accumulate and as lacustrine diatomaceous sediments become better dated. We present this information as our knowledge to date and hope that it will stimulate comparative studies in the Western United States and in other regions worldwide. MATERIALS AND METHODS Our data are derived from 115 localities in the Western United States, including Alaska, mostly from the Great Basin (fig. 2 and “Appendix”). From these localities, several hundred samples were collected and analyzed for their lacus- trine diatom content. Forty-nine of these sites have radio- metric dates or have age estimates based on stratigraphic relationships with other dated units. Of these 49 dated local- ities, 28 have obligate lacustrine species of Actinocyclus— that is, they are found only in continental (lake) deposits and only in association with other nonmarine diatom taxa (see chapter A). Unfortunately, the exact stratigraphic and depo- sitional relationships of diatomaceous samples to the dated volcanic rock(s) are often obscure or poorly documented. In addition, radiometric dates may be inaccurate and conflict- ing. We are confident, however, that the general pattern of lacustrine diatom biochronology in the Western United States presented in figure 1 is accurate and that the species ranges of Actinocyclus (fig. 3) reflect evolutionary and (or) environmental changes during the Miocene. Natural reworking and the rare occurrence of whole specimens or fragments poses problems of interpretation (Krebs and others, 1987). Excluding contamination during collecting and processing, rare occurrences of poorly pre- served specimens older than the oldest known occurrence are regarded as significant and merit range extension. Rare (occasionally common) occurrences and fragments younger than the youngest true occurrence may be the result of natu- ral reworking. Clearly, large upward range extensions based on rare occurrences evoke suspicion. Also, poor'preservation (abrasion and (or) corrosion) of frustules relative to those of 53 54 THE DIATOM GENUS ACT INOCYCLUS IN THE WESTERN UNITED STATES I f . . . Ma E {$33331 MaNm'fia'Tirg'gfi Relative Dwersuty 0 (ED Rancholabrean 14 a‘ Calabrian Irvingtonian 5 _ 2 _ % Piacenzian 8 Blancan 23 25 4 _ Q .1 Zanclean 45 CL 3105 , _ 92113 6 _ L2: Messmlan 115 g Hemphillian 1211 Cydoswphanos 8 _ — . 52 E Tortonlan 2104 ,— n 10 5 Last. Clarendonian 43923391 — — —- - . ————————————— % 53 Mesod/ctyon 12 - t“) 7 5083 O Serra- 7586 3 vallian 43 ” _ . 1 4 Lu B arst ovi a n Thalassmszra d 5' - 27 Q 46 3 2° 33 3519459 16 Langhian ‘3 25132 _______________ 6 Lu E 18 — o . _ . . . o Hemlngfordlan Family Thalassuosnraceae g Burdigalian 1s 20 — Z . . . 3:): - Family Hemldlscaceae LU Arikareean 22 Figure 1. Biochronology and general relative diversities of six lacustrine diatom genera. Western United States. The numbers represent localities with radiometric ages (see “Appendix" and fig. 2). Diversity patterns are qualitative and not comparable between genera. Time scale is from Berggren and others (1985) and Haq and others (1987). other diatoms in a sample may indicate reworking. In any case, we have queried occurrences and dashed lines where there is sufficient doubt about absolute age and (or) rare occurrences. Additional localities and closer examination of questionable occurrences may resolve these uncertainties. RESULTS The geologic ranges of lacustrine Actinocyclus species will be discussed in alphabetical order rather than by oldest first occurrence, which may change with additional informa- tion. Figure 3 is a range chart of these species. Actinocyclus acamhus Bradbury & Krebs Actinocyclus acanthus was originally described as Ces- lodiscus apiculatus by Lohman (1957) from the Esmeralda Formation (Miocene) at Cedar Mountain, Nye County, Nevada (10¢. 74). Evemden and others (1964) obtained two radiometric dates from this formation in the Cedar Mountain area whose corrected average is 11.4 Ma. These two dates were taken 6] m and 76 m, respectively, above early Claren- donian (5 12 Ma) vertebrates. J. H. Stewart (oral commun., 1988), however, reported that the lower (diatomaceous) half of the Esmeralda Formation dates from about 14 to 12 Ma (Barstovian). Furthermore, recent field work in this area has demonstrated that there is an unconformity between the lower half of the “Esmeralda Formation” and the upper-half that yielded Clarendonian vertebrates and the dates of Evem- den and others (1964) (H. E. Schom, oral commun., 1989). Barstovian vertebrates have been found in the lower diato- maceous portion beneath the unconformity, and a radiomet- ric date of 15.1 Ma obtained from this unit nearby (loc. 20) confirms this age. We, therefore, assign a Barstovian age to the diatomites collected by Lohman at Cedar Mountain GEOLOGIC RANGES OF LACUSTRINE ACT INOC YCLUS SPECIES, WESTERN UNITED STATES 40° WYOMING COLORADO .104 ARIZONA 350 NEW MEXICO 15° ° 92 0 300 KILOMETERS 1 I 1_____! f 105° 110° Figure 2. Location of sample sites (see “Appendix”). 56 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES Ma 5 European N.Amer. - 0 g Stages MammalAqes GeOIOQ'C Ranges % Rancholabrean 14 E.‘ Calabrian 'ngton'a" 5 2_LLI . . z PlacenZIan LU 8 Blancan 2325 4__ E' Zanclean £16105 m13—_——————————_—— 6-12.: Messinian ”5 B Hemphillian 1211 g N h E a; 52 s g s: a e Lu Tononian 2‘04 § .3 a :3 E = N }— ? 9 m a; E E Q «5 § 5 {541 a 9 § 5% .44 S a. > 10— _ <5 <:' a . <5 <6 <5 ; E m L; 53 7 § ‘8 9 9 ‘8 S § 12-'-'-' 7 - N := , N . 8 Serra- 75526 g ? 3 _§ A’Ctic Circle . 170° C\ '2 I “in“ ALA O 1; SKA a\% a? r“\ U3 . 60° \ \ O 9&7 g} Gulf of Alaska a0 :3 0 0 GD 0% 0 200 400 500 KILOMETERS 3‘: WAJ—g / | \ \ Figure 1. Map showing portion of continental shelf sampled for this study. Class OSTRACODA Latrielle, 1806 Order PODOCOPIDA G.W. Mueller, 1894 Suborder PODOCOPA Sars, 1866 Family CYTHERURIDAE G.W. Mueller, 1894 Subfamily CYTHERURINAE G.W. Mueller, 1894 Genus CYTHERURA Sars, 1866 Type species.—Cythere gibba O.F. Mueller, 1785 (Type by subsequent designation) CYTHERURA BURROUGHSENSIS new species Plate 1, figure 2; plate 2, figures 1—4 Cytherura sp. C Brouwers, 1981, p. 10; Brouwers, 1982a, p. 11; Brouwers, 1983. Etymology—After Burroughs Glacier, which empties into the Muir Inlet of Glacier Bay, southeast Alaska. Diagnosis.—Characterized by elongate, trapezoidal lateral outline; straight dorsum; broadly sinuous venter; pro— nounced, long, narrow caudal process; reticulate ornament; longitudinal Y—shaped ridge; thin dorsal ridge; strong, sharp ventral ridge; distinctive secondary papillae located in small pits; and normal pores with apophysis. Description—Adult valves elongate, trapezoidal in lat- eral view. Dorsal margin nearly straight; anterodorsal mar— gin concave in right valve; anteroventral margin drawn-out with apex near corner; ventral margin with subtle concavity; posteroventral margin concave; posterodorsal margin with pronounced, long, narrow caudal process. Several short ante- rior marginal denticles, weakly developed. Greatest length through caudal process; greatest height through anterior hinge element. Valve surface covered with reticulation. Surface domi- nated by Y—shaped reticulation ridge originating at anterior and opening toward caudal process and posteroventral cor- ner. Smaller reticulation ridges more chaotically arranged. Thin dorsal ridge originates at middle of anterior margin and ends along caudal process. Strong, sharp ventral ridge overhangs margin and ends posteriorly as sharp point. Solum floors covered with distinctive secondary papillate ornament, each occurring within small pit. Anterior margin with moderate, flattened flange. Twenty-seven simple-type normal pores evenly distributed over surface, both on .NCBENEEL Sinus @883 25:82 038% wagonm 922 .N 0.5»:— SYSTEMATIC PALEONTOLOGY uczcm \ 390 O O L), o Ezeo/ @523; ON a O Sicmituk x . 71f; 3.22 32:32 am 2 a .822 c8252 2 1.); . «Sufi—«6% cow — 03» — omv F 4 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 solum floors and reticulation ridges. Normal pores with high, built-up mound surrounding each pore. Inner margin and line of concrescence coincide. Inner margin parallels valve outline. Inner lamella moderate in width, even width throughout. Selvage well developed. Remarks.—The inner lamella of C. burroughsensis specimens illustrated here is not well preserved, but addi- tional material shows clearly that the species belongs to Cytherura. C0mparis0ns.—Cytherura burroughsensis n. sp. dif- fers from C. skippa Hanai, 1957 (Holocene, central Japan) by having a high, short lateral outline; reticulate ornament; secondary pustules; and lack of strong oblique ridges. C. burroughsensis differs from Semicytherura miurensis (Hanai, 1957) (Quaternary, central Japan) by having a longer dorsum; drawn—out anterior; strong ventral ridge; strong reticulation; secondary pustules; and high, short valve out- line. The Y—shaped ridge of C. burroughsensis is similar to that of Kangarina pervadera Ishizaki and Gunther, 1974 (Holocene, Gulf of Panama). Occurrence—Cruise EGAL-75-KC, localities 4, 6, 202. Cruise DC1-79—EG, localities 17,45. Cruise DC2—80- EG, locality 174. Distribution—Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf. Material.——Nine adult valves, two juvenile valves. Type specimens.—Holotype: USNM 408413, left valve (pl. 1, fig. 2), locality EGAL-75—KC-202, length 0.43 mm, height 0.23 mm. Paratypes: USNM 408414, left valve (pl. 2, figs. 1, 3), locality EGAL-75-KC—6, length 0.48 mm, height 0.26 mm. USNM 408415, right valve (pl. 2, figs. 2, 4), locality EGAL- 75-KC—6, length 0.46 mm, height 0.26 mm. CYTHERURA WACH USE TTENSIS new species Plate 1, figure 6 Cytherura sp. D Brouwers, 1981, p. 10; Brouwers, 1982b, p. 8; Brouwers, 1983. Etymology.—After Wachusetts Inlet, a small fiord of Muir Inlet, Glacier Bay. Diagnosis.—Characterized by elongate, crescentic lat- eral outline; round, broad caudal process located ventral 0f midline; longitudinal reticulation; small secondary pits on solum floors; anterior arcuate vestibule; and large, crescentic posteroventral and ventral vestibules. Description.—Adult valves are elongate, crescentic in lateral View. Dorsal margin broadly arched; anterior margin smoothly curved, with maximum width ventral of midline; ventral margin with wide, shallow concavity; posterior mar- gin with rounded, broad caudal process, located ventral of midline. Greatest length through caudal process; greatest height through anterior hinge element. Valve surface covered with reticulation network, pre— dominantly longitudinal with scattered cross ridges. Small secondary pits arranged on solum floors. Thirty-five normal pores scattered over valve, occurring between ridges. Inner margin and line of concrescence coincide at pos- terodorsal margin and concavity. Moderate, arcuate anterior vestibule. Small posterior vestibule at caudal process which connects with large, crescentic vestibular space along poster- oventral and ventral margins. Inner lamella widest at ante- rior. Strong, well—developed selvage. Thirteen radial pore canals, most anterior. Radial pores are long, straight, and simple. Hingement in right valve consists of elongate, crenulate terminal elements and finely crenulate median groove. C0mparisons.—Cytherura wachusettensis n. Sp. differs from C. johnsonoides Swain, 1967 (Holocene, Gulf of Cali- fornia, Nicaragua) by having a long, low valve outline; blunt, weak caudal process; large secondary pits; different course of inner lamella; and different terminal hinge elements. C. wachusettensis differs from C. miurensis Hanai, 1957 (Holocene, central Japan) by having a squared valve shape; blunt, short caudal process; different hinge; and lack of a ventral ridge and a wide inner lamella at the anterior and pos- terior. C. wachusettensis differs from Semicytherura waka- murasaki Yajima, 1982 (late Pleistocene, central Japan) by having a less pronounced, wide caudal process; different size and shape of the vestibules; obtuse posterodorsal and antero- dorsal cardinal angles; and concave venter. Occurrence—Cruise EGAL-75-KC, localities 11, 17, 162, 428. Distribution.—Pleistocene (?), Alaska, Cook Inlet, Kodiak Shelf. Material.—Seven adult valves, five juvenile valves. Type specimens.—Holotype: USNM 408422, male right valve (pl. 1, fig. 6), locality EGAL-75-KC-11, length 0.53 mm, height 0.25 mm. Holocene: Gulf of CYTHERURA sp. G Plate 1, figure 5 Cytherura sp. G Brouwers, 1981, p. 10; Brouwers, 1982b, p. 9; Brouwers, 1983. Diagnosis—Characterized by subquadrate, squared valve outline; flattened, broad caudal process; concentrically arranged reticulate ornament; smooth anterior end. Occurrence—Cruise EGAL-75-KC, localities 39, 128, G4. Distribution.—Pleistocene (?), Holocene: Gulf of Alaska, Pribilof Islands. Material.—Three adult valves. Illustrated specimen.——USNM 408418, female left valve (pl. 1, fig. 5), locality EGAL—75-KC-39, length 0.53 mm, height 0.30 mm. SYSTEMATIC PALEONTOLOGY 5 CYTHERURA sp. H Plate 1, figure 1 Cytherura sp. H Brouwers, 1982b, p. 9; Brouwers, 1983. Diagnosis—Characterized by elongate, subquadrate lateral outline; straight, subparallel dorsal and ventral mar- gins; sharp caudal process located dorsal of midline; five blunt anterior marginal denticles; vertically arranged reticu- lation ridges; massive, overhanging ventral ala; and coinci- dent inner margin and line of concrescence. 0ccurrence.—Cruise EGAL-75-KC, localities 157, G4. Distribution.—Pleistocene, Holocene (7): Alaska, Cook Inlet, Kodiak Shelf. Material.—~One adult valve, one juvenile valve. Illustrated specimen.—USN M 408412, left valve (pl. 1, fig. 1), locality EGAL-75-KC-157, length 0.44 mm, height 0.20 mm. Gulf of CYTHERURA sp. I Plate 6, figure 6 Diagnosis—Characterized by squat, subcylindrical lateral outline; subparallel dorsal and ventral margins; smooth valve surface; coincident inner margin and line of concrescence; inner lamella shallow at posterior, deep at anterior; well-developed selvage; radial pore canals enlarged terminally. Distribution—Holocene: Glacier Bay, Gulf of Alaska. 0ccurrence.—Locality G4. Material—One adult valve. Illustrated specimen.—USNM 408469, female left valve (pl. 6, fig. 6), locality G4, length 0.41 mm, height 0.25 mm. CYTHERURA sp. J Plate 1, figure 3 Cytherura sp. J Brouwers, 1982b, p. 9; Brouwers, 1983. Diagnosis—Characterized by subcylindrical lateral outline; wide concavity; subparallel dorsal and ventral mar— gins; concentric reticulation; weak, sinuous ventral ridge; thin anterior marginal ridge; and coincident inner margin and line of concrescence. 0ccurrence.—Cruise EGAL-75-KC, locality 69. Distribution.——P1eistocene: Gulf of Alaska. Material—One adult valve. Illustrated specimen.—USNM 408416, female left valve (pl. 1, fig. 3), length 0.54 mm, height 0.28 mm. Genus E U C YT HER URA G.W. Mueller, 1894 Type species.——Cythere complexa Brady, 1867 (Type by subsequent designation) E UCYTHERURA HAZELI new species Plate 2, figures 9—14; plate 4, figures 14—15; figure 3 Eucytherura sp. C Brouwers, 1981, p. 10; Brouwers, 1982a, p. 11; Brouwers, 1983. Etymology—After Dr. Joseph E. Hazel, Louisiana State University, a specialist in ostracodes and chronostrati- graphic methods. Diagnosis.—Characterized by subquadrate to subrect- angular lateral outline; sinuous ventral margin with pro- nounced concavity; ventral margin sharply inclined at posterodorsum; blunt caudal process; large, rounded, subo- void pits arranged concentrically at anterior and Chaotically at posterior; rounded, heavily calcified reticulation ridges; large, high ventral tubercle that overreaches ventral margin; pore clusters; and secondary sponge-like ornament. Description.—Adult valves short, subquadrate to sub- rectangular in lateral view. Dorsal margin straight; anterior margin smoothly curved, with greatest width ventral of mid- line; ventral margin with pronounced concavity; ventral margin inclined sharply toward posterodorsal; posterior mar- gin truncated, with wide, blunt caudal process. Distinct, obtuse anterodorsal and posterodorsal cardinal angles. Left valve with truncated caudal process; broad, shallow concav- ity; and pronounced anterodorsal cardinal angle. Greatest length through midline of valve; greatest height through anterior hinge element. Valve covered with low, massive reticulation network. Large, rounded, subovoid pits arranged in concentric pattern at anterior and chaotic at posterior. Reticulation ridges are broad, rounded, heavily calcified. Two parallel anterior mar- ginal ridges; sinuous median ridge originates near anterodor- sal comer, proceeds horizontally across valve, and splits into vertical posterior ridge. Narrow anterior and posterior mar— ginal rim or flange. Large, prominent, highly arched ventral node or tubercle that proceeds obliquely along margin, over- hanging posterior end. Each reticulation fossa with two to nine pore clusters. Secondary fine-scale sponge—like network rims each reticulation fossa. Simple-type normal pores on reticulation ridges; normal pores with recessed marginal rim. Small eye spot. Wide inner lamella parallels valve outline. moderately developed. Hingement in right valve consists of bifid anterior tooth complex, with subtriangular tooth and elongate, trapezoidal tooth; anteromedian small tooth and socket; finely crenulate median groove; and bifid, crescentic posterior tooth. Four adductor muscle scars form vertical row. Dorsal scar is kidney—shaped; dorsomedian scar is dumbbell- shaped; ventromedian scar is elongate, with enlarged, ven— trally drooping anterior; ventral scar is boomerang-shaped. Rounded, large fulcral point. Frontal scar forms rounded heart shape. Moderate number of irregularly shaped dorsal muscle scars. Selvage 6 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 Measurements.-—X—Y plot based on 13 specimens (fig. 3). Remarks.—Typhlocythere Bonaduce, Ciampo, and Masoli, 1975 is similar in ornamentation and shape to Eucytherura but differs in lacking eye spots. Eucytherura hazeli and E. ishizakii both have eye spots and hence are placed into Eucytherura. Comparisons.—Eucytherura hazeli n. sp. differs from E. utsusemi Yajima, 1982 (upper Pleistocene, central Japan) by having a low, long valve outline; high ventral ridge with less ventral overhang; rounded reticulation pits; and a weakly developed eye spot. Occurrence.—Cruise EGAL-75-KC, locality 52A. Cruise DCl-79-EG, locality 47. Cruise DC2-80-EG, locali- ties 67, 73, 82, 86, 186, 195. Distribution.—Pleistocene (?), Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf. Outer sublittoral. Material.——Thirty-six adult valves. Type specimens.—Holotype: USNM 408427, left valve (pl. 2, figs. 9, 12), locality DC2—80~EG—195, length 0.35 mm, height 0.20 mm. Paratypes: USNM 408428, right valve (pl. 2, fig. 10), locality DC2-80-EG-l95, length 0.35 mm, height 0.20 mm. USNM 408429, right valve (pl. 2, figs. 11, 13, 14; pl. 4, fig. 14), locality DC21-80-EG-195, length 0.36 mm, height 0.20 mm. USNM 408430, left valve (pl. 14, fig. 15), locality DC2—80—EG—195, length 0.35 mm, height 0.23 m. E U C YTHER URA ISHIZAKII new species Plate 1, figure 8; plate 3, figure 1', plate 4, figures 6—13; figures 4, 5 Eucytherura sp. A Brouwers, 1981, p. 10; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 9; Brouwers, 1983. Etymology—After Dr. Kunihiro Ishizaki, Tohoku Uni- versity, Japan. Diagnosis.—Characterized by subtriangular lateral out- line; pronounced concavity; wide, broad caudal process; dor- sal and ventral margins converge at posterior; anteroventral marginal denticles; subtle dimorphism; low massive reticu- lation; ovoid pits arranged vertically in subparallel rows; inverted V-shaped anterior ridge; prominent, arcuate, over- hanging ventral ridge; eye spot; smooth posterior marginal rim; crescentic anterior and arcuate posterior vestibules. Description.———Adult valves short, subtriangular in lat— eral view. Dorsal margin broadly sinuous, inclined toward posterior; smoothly curved anterodorsal margin and irregu- larly curved anteroventral margin; anterior margin with greatest width ventral of midline; ventral margin with pro- nounced concavity; venter inclined sharply toward postero- dorsal; posterior margin attenuated, with wide, broad caudal process. Dorsal and ventral margins converge toward poste- rior. Many small, sharp anteroventral marginal denticles. Right valve with low anterodorsal corner; convergent poste- rior; and inclined dorsum. Subtle dimorphism: males differ 0.25 I I I I I I I I I l I I I I U) >— _ D: 0 Lu '— _ _ LIJ E _ _ ._.I d E [120— . . “‘ Z 1 — o o — I— 35 — 0 o o o — E I _ _ _ . _ [115— — I I I I l I I I I l I I I r 0.30 0.35 0.40 [1.45 LENGTH, IN MILLIMETERS Figure 3. Plot of length versus height for Eucytherura hazeli. Dot may represent more than one specimen. in having short, low valve outline, convergent posterior. Greatest length through midline of valve; greatest height through anterior hinge element. Valve surface covered with low, massive reticulation. Pits are moderate in size, rounded, subovoid to elongate- ovoid; arranged in vertical pattern of subparallel rows. Retic- ulation ridges are broad, rounded, heavily calcified. Large anterior marginal ridge proceeds to anterodorsal corner, con- necting with second vertical ridge, forming inverted V- shape. Ventral marginal ridge angles obliquely to middle of venter. Oblique ridge forms outer edge of prominent, arcuate ventral ridge which overhangs posteroventral margin and terminates as tubercle. Posterior margin with vertical ridge. Prominent, smooth, subovoid eye spot. Broad, flat, smooth posterior marginal rim. Sola pore clusters within ornament pits. Thirty-six simple-type normal pores scattered over sur- face, on reticulation ridges. Normal pores with subtle mar- ginal rim. Inner margin and line of concrescence coincide along venter. Deep, crescentic anterior vestibule; arcuate posterior vestibule. Selvage well developed. Hingement in left valve consists of large, subquadrate anterior socket with heavy dorsal rim; finely crenulate median bar; and large, elongate, subovoid posterior socket. Median element enlarged terminally, sinuous in course. Anterior and posterior hinge element with reinforced, heavily calcified platform. Four adductor muscle scars in a row, inclined postero- dorsally. Dorsal scar is elongate-ellipsoidal; dorsomedian scar is subquadrate; ventromedian scar is elongate, subquad- rate; ventral scar is semicircular. J-shaped frontal scar. Few, large dorsal muscle scars. Measurements.—X—Y plot based on 32 specimens (fig. 4). SYSTEMATIC PALEONTOLOGY 7 0.30 I | I I I I I I I I I I I I I I I - C O O - g — o o o o — Enzs— O O O O — LlJ g - O O - e - 0 - E - 3 Z _ _ I£0.20— — Q _ _ Lu I _ _ 0.15— _ I I I I I I I I I I I I I I I I I I 0.30 0.35 0.4 0.45 LENGTH, IN MILLIMETERS Figure 4. Plot of length versus height for Eucytherura ishizakii. Dot may represent more than one specimen. C0mparisons.—Eucytherura ishizakii n. sp. differs from E. utsusemi Yajima, 1982 (lower Pleistocene, central Japan) by having a triangular lateral outline; narrow poste- rior; wide, less pointed ventral ridge; V-shaped anterior ridge; ovoid pits; and pitting arranged in vertical rows. 0ccurrence.—Assemblages II, III, IV. Table 2; figure 5. Distribution.——Pleist0cene through Holocene: Cook Inlet, Kodiak Shelf, Gulf of Alaska. Middle-outer sublittoral, upper bathyal. Material.——One hundred twenty-eight adult valves, forty-three juvenile valves. Type specimens.—Holotype: USNM 408431, female left valve (pl. 1, fig. 8), locality EGAL-75—KC—284, length 0.40 mm, height 0.28 mm. Paratypes: USNM 408432, male left valve (pl. 3, fig. 1), locality EGAL—75-KC-284, length 0.41 mm, height 0.26 mm. USNM 408433, right valve (pl. 4, figs. 6, 8, 9), locality EGAL—75-KC-268, length 0.39 mm, height 0.26 mm. USNM 408434, left valve (pl. 4, fig. 7), locality EGAL-75- KC-268, length 0.40 mm, height 0.28 mm. USNM 408435, right valve (pl. 4, figs. 10, 12), locality EGAL-75-KC—268, length 0.40 mm, height 0.24 mm. USNM 408436, left valve (pl. 4, fig. 11), locality EGAL-75-KC—268, length 0.40 mm, height 0.25 mm. USNM 408437, right valve (pl. 4, fig. 13), locality EGAL-75-KC-268, length 0.41 mm, height 0.25 mm. Genus HEMICYTHERURA Elofson, 1941 Type species.—Cythere cellulosa Norman, 1865 (Type by subsequent designation) HEMICYTHERURA DAGELETENSIS new species Plate 3, figures 2, 3; plate 5, figures 1—3; figures 6, 7 Hemicythemra sp. A Brouwers, 1981, p. 10; Brouwers, 1982a, p. 12; Brouwers, 1982b, p. 9; Brouwers, 1983. Hemicytherura sp. A Valentine, 1976, p. 22, pl. 6, figs. 5, 6. Etymology.—After Mount Dagelet, the source of LaPerouse Glacier, central Fairweather Range. Diagnosis.—Characterized by elongate-ovoid to subtri- angular lateral outline; broadly convex ventral margin; T- shaped median ridge; strong, arcuate, overhanging ventral ridge; pits arranged in horizontal to arcuate pattern, follow- ing T—shaped ridge; secondary fine ridges on primary ridge and caudal process; coincident inner margin and line of con- crescence; long, sinuous, simple radial pore canals. Description—Adult valves elongate—ovoid to subtrian- gular in lateral view. Left valve with broadly arched dorsal margin; anterior margin evenly curved, with greatest width ventral of midline; ventral margin broadly convex; posterior margin with distinct, broad, centrally located caudal process. Right valve with highly arched dorsal margin; concave 20 I I I I I NUMBER OF VALVES | 50 70 90 110 I30 150 DEPTH, IN METERS 170 190 210 230 250 270 Figure 5. Plot of abundance versus water depth for Eucytherura ishizakii. 8 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 anterodorsal margin; attenuated anteroventral margin; sinu- ous ventral margin; posterior margin with small, sharp, dis— tinct caudal process, located ventral of midline. Four long, sharp anteroventral marginal denticles. Left valve differs in having low, short valve dimensions; considerably less arched dorsum; centrally located, broad caudal process; and convex anterodorsal margin. Greatest length through caudal process; greatest height midvalve in right valve and through anterior hinge element in left valve. Valve surface covered with reticulation and ridges. Ornament dominated by T-shaped ridge extending across valve midline; short vertical part of T- shape proceeds from midvalve to midventer. Strong, arcuate ventral ridge over- hangs margin. Thin, weak marginal ridge runs from caudal process along dorsum, terminating anteriorly at T-shaped ridge. Reticulation pits are large, ovoid to elongate—ovoid; arranged in horizontal to arcuate pattern, paralleling horizon- tal part of T—ridge. Marginal pits very small. Secondary fine ridges on caudal process and primary ridges. Thirty-seven to thirty-nine simple-type normal pores evenly scattered over surface, on reticulation ridges. N ormal pores with marginal rim. Inner margin and line of concrescence coincide throughout; inner margin parallels valve outline. Inner lamella wide throughout, particularly along anterior. Strong, well-developed selvage. Twenty to twenty-four radial pore canals, three false radial pore canals, most anterior. Radial pores long, sinuous, simple. Radial pores enter anteroventral marginal denticles. Anterior radial pores cluster into groups of two to four. Measurements.—X—Y plot based on 26 specimens (fig. 6). Comparisons.—Hemicytherura dageletensis n. sp. dif- fers from H. santosensis Swain and Gilby, 1974 (Holocene, Baja California) by having a higher, shorter valve outline; arched dorsum; T-shaped median ridge; and sharp caudal process. H. dageletensis differs from H. cuneata Hanai, 1957 (Holocene, Inland Sea, central Japan) by having an arched dorsum; T-shaped median ridge; short caudal process; and no secondary ornament. H. dageletensis differs from H. clathrata (Sars) (Quaternary, North Atlantic, European Arc— tic) by having a long, low lateral outline; T-shaped median ridge; less extended caudal process; no secondary ornament; and small reticulation pits. 0ccurrence.—Assemblages II, III, V. Table 2; figure 7. Distribution.—Pleistocene through Holocene: Gulf of Alaska, Cook Inlet and Kodiak Shelf, Pribilof Islands, cen- tral—northern California, Washington, and Oregon (Channel Islands to Puget Sound). Middle-outer sublittoral; warm to cold temperate. Material.—One hundred seventy-nine adult valves, thirty-one juvenile valves. Type specimens.—Holotype: USNM 408438, left valve (pl. 3, fig. 2), locality DC2—80-EG—195, length 0.40 mm, height 0.24 mm. 0.35 l I I I I I I : 0 g; [1.30 — O . — E — _ L|.| - .. _ g _ _ 2' - o o — E 0.25 — O O O — z — o — i; - o 000. — L9 _ _ Lu _ I 0.20 — — 0415 l i I i I i 0.2 0.3 0.4 0.5 0.5 LENGTH, IN MILLIMETERS Figure 6. Plot of length versus height for Hemicytherura dageletensis. Dot may represent more than one specimen. Paratypes: USNM 408439, right valve (pl. 3, fig. 3), locality DC2-80-EG-195, length 0.41 mm, height 0.26 mm. USNM 408440, left valve (pl. 5, figs. 1, 3), locality DC2-80— EG-195, length 0.41 mm, height 0.23 mm. USNM 408441, right valve (pl. 5, fig. 2), locality DC2-80-EG-195, length 0.43 mm, height 0.30 mm. HEMICY T HERURA LEMESURIENSIS new species Plate 3, figure 4; plate 5, figures 4—6; figure 8 Hemicytherura sp. J Valentine, 1976, p. 22, pl. 6, fig. 11. Hemicytherura sp. C Brouwers, 1981, p. 10; Brouwers, 1982a, p. 12; Brouwers, 1982b, p. 9; Brouwers, 1983. Etymology—After Lemesurier Island in Icy Strait, southeast Alaska. Diagnosis.—Characterized by straight anterodorsal margin; broadly concave venter; three longitudinal ridges; thin, overhanging ventral ridge; thin, semicircular dorsal ridge; large reticulation pits arranged horizontally at anterior and concentrically at posterior; fine marginal pits and ridges; and very wide anterior inner lamella. Description.—Adult valves subtriangular in lateral out- line. Dorsal margin arched; anterodorsal margin straight, inclined sharply toward anteroventer; anteroventral margin extended; greatest anterior margin width at anteroventer; ventral margin broadly concave; posterior margin with small, sharp, distinct caudal process located near midline. Four sharp anteroventral marginal denticles. Greatest length through midline of valve; greatest height through median hinge element. Valve surface with reticulation and ridges. Three pri- mary longitudinal ridges traverse valve; ridges originate together in posteromedian region and radiate toward anterior. SYSTEMATIC PALEONTOLOGY 9 I I I | I l 120— 60— NUMBER OF VALVES 40 20 30 50 70 90 110 I30 150 170 190 | I l | | I 210 230 DEPTH, IN METERS Figure 7. Plot of abundance versus water depth for Hemicytherura dageletensis. Sinuous dorsal ridge proceeds to anterodorsal corner. Median ridge proceeds to anterior margin. Ventral ridge proceeds obliquely to anteroventral comer. Thin ventral ridge proceeds obliquely to anteroventral corner. Thin, semicircular dorsal marginal ridge. Large, subovoid reticulation pits occur between ridges. Pits arranged horizontally at anterior and con- centrically at posterior. Very small secondary pitting and fine ridges at margins. Twenty-one t0 twenty-seven normal pores evenly distributed over surface, on reticulation ridges. Inner margin and line of concrescence coincide throughout; inner margin parallels valve outline. Inner lamella very wide at anterior, moderately wide at posterior. Well-developed selvage. Eleven radial pore canals, most anterior. Radial pores are long, sinuous, simple, and tend to cluster into groups of two to four. Radial pores enter anteroventral denticles. Hingement in left valve consists of anterior quadrate socket; five small, quadrate anteromedian teeth; smooth median bar; seven small, quadrate posteromedian teeth; and elongate, rectangular posterior socket. Four adductor muscle scars form vertical row. Dorsal scar is elongate-ellipsoidal; dorsomedian scar is elongate, subquadrate; ventromedian scar is elongate, with inflated anterior; ventral scar is semicircular. Few, large, ovoid dor- sal muscle scars. Measurements.—X—Y plot based on 11 specimens (fig. 8). Comparisons.—Hemicythemra lemesuriensis n. sp. differs from H. kajiyamai Hanai, 1957 (Holocene, central Japan) by having a low, long valve outline; less arched dor- sum; weak reticulation ridges; and numerous, small reticula— tion pits. H. lemesuriensis differs from H. cuneata Hanai, 1957 (Holocene, central Japan) by having a long, low lateral outline; less arched dorsum; straight anterodorsal margin; weak, short caudal process; and different arrangement of pits. H. lemesuriensis is distinguished from H. santosensis‘ Swain and Gilby, 1974 (Holocene, Baja California) by hav— ing a less arched dorsum; small caudal process; straight anterodorsal margin; narrow reticulation ridges; numerous reticulation pits; and secondary marginal ornamentation. 10 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 0.25 I l | l I (I) _ CC UJ _ _ '— LLI _ _ E a - ° - E 0.20 — g _ é — o o o — E ~ 0 — Q _ _ LLl I _ _ 0.75 I l I l I 0.2 0,3 0.4 0,5 LENGTH, IN MILLIMETERS Figure 8. Plot of length versus height for Hemicytherura lemesuriensis. Dot may represent more than one specimen. Occurrence.—Cruise EGAL-75-KC, localities 11, 159, 429. Cruise DC1—79-EG, locality 46. Cruise DC2-80-EG, locality 195. Assemblages II, V. Distribution—Upper Pliocene through Holocene: Gulf of Alaska, Baja California, California, Washington, and Ore- gon (northern Baja California to Puget Sound). Middle sub- littoral; warm to cold temperate. Material.—Twenty-five adult valves, three juvenile valves. Type specimens.—Holotype: USNM 408442, left valve (pl. 3, fig. 4), locality DC2-80-EG-195, length 0.35 mm, height 0.20 mm. Paratypes: USNM 408443, female right valve (pl. 5, fig. 4), locality DC2—80-EG-195, length 0.35 mm, height 0.20 mm. USNM 408444, female left valve (pl. 5, figs. 5, 6), locality DC2-80-EG-195, length 0.35 mm, height 0.19 mm. HEMICYTHERURA SITAKADA YENSIS new species Plate 3, figures 5, 6; plate 5, figures 7—14; figure 9 Hemicytherura sp. B Brouwers, 1981, p. 10; Brouwers, 1982a, p. 12; Brouwers, 1982b, p. 9; Brouwers, 1983. Etymology—After Sitakaday Narrows, located at the southern Beardslee Entrance to Glacier Bay, southeast Alaska. Diagnosis.—Characterized by elongate subtriangular lateral outline; broadly convex ventral margin; sharply inclined posteroventral margin; subtle dimorphism; coarse reticulation-ridge system with sinuous longitudinal median ridge and evenly spaced ridges radiating to dorsum and ven- ter; crescentic, overhanging ventral and dorsal ridges; fine connecting ridges forming large, rounded, irregular fossae; secondary fine-scale reticulation. Description—Adult valves elongate, subtriangular in lateral view. Left valve with broadly arched dorsal margin; anterior margin smoothly curved with greatest width ventral of midline; ventral margin broadly convex, with sharply inclined posteroventral corner; posterior margin with large, broad caudal process dorsal of midline. Right valve with moderately arched dorsal margin; straight, inclined antero- dorsal margin; drawn-out anteroventral margin; greatest anterior margin width near anteroventral corner; ventral margin broadly concave; posterior margin with small, sharp, caudal process ventral of midline. Five sharp anteroventral marginal denticles. Left valve differs in less arched dorsum; large caudal process; and lower, longer valve outline. Subtle dimorphism: males differ in a lower, longer lateral outline; pronounced caudal process; less arched dorsum; and less concave anterodorsal margin. Greatest length through caudal process; greatest height through midline of valve. Valve surface with coarse reticulation-ridge system. Primary, sinuous median ridge proceeds obliquely across valve from anterior margin to posterodorsal corner. Four ridges originate at median ridge and proceed obliquely to venter. Five ridges radiate from median ridge to dorsum. Two crescentic ridges overhang dorsal and ventral margins. Fine ridges connect large ridges, forming reticulation net- work with resultant very large, rounded, irregular fossae. Secondary fine—scale reticulation on solum floors. Thirty- one simple-type normal pores evenly distributed over sur- face, within fossae. Normal pores are celate with apophysis with marginal rim. Inner margin and line of concrescence coincide throughout; inner margin parallels valve outline. Inner lamella very wide at anterior, moderately wide at posterior. Very strong, well-developed selvage. Nineteen radial pore canals, most anterior. Radial pores are long, sinuous, simple, with inflated median region. Pores occur in clusters of three to four pores. Radial pores enter marginal denticles. Hingement in left valve consists of elongate, rectangu- lar anterior socket; four quadrate anteromedian teeth; smooth median bar; six quadrate posteromedian teeth; and elongate-ellipsoidal posterior socket. Anteromedian and posteromedian elements formed by terminal enlargement of median element. Dorsal margin of right valve enfolded into accommodation groove to receive dorsal edge of left valve. Four adductor muscle scars form vertical row. Dorsal scar is semicircular; dorsomedian scar is elongate, with inflated posterior; ventromedian scar is dumbbell-shaped; and ventral scar is oblate-ovoid. Frontal scar is rounded, sub— triangular. Numerous large, irregularly shaped dorsal muscle scars. Measurements.—X—Y plot based on 61 specimens (fig. 9). Comparisons.—Hemicytherura sitakadayensis n. Sp. differs from H. sp. F of Valentine, 1976 (Holocene, Baja California, southern-central California) by having a small, ventrally located caudal process; weak ventral ridge; con- cave anterodorsal margin; small, attenuated anteroventral corner; and different dorsal ridge. H. sitakadayensis differs from H. santosehsis Swain and Gilby, 1974 (Holocene, Baja California) by having a low, long valve outline; high, strong reticulation ridges; large, few fossae; attenuated. SYSTEMATIC PALEONTOLOGY 11 anteroventral corner; and narrow, extended caudal process. H. sitakadayensis is different from H. cuneata Hanai, 1957 (Holocene, central Japan) by having an evenly curved dor- sum; caudal process along the midline; single, strong, longi- tudinal median ridge; and few, large fossae. H. sitakadayensis differs from H. clathrata (Sars) (Quaternary, North Atlantic) by having a low, long valve outline; few, large reticulation pits; weak, less overhanging ventral ridge; and dorsal and ventral ridges radiating from median ridge. 0ccurrence.—Assemblages II, V. Table 2. Distribution.—Pleistocene through Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf. Middle sublittoral. Material.—One hundred twenty-eight adult valves, twelve juvenile valves. Type specimens.—Holotype: USNM 408445, left valve (pl. 3, fig. 5), locality DC2-80-EG—195, length 0.46 mm, height 0.23 mm. Paratypes: USNM 408446, right valve (pl. 3, fig. 6), locality DC2-80-EG-195, length 0.47 mm, height 0.27 mm. USNM 408447, female left valve (pl. 5, fig. 7), locality DC2- 80-EG-195, length 0.50 mm, height 0.26 mm. USNM 408448, female right valve (pl. 5, fig. 8), locality DC2-80- EG-195, length 0.46 mm, height 0.26 mm. USNM 408449, male left valve (pl. 5, figs. 9, 10), locality DC2-80—EG—l95, length 0.44 mm, height 0.24 mm. USNM 408450, male right valve (pl. 5, fig. 11), locality DC2-80-EG-195, length 0.42 mm, height 0.25 mm. USNM 408451, male left valve (pl. 5, figs. 12, 14), locality DC2-80-EG-195, length 0.43 mm, height 0.22 mm. USNM 408452, female right valve (pl. 5, fig. 13), locality DC2—80-EG—195, length 0.43 mm, height 0.24 mm. Genus SEMICY T HERURA Wagner, 1957 Type species.——Cythere nigrescens Baird, 1838 (Type by subsequent designation) SEMICYTHERURA BALROGI new species Plate 5, figures 15—18; plate 6, figures 1, 2; plate 7, figures 1—3, 6; figure 10 Semicytherura ajf S. undata (Sars, 1865). Brouwers, 1981, p. 12; Brouwers, 1982a, p. 12; Brouwers, 1982b, p. 10; Brouwers, 1983. Etymology.——After the Balrog, an evil character in J .R.R. Tolkien‘s adventures of Middle Earth. Diagnosis.—Characterized by subquadrate lateral out- line; oblique posteroventral margin; short, broad caudal pro- cess; moderate dimorphism; two sinuous, obliquely arranged primary ridges; weak vertical ridges at anteromedian and posteromedian; fine—scale reticulation defining polygonal fossae; small, elongate to subovoid secondary pits with raised rim; simple-type normal pores with raised marginal rim. Description—Adult valves elongate, subquadrate in lateral view. Dorsal margin straight; anterior margin 0.35 I I I I 1 (I) 0.30 — —“ E — o o — E o o o — g a... o o :1 u .00 o o — S 025 — on 00 _ g I 0 O. — . O 0 g o o o E — .. . ‘ I 0.20 — o _ - O ‘1 _ I l I I l I I _ 0 50.2 0.3 0.4 0.5 0.6 LENGTH, IN MILLIMETERS Figure 9. Plot of length versus height for Hemicytherura sitaka- dayensis. Dot may represent more than one specimen. smoothly curved, with greatest width ventral of midline; ventral margin straight; posterior margin with steeply oblique posteroventral margin and short, broad caudal pro- cess dorsal of midline. Four short, blunt anteroventral mar- ginal denticles. Right valve with more arched dorsum; ventrally slung anteroventral comer; and small, acute caudal process. Moderate dimorphism: males are longer, lower. Greatest length through caudal process; greatest height through anterior hinge element. Valve surface covered with ridges and reticulation. Two sinuous oblique ridges proceed across valve. Dorsal ridge originates at anterior margin, proceeds obliquely toward posterodorsal corner, loops back to form U-shape. Ventral ridge parallel to margin. Weak vertical ridges con- nect longitudinal ridges at anteromedian and posteromedian. Sinuous, overhanging ventral ridge. Fine reticulation between. Fine polygonal fossae. Numerous small, elongate to subovoid secondary pits on solum floors and primary ridges. Secondary pits distinctive by raised rim which sur— rounds and highlights each pit. Thirteen to fifteen simple- type normal pores evenly distributed over surface, occurring on solum floors. Normal pores with prominent, raised mar— ginal rim. Inner lamella and line of concrescence coincide at ante- rior. Anterior inner lamella very wide. Radial pore canals are very long, sinuous, simple; radial pores tend to occur in clusters. Measurements.—X—Y plot based on 16 specimens (fig. 10). Comparisons.—Semicytherura balrogi n. sp. differs from Hemicytherura tricarinata Hanai, 1957 (Holocene, central Japan) by having a subquadrate lateral outline; broad caudal process; two horizontal ridges; and rimmed 12 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 secondary ornament pits. S. balrogi differs from S. undata (Sars) (Quaternary, North Atlantic) by having a high, short valve outline; straight dorsum; small, distinct caudal pro- cess; two horizontal ridges; distinctive secondary ornament; and different arrangement of vertical crossing ridges. 0ccurrence.——Cruise EGAL-75-KC, localities 11, 157, 159. Cruise DC2—80-EG, locality 195. Assemblage V. Distribution.—Pleistocene through Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf, Pribilof Islands. Material.—Thirty-seven adult valves. Type specimens.—Holotype: USNM 408453, female left valve (pl. 6, fig. 1), locality DC2-80—EG-195, length 0.35 mm, height 0.20 mm. Paratypes: USNM 408454, female right valve (pl. 6, fig. 2), locality DC2—80-EG-195, length 0.35 mm, height 0.20 mm. USNM 408455, left valve (pl. 5, figs. 15, 18), locality DC2-80-EG-195, length 0.32 mm, height 0.16 mm. USNM 408456, left valve (pl. 5, figs. 16, 17), locality DC2- 80-EG-195, length 0.32 mm, height 0.21 mm. USNM 408457, right valve (pl. 7, figs. 1—3, 6), locality DC2-80-EG— 195, length 0.35 mm, height 0.21 mm. SEMICYTHERURA HENRYI new species Plate 6, figures 3, 4; plate 7, figures 4, 5, 7, 8 Semicytherura sp. D Brouwers, 1981, p. 12; Brouwers, 1983. Etymology.—After Dr. T.W. Henry, US. Geological Survey, a specialist in upper Paleozoic mega—invertebrates. Diagnosis.—Characterized by elongate, trapezoidal lateral outline; broadly concave dorsum; pronounced con- cavity; sharp caudal process located dorsal of midline; series of subparallel longitudinal ridges which converge at anterior and posterior; and longitudinal reticulation network with small, subovoid fossae. Description—Adult valves elongate, trapezoidal in lat— eral view. Dorsal margin straight; anterior margin smoothly curved, with greatest width ventral of midline; ventral mar— gin with pronounced concavity; posterior margin with straight, sharply inclined ventral portion and small, sharp caudal process in dorsal portion; caudal process dorsal of midline. Left valve with attenuated caudal process; less evenly curved, more ventrally slung anteroventral corner; and posteriorly convergent dorsum. Greatest length through midline of valve; greatest height through anterior hinge ele- ment. Valve surface with ridges and reticulation. Primary ornament is series of subparallel longitudinal ridges, con- verging at anteromedian and posteromedian. Moderate, sin- uous, overhanging ventral marginal ridge. Reticulation network developed between longitudinal ridges, forming small subovoid fossae which are largest at median and smaller marginally. Reticulation arranged in longitudinal pattern, aligned with subparallel ridges. Thirteen to eighteen 0.30 I I I I | U) _ _ I LU '— I.u ’ _ E _I d E _ _ Z O O I; w _ g 0.20 00 I - O. O ‘ C _ . _ 0.14 | | | | I 0.25 0.45 0.55 0.35 LENGTH, IN MILLIMETERS Figure 10. Plot of length versus height for Semicytherura balro- gi. Dot may represent more than one specimen. small, simple—type normal pore canals scattered over sur- face, most within fossae. Nine to ten radial pore canals, most anterior. Radial pores long, straight, simple. Strong, well-developed selvage. Comparisons.——Semicytherura henryi n. sp. differs from Cytherura skippa Hanai, 1957 (Holocene, central Japan) by having a large, high lateral outline; weak ventral ridge; numerous subparallel ridges; and reticulation. S. hen- ryi differs from S. mukaishimensis Okubo, 1980 (Holocene, Inland Sea of Japan) by having a straight dorsum; evenly curved anterior; concave venter; short, dorsally located cau- dal process; subparallel longitudinal ridges; and fine reticu— lation. 0ccurrence.—Cruise EGAL—75-KC, localities 4, 18. Cruise DC1—79-EG, locality 45. Distribution.—Pleistocene, Holocene (7): Alaska. Material.—Nine adult valves. Type specimens.—Holotype: USNM 408460, left valve (pl. 6, fig. 3), locality EGAL-75-KC-18, length 0.36 mm, height 0.18 mm. Paratypes: USNM 408461, right valve (pl. 6, fig. 4), locality EGAL-75-KC—18, length 0.38 mm, height 0.18 mm. USNM 408462, left valve (pl. 7, figs. 4, 7), locality EGAL- 75-KC-4, length 0.38 mm, height 0.19 mm. USNM 408463, right valve (pl. 7, figs. 5, 8), locality EGAL-75-KC—4, length 0.37 mm, height 0.19 mm. Gulf of SEMICYTHERURA MIURENSIS Hanai, 1957 Plate 2, figure 6 Cytherura miurensis Hanai, 1957, p. 18—19, pl. 2, figs. 4a,b; text-figs. 4a,b; Hanai, 1961, p. 358, text—fig. 2, figs. 4a,b; Ishizaki, 1968, p. 19, pl. 5, figs. 15, 16. SYSTEMATIC PALEONTOLOGY 13 0.36 I l I - G _ . _ . (é) 0.30 — . — LIJ . E - o o — g C j ‘ . “ E Z _ _ F :1: - _ 9 ‘i‘ 0.20 — — 0.14 l l l l l | 0.25 0.35 0.45 0.55 0.65 LENGTH, IN MILLIMETERS Figure 11. Plot of length versus height for Semicytherura skag- wayensis. Semicythemra miurensis Hanai. Yajima, 1988, pl. 1, fig. 11. Cytherura sp. F Brouwers, 1981 (partim), p. 10; Brouwers, 1982b (partim), p. 8; Brouwers, 1983 (partim). Diagnosis—Characterized by subovoid-elongate lat- eral outline; broadly arched dorsum; concave venter; pro- nounced caudal process; fine reticulation network, with low ridges bordered by rows of small pits; solum floors smooth; weak, angular, ventral ridge. 0ccurrence.—-Cruise EGAL-75-KC, localities 144U, 181. Distribution.—-Early middle Miocene, Holocene: cen- tral Japan. Pleistocene, Holocene (?): Gulf of Alaska, Cook Inlet, Kodiak Shelf. Comparisons.—Semicytherura miurensis differs from S. sp. 1 Whatley and others, 1988 (Holocene, southwest Atlantic) by having a more dorsally placed caudal process, weaker horizontal ridges, anterior denticles, and posteroven- tral flange; S. miurensis differs from S. afifinis (Sars) Neale and Howe, 1975 (Holocene, Novaya Zemlya) by having finely punctate ornamentation. Material.—Six adult valves, one juvenile valve. Illustrated specimens.—USNM 408417, left valve (pl. 2, fig. 6), locality EGAL—75-KC-422, length 0.68 mm, height 0.34 mm. SEMICYTHERURA SKAGWAYENSIS new species Plate 6, figure 5; plate 7, figures 9—16; figure 11 Semicytherura sp. F Brouwers, 1981, p. 12; Brouwers, 1982a, p. 12; Brouwers, 1982b, p. 10; Brouwers, 1983. Etymology—After Skagway, northern Chilkoot Inlet, southeast Alaska. Diagnosis—Characterized by elongate-ellipsoidal lat- eral outline; broadly arched dorsum; wide, shallow concav- ity; narrow, pronounced caudal process; subtle dimorphism; weak reticulation, stronger marginally; small pits adjacent to reticulation ridges; marginal pits; low, arcuate, overhanging ventral ridge; and five low, radiating ridges at anteroventral region. Description—Adult valves elongate-ellipsoidal in lat- eral view. Dorsal margin straight; anterior margin smoothly curved; ventral margin broadly concave, with wide, shallow concavity; posterior margin with narrow, extended, pro- nounced caudal process. No cardinal angles; valve outline is rounded. Left valve with more arched dorsum; ventrally drooping anteroventral corner; and extended caudal process. Subtle dimorphism: males are slightly longer, lower. Great- est length through caudal process; greatest height through anterior hinge element. Valve surface covered with weak reticulation, most developed at the margins. Ridges accentuated by series of small pits adjacent to ridges. Pitting covers entire solum floors at valve margins. Low, arcuate ridge occurs along and over- hangs venter. Series of five low ridges radiate from anterior end of ventral ridge to anteroventral region. Thirty simple- type normal pores evenly distributed over valve surface, occurring within fossae. Normal pores with marginal rim. Inner lamella and line of concrescence coincide throughout. Inner lamella very wide at anterior. Posterior inner margin forms broad, tongue-like extension into valve interior. Strong, well-developed selvage. Thirteen radial pores, two false radial pores, most anterior. Radial pore canals are long, slightly sinuous, and simple. Radial pores clustered in groups of two to four. Hingement in right valve consists of bifid anterior tooth; smooth, large median groove; and trifid posterior tooth. Dorsal margin of right valve enfolded to form accom- modation groove to accept dorsal edge of left valve. Measurements.—X—Y plot based on nine specimens (fig. 11). Comparisons.—Semicytherura skagwayensis n. sp. differs from S. kishinouyei (Kajiyama, 1913) (Quaternary, central Japan) by having a weak ventral ridge; less conver- gent posterodorsal margin; few, small pits; and narrow, long caudal process. S. skagwayensis differs from S. miu- rensis (Hanai, 1957) (Quaternary, central Japan) by having a weak posteroventral ridge; long, straight dorsum; strong concavity; and weak reticulation. S. skagwayensis differs from S. afiinis (Sars) (Quaternary, North Atlantic) by hav- ing a straight, less arched dorsum; strong concavity; weak reticulation; and few pits. S. skagwayensis differs from Cytherura johnsonoides Swain and Gilby, 1974 (Holocene, Baja California) by having a long, narrow cau- dal process; strong concavity; median sulcus; and weak 14 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 reticulation. S. skagwayensis differs from all of the above species by having a long, low lateral outline. Occurrence—Cruise EGAL-75-KC, localities 20, 159. Cruise DC2-80—EG, locality 195. Assemblage V. Distribution.—Pleistocene (?), Holocene: Alaska, Cook Inlet, Kodiak Shelf, Pribilof Islands. Material.—Twenty—five adult valves, nine juvenile valves. Type specimens.—Holotype: USNM 408464, left valve (pl. 6, fig. 5), locality DC2-80-EG-195, length 0.65 mm, height 0.32 mm. Paratypes: USNM 408465, left valve (pl. 7, figs. 9, l6), locality DC2-80-EG-l95, length 0.69 mm, height 0.34 mm. USNM 408466, left valve (pl. 7, fig. 10), locality DC2-80- EG-195, length 0.62 mm, height 0.29 mm. USNM 408467, right valve (pl. 7, figs. 11, 12), locality DC2—80—EG-195, length 0.63 mm, height 0.30 mm. USNM 408468, right valve (pl. 7, figs. 13, 14, 15), locality DC2-80—EG-195, length 0.62 mm, height 0.26 mm. Gulf of SEMICYTHERURA TAURONAE new species Plate 1, figure 4; plate 2, figures 5, 7—8 Cytherura sp. F Brouwers, 1981, p. 10 (partim); Brouwers, 1982b, p. 8 (partim); Brouwers, 1983 (partim). Semicytherura sp. A Ishizaki and Matoba, 1985, p. 9, pl. 7, figs. 8, 9. Etymology—After Tauron, a character in J .R.R. Tolk- ien's adventures of Middle Earth. Diagnosis.—Characterized by subtriangular lateral out- line; highly arched dorsum; pronounced, narrow caudal pro- cess; small ovoid pitting which becomes finer marginally; narrow, angular, overhanging ventral ridge, ending at poste- rior as a flat flange and at anterior as fine radiating ridges; dorsal region with thickened smooth region; vertical median sulcus; and coincident inner margin and line of concres- cence. Description—Adult valves subtriangular in lateral View. Dorsal margin highly arched; anterior margin smoothly curved, with greatest extent ventral of midline; ventral margin with subtle concavity; posterior margin with pronounced, narrow caudal process. Greatest length through caudal process; greatest height through median hinge ele- ment. Valve surface with small ovoid pitting. Pits small in median valve region, becoming much finer marginally. Nar- row, angular ridge overhangs venter, ending at posterior as flattened flange and at anterior as series of fine radiating ridges. Dorsal margin with thickened, smooth region. Ver- tical median sulcus. Smooth caudal process. Forty-six simple-type normal pores evenly distributed over valve. Inner margin and line of concrescence coincide throughout. Inner lamella widest at anterior. Inner margin parallels valve outline. Eleven radial pore canals, most anterior. Radial pore canals are long and straight; several radial pores bifurcate, most are simple. Weakly developed selvage. Hingement in left valve consists of series of fine termi- nal crenulae forming elongate socket at anterior and poste- rior and smooth median bar. Remarks.—Semicytherura tauronae n. sp. is similar to Semicytherura sp. A of Ishizaki and Matoba (1985) in pitted ornament, ventral ridges, and valve shape; S. tauronae dif- fers from S. sp. A by having a more arched dorsum and slight differences in the radiating ventral ridges. These two taxa belong to the same species group, however, and I am synon— ymizing the two species. Comparisons.—Semicytherura tauronae differs from S. miurensis by its lack of reticulation, larger ornament pits, less quadrate shape, and arched dorsum. Occurrence—Cruise EGAL-75-KC, localities 52A, 144U, 422. Distribution.—Pleistocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf, central Japan. Material.—Eight adult valves. Type specimens.—Holotype: USNM 408419, female right valve (pl. 1, fig. 4), locality EGAL-75—KC—l44U, length 0.58 mm, height 0.33 mm. Paratypes: USNM 408420, left valve (pl. 2, fig. 5), locality EGAL—75-KC-144U, length 0.55 mm, height 0.30 mm. USNM 408421, right valve (pl. 2, figs. 7, 8), locality EGAL-75-KC-l44U, length 0.54 mm, height 0.30 mm. SEMICYTHERURA sp. E Plate 3, figures 7, 8 Cytherura sp. E Brouwers, 1981, p. 10; Brouwers, 1983. Diagnosis.—Characterized by squat, ovoid lateral out- line; broadly arched dorsum; short, broad caudal process; ovoid pitted ornament; U-shaped indentation along poster- oventral inner lamella; V—shaped indentation at posterodorsal inner lamella; strong selvage; radial pores clustering at anteroventral and posteroventral corners; and radial pores often as pairs. Occurrence.—Cruise Assemblage V. Distribution.—Pleistocene: Gulf of Alaska. Material.—Two adult valves. Illustrated specimens.—USNM 408458, left valve (pl. 3, fig. 7), locality EGAL-75-KC-11, length 0.35 mm, height 0.19 mm. USNM 408459, right valve (pl. 3, fig. 8), locality EGAL-75-KC-11, length 0.35 mm, height 0.20 mm. EGAL-75-KC, locality 11. SEMICYTHERURA sp. F Plate 6, figures 7, 8; plate 7, figures l7, l8 Semicytherura sp. E Brouwers, 1981, p. 12; Brouwers, 1983. Diagnosis.—Characterized by rounded, rectangular lat- eral outline; broad, deep concavity; weak, low marginal SYSTEMATIC PALEONTOLOGY 1 5 reticulation; wide anterior inner lamella; wedge-shaped pos- terior inner lamella; indentation of inner lamella at postero- dorsal and posteroventral comers; strong selvage; and long, sinuous radial pores in clusters of two to four. Description—Adult valves rounded, subcylindrical in lateral view. Dorsal margin broadly convex; anterior margin smoothly curved, with greatest width ventral of midline; ventral margin with broad, deep concavity; posterior margin with small, sharp caudal process. Greatest length through caudal process; greatest height through posterior hinge ele- ment. Valve surface predominantly smooth. Weak, low retic- ulation network developed marginally. Subtle, low, arcuate ventral ridge overhangs concavity. Twenty to twenty-four simple-type normal pores scattered over surface. Normal pores with prominent marginal rim. Inner margin and line of concrescence coincide throughout. Inner lamella very wide along anterior, parallels valve outline. Ventral inner lamella narrower, with concave inner margin. Posterior inner lamella with large, broad, wedge-shaped projection into valve interior. Posterodorsal and posteroventral corners of inner lamella with conspicuous indentation towards valve exterior. Strong, well-developed selvage. Nineteen to twenty-six radial pore canals, 6 to 13 false radial pore canals, most anterior. Radial pores very long, slightly sinuous, simple; radial pores in clusters of two to four, forming a distinct, small indentation of inner margin. Long posterior radial pores traverse length of wedge projec- tion. Posterior radial pores originate at and near posterodor— sal and posteroventral indentations. Four adductor muscle scars form vertical row. Scars are large, ovoid in shape. Comparisons.—Semicytherum sp. F differs from S. hiberna Okubo, 1980 (Holocene, Inland Sea of Japan) by having a straight dorsum; strong concavity; strong caudal process; small posterior extension of inner lamella; and few radial pore canals. S. sp. F differs from Semicytherura sp. B of Ishizaki and Matoba (1985) (lower Pleistocene, central Japan) by having a strong caudal process; strong concavity; less arched dorsum; and less median reticulation. 0ccurrence.—Cruise EGAL-75-KC, locality 11. Distribution.——Pleistocene: Gulf of Alaska. Illustrated specimens.—USNM 408470, left valve (pl. 6, fig. 7), locality EGAL-75-KC-11, length 0.51 mm, height 0.27 mm. USNM 408471, right valve (pl. 6, fig. 8), locality EGAL-75-KC-l 1, length 0.51 mm, height 0.26 mm. USNM 408472, right valve (pl. 7, figs. 17, 18), locality EGAL-75- KC-l 1, length 0.53 mm, height 0.28 mm. Subfamily CYTHEROPTERINAE Hanai, 1957 Genus CYTHEROPTERON Sars, 1866 Type species.—Cythere latissima Norman, 1865 (Type by subsequent designation) CYTHEROPTERON BROKENOARENSIS new species Plate 9, figure 2; plate 8, figures 7—1 1; figures 12, 13 Cytheropteron sp. G Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Etymology—After Broken Oar Cove, located in the southeastern part of Yakutat Bay, southeast Alaska. Diagnosis—Characterized by subtriangular lateral out- line; moderately arched dorsum; broadly rounded anterior; convex venter; small, broad caudal process; ovoid pitting arranged in vertical rows, separated by low ridges; pitting smaller marginally; dorsal marginal sulcus; secondary retic- ulation between ridges and on caudal process. Description—Adult valves subtriangular in lateral view. Dorsal margin moderately arched; anterior margin broadly rounded, with greatest width ventral of midline; ven- tral margin with slight concavity; posterior margin with small, broad caudal process. Caudal process with maximum extent dorsal of midline. Left valve with less arched dorsal margin, more pronounced caudal process. Greatest length through midline; greatest height through median hinge. Valve covered with ovoid pitting of various sizes arranged in vertical rows separated by low ridges. Ridge development strongest at posterior. Rows of pits arranged parallel to anterior margin. Pits largest near middle of valve, smaller toward margins. Dorsal marginal sulcus, especially developed in right valve. Secondary fine reticulation between ridges at posterior and on caudal process. Low, subdued ridge overhangs venter. Fifty-nine simple-type nor- mal pores scattered over surface, occurring within pits. Inner margin and line of concrescence coincide throughout; moderately developed selvage. Inner lamella of even width, follows valve outline. Eleven straight, simple radial pore canals. Hingement in left valve consists of rectangular, elon- gate anterior sockets; smooth median bar which thickens and enlarges into anteromedian and posteromedian set of quad- rate teeth; and rectangular, elongate posterior sockets. Median bar formed by dorsal edge of valve. Right valve with dorsal edge enfolded to form accommodation groove. Four adductor muscle scars in vertical row. Frontal scar split into peanut—shaped posterior scar and smaller, round anterior scar. Small ovoid fulcral point posterodorsal of fron- tal scars. Measurements.—X—Y plot based on 59 specimens (fig. 12). Comparisons.—Cyther0pter0n brokenoarensis n. sp. differs from C. dimlingtonensis Neale and Howe, 1973 (Quaternary, North Atlantic) by its high, short valve outline; small caudal process; strong, rounded ventral ridge; and pits arranged in vertical rows. C. brokenoarensis differs from C. latissimum of Neale and Howe (1974) (Holocene, Novaya Zemlya) by its short valve outline; highly arched dorsum; weak caudal process; pronounced ventral ala; and large, numerous pits. C. brokenoarensis differs from C. Champlai- num Cronin, 1981 (Quaternary, North Atlantic) by its short, 16 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 high valve outline; rounded ventral ridge; large, ovoid pits; and lack of large anterior marginal rim. 0ccurrence.—Assemblages II, III, IV, V. Table 2; fig— ure l3. Distribution.—Pleistocene through Holocene: Cook Inlet, Kodiak Shelf, Gulf of Alaska. Middle—outer sublittoral, upper bathyal. Material.—One hundred nine adult valves, forty juve- nile valves. Type specimens.-—Holotype: USNM 408477, left valve (pl. 9, fig. 2), locality EGAL-75—KC-52A, length 0.52 mm, height 0.32 mm. Paratypes: USNM 408478, left valve (pl. 8, figs. 7, 9), locality EGAL-75-KC-52A, length 0.53 mm, height 0.33 mm. USNM 408479, right valve (pl. 8, fig. 8), locality EGAL-75-KC—52A, length 0.51 mm, height 0.34 mm. USNM 408480, left valve (pl. 8, figs. 10, ll), locality EGAL-75-KC-52A, length 0.54 mm, height 0.33 mm. 0.40 I I I l r I I I I I I I I — . 2035— 0000 — E — o o. L” — ... - E — o 00 o — :‘ _ . — 2030— .... . — z 0 0000.0 - F ~ 0 o o — E — ....... - m - 0 r 1025— — 0.20 I I I I I I I I I I I I I 0.3 0.5 0.4 0.5 LENGTH, IN MILLIMETERS Figure 12. Plot of length versus height for Cytheropteron bro- kenoarensis. Dot may represent more than one specimen. 70 I I 60 50 J; 0 NUMBER OF VALVES 20 60 80 100 1 20 140 160 180 200 220 240 DEPTH, IN METERS Figure 13. Plot of abundance versus water depth for Cytheropteron brokenoarensis. SYSTEMATIC PALEONTOLOGY l7 0'40 I I I I I I I I I I I I g _ _ LIJ 0.35 — _ '— — _ g _ _ 3 r C r =‘ — . _ E 0 30 — 0.00 — Z ’ C O ‘ '5 _ o 3 ' 0 _ 5 ~ 00 I 0.25 _ _ 0.20 _ I I I I I I I I I l I I I I — 0.3 0.4 0.5 0.5 LENGTH, IN MILLIMETERS Figure 14. Plot of length versus height for Cytheropteron caro- lae. Dot may represent more than one specimen. CYTHEROPTERON CAROLAE new species Plate 9, figures 3, 4; plate 8, figures 12—14; figure 14 Cytheropteron sp. H Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11, Brouwers, 1982b, p. 8; Brouwers, 1983. Cytheropteron sp. Ishizaki and Matoba, 1985, p. 9, pl. 3, figs. 9, 10. Cytheropteron sp. 3 Tabuki, 1986, p. 102, pl. 17, figs. 11, 12. Etymology.—After Carol Barnhard, a personal friend of the author. Diagnosis.—Characterized by subtriangular lateral out— line; highly arched dorsum; concave anterodorsal corner; sinuous venter with deep concavity; sharp caudal process located near posteroventral corner; subtle dimorphism; numerous, small, ovoid pits arranged in concentric pattern; and high ala forming large, flattened ventral surface. Description—Adult valves subtriangular in lateral view. Dorsal margin highly arched; anterodorsal corner con- cave; anterior margin smoothly curved, with greatest width ventral of midline; ventral margin sinuous, with pronounced, deep concavity; posterior margin with sharp, narrow caudal process located near posteroventral corner. Subtle dimor- phism: males are slightly shorter, lower. Greatest length through caudal process; greatest height through median hinge element. Valve surface covered with many small, ovoid pits arranged in concentric pattern. Pits become smaller margin- ally. Dorsal margin with subparallel ridge and sulcus. Venter with high ala, forming large flattened ventral surface. Lead- ing edge of ala is heavily calcified, smooth. Thirty-four sim- ple-type normal pores scattered over surface, occurring on ridges between pits. Normal pores with low marginal rim. Inner margin and line of concrescence coincide throughout; inner margin follows valve outline. Inner lamella wide, of even width throughout. At least seven radial pore canals, most anterior. Radial pore canals are short, straight, simple. Strong, well-developed selvage. Hingement in right valve consists of small anterior tooth; seven small anteromedian sockets; smooth median groove; seven small posteromedian sockets; and elongate posterior tooth. Anteromedian and posteromedian elements formed by terminal enlargement of median element. Hinge is weak, not heavily calcified. Measurements.—-—X—Y plot based on 18 specimens (fig. 14). 0ccurrence.—Assemblages II, III, IV, V. Table 2. Distribution—Pliocene and Pleistocene: central Japan. Pleistocene through Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf, Pribilof Islands. Middle-outer sublittoral, upper bathyal. Material.—Twenty-three adult valves, thirty-five juve- nile valves. Type specimens.——Holotype: USNM 408481, female right valve (pl. 9, fig. 3), locality EGAL—75—KC-68A, length 0.53 mm, height 0.35 mm. Paratypes: USNM 408482, male right valve (pl. 9, fig. 4), locality EGAL-75-KC-68A, length 0.50 mm, height 0.33 mm. USNM 408483, right valve (pl. 8, figs. 12, 13), locality EGAL-75-KC-52A, length 0.45 mm, height 0.28 mm. USNM 408484, right valve (pl. 8, fig. 14), locality EGAL— 75-KC-141, length 0.50 mm, height 0.28 mm. CYTHEROPTERON CHAMPLAINUM Cronin, 1981 Plate 14, figure 8; plate 16, figure 18; plate 17, figures 1—6; figure 15 Cytheropteron champlainum Cronin, 1981, p. 404, pl. 8, figs. 7, 8; Cronin, 1988, p. 136, pl. 4, fig. 7. Cytheropteron paralatissimum Swain. Neale and Howe, 1975, p. 429, pl. 6, figs. 7, 9; pl. 7, fig. 6. Cytheropteron sp. W Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1983. Diagnosis—Characterized by subtriangular lateral out- line; pronounced concavity; moderately arched dorsum; truncated caudal process; large, ovoid ornament pits at pos- terior, smaller at anterior; pits in vertical rows; and irregu- larly arranged posterior ridges. Description—Adult valves rounded, subtriangular in lateral View. Left valve with moderately arched dorsal mar- gin; smoothly curved anterior margin with greatest width near anteroventral corner; ventral margin with pronounced concavity; posterior margin with broad, truncated caudal process. Right valve with more arched dorsum; concave anterodorsal corner; narrow, pronounced caudal process. Subtle dimorphism: males are slightly lower, longer. Great- est length through caudal process; greatest height through median hinge element. Valve surface covered with pitting and fine ridges. Ornament pits are large, ovoid at posterior, becoming 18 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 0.46 | I I I | I I 0.40 — _ HEIGHT, IN MILLIMETERS O 0.20 — — D.I4 I I I I I I I 0.3 0.4 0.5 0.5 0.7 LENGTH, IN MILLIMETERS Figure 15. Plot of length versus height for Cytheropteron cham- plainum. Dot may represent more than one specimen. smaller at anterior; pits arranged in vertical rows. Posterior rows separated by irregularly arranged ridges. Anterior and posterior margins with wide, flat, smooth area. Venter with heavy, smooth, crescentic ridge which overhangs concavity. Dorsum with marginal rim and sulcus. Secondary fine cor- rugation on floor of larger pits. Normal pores simple-type, with marginal rim. Normal pores both within pits and on surface. Hingement in left valve consists of elongate anterior socket; coarsely crenulate median bar; and elongate poste- rior socket. Median element enlarged terminally, forming series of large quadrate teeth. Hinge highly arched, follow- ing course of dorsal margin. Four adductor muscle scars form oblique row, inclined posterodorsally. Dorsal scar is quadrate; dorsomedian scar is trapezoidal; ventromedian scar is quadrate; ventral scar is elongate and quadrate. J—shaped frontal scar. Measurements.—X—Y plot based on seven specimens (fig. 15). Comparisons.—Cyther0pter0n Champlainum differs from C. dorsocostatum Whatley and Masson, 1979 (Quater— nary, northeast Atlantic) by having a rounded outline; arched dorsum; weak ventral ridge; and small, numerous ornament pits. C. Champlainum differs from C. dimlingtonensis Neale and Howe, 1973 (Pleistocene, circum-arctic regions) by hav- ing a long, low valve outline; less arched dorsum; small cau— dal process; and small, numerous ornament pits. Occurrence—Cruise EGAL-75-KC, localities 6, 46, 260, 285. Cruise DC1-79-EG, locality 42. Assemblages II, 111, V. Distribution.—Pleistocene through Holocene: North Atlantic. Pleistocene: Gulf of Alaska. Middle-outer sub- littoral. Material.—Twenty—one adult valves, four juvenile valves. Illustrated specimens—USNM 408553, right valve (pl. 14, fig. 8), locality EGAL—75-KC-6, length 0.55 mm, height 0.36 mm. USNM 408554 left valve (pl. 16, fig. 18; pl. 17, figs. 1, 3), locality EGAL-75-KC—6, length 0.54 mm, height 0.33 mm. USNM 408555, right valve (pl. 17, fig. 2), locality EGAL-75-KC-6, length 0.53 mm, height 0.36 mm. USNM 408556, left valve (pl. 17, fig. 4), locality EGAL-75- KC-6, length 0.53 mm, height 0.33 mm. USNM 408557, left valve (pl. 17, figs. 5, 6), locality EGAL-75-KC-6, length 0.55 mm, height 0.35 mm. C YT HEROPTERON CHICHAGOFENSIS new species Plate 9, figures 7, 8; plate 10, figures 11—13; figure 16 Cytheropteron sp. X Brouwers, 1981, p. 10; Brouwers, 1982b, p. 8; Brouwers, 1983. Etymology—After Chichagof Island, southern Cross Sound, near Juneau. Diagnosis.—Characterized by subtriangular lateral out- line; highly arched dorsum; anterior margin with greatest width ventral of midline; sinuous convex venter; small, sharp, centrally located caudal process; moderate-sized ovoid pits arranged in vertical rows at posterior, concentric at anterior; and large, arcuate, overhanging ala. Description—Adult valves subtriangular in lateral View. Dorsal margin highly arched; anterodorsal corner con- cave; anterior margin smoothly curved, with greatest extent ventral of midline; ventral margin sinuous, convex; posterior margin with small, sharp, centrally located caudal process. Left valve differs in a less arched dorsum; wide, broad cau- dal process; convex anterodorsal corner; and less ventrally extended anteroventral corner. Greatest length through cau- dal process; greatest height through median hinge element. Valve covered with moderate-sized ovoid pits. Pits arranged in vertical rows at posterior, concentrically at ante- rior. Largest pits located medially and posteriorly, becoming smaller toward dorsal and anterior. Venter with large, arcu— ate ala which overhangs margin. Edge of ala is smooth, heavily calcified. Dorsum with thin marginal ridge and adja- cent sulcus. Sixty-four to seventy-one simple-type normal pore canals scattered over surface, both on smooth surface and within ornament pits. Normal pores highlighted by mar- ginal rim. Inner lamella and line of concrescence coincide throughout; inner margin follows valve outline. Inner lamella of moderate, even width throughout. Strong, well- developed selvage. Eleven to thirteen radial pore canals, most anterior. Radial pore canals straight, simple. Hingement in right valve consists of four elongate, quadrate anterior teeth; crenulate median groove; and six elongate, quadrate posterior teeth. Median element is enlarged terminally to form large crenulae. SYSTEMATIC PALEONTOLOGY 19 Four adductor muscle scars form row, inclined slightly posterodorsally. Dorsal scar is elongate with enlarged ante- rior; dorsomedian and ventromedian scars are elongate, sub- rectangular; ventral scar is inflated, subquadrate. Measurements.—X—Y plot based on eight specimens (fig. 16). Comparisons.—Cyther0pter0n chichagofensis n. sp. differs from C. champlainum Cronin, 1981 (Quaternary, North Atlantic) by having a small, centrally located caudal process; round posterodorsal comer; dorsal sulcus; small, ovoid pits; and lack of ridges between rows of ornament pits. C. chichagofensis differs from C. nodosum Brady, 1868 (Quaternary, North Atlantic) by having a less arched dor- sum; weak, rounded ala; and small, numerous, organized ornament pits. C. chichagofensis differs from C. broken- oarensis by having a larger size and more defined, narrow caudal process. 0ccurrence.—Cruise EGAL-75-KC, localities 26, 84, 128, 141, 285, 341. Cruise DC2-80-EG, locality 67. Distribution.—P1eistocene, Holocene (‘2): Gulf of Alaska. Upper bathyal. Material.—Six adult valves, two juvenile valves. Type specimens.——Holotype: USNM 408495, left valve (pl. 9, fig. 7), locality DC2-80-EG-67, length 0.58 mm, height 0.35 mm. Paratypes: USNM 408496, right valve (pl. 9, fig. 8), locality DC2-80-EG-67, length 0.55 mm, height 0.35 mm. USNM 408497, right valve (pl. 10, figs. 11, 12, 13), locality EGAL-75—KC-141, length 0.53 mm, height 0.38 mm. CYTHEROPTERON DIMLINGTONENSIS Neale and Howe, 1973 Plate 8, figures 1—6; plate 9, figure 1; figure 17 Cytheropteron dimlingtonensis Neale and Howe, 1973, p. 242—243, pl. 1, figs. 3, 5a,b. Cytheropteron sp. C Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Diagnosis—Characterized by subtriangular lateral out- line; broadly arched dorsum; sinuous venter with strong con- cavity; moderate caudal process; ovoid pitting arranged in vertical rows; small marginal pits with low marginal ridges; dorsal marginal sulcus; smooth, flattened rim at anterior and posterior; secondary marginal pitting; and strong, sinuous, overhanging posteroventral ridge. Description—Adult valves subtriangular in lateral view. Dorsal margin broadly arched; anterior margin broadly rounded, with greatest length ventral of midline; ventral margin sinuous, with strong concavity; posterior margin with broad caudal process. Caudal process most attenuated dorsal of midline. Left valve with less arched dorsum and broad, blunt development of caudal process. No dimorphism observed. Greatest length through midline of valve; greatest height through median hinge element. 0.45 1 | 1 1 1 1 (on: 0.40 — . _ E - O O - E _ _ j — o 8 . — E 0 Z _ _ I; 0.31% — ‘3 z m _ I 020 1 1 | l 1 1 1 1 I 1 1 1 1 0.3 0.4 0.5 0.8 LENGTH, IN MILLIMETERS Figure 16. Plot of length versus height for Cytheropteron chich- agofensis. Valve covered with ovoid pitting of various sizes. Pits in vertical rows separated by low ridges near anterior and posterior margins. Pits are large, elongate at middle of valve, becoming smaller marginally. Subdued marginal sulcus along dorsum, especially developed in right valve. Smooth, flattened anterior and posterior rim. Secondary fine pitting along valve margins. Strong sinuous ridge overhangs poster- oventral margin; ridge is strengthened by heavy calcifica- tion. Sixty—three simple—type normal pores evenly distributed over surface, most within pits. Normal pores with raised marginal rim. Inner margin and line of concrescence coincide at pos— terior and venter; moderate, arcuate anterior vestibule. Inner lamella widest at anterior, of even width at posterior and ven- ter. Inner margin parallels valve outline. Very well devel- oped selvage. At least seven radial pores, most anterior; pores are straight, short, simple. Hinge in left valve consists of two anterior quadrate sockets; weakly crenulate median bar which thickens and enlarges terminally into two anteromedian and three poster- omedian quadrate teeth; and three posterior quadrate sock- ets. Median bar formed by dorsal valve edge. Right valve hingement with dorsal edge enfolded to form accommoda- tion groove. Four adductor muscle scars in row, inclined posterodor- sally. Dorsal scar is dumbbell-shaped, with pinched middle; dorsomedian scar is sinuous, forming L-shape; ventromedian scar is quadrate; ventral scar is ovoid. Frontal scar split into larger, peanut-shaped posterior scar and small, round ante— rior scar. Two elongate, ellipsoidal mandibular scars located ventral of frontal scars. Dorsal scars are small, irregular in shape, few in number. 20 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 Measurements.—X—Y plot based on 10 specimens (fig. 17). Comparisons.—Cyther0pter0n dimlingtonensis differs from C. latissimum (Norman, 1865) (Quaternary, North Atlantic) by having a rounded dorsum; weak ventral ridge; and large organized pitting. C. dimlingtonensis differs from C. nodosoalatum Neale and Howe, 1973 (Quaternary, north- east Atlantic) by having a quadrate shape; sinuous venter; broad caudal process; and vertically arranged ornament pits. Occurrence—Cruise EGAL—75—KC, localities 4, 26, 123, 127, 209, 257, 320. Distribution.—Pleistocene: Northeast Atlantic. Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf. Material.—Ten adult valves, one juvenile valve. Illustrated specimens.—USNM 408473, left valve (pl. 9, fig. 1), locality EGAL—75-KC-l27, length 0.57 mm, height 0.34 mm. USNM 408474, left valve (pl. 8, figs. 1, 3), locality EGAL-75-KC-123, length 0.51 mm, height 0.33 mm. USNM 408475, right valve (pl. 8, figs. 2, 6), locality EGAL-75-KC-123, length 0.50 mm, height 0.30 mm. USNM 408476, left valve (pl. 8, figs. 4, 5), locality EGAL- 75—KC—320, length 0.52 mm, height 0.32 mm. CYTHEROPTERON DISCOVERIA new species Plate 11, figure 5; plate 13, figures 1—6, 9; figure 18 Cytheropteron sp. K Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1983. Etymology.—After NOAA oceanographic vessel R/V Discoverer, utilized during cruises DC1-79-EG and DC2- 80-EG. Diagnosis—Characterized by subtriangular lateral out- line; highly arched dorsum; narrow, prolonged caudal pro— cess; sinuous posterodorsal comer; pronounced dimorphism; pitting oriented vertically at median, concentrically at mar— gins; low anterior and posterior marginal ridges; strong right—angle posterior ridge; pronounced ventral ala; second- ary fine corrugated ornament. Description.#Adult valves subtriangular in lateral View. Dorsal margin highly arched; anterior margin evenly rounded; ventral margin sinuous, with pronounced concav— ity; posterior margin with highly attenuated, narrow caudal process; posterodorsal margin sinuous, predominantly con- cave. Caudal process located dorsal of midline. Left valve with less arched dorsal margin, less concave posterodorsal margin. Pronounced dimorphism: males considerably lower, somewhat shorter, with significantly less arched dorsal mar- gin, less evenly rounded anterior margin, and dorsally located caudal process. Greatest length through caudal pro- cess; greatest height through median hinge element. Valve surface covered with pitting and ridges. Pitting vertical at median and concentric at margins. Rows of pits separated by low ridges along anterior and posterior mar- gins. Pits are ovoid in shape; largest pits toward venter, 0.40 I I I I | I I I I I I I _ I I J _ . _ (D __ _ 0.35 a: ILE — O C ‘ LI.I — . _ 2 _ . _ _I d - _ E 0.30 0 Q — g — O. ‘ Ii. _ 9 : ° _ LI.I I 0.25 _ _ 0.20 _ I I I I I I I I I l I I I I 0.3 0.4 0.5 0.5 LENGTH, IN MILLIMETERS Figure 17. Plot of length versus height for Cytheropzeron dim— lingtonensis. smaller toward anterior, dorsal, and posterior margins. Strong ridge originates at middle of dorsum, proceeds mar- ginally to posterodorsal corner, where it forms a right angle and proceeds obliquely to venter. The ridge connects with a pronounced ventral alar ridge which originates at anterior and overhangs margin, terminating as prominent ala. Ventral edge of alar ridge strengthened by moderate calcification. V- shaped smooth region on caudal process. Secondary fine corrugation on solum floors. Twenty-eight simple—type nor- mal pores evenly distributed over surface; most within pits, some on surface. Normal pores with subdued marginal rim. Inner margin parallels valve outline. Weakly devel— oped selvage. Hinge in right valve consists of strong, quadrate, ante- rior tooth; crenulate median groove; posteromedian ovoid tooth; four quadrate sockets; and three ovoid posterior teeth. Hinge is sinuous in outline, following course of dorsal mar- gin. Median groove is enlarged terminally. Four adductor muscle scars form row, inclined postero- dorsally. Dorsal scar is kidney-shaped; dorsomedian scar is elongate, crescentic; ventromedian scar is elongate, I-shaped; ventral scar is ellipsoidal. Frontal scar is I-shaped. Very weak fulcral point. Several large, ovoid dorsal muscle scars imme- diately above central muscle-scar field. Measurements.—X—Y plot based on 17 specimens (fig. 18). C0mparis0ns.——Cyther0pteron discoveria n. sp. differs from C. punctatum Brady, 1868 (Quaternary, northeast Atlantic, Adriatic) by having a strong, oblique posterior ridge; strong dimorphism; arched, sinuous dorsum; weaker ventral ala; and evenly rounded anterior. C. discoveria dif- fers from C. inornatum Brady and Robertson, 1872 (Holocene, Britain, Adriatic Sea) by having an arched SYSTEMATIC PALEONTOLOGY 21 0,5 l | (I) _ _ CC E 0.4 — — LLI g — _ _l d _ _ E z _ _ r: _ O O _ I 0 ‘2 0.3 — O. . ~ LU I r O O - 0.2 I I . I 0.3 0.5 0.7 LENGTH, IN MILLIMETERS Figure 18. Plot of length versus height for Cytheropteron dis- coveria. Dot may represent more than one specimen. dorsum; evenly rounded anterior; concave posterodorsal margin; and punctate ornament. Occurrence—Cruise EGAL-75-KC, localities 19, 52A, 150, 328. Cruise DC2-80-EG, localities 183, 186, 189, 195. Assemblage III. Distribution.—Pleistocene through Holocene: Gulf of Alaska, Cook Inlet and the Kodiak Shelf, Pribilof Islands. Outer sublittoral. Material.—Twenty-seven adult valves, three juvenile valves. Type specimens.—Holotype: USNM 408516, left valve (pl. 11, fig. 5), locality DC2-80-EG-195, length 0.45 mm, height 0.26 mm. Paratypes: USNM 408517, left valve (pl. 13, figs. 1, 3), locality DC2—80—EG-186, length 0.43 mm, height 0.28 mm. USNM 408518, right valve (pl. 13, fig. 2), locality DC2-80— EG-186, length 0.46 mm, height 0.28 mm. USNM 408519, left valve (pl. 13, fig. 4), locality EGAL—75-KC-150, length 0.53 mm, height 0.29 mm. USNM 408520, right valve (pl. 13, figs. 5, 6, 9), locality DC2-80—EG-186, length 0.45 mm, height 0.25 mm. CYTHEROPTERON DR YBA YENSIS new species Plate 11, figure 7; plate 13, figures 7—8, 10—15; plate 14, figure 7; plate 17, figures 7—12; plate 18, figure 1; figure 19 Cytheropteron sp. B Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Cytheropteron sp. Q Brouwers, 1981, p. 9', Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983 Etymology—After Dry Bay, at the mouth of the Alsek River, southeast Alaska. Diagnosis.—Characterized by subtriangular lateral out- line; highly sinuous Venter with pronounced concavity; sharp caudal process; convergent anterior and posterior mar- gins; mostly smooth surface with small ovoid pits; broad flat anterior and posterior marginal regions; strong, high ventral ala terminating as spine; large, deep, arcuatc anterior vesti- bule; and small, irregular posterior vestibule. Description—Adult valves subtriangular to ellipsoidal in lateral View. Dorsal margin highly arched; anterior margin smoothly rounded, drawn—out; ventral margin highly sinu- ous, with broad, pronounced concavity; posterior margin with sharp caudal process. Dorsal and ventral margins con- verge at anterior and posterior. Caudal process dorsal of mid- line. Valve surface primarily smooth, with small ovoid pits scattered over valve. Anterior and posterior margins with broad, flat regions. Posterodorsal corner with subtle ridge- depression region. Venter with strong, high ala terminating as a spine. Ala with several small, subtle, discontinuous ridges. Twenty-one simple-type normal pores, most at pos- terodorsum and anteroventer. Pores have raised marginal rim. Inner margin and line of concrescence coincide along ventral and posteroventral margins. Large, deep, arcuate, anterior vestibule and small, irregular, posterior vestibule at caudal process. Inner margin parallels valve outline. Eight radial pore canals, most anterior. Radial pores are straight, short, simple. Hinge in right valve consists of six quadrate anterior teeth; crenulate median groove; and small, quadrate, poste- rior teeth. Median element enlarged terminally into larger crenulae. Hinge is highly arched, sinuous, following course of dorsal margin. Four adductor muscle scars form vertical row. Dorsal scar is subcylindrical; dorsomedian scar is I-shaped; ventro- median scar is elongate, with enlarged posterior; ventral scar is semicircular. Measurements.—X—Y plot based on 13 specimens (fig. 19). Comparisons.—Cyther0pter0n drybayensis n. sp. dif- fers from C. monoceros Bonaduce, Ciampo, and Masoli, 1976 (Holocene, Britain, Adriatic Sea) by having a narrow, prolonged caudal process; fine ornament pits; and short, delicate ala. C. drybayensis differs from C. volantium Whatley and Masson, 1979 (Holocene, Scotland) by hav- ing a shorter valve shape; less prolonged caudal process; fine ornament pitting; and delicate ala. C. dlybayensis dif- fers from C. alatum Sars, 1866 (Holocene, northeast Atlan- tic) by having a shorter valve outline; narrow, prolonged caudal process; delicate ala; and fine ornament pitting. C. drybayensis n. sp. differs from C. paralatissimum Swain, 1963 (Quaternary, Arctic) by having a longer, lower valve 22 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 outline; smaller ala; narrow, prolonged caudal process; and scattered ornament pits. Occurrence.—Assemblages II, III, IV. Table 2. Distribution.—Pleistocene through Holocene: Gulf of Alaska. Middle-outer sublittoral, upper bathyal. Material.—Fifty adult valves, sixty-six juvenile valves. Type specimens.—Holotype: USNM 408522, right valve (pl. 11, fig. 7), locality EGAL-75-KC-95, length 0.55 mm, height 0.38 mm. Paratypes: USNM 408523, left valve (pl. 13, fig. 7), locality EGAL~75—KC-128, length 0.63 mm, height 0.35 mm. USNM 408524, right valve (pl. 13, figs. 8, 11, 12), locality DC2-80-EG-186, length 0.60 mm, height 0.34 mm. USNM 408525, right valve (pl. 13, figs. 10, 13—15), locality EGAL-75—KC-128, length 0.65 mm, height 0.40 mm. USNM 408552, left valve (pl. 14, fig. 7), locality EGAL-75- KC-6, length 0.55 mm, height 0.35 mm. USNM 408558, right valve (pl. 18, fig. 1), locality EGAL-75-KC-124A, length 0.65 mm, height 0.38 mm. USNM 408559, left valve (pl. 17, figs. 7, 8, 9), locality EGAL-75-KC-123, length 0.68 mm, height 0.34 mm. USNM 408560, left valve (pl. 17, figs. 10, ll, 12), locality EGAL-75-KC-106, length 0.60 mm, height 0.31 mm. CYTHEROPTERON EICHERI new species Plate 11, figure 8; plate 15, figures 1—5; figure 20 Cytheropteron sp. 0 Brouwers, 1981, p. 9; Brouwers, 1982b, p. 8; Brouwers, 1983. Etymology—After Dr. Don L. Eicher, University of Colorado, a specialist in Cretaceous foraminifers. Diagnosis.—Characterized by subtriangular lateral out- line; highly arched dorsum; sinuous venter with pronounced concavity; narrow, prolonged caudal process; two short pos— teroventral denticles; smooth valve surface; large, high ala with heavily calcified leading edge and spines at posterior; anterior marginal flange; small dorsal sulcus; strong selvage; and large, crescentic anterior vestibule. Description—Adult valves subtriangular in lateral View. Dorsal margin highly arched; anterior margin drawn- out, smoothly curved, with greatest width ventral of midline; ventral margin sinuous with pronounced concavity; posterior margin with narrow, drawn-out caudal process, centrally located. Anteroventral margin with crenulations; poster- oventral margin with two short, blunt denticles. Greatest length through midline; greatest height through median hinge element. Valve surface is smooth, dominated by very large, high ventral ala which forms broad, flat, triangular ventral surface or platform. Anterior side of alar structure is heavily calci— fied, with massive leading edge. Posterior ala contains numerous large, sharp denticles or spines. Posterior spines become progressively larger outward along ala, ending with large, long terminal spine at end of ala. Anterior margin with 0.5 L l | I m _ _ E O 0.4 — — E o E ‘ 0 ‘ .1 :1 _ _ 2 O. _ Z 0 8 |_. _ _ I 0 <2 0-3— o o _ LL] 0 I — _ 0.2 | I l 0.3 0.5 0.7 LENGTH, IN MILLIMETERS Figure 19. Plot of length versus height for Cytheropteron dry- bayensis. Dot may represent more than one specimen. broad, flat flange. Dorsal margin with small, subtle sulcus. Forty-eight small, simple-type normal pores evenly distrib- uted over surface. Inner margin and line of concrescence coincide along venter and posterior; large, crescentic anterior vestibule. Inner margin follows valve outline. Inner lamella moder- ately wide at posterior, very wide at anterior. Strong, well- developed selvage. Nine radial pore canals, most anterior. Radial pores are short, straight, simple. Hingement in left valve consists of narrow, elongate anterior socket; weakly crenulate median bar; and elongate, narrow posterior socket. Median bar enlarged terminally, forms larger, quadrate crenulae, expressed as anteromedian and posteromedian teeth. Anterior and posterior sockets with weak ventral rim. Hinge is arched, sinuous, follows course of dorsal margin. Measurements.—X—Y plot based on four specimens (fig. 20). Comparisons.—Cyther0pter0n eicheri n. sp. differs from C. volantium Whatley and Masson, 1979 (Holocene, Scotland) by having an arched dorsum; less extended caudal process; strong terminal spine on ala; and concave antero- dorsal cardinal angle. C. eicheri differs from C. alatum Sars, 1866 (Holocene, northeast Atlantic) by having a narrow cau- dal process; arched dorsum; concave anterodorsal cardinal angle; and strong terminal spine on ala. C. eicheri differs from C. paralatissimum Swain, 1963 (Pleistocene, Alaska) by having a longer valve shape; extended caudal process; thinner ala; and lack of ornamentation. 0ccurrence.—-—Cruise EGAL-75-KC, localities 52A, 77, 80, 209. SYSTEMATIC PALEONTOLOGY 23 [1.4 I l HEIGHT, IN MILLIMETERS | O O | 0.2 I l I I 0.5 0.7 LENGTH, IN MILLIMETERS Figure 20. Plot of length versus height for Cytheropte ron eicheri . Distribution.—Pleistocene, Holocene (7): Gulf of Alaska. Middle sublittoral. Material.—Three adult valves, one juvenile valve. Type specimens.—Holotype: USNM 408526, right valve (pl. 11, fig. 8), locality EGAL-75-KC-77, length 0.56 mm, height 0.30 mm. Paratypes: USNM 408527, right valve (pl. 15, figs. 1, 3), locality EGAL-75-KC-30, length 0.73 mm, height 0.34 mm. USNM 408528, left valve (pl. 15, figs. 2, 4, 5), locality EGAL-75-KC—30, length 0.68 mm, height 0.30 mm. CYTHEROPTERON EIAENI Cronin, 1988 Plate 21, figure 2; plate 22, figures 11—13 Cytheropteron nealei Cronin, 1981, p. 406, pl. 7, fig. 7. Cytheropteron elaeni Cronin, 1988, p. 138, pl. 5, fig. 8. Cytheropteron sp. Y Brouwers, 1981, p. 10; Brouwers, 1982b, p. 8; Brouwers, 1983. Diagnosis.——Characterized by subtriangular shape; highly arched anterodorsum, concave posterodorsum; sinu- ous venter; attenuated posterior; broad, elongate caudal pro- cess; pits in rows at posterior, concentric at anterior; overhanging ala; large posteroventral tubercle; and split frontal scar. Description—Adult valves subtriangular in lateral View. Highly arched anterodorsum, concave posterodorsum; anterior margin smoothly curved with greatest width ventral of midline; ventral margin sinuous with pronounced concav- ity; posterior margin attenuated, with broad, elongate caudal process. Obtuse posterodorsal cardinal angle. Greatest length through caudal process; greatest height anterior of midvalve. Valve predominantly smooth; scattered small pits mostly at margins. Pits oriented in oblique rows at posterior and concentric to anterior margin. Low, strong, heavily cal- cified ala overhangs venter; ala is sinuous in shape, originat- ing as bifurcated ridge at anterior and terminating as large tubercle at posteroventer. Posterior margin with oblique ridges between pit rows. Seventy simple-type normal pores evenly distributed over surface, both in pits and on surface. Normal pores with distinct marginal rim. Inner margin and line of concrescence coincide throughout. Inner lamella narrow, of even width throughout, parallels valve outline. Ten radial pores, one false radial pore, most anterior. Hingement in right valve consists of three small, quad— rate anterior teeth; crenulate median bar; and four to five quadrate posterior teeth. Anterior and posterior teeth form the enlarged terminus of median bar. Median element formed by dorsal edge of valve. Four adductor muscle scars form vertical row. Dorsal scar is ellipsoidal, sharply inclined; dorsomedian scar is elongate, teardrop—shaped; ventromedian scar is elongate, ellipsoidal; ventral scar is ovoid, inflated. Frontal scar split into ventral L—shaped scar and dorsal, small, circular scar. Weak fulcral point impression. Few, paired, irregularly shaped dorsal muscle scars. Comparisons.—Cyther0pter0n elaeni is distinctive and does not resemble any described species of Cytheropteron. Occurrence.—Cruise EGAL-75-KC, localities 53, 55, 122A, 157, 159. Assemblage V. Distribution.—Pleistocene: Champlain Sea. Holocene: Novaya Zemlya. Pleistocene, Holocene (?)2 Gulf of Alaska, Bering Sea, Beaufort Sea. Illustrated specimens—USNM 408602, left valve (pl. 21, fig. 2), locality EGAL-75-KC-159, length 0.43 mm, height 0.28 mm. USNM 408603, left valve (pl. 22, figs. 11, 12, 13), locality EGAL—75-KC—55, length 0.41 mm, height 0.28 mm. CYTHEROPTERON EREMITUM Hanai, 1959 Plate 11, figure 4; plate 12, figures 8—17; figure 21 Cytheropteron rarum Hanai, 1957, p. 28—29, pl. 4, fig. 3. Cytheropteron eremitum Hanai, 1959a, p. 418. Cytheropteron eremitum Hanai. Ishizaki and Matoba, 1985, pl. 3, figs. 5, 6. Cytheropteron sp. AA Brouwers, 1982a, p. 8; Brouwers, 1983. Diagnosis.——Characterized by drawn-out anterior mar- gin; sinuous venter with pronounced concavity; dorsal and ventral margins converge at posterior; subdued reticulation consisting of low, narrow, vertical ridges; weak ventral ala; central muscle scars reflected externally; anterior and poste- rior with flattened marginal rim; and secondary fine pitted ornament. Description.‘Adult valves subtriangular in lateral view. Right valve with highly arched dorsal margin; antero- dorsal corner markedly concave; anterior margin drawn-out, smoothly curved; ventral margin sinuous, with pronounced concavity; posterior margin with small, attenuated caudal process. Left valve differs in large, broad caudal process; 24 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 0.5 | I I m _ _ E 04— — |_ . LIJ g — _ _l :1 _ _ 2 0 Z _ _ F _ _ 5 m 0 3 — O — I _ . . _ _ . _ . _ 0.2 I | I 0.3 0.5 0.7 LENGTH, IN MILLIMETERS Figure 21. Plot of length versus height for Cytheropteron eremi— tum. convex anterodorsal margin; flattened, broadly arched dor- sum; and smoothly curved ventral margin. Dorsal and ven- tral margins converge at posterior. Slight dimorphism: males are lower, longer. Greatest length through caudal process; greatest height through anterior hinge element. Valve surface covered with subdued reticulation pat- tern. Ridges are narrow and low, occurring as longitudinal ovoids oriented in vertical rows. Slightly thickened ridges along dorsal margin and at edge of ventral ala. Ventral ala is weak, forming smooth arch over concavity. Central muscle- scar field reflected externally as thickened smooth regions. Anterior and posterior have flattened rim. Secondary fine pitting over surface between ridges. Fifty-eight normal pores evenly distributed over surface, occurring on or imme- diately adjacent to reticulum ridges. Normal pores simple type, with raised marginal rim. Normal pore setae of two types: long, straight, and simple, and short and multi- branched. Inner margin and line of concrescence coincide throughout; inner margin parallels valve outline. Inner lamella of even width throughout. Weakly developed sel- vage. At least eight radial pores; pores are straight, short, and simple. Hinge in left valve consists of three anterior quadrate sockets; crenulate median bar expanded terminally into strong, elongate, quadrate anteromedian and posteromedian tooth elements; and three posterior sockets. Median bar formed in part by dorsal edge of valve. Right valve hinge- ment with dorsal edge enfolded to form accommodation groove. Anterior and posterior hinge sockets rimmed dor- sally by expanded hinge “ears.” Four adductor muscle scars in row, inclined posterodor- sally. Dorsal scar is an inclined trapezoid; dorsomedian scar is elongate, quadrate; ventromedian scar is I-shaped; ventral scar is subtriangular. Frontal scar split into larger, L-shaped posterior scar and small, round anterior scar. Numerous small, ovoid dorsal scars scattered above central scar field. Measurements.—X—Y plot based on six specimens (fig. 21). Comparisons.—Cyther0pteron eremitum differs from C. nodosum Brady, 1868 (Quaternary, North Atlantic) by having a low, broad dorsum; weak ventral ridge; thin vertical ridges; externally reflected central muscle scars; and fine secondary ornament pitting. C. eremitum differs from C. dimlingtonensis Neale and Howe, 1973 (Pleistocene, north- east Atlantic) by having along, 10w valve outline; low broad dorsum; thin vertical ridges; fine secondary ornament pits; and externally reflected central muscle scars. Occurrence—Cruise EGAL—75-KC, localities 106, BFM-78—l. Distribution—Holocene: Gulf of Alaska. Material.—Eight adult valves, thirty-four juvenile valves. Illustrated specimens—USNM 408511, left valve (pl. 11, fig. 4), locality BFM-78-1, length 0.48 mm, height 0.26 mm. USNM 408512, female right valve (pl. 12, figs. 8, 9, l4), locality BFM—78-1, length 0.46 mm, height 0.30 mm. USNM 408513, male left valve (pl. 12, figs. 10, 12, 13), locality BFM-78—1, length 0.45 mm, height 0.28 mm. USNM 408514, male right valve (pl. 12, fig. 11), locality BFM-78-l, length 0.43 mm, height 0.28 mm. USNM 408515, male left valve (pl. 12, figs. 15, 16, 17), locality BFM-78-l, length 0.44 mm, height 0.25 mm. C YT HEROPT ERON F ORES TERI new species Plate 17, figures 13—18; plate 18, figures 2, 3, 6; plate 19, figures 1—4; plate 20, figures 10, 11; figures 22, 23 Cytheropteron sp. A Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Cytheropteron sp. S Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Etymology.——After Richard M. Forester, U.S. Geologi- cal Survey, a specialist in nonmarine systems and hydro- chemistry. Diagnosis.—Characterized by subtriangular lateral out- line; moderately arched dorsum; pronounced concavity; broad, pronounced caudal process; posteriorly convergent dorsum and venter; four small, blunt, anterior marginal den- ticles; smooth surface with few pits; low, subdued, over- hanging ventral ala with posterior terminal spine; weak eyespot; and arcuate anterior vestibule. Description—Adult valves subtriangular in lateral view. Dorsal margin moderately arched; anterior margin broadly rounded, with greatest width ventral of midline; SYSTEMATIC PALEONTOLOGY 25 ventral margin sinuous with pronounced concavity; poste— rior margin with broad, pronounced caudal process. Dorsal and ventral margins converge posteriorly. Caudal process with greatest extent ventral of midline. Four small blunt anterior marginal denticles. Left valve with less arched dor- sum and broad, less extended caudal process. Females dif- fer in being slightly shorter, higher in lateral View. Valve surface primarily smooth, with small number of pits evenly distributed over surface. Low, subdued ventral ala, bearing several median blunt tubercles, overhangs ven- ter. Ala terminates at posterior as sharp spine—like structure. Subtle anterior marginal sulcus. Slight elongate ridge forms weak eyespot. Sixty-five to seventy—two simple-type normal pores evenly distributed over surface, occurring within pits. Normal pores with raised marginal rim. Inner margin and line of concrescence coincide at pos- terior and venter; moderate, arcuate anterior vestibule. Inner margin parallels valve outline. Weakly developed selvage. Nine to eleven radial pores, one false radial pore; pores are straight, short, simple. Hinge in left valve consists of three quadrate anterior sockets; four small rounded anteromedian teeth; coarsely crenulate median bar; five rounded posteromedian teeth; and two elongate posterior sockets. Anteromedian and postero- median teeth form enlarged terminal ends of median ele- ment. Median bar formed by dorsal valve edge. Right valve with dorsal edge enfolded to form accommodation groove. Four adductor muscle scars in vertical row; dorsal scar elongate, dorsomedian scar elongate-sinuous, ventromedian scar I-shaped, ventral scar subrounded. Frontal scar split into peanut-shaped posterior scar and small, round anterior scar. Small ovoid fulcral point located posterodorsal of frontal scars. Many smaller subtriangular to subelliptical dorsal scars above adductor row; elongate, larger dorsal scars just below hinge. Measurements.—X—Y plot based on 29 specimens (fig. 22). Comparisons.—Cyther0pter0n foresteri n. sp. differs from C. hyalinosa Hanai, 1957 (lower Pleistocene, Hok- kaido, northern Honshu) by its smaller ala; less drawn out posterior; less arched dorsum; and presence of small oma- ment pits. Occurrence.—Assemblages 11*, III*, IV, V. Table 2; figure 23. Distribution.-—Pleistocene through Holocene: Gulf of Alaska, Pribilof Islands. Middle—outer sublittoral, upper bathyal. Material.—Two hundred ninety-seven adult valves, three hundred twenty-two juvenile valves. Type specimens.—Holotype: USNM 408561, female left valve (pl. 18, fig. 2), locality EGAL—75-KC-432, length 0.51 mm, height 0.30 mm. Paratypes: USNM 408562, male right valve (pl. 18, fig. 3), locality EGAL—75-KC-432, length 0.54 mm, height 0.30 mm. USNM 408563, female left valve (pl. 17, figs. 13, 15), 0.4 (I) E ,_ — o o — w o g _ _ _l a o 00 2 0.3— 000000. — z o 0 .—~ — o — I <2 _ m _ I 02 l l | 0.3 0.5 0.7 LENGTH, IN MILLIMETERS Figure 22. Plot of length versus height for Cytheropteronforest- eri. Dot may represent more than one specimen. locality EGAL-75—KC—432, length 0.53 mm, height 0.30 mm. USNM 408564, female right valve (pl. 17, figs. 14, 18), locality EGAL—75—KC—432, length 0.53 mm, height 0.31 mm. USNM 408565, male left valve (pl. 17, fig. 16), locality EGAL-75-KC-432, length 0.55 mm, height 030 mm. USNM 408566, male right valve (pl. 17, fig. 17), locality EGAL-75—KC-432, length 0.49 mm, height 0.30 mm. USNM 408567, female right valve (pl. 19, fig. 1), locality EGAL-75-KC—432, length 0.48 mm, height 0.30 mm. USNM 408568, female left valve (pl. 19, figs. 2, 3, 4), local- ity EGAL-75—KC-432, length 0.50 mm, height 0.30 mm. USNM 408586, right valve (pl. 18, fig. 6), locality EGAL— 75-KC-117, length 0.50 mm, height 0.31 mm. USNM 408587, left valve (pl. 20, figs. 10, 11), locality DC2—80-EG- 195, length 0.53 mm, height 0.30 mm. C YTHEROI’TERON HA YDENENSIS new species Plate 14, figures 2, 3; plate 15, figures 6—15; figure 24 Cytheropteron sp. T Brouwers, 1981, p. 9; Brouwers, 1983. Etymology—After Hayden Glacier, Malaspina Glacier, southeast Alaska. adjacent to Diagnosis.—Characterized by rounded, subtriangular lateral outline; moderately arched dorsum; sinuous venter with small concavity; truncated caudal process; concave posterodorsal corner; pronounced dimorphism; ovoid oma- ment pits separated by low ridges; pits arranged in vertical rows at posterior and concentrically at anterior; low, mas- sive, crescentic ridge along and overhanging venter; and sec- ondary fine papillae and wart-like ornament. Description—Adult valves subtriangular, rounded in lateral View. Left valve with moderately arched dorsal mar- gin; smoothly curved anterior margin with greatest width 26 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 45l‘ll'l’ 35— T NUMBER OF VALVES 20 4U 60 80 100 I 120 DEPTH, IN METERS 140 160 180 200 220 Figure 23. Plot of abundance versus water depth for Cytheropteronforesteri. ventral of midline; ventral margin sinuous, with shallow, small concavity; posterior margin with truncated caudal pro— cess. Posterodorsal corner concave, with rounded, obtuse cardinal angle. Right valve differs in highly arched dorsum; narrow, prolonged caudal process; strong posterodorsal car- dinal angle; concave anterodorsal corner; and down-slung anterior margin. Pronounced dimorphism: males somewhat lower, longer. Greatest length through caudal process; great- est height through median hinge element. Valve surface covered with ovoid pits. Pits arranged in rows, trending vertically at posterior and concentric to mar— gin at anterior. Pits are largest in median region, smaller mar- ginally. Posterior rows of pits separated by series of low ridges. Low, smooth, massive, crescentic ridge along and overhangs venter. Secondary fine papillae and wart-like pro— jections cover solum floors. Sixty simple-type normal pores evenly scattered over surface, both within pits and on sur— face. Pores within pits are celate; pores on surface have thickened marginal rim. Inner margin and line of concrescence coincide ven- trally. Deep, crescentic anterior vestibule; small, shallow, irregularly shaped posterior vestibule. Inner margin paral— lels valve outline. Fused inner lamella narrow at anterior, wider at posterior. Moderately developed selvage. Eight radial pore canals, most anterior. Radial pores are short, straight, simple. Hingement in right valve consists of smooth, elongate anterior tooth; six quadrate anteromedian sockets; coarsely crenulate median groove; seven quadrate posteromedian sockets; and massive, elongate posterior tooth. Median ele- ment enlarged terminally to form anteromedian and postero- median sockets. Hinge arcuate in shape, following course of dorsal margin. Four adductor muscle scars form oblique row, inclined posterodorsally. Frontal scar is J-shaped. Measurements.—X—Y plot based on 13 specimens (fig. 24). SYSTEMATIC PALEONTOLOGY 27 Comparisons.—Cyther0pter0n haydenensis n. sp. dif- fers from C. arcticum Neale and Howe, 1973 (Quaternary, North Atlantic) by its weak, smooth ventral ridge; sharp, nar- row caudal process; less arched dorsum; narrow anterior; and vertically aligned ornament pits. C. haydenensis differs from C. champlainum Cronin, 1981 (upper Pleistocene, northwest Atlantic) by its wide anterior; rounded, massive ventral ridge; narrow caudal process; and small, ovoid orna- ment pits. Occurrence—Cruise EGAL-75-KC, localities 17, 46, 283, 341. Cruise DC1-79-EG, localities 5, 41, 46. Assem- blages II, V. Distribution.—Pleistocene, Holocene (7): Gulf of Alaska, Pribilof Islands. Middle sublittoral. Material.—Twenty—one adult valves, thirteen juvenile valves. Type specimens.—Holotype: USNM 408530, left valve (pl. 14, fig. 2), locality EGAL-75-KC-46, length 0.45 mm, height 0.25 mm. Paratypes: USNM 408531, right valve (pl. 14, fig. 3), locality EGAL-75-KC-46, length 0.45 mm, height 0.25 mm. USNM 408532, left valve (pl. 15, figs. 6, 7, 9), locality EGAL-75—KC-46, length 0.45 mm, height 0.30 mm. USNM 408533, right valve (pl. 15, fig. 8), locality EGAL—75-KC-46, length 0.44 mm, height 0.28 mm. USNM 408534, left valve (pl. 15, figs. 10, 11, 12), locality EGAL-75-KC-46, length 0.45 mm, height 0.28 mm. USNM 408535, right valve (pl. 15, figs. 13, 15), locality EGAL-75-KC-46, length 0.44 mm, height 0.26 mm. USNM 408536, left valve (pl. 15, fig. 14), locality EGAL—75-KC-46, length 0.40 mm, height 0.26 mm. CYTHEROPTERON HOPKINS] new species Plate 14, figure 6; plate 16, figures 10—17; figure 25 Cytheropteron sp. L Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Etymology—After Dr. David M. Hopkins, University of Alaska, specialist in glaciomarine sedimentology of northern Alaska and Beringia. Diagnosis—Characterized by subtriangular lateral out- line; broadly arched dorsum; sinuous venter with strong con— cavity; sharp, narrow caudal process; subtle dimorphism; ovoid pitting in concentric rows, smaller marginally; series of low posterior ridges which splay out dorsally and posteri- orly; and strong, overhanging ventral ridge with tubercle at posterodorsal terminus. Description—Adult valves subtriangular in lateral view. Dorsal margin broadly arched; anterior margin broadly rounded, with greatest extent ventral of midline; ventral margin with strong concavity; posterior margin with sharp, narrow caudal process. Posterodorsal margin con- cave. Left valve with less arched dorsal margin, broad cau- dal process. Subtle dimorphism: males lower, with less 0.4 I m _ _ n: LLl _ E _ E _ ° _ é o E 0.3 — O — g C F: _ ... - :x: g — O O. ‘ LLI I _ O. _ 02 l I 0.3 0.7 0.5 LENGTH, IN MILLIMETERS Figure 24. Plot of length versus height for Cytheropteron hay- denensis. Dot may represent more than one specimen. pronounced caudal process. Greatest length through caudal process; greatest height through median hinge element. Valve covered with ovoid pitting of various sizes, occurring in rows parallel to valve outline. Pits are large, cir- cular at middle of valve, smaller marginally. Posterior rows of pits separated by series of low ridges which originate at posteroventral corner and splay out dorsally and posteriorly. Smooth, flattened anterior and posterior rims. Overhanging ventral ridge, strongly calcified along outer edge; postero— dorsal terminus of ala forms tubercle. Two small anterior ridges extend toward median valve from ventral ridge; ridges separated by two depressed regions. Caudal process is smooth, flat. Thirty-five simple-type normal pores distrib- uted over surface, most anterior; pores on surface between pits. Normal pores with low marginal rim. Inner margin and line of concrescence coincide at pos— terior and venter; arcuate anterior vestibule. Fused inner lamella of even width throughout. Weakly developed sel- vage. Inner margin parallels valve outline. Eleven radial pore canals, most anterior. Radial pores are straight, simple; posterior radial pores longer than anterior. Hingement in right valve consists of large, tabular ante- rior tooth; four anteromedian teeth and sockets; weakly crenulate median groove, enlarged terminally; four postero- median teeth and sockets; and narrow, elongate posterior tooth. Dorsal edge of valve enfolded to form accommodation groove. Four adductor muscle scars in row, inclined posterodor— sally. Dorsal scar is ovoid; dorsomedian scar is narrow, elon- gate; ventromedian scar is subrectangular, elongate; ventral scar is subcircular. Frontal scar split into larger, kidney— shaped posterior scar and small, round anterior scar. Fulcral point ovoid, located above posterior frontal scar. Dorsal scars are large, irregular in shape, few in number. 28 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 0.48 I I I | 0.40 — _ O m - - D: E — ._ LLI _ . . - g 0 _| _ _ :1 0 g E 0.30 — Q... . _ Z — . — F I r O r g H _ LLI I _ _ 0.20 — _ 0.14 I | I | I | 0.3 0.4 0.5 0.8 0.7 LENGTH, IN MILLIMETERS Figure 25. Plot of length versus height for Cytheropteron hop- kinsi. Dot may represent more than one specimen. Measurements.—X—Y plot based on 16 specimens (fig. 25). Comparisons.—Cytheropter0n hopkinsi n. sp. differs from C. pararcticum Whatley and Masson, 1979 (Pleis- tocene, Britain) by its high arched dorsum; high ala; large ornament pits; and long, narrow caudal process. C. hopkinsi differs from C. punctatum Brady, 1868 (Quaternary, north- east Atlantic) by its long, low valve outline; thin, high ala; long caudal process; and large ornament pits. Occurrence.—Assemblages II, III, IV. Table 2. Distribution.—Pleistocene through Holocene: Gulf of Alaska. Middle—outer sublittoral, upper bathyal. Material.—Twenty-five adult valves, twenty-five juve- nile valves. Type specimens.—Holotype: USNM 408546, right valve (pl. 14, fig. 6), locality EGAL-75-KC—l 1, length 0.53 mm, height 0.33 Inm. Paratypes: USNM 408547, left valve (pl. 16, figs. 10, 15), locality EGAL-75-KC-5, length 0.48 mm, height 0.26 mm. USNM 408548, right valve (pl. 16, figs. 11, 12), local- ity EGAL-75-KC-263, length 0.53 mm, height 0.31 mm. USNM 408549, left valve (pl. 16, figs. 13, 14), locality EGAL-75—KC-333, length 0.53 mm, height 0.29 mm. USNM 408550, right valve (pl. 16, fig. 16), locality EGAL- 75-KC-333, length 0.50 mm, height 0.30 mm. USNM 408551, right valve (pl. 16, fig. 17), locality EGAL-75-KC— 6, length 0.51 mm, height 0.35 mm. CYTHEROPTERON LI TU YAENSIS new species Plate 19, figures 5—7, 9; figures 26, 27 Cytheropteron aff. C. latissimum of Neale and Howe (1975). Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouw- ers, 1982b, p. 8; Brouwers, 1982c, p. 2; Brouwers, 1983. Etymology—After Lituya Bay, a fiord near the Fair— weather Range, southeast Alaska. Diagnosis—Characterized by subtriangular lateral out- line; highly arched dorsum; small, well-developed caudal process; convex posterodorsal corner; shallow, ovoid orna- ment pits arranged vertically at median and concentrically at margins; low subdued ridges that separate pit rows; smoothly curved, strong, overhanging ventral ridge, bifur- cates at anterior. Description—Adult valves subtriangular in lateral view. Right valve with highly arched dorsal margin; smoothly curved anterior margin with maximum width ven- tral of midline; ventral margin sinuous with pronounced con- cavity; posterior margin with small, well—developed caudal process and convex posterodorsal corner. Left valve differs in a lower, sinuous dorsum; broad, less protruding caudal process; less concave ventral margin. Greatest length through caudal process; greatest width through median dor- sal margin. Valve covered with moderate-sized, ovoid, shallow pits oriented in vertical rows at middle; rows curve to follow anterior and posterior margins. Low, subdued ridges between rows of pits. Broad, shallow dorsal sulcus; sulcus floor covered by small ovoid pits. Smoothly curved, strong ridge overhangs venter; anterior end of ridge bifurcates near margin. Shallow, subtle sulcus proceeds from middle of ventral ridge, terminates at median valve region. Fifty-one to sixty-two simple-type normal pores evenly distributed over surface; normal pores both within pits and on low ridges. Inner margin and line of concrescence coincide throughout; inner margin follows valve outline. Inner lamella of even width throughout. Moderately developed 0.4 | | (D 0: Lu _ _ '— Lu g _ _ _J :‘ E 0.3 — Q. _ Z O... . F — 0 O — 35 E — . C — I . 00 . _ . . _ 0,2 I | | 0.3 0.7 0.5 LENGTH, IN MILLIMETERS Figure 26. Plot of length versus height for Cytheropteron lituyaensis. Dot may represent more than one specimen. SYSTEMATIC PALEONTOLOGY 29 260 I I 240 — NUMBER OF VALVES 20 4O 60 80 100 120 l l | | 141] 160 180 DEPTH, IN METERS 200 220 Figure 27. Plot of abundance versus water depth for Cytheropteron lituyaensis. selvage, strongest along anterior. Eight radial pore canals, most anterior; radial pores are short, straight, simple. Hingement in right valve consists of bifid anterior tooth; six elongate, quadrate, anteromedian teeth; coarsely crenulate median groove; seven elongate, quadrate, postero- median teeth; strong, rounded, bifid posterior tooth. Adductor muscle scars form vertical row. Dorsal scar is squat, ovoid; dorsomedian scar is elongate, I-shaped; ventro- median scar is elongate, subquadrate; ventral scar is narrow, elongate. Numerous small, ovoid dorsal muscle scars. Measurements.—X—Y plot based on 25 specimens (fig. 26). Comparisons.—-Cytheropteron lituyaensis n. sp. dif- fers from C. nodosum Brady, 1868 (Quaternary, North Atlantic) by having a small size; sharp caudal process; rounded ventral ridge; and small, organized ornament pits. C. lituyaensis differs from C. dimlingtonensis Neale and Howe, 1973 (Pleistocene, North Atlantic, Beaufort Sea) by having a small size; less arched dorsum; small, sharp caudal process; and small, organized ornament pits. C. lituyaensis differs from C. latissimum (Norman, 1864) (upper Pliocene through Holocene, North Atlantic) by having a small size; arched dorsum; small, sharp caudal process; rounded ven- tral ridge; and organized ornament pits. Occurrence.—Assemblages II, III, IV, V. Table 2; figure 27. Distribution.—Pleistocene through Holocene: Gulf of Alaska, Cook Inlet and Kodiak Shelf. Middle-outer sublit— toral, upper bathyal. Material.—F0ur hundred ninety-nine adult valves, three hundred seventy-seven juvenile valves. Type specimens.—Holotype: USNM 408571, right valve (pl. 19, figs. 5, 6), locality EGAL-75—KC-17, length 0.38 mm, height 0.25 mm. Paratypes: USNM 408569, left valve, locality EGAL- 75—KC-17, length 0.43 mm, height 0.26 mm. USNM 408570, right valve, locality EGAL-75-KC—17, length 0.43 mm, height 0.25 mm. USNM 408572, right valve (pl. 19, figs. 7, 9), locality EGAL—75-KC— 17, length 0.40 mm, height 0.24 mm. 30 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 0.30 | l | | 3 ’LLJ 0.20 — . _ U21 . C. 3 — o o o — d o. o. E 022— _ Z O O 13—; - .0. O O O — o o o m 0.18 —— Q — I 0.14 l | l | 0.30 0.35 0.40 0.45 0.50 0.55 LENGTH, IN MILLIMETERS Figure 28. Plot of length versus height for Cytheropteron lordi. Dot may represent more than one specimen. CY THEROPTERON LORDI new species Plate 14, figures 4, 5; plate 16, figures 1—9; figures 28, 29 Cytheropteron sp. D Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Etymology—After Alan Lord, University College of London. Diagnosis.—Characterized by small size; subtriangular lateral outline; highly arched dorsum; deeply indented con- cavity; small, sharp caudal process; subtle dimorphism; strong, smooth, heavily calcified, overhanging ventral ridge; large posteroventral tubercle; series of thin, vertical ridges and sulci at posterior; arcuate sulcus and thin ridge along dorsum; and marginal pitting. Description—Adult valves subtriangular in lateral view. Right valve with highly arched dorsal margin; concave anterodorsal corner; smoothly curved anterior margin, with greatest width ventral of midline; ventral margin sinuous with deeply indented concavity; posterior margin with small, sharp caudal process. Left valve with less arched dorsal mar- gin, broad caudal process, and posterodorsal hinge ear. Sub- tle dimorphism: males lower, with pronounced posterodorsal cardinal angle. Valve surface covered with pits and ridges. Strong ridge overhangs venter, originating at posteroventral corner and terminating as wide ridge at anterior. Ventral ridge is smooth, heavily calcified. Three large trapezoidal depres- sions prominent along dorsal edge of ventral ridge, located at middle of ridge. Large subcircular tubercle posterior of depressions. Series of thin vertical ridges and wider sulci dominate posterior, proceeding from dorsum to ventral mar- gin or to ventral ridge. Arcuate sulcus and thin ridge along dorsum. Dorsal valve edge thickened to form prominent raised rim. Anterior margin with smooth, flat rim or flange. Pitting along dorsal, anterior, and ventral margins; median valve region and posterior margin are smooth. Pits are ovoid, tend to occur in concentric rows paralleling valve outline. Forty-three to fifty-six simple-type normal pores evenly dis- tributed over surface, both within pits and on surface. Pores with raised marginal rim. Inner lamella and line of concrescence coincide ven- trally. Shallow arcuate vestibule at caudal process. Inner lamella widest at anterior. Strong, well-developed selvage. Eight to twelve radial pore canals, most anterior. Radial pores are short, straight, simple. Hingement in right valve consists of two strong, large, quadrate anterior teeth; strongly crenulate median groove which expands terminally; strong, large, triangular postero- median tooth and ovoid socket; and two large, ovoid, poste- rior teeth. Dorsal edge of right valve enfolded to form accommodation groove for dorsal edge of left valve. Hinge- ment strong, well developed; most specimens occur as cara- paces, and splitting the valves is very difficult. Adductor muscle scars form inclined row, with ventral two scars within ornament tubercle. Dorsal scar is semicircu- lar; dorsomedian scar is elongate, subquadrate; ventrome- dian scar is elongate, with inflated ends. Frontal scar forms upside-down J—shape, with long axis oriented posterior and vertical. Numerous subovoid to subquadrate dorsal muscle scars between central scar field and hinge line. Dorsal scars occur in pairs. Measurements.—X—Y plot based on 31 specimens (fig. 28). Comparisons.—Cyther0pteron lordi is a very distinct taxon that is not morphologically similar to any described or illustrated forms. 0ccurrence.—Assemblages 11*, III, IV. Table 2; fig- ure 29. Distribution.—Pleistocene through Holocene: Gulf of Alaska. Material.—One hundred fifty-five adult valves, four juvenile valves. Type specimens.—Holotype: USNM 408537, left valve (pl. 14, fig. 4), locality DC2-80-EG—l95, length 0.35 mm, height 0.20 mm. Paratypes: USNM 408538, right valve (pl. 14, fig. 5), locality DC2-80-EG-195, length 0.35 mm, height 0.19 mm. USNM 408539, female left valve (pl. 16, fig. 1), locality DC2-80-EG—86, length 0.38 mm, height 0.24 mm. USNM 408540, female right valve (pl. 16, figs. 2, 3), locality DC2- 80-EG-195, length 0.36 mm, height 0.25 mm. USNM 408541, male left valve (pl. 16, fig. 4), locality DC2—80-EG— 195, length 0.35 mm, height 0.20 mm. USN M 408542, male right valve (pl. 16, fig. 5), locality DC2—80-EG-l95, length 0.35 mm, height 0.20 mm. USNM 408543, left valve (pl. 16, figs. 6, 8), locality DC2—80—EG-86, length 0.34 mm, height 0.18 mm. USNM 408544, right valve (pl. 16, fig. 7), locality DC2-80—EG-86, length 0.38 mm, height 0.20 mm. USNM 408545, left valve (pl. 16, fig. 9), locality DC2-80—EG—195, length 0.40 mm, height 0.20 mm. SYSTEMATIC PALEONTOLOGY 31 NUMBER OF VALVES 20 40 SD 80 100 120 DEPTH, IN METERS | l 140 180 180 200 220 240 Figure 29. Plot of abundance versus water depth for Cyz‘heropteron lordi. C YTHEROPTERON MIDTIMBERENSIS new species Plate 19, figures 8, 10—14; figure 30 Cytheropteron sp. N Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Etymology—After Midtimber Lake, a proglacial lake of Bering Glacier, southeast Alaska. Diagnosis.—Characterized by subtriangular to sub- quadrate lateral outline; wide, centrally located caudal pro— cess; marked dimorphism; small, ovoid ornament pits in radiating vertical rows; massive, heavily calcified, sinuous, overhanging ventral ridge; two large, oblique ridges from ventral ridge to posterodorsal and anterodorsal cardinal angles. Description—Adult valves subtriangular to subquad- rate in lateral view. Left valve with highly arched dorsal mar- gin; smoothly curved anterior margin with greatest width ventral of midline; ventral margin broadly sinuous; posterior margin with wide caudal process at midvalve. Right valve with less arched dorsum. Marked dimorphism: males consid- erably longer, lower, with more quadrate shape and wider caudal process. Greatest length through caudal process; greatest height through middle of valve. Valve covered with pitting and ridges. Pits are small, ovoid, occurring primarily along margins and sparsely in median region. Pits arranged as vertical rows radiating from venter. Pits smaller toward margins. Dorsal margin with sul- cus and thin marginal ridge. Venter dominated by massive, heavily calcified, sinuous ridge which overhangs margin. Dorsal edge of ventral ridge with deep depression. Two large ridges originate at anterior and posterior end of ventral ridge, proceed toward posterodorsal and anterodorsal corners, respectively. Normal pores simple-type, both within orna— ment pits and on surface. Left valve hingement consists of two quadrate anterior sockets; five anteromedian crenulae; smooth median bar; five posteromedian crenulae; and elongate posterior socket. 32 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 0.45 I l I 0.40» O O — U) _ _ a: O O ”.1 Lu ~ .0. - § 00000 =I - _ E O O 0 g — _ I£030 : . — 9 Lu I ~ _ 0.20 | l | 0.3 05 0.7 LENGTH, IN MILLIMETERS Figure 30. Plot of length versus height for Cytheropteron midtimberensis. Dot may represent more than one specimen. Anteromedian and posteromedian elements are terminal enlargement of median element. Measurements.~—X—Y plot based on 22 specimens (fig. 30). Comparisons.—Cyther0pteron midtimberensis n. sp. differs from C. eremitum Hanai, 1959 (lower Pleistocene, central Japan) by having a shorter, higher lateral outline; more arched dorsum; strong ventral ridge; two strong oblique ridges at anterior and posterior; and fewer ornament pits. C. midtimberensis differs from C. haydenensis by hav- ing a more arched dorsum, different shape of the ventral ridge, different ornament with fewer pits, and lack of vertical ribs. Occurrence.——Assemblages II, 111, V. Table 2. Distribution.—Pleistocene through Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf. Material.—One hundred forty-two adult valves, one hundred thirty-four juvenile valves. Type specimens.—Holotype: USNM 408575, left valve (pl. 19, figs. 8, 10), locality DC2-80-EG-195, length 0.55 mm, height 0.35 mm. Paratypes: USNM 408573, left valve, locality DC2-80- EG-195, length 0.64 mm, height 0.34 mm. USNM 408574, right valve, locality DC2—80-EG-195, length 0.64 mm, height 0.40 mm. USNM 408576, right valve (pl. 19, fig. 11), locality DC2—80-EG—195, length 0.55 mm, height 0.36 mm. USNM 408577, left valve (pl. 19, fig. 12), locality DC2-80- EG-195, length 0.56 mm, height 0.35 mm. USNM 408578, left valve (pl. 19, figs. 13, 14), locality DC2-80—EG-195, length 0.59 mm, height 0.31 mm. CYTHEROPTERON NODOSOALATUM Neale and Howe, 1973 Plate 11, figure 3; plate 12, figures 2—7; figures 31, 32 Cytheropteron nodosoalatum Neale and Howe, 1973, p. 240—242, pl. 1, figs. 6, 7a, b. Cytheropteron aff. C. nodosoalatum Neale and Howe. Brou- wers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1982c, p. 2; Brouwers, 1983. Diagnosis.—Characterized by subtriangular lateral out- line; smoothly curved anterior margin; sinuous venter with moderate concavity; concave posterodorsal corner; pro- nounced dimorphism; strong, overhanging alar ridge termi- nating at anterior as bifurcating fork; ornament pits aligned vertically in median area and concentrically at margins; sec— ondary fine pits and ridges; shallow arcuate anterior vesti— bule; and very small, irregular posterior vestibule. Description—Adult right valve subtriangular, left valve subquadrate in lateral view. Right valve with broadly arched dorsal margin; smoothly curved anterior margin with concave anterodorsal corner and with maximum width ventral of midline; ventral margin sinuous, with moderately incurved concavity; posterior margin with blunt caudal process; concave posterodorsal corner. Left valve with strong, obtuse, posterodorsal cardinal angle; convex anterodorsal corner; broad, flattened posterior. Pro— nounced dimorphism: males are more quadrate, lower in height, longer. Greatest height through midline; greatest length through caudal process. Valve surface covered with pits and ridges. Strong alar ridge overhangs venter, originating at posteroventral corner and terminating at anterior as bifurcating fork. Alar ridge is smooth, heavily calcified, with two dorsal—pointing 0.5 I I _ . _ _ . _ - . _ m _ .0 _ E 0 4 . 0.: E i x O C _ 3 C . C S _ O. O _ E E: — _ o 03 — . _ E I - _ [12 I I I I 0.3 0.5 0.7 LENGTH, IN MILLIMETERS Figure 31. Plot of length versus height for Cytheropteron noda— soalamm. SYSTEMATIC PALEONTOLOGY 33 50 l I NUMBER OF VALVES 30 50 70 90 110 15D 170 190 210 230 DEPTH, IN METERS Figure 32. extensions forming U-shape near middle of ridge. Pits are aligned in vertical rows at median valve, become concentric marginally. Pits are large, ovoid at posteromedian, becom— ing smaller anteriorly. Dendritic ridges between rows of pits at posteromedian. Secondary fine marginal pits and ridges. Sixty-one simple-type normal pores scattered over valve surface, occurring within pits. Inner lamella and line of concrescence coincide at pos— teroventer and venter. Shallow arcuate anterior vestibule; very small, irregular vestibule at caudal process. Fused inner lamella of even width throughout. Strong, well-developed selvage. Seven radial pore canals, one false radial pore canal; most anterior. Radial pores are long, straight, simple. Hingement in right valve consists of two small, ovoid anterior teeth; finely crenulate median groove; two ellipsoi- dal posterior teeth. Median groove enlarged terminally, with separated, round crenulate elements. Dorsal edge of right valve enfolded to form accommodation groove for left valve dorsal edge. Plot of abundance versus water depth for Cyzheropteron nodosoalamm. Adductor muscle scars form curved row; scars are immediately adjacent. Frontal scar is J-shaped. Scar impressions are weak. Measurements.———X—Y plot based on 22 specimens (fig. 31). Comparisons.wCytheropteron nodosaalatum differs from C. latissimum (Norman, 1864) (upper Pliocene through Holocene, northeast Atlantic) by having an arched dorsum; strong ventral ridge; pronounced, narrow caudal process; and organized, vertically arranged ornament pits. C. noda- soalatum differs from C. nodosum Brady, 1868 (Quaternary, northeast Atlantic) by having a less arched dorsum; weak, sinuous ventral ridge; evenly rounded anterior; and lack of dorsal tubercles. C. nodosoalatum differs from C. Champlai- num Cronin, 1981 (Holocene, North Atlantic) by having a strong posterodorsal cardinal angle; massive, sinuous ventral ridge; long, low valve outline; and broad caudal process. Occurrence.—Assemblages 1*, II, 111, V. Table 2; fig- ure 32. 34 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 0.4 I m n: LIJ _ _ '— LIJ g _ _ ._| d O O 203— . — Z O .0. I—‘ — O O O — E m ~ g _ I .0 _ . . _ 0.2 | I 1 0.3 0.5 0.7 LENGTH, lN MILLIMETERS Figure 33. Plot of length versus height for Cytheropteron squirei. Dot may represent more than one specimen. Distribution—Holocene: Novaya Zemlya, Franz Joseph Land, Barents Sea. Pleistocene through Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf. Sublittoral, upper bathyal. Material.~—One hundred fifteen adult valves, one hun- dred thirty—three juvenile valves. Illustrated specimens.—USNM 408505, right valve (pl. 11, fig. 3), locality DC2-80—EG-195, length 0.65 mm, height 0.43 mm. USNM 408506, left valve (pl. 12, figs. 2, 3), locality DC2-80-EG-63, length 0.65 mm, height 0.38 mm. USNM 408507, left valve (pl. 12, fig. 4), locality DC2-80- EG-195, length 0.65 mm, height 0.36 mm. USNM 408508, right valve (pl. 12, fig. 5), locality DC2—80—EG-63, length 0.60 mm, height 0.35 mm. USNM 408509, left valve (pl. 12, fig. 6), locality DC2-80-EG-195, length 0.61 mm, height 0.35 mm. USNM 408510, right valve (pl. 12, fig. 7), locality DC2-80-EG-195, length 0.63 mm, height 0.36 mm. CYTHEROPTERON SQUIREI new species Plate 18, figures 7, 8; plate 20, figures 12—18; plate 22, figures 1—3; figure 33 Cytheropteron sp. I Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Cytheropteron sp. 2 Tabuki, 1986, p. 101, pl. 18, figs. 9, 10. Etymology—After John Squire, engineering geologist, British Petroleum. Diagnosis.—Characterized by quadrate lateral outline; straight dorsum; pronounced concavity; broad caudal pro- cess; marked dimorphism, males longer, lower; reticulation in vertical rows of elongate to ovoid pits; strong, high, heavily calcified ala with terminal tubercles separated by median depression. Description—Adult valves quadrate in lateral view. Left valve with broadly arched dorsum; smoothly rounded anterior margin with greatest width ventral of midline; ven- tral margin sinuous with pronounced concavity; posterior margin with broad caudal process. Right valve with more arched dorsum; smaller, longer caudal process; more sinuous venter; and concave anterodorsal corner. Marked dimor- phism: males considerably longer, lower, with coarse orna- ment pattern, prolonged caudal process, straight dorsum, and stronger ventral ridge. Greatest length through caudal pro— cess; greatest height through anterior hinge element. Valve covered with reticulation and ridges. Moderately developed reticulation arranged in vertical rows. Pits are elongate to ovoid, arranged with long axis vertical. Ventral margin dominated by strong, high, heavily calcified, over— hanging ridge or ala. Anterior and posterior ends of ventral ridge enlarged into tubercles, separated by median depres- sion. Simple—type normal pores scattered over surface; pores with small marginal rim. Hingement in right valve consists of elongate, narrow anterior tooth; small anteromedian crenulae; finely crenulate median groove; small posteromedian crenulae; and elongate, narrow posterior tooth. Anteromedian and posteromedian crenulae form terminal enlargement of median element. Four adductor muscle scars form oblique row, inclined posterodorsally. Adductor scars are inflated, subovoid in shape. Frontal scar is J-shaped. Weak, circular fulcral point. Scattered, large, elongate dorsal muscle scars. Measurements.—X—Y plot based on 18 specimens (fig. 33). Comparisons.—Cyther0pteron squirei n. sp. differs from C. latissimum (Norman, 1864) (upper Pliocene through Holocene, North Atlantic) by having an elongate, quadrate valve outline; blunt caudal process; pronounced dimor- phism; vertical rows of ornament pits; and strong ventral tubercles. C. squirei differs from C. rarum Hanai, 1957 (upper Pliocene, Japan) by having a weaker ventral ridge; narrow, blunt caudal process; pronounced dimorphism; and small, ovoid, less organized ornament pits. 0ccurrence.—Assemblages II, V. Table 2. Distribution—Pliocene and Pleistocene: central Japan. Pleistocene, Holocene (?): Gulf of Alaska, Cook Inlet, Kodiak Shelf, Pribilof Islands. Middle sublittoral. Material.—Fifty-eight adult valves, thirty-four juvenile valves. Type specimens.—Holotype: USNM 408588, female left valve (pl. 18, fig. 7), locality EGAL-75—KC-52A, length 0.45 mm, height 0.25 mm. Paratypes: USNM 408589, male left valve (pl. 18, fig. 8), locality DC2-80—EG-195, length 0.50 mm, height 0.29 mm. USNM 408590, male right valve (pl. 20, figs. 12, 17, 18), locality DC2-80—EG-195, length 0.50 mm, height 0.28 mm. USNM 408591, female left valve (pl. 20, fig. 13), local- ity EGAL-75-KC-32, length 0.49 mm, height 0.29 mm. USNM 408592, female right valve (pl. 20, fig. 14), locality SYSTEMATIC PALEONTOLOGY 35 DC2-80-EG-195, length 0.58 mm, height 0.31 mm. USNM 408593, female left valve (pl. 20, fig. 15), locality DC2—80— EG-195, length 0.45 mm, height 0.29 mm. USNM 408594, male left valve (pl. 20, fig. 16), locality DC2—80—EG—195, length 0.48 mm, height 0.25 mm. USNM 408595, female right valve (pl. 22, fig. 1), locality DC2-80-EG-195, length 0.48 mm, height 0.24 mm. USNM 408596, female left valve (pl. 22, figs. 2, 3), locality DC2-80-EG-195, length 0.49 mm, height 0.29 mm. CYTHEROPTERON SUZDALSKYI Lev, 1972 Plate 18, figures 4, 5', plate 20, figures 1—9; figure 34 Cytheropteron suzdalskyi Lev, 1972, p. 19, pl. 1, figs. 1—5. Cytheropteron sp. Z Brouwers, 1982b, p. 8; Brouwers, 1983. Diagnosis.——Characterized by quadrate lateral outline; sinuous dorsum; drawn—out anterior and posterior; small concavity; pronounced caudal process; marked dimorphism; fine reticulation with vertical or concentric orientation at margins and chaotic arrangement medially; fine secondary papillae; anterior and posterior flattened marginal rim; large, rounded tubercles at posterodorsal, anterodorsal, anteroven- tral, and posteroventral corners; weak, sinuous ventral ridge; arcuate anterior vestibule; and four deep internal depressions reflecting external tubercles. Description—Adult valves subtriangular in lateral view. Right valve with concave posterodorsum, arched median dorsum, concave anterodorsum; broadly curved anterior margin; sinuous ventral margin with small concav- ity; posterior margin drawn-out with pronounced caudal pro- cess. Caudal process most attenuated dorsal of midline. Left valve with obtuse anterodorsal corner; straight median dor- sal margin; broad, blunt caudal process. Pronounced dimor- phism: males are longer, lower, with less arched dorsum, broader caudal process, attenuated anterior, and strong pos- terior convergence of anterior and posterior margins. Great- est length through caudal process; greatest height through anterior hinge element. Valve covered with fine reticulation network. Ridges vertical or parallel to margin at anterior and posterior, with few oblique connecting cross-ridges. Reticulation more cha- otic, ridges heavier in median valve region. Secondary fine papillae cover surface between ridges. Some fine pitting along anterior and posterior margins between reticulation. Anterior and posterior flattened rim. Large rounded tubercle along anterodorsal margin; three weaker tubercles at poster— odorsal, posteroventral, and anteroventral corners. Tubercles covered by reticulation and ornament papillae. Weak sinu- ous ridge parallels ventral margin. Sixty—six to sixty—eight simple-type normal pores evenly distributed over surface, both on and adjacent to ridges. Normal pores with raised marginal rim. Inner margin and line of concrescence coincide along posterior and venter; arcuate anterior vestibule. Inner margin 0.4 | I m n: C E ‘ 0 - LL] 0 0 g — _ j C. E 0.3 — O O. — g C O F _ _ :1: ‘2 _ - LLI I 0.2 I I | 0.3 0.5 0.7 LENGTH, IN MILLIMETERS Figure 34. Plot of length versus height for Cytheropteron suzdalskyi. Dot may represent more than one specimen. widest at anterior. Inner margin parallels valve outline. Moderately developed selvage. Ten to twelve radial pores, most anterior; pores are straight, short, simple. Two short false radial pores. Tubercles reflected internally as large, rounded, deep depressions. Hinge in left valve consists of two anterior rectangular sockets; weakly crenulate median bar which thickens and enlarges terminally into six anteromedian and nine postero- median quadrate teeth; and three posterior quadrate sockets. Median bar formed by dorsal valve edge. Anterior and pos- terior sockets rimmed dorsally by hinge ears. Four adductor muscle scars in row, inclined slightly posterodorsally. Dorsal scar trapezoidal; dorsomedian scar an elongate ellipsoid; ventromedian scar elongate, arched; ventral scar ovoid. Few dorsal scars, with rounded to ovoid scars near central scar field, elongate scars along dorsum. Measurements.——X—Y plot based on 16 specimens (fig. 34). Comparisons.—Cyther0pter0n suzdalskyi differs from C. angulatum Brady and Robertson, 1872 (Quaternary, North Atlantic) by having an elongate, quadrate valve shape; strong tubercles; extended caudal process; weak ventral ridge; ornament ridges. 0ccurrence.——Cruise EGAL—75—KC, localities 115, 130, BFM-78-1, G-4. Distribution.—Pleistocene: Russian Arctic. Holocene: Gulf of Alaska. Material.—Twenty-one adult valves, juvenile valves. Illustrated specimens—USNM 408579, female left valve (pl. 18, fig. 4), locality BFM—78—1, length 0.56 mm, height 0.33 mm. USNM 408580, male left valve (pl. 18, fig. 5), locality BFM-78-1, length 0.53 mm, height 0.29 mm. USNM 408581, female left valve (pl. 20, fig. 1), locality twenty—eight 36 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 BFM-78-1, length 0.56 mm, height 0.31 mm. USNM 408582, female right valve (pl. 20, figs. 2, 3), locality BFM- 78-1, length 0.54 mm, height 0.33 mm. USNM 408583, male left valve (pl. 20, fig. 4), locality BFM-78— 1, length 0.55 mm, height 0.31 mm. USNM 408584, male right valve (pl. 20, figs. 5, 6), locality BFM-78-1, length 0.53 mm, height 0.30 mm. USNM 408585, left valve (pl. 20, figs. 7, 8, 9), locality BFM-78-1, length 0.54 mm, height 0.30 mm. CYTHEROPTERON TARRENSIS new species Plate 2], figure 1; plate 22, figures 4—10; figure 35 Cytheropteron sp. M Brouwers, 1981, p. 9; Brouwers, 1982b, p. 8; Brouwers, 1983. Etymology—After Tarr Inlet, a fiord of Glacier Bay at the mouth of Grand Plateau Glacier. Diagnosis—Characterized by subtriangular lateral out- line; moderately arched dorsum; highly convex venter with small concavity; subtle dimorphism; pits in vertical rows; dorsomedian ridges; anterior and posterior smooth, flattened marginal rim; secondary corrugation and papillae on solum floors; strong, sinuous, overhanging ventral ridge, bifurcates at anterior in right valve; and elongate, vertical posteroven— tral depressions. Description—Adult valves subtriangular in lateral View. Dorsal margin arched; anterior margin smoothly rounded with greatest width ventral of midline; ventral mar- gin convex with small concavity; posterior margin with pro— nounced caudal process. Left valve with less arched dorsum; no concave posterodorsal corner; broad, blunt caudal pro- cess. Subtle dimorphism: males slightly shorter, lower; less arched dorsum; broad, weak caudal process. Greatest length through caudal process; greatest height through median hinge element. Valve covered with ovoid pitting of various sizes arranged in vertical rows. Dorsomedian pit rows separated by low ridges. Pits are large, elongate in middle, smaller at margins. Subdued dorsal marginal sulcus, especially devel- oped in right valve. Anterior and posterior smooth, flattened marginal rim. Secondary fine corrugations and papillae on solum floors. Strong, sinuous ridge overhangs posteroventer; ridge strengthened by heavy calcification. Ventral ridge originates at posteroventer, bifurcates at anterior. Elongate, vertical depressions at posteroventral corner where ventral ridge originates. Fifty-seven simple—type normal pores scat- tered over surface, both on ridges and in pits. Pores on ridges have raised marginal rim, pores within pits are celate. Inner margin and line of concrescence coincide at pos- terior and venter; shallow, arcuate, anterior vestibule. Inner lamella widest at anterior, of even width at posterior and ven- ter. Inner margin parallels valve outline. Moderately devel- oped selvage. Ten radial pores, most anterior; pores are straight, simple, long. 0.46 I I I I I I I I I I I I I I _ . _ (/3 0.40 _ _ I LlJ _ _ '— Lu g — _ j _ 00 . _ E ”O 2 _ _ l: O C O (:5 0.30 ~ . _ m " 0 ‘ I 020 I I I I I I I I I I I I I I 0.4 0.5 0.6 0.7 LENGTH, IN MILLIMETERS Figure 35. Plot of length versus height for Cytheropteron tarren- sis. Dot may represent more than one specimen. Four adductor muscle scars in row, inclined posterodor— sally. Dorsal scar is subcylindrical; dorsomedian scar is elongate, I-shaped; ventromedian scar is elongate, with inflated ends; ventral scar is large, subquadrate. V-shaped frontal scar. Two mandibular scars located ventral of frontal scar; anterior scar is circular, posterior scar is elongate, ellip- soidal. Measurements.——X—Y plot based on 16 specimens (fig. 35). Comparisons.—Cyther0pteron tarrensis n. sp. differs from C. Champlainum Cronin, 1981 (Quaternary, North Atlantic) by having a sinuous, overhanging ventral ridge; broad caudal process; less arched dorsum; large ovoid pits; prolonged anterior; and lack of ridges between pit rows. C. tarrensis differs from C. nodosum Brady, 1868 (Quaternary, North Atlantic) by its less arched dorsum; long, low valve outline; large, ovoid ornament pits; smooth caudal process. Occurrence—Cruise EGAL-75-KC, localities 4, 6, 90, 105, 202, 216. Assemblages II, III, V. Distribution.——Pleistocene: Gulf of Alaska. middle sublittoral. Material.—Twenty-eight adult valves, one juvenile valve. Type specimens.——Holotype: USNM 408597, left valve (pl. 21, fig. 1), locality EGAL-75—KC-6, length 0.54 mm, height 0.33 mm. Paratypes: USNM 408598, left valve (pl. 22, fig. 4), locality EGAL-75—KC—6, length 0.56 mm, height 0.41 mm. USNM 408599, right valve (pl. 22, figs. 5, 6), locality EGAL-75-KC—6, length 0.53 mm, height 0.31 mm. USNM 408600, left valve (pl. 22, fig. 7), locality EGAL-75-KC-6, length 0.49 mm, height 0.30 mm. USNM 408601, left valve (pl. 22, figs. 8, 9, 10), locality EGAL-75-KC-6, length 0.54 mm, height 0.28 mm. Inner- SYSTEMATIC PALEONTOLOGY 37 0'46 I I l I I I I I I I I m 0.40 — ‘— I u_| _ - |—- E _ _ 2‘ — o . — E _ . ”O . _ E 0 on F 0-30 _ . O. _ I (2 _ .. ... _ LU I _ _ [120 | I I I I I I I l I I 1 I 0.3 0.4 0.5 0.5 LENGTH, IN MILLIMETERS Figure 36. Plot of length versus height for Cytheropteron tsug- aruense. Dot may represent more than one specimen. CYTHEROPTERON TSUGARUENSE Tabuki, 1986 Plate 10, figures 8, 14—18; plate 11, figures 1, 2; plate 12, figure 1; figures 36, 37 Cytheropteron tsugaruense Tabuki, 1986, p. 100-101, pl. 18, figs. 1—6; pl. 20, fig. 8; text-figs. 17—5, 17—6. Cytheropteron sp. F Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1982c, p. 2; Brouwers, 1983. Diagnosis.——Characterized by subtriangular lateral out- line; highly arched, sinuous dorsal margin; blunt, broad cau- dal process; strong posterodorsal cardinal angle; moderate dimorphism; strong, sinuous, overhanging ventral ridge end- ing as posteroventral tubercle; ornament pits arranged verti- cally and radially; large anterodorsal tubercle. Description—Adult valves subtriangular in lateral View. Left valve with highly arched, sinuous dorsal margin; posterior third of dorsal margin highly concave; anterior margin smoothly curved, with greatest width ventral of mid- line; ventral margin sinuous, with pronounced concavity; posterior margin with blunt, broad caudal process; strong posterodorsal cardinal angle. Right valve with highly arched dorsal margin; pronounced, pointed caudal process; and lack of concave posterodorsal margin. Moderate dimorphism: males are slightly shorter, considerably lower. Greatest length through caudal process; greatest height through median hinge element. Valve surface covered with ovoid pitting and ridges. Strong sinuous ridge overhangs venter; ridge is strengthened by heavy calcification. Ridge originates at posterodorsal cor- ner as large tubercle, proceeds vertically to posteroventral corner, swings across to form blunt, sinuous, alar structure, and terminates at anteroventral comer. Posteroventral ala forms large, blunt tubercle; smooth tubercle at median ala. Two large ovoid depressions along ventral alar ridge. Low ridge-reticulation system covers valve, oriented radially and concentrically from ventral ridge. Secondary small pitting along dorsal margin. Caudal process is smooth, flat. Forty- two to fifty-nine simple-type normal pores evenly distrib— uted over surface, occurring within pits and on surface. Nor— mal pores with marginal rim. Inner margin and line of concrescence coincide along venter; shallow, arcuate anterior vestibule and small, irregu— larly shaped posterior vestibule. Inner margin parallels valve outline; inner lamella widest at anterior. Strong, well- developed selvage. Twelve to fourteen radial pores, most anterior; radial pores are straight, simple. Hingement in right valve consists of two rounded ante— rior teeth; coarsely crenulate median groove; and three rounded posterior teeth. Median element is enlarged termi- nally to form large crenulae. Dorsal edge of right valve enfolded to form accommodation bar. Measurements.——X—Y plot based on 29 specimens (fig. 36). Comparisons.flCytheropteron tsugaruense Tabuki, 1986 differs from C. angulatum Brady and Robertson, 1872 (Quaternary, North Atlantic, Arctic) by having an arched dorsum; pointed caudal process; strong posterior vertical ridge; rounded posterior in left valve; vertically arranged ornament pits; and different anterior and posterior hinge ele— ments. C. tsugaruense differs from C. pyramidale Brady, 1868 (Quaternary, northeast Atlantic) by having a strong posterodorsal cardinal angle; rounded anterior; rounded pos- terior in left valve; heavily calcified, sinuous ventral ridge; and evenly sized, vertically arranged ornament pits. 0ccurrence.—-Assemblages II, III, V. Table 2; figure 37. Distribution—Pliocene and Pleistocene: central Japan. Pleistocene through Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf, Chukchi Sea. Middle-outer sublittoral. Material.—One hundred twenty-three adult valves, sixty—one juvenile valves. Illustrated specimens—USNM 408498, left valve (pl. 11, fig. 1), locality DC2-80—EG~195, length 0.49 mm, height 0.31 mm. USNM 408499, right valve (pl. 11, fig. 2), locality DC2-80-EG—195, length 0.49 mm, height 0.30 mm. USNM 408500, female left valve (pl. 10, figs. 14, 18), locality DC2- 80-EG—195, length 0.50 mm, height 0.29 mm. USNM 408501, female right valve (pl. 10, fig. 15), locality DC2-80- EG-195, length 0.49 mm, height 0.33 mm. USNM 408502, male left valve (pl. 10, fig. 16), locality DC2-80-EG-195, length 0.46 mm, height 0.29 mm. USNM 408503, male right valve (pl. 10, fig. 17), locality DC2—80-EG-195, length 0.46 mm, height 0.31 mm. USNM 408504, male right valve (pl. 10, fig. 8; pl. 12, fig. 1), locality DC2-80-EG-195, length 0.48 mm, height 0.33 mm. 38 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 121] 101] 00 c: NUMBER OF VALVES 41] 20 40 60 80 100 l | ' | ‘ I 120 140 160 180 DEPTH, IN METERS Figure 37. Plot of abundance versus water depth for Cytheropteron tsugaruense. C Y T HEROPTERON VERNRITCHIENSIS new species Plate 21, figure 3; plate 22, figures 14, 15; plate 23, figures 1—6 Cytheropteron sp. P Brouwers, 1981, p. 9; Brouwers, 1982c, p. 2; Brouwers, 1983. Cytheropteron sp. 1 Tabuki, 1986, p. 101, pl. 18, figs. 7, 8; text-fig. 19—4. Etymology—After Vern Ritchie Glacier, originating in the Juneau icefields, southeast Alaska and British Columbia. Diagnosis.—Characterized by subtriangular lateral out- line; highly arched dorsum; sinuous venter; broad, pro— nounced caudal process; large ovoid to elongate pits in vertical rows at median and concentric at margins; pitting variable between individuals; 10W, strong, heavily calcified, overhanging ventral ala. Description.—Adult valves ellipsoidal to subtriangular in lateral View. In left valve, dorsal margin broadly arched; anterior margin smoothly curved, with maximum width ven- tral of midline; ventral margin sinuous with concave and convex parts; broad, pronounced caudal process. Obtuse, rounded posterodorsal corner; broad concave anterodorsal margin. Right valve differs in a high, arched dorsal margin; pointed, drawn-out caudal process; pronounced concave anterodorsal margin; lack of cardinal angle; attenuated ante- rior margin. Valve covered with primary and secondary pitting, low ridges, pronounced ventral alar structure. Primary large ovoid to elongate pits oriented in vertical rows near median, radial rows at anterior and posterior margins. Pits largest at median, smaller at margins. Pitting variable between indi- viduals, ranging from large ovoid, elongate pits to smaller, circular to ovoid pits. Low, strong, heavily calcified ala overhangs venter; ala crescentic, originating as bifurcate ridge at anterior and terminating at posteroventral corner. Ventral alar edge is smooth; dorsal alar side with large pits and large polygonal depressions. Low ridge and companion sulcus parallel and adjacent to dorsum. Five to six low, sub- parallel ridges dominate posterior; ridges originate at poster— odorsal corner, proceed obliquely in anteroventral direction SYSTEMATIC PALEONTOLOGY 39 to midline, and follow vertical course to posterodorsal mar- gin. Secondary fine pits and punctae along dorsum. Caudal process and anteroventral margin have broad, smooth, flat region. Sixty-five simple-type normal pores evenly distrib- uted over surface, both in pits and on surface. Normal pores with distinct marginal rim. Inner margin and line of concrescence coincide at ven- ter and posterior. Deep, arcuate anterior vestibule. Moder- ately developed selvage, strongest along anterior. Fused inner lamella of even width throughout; inner margin paral— lels valve outline. Nine radial pore canals, most anterior. Radial pores short, straight, simple. Small ellipsoidal ocular sinus below anterior hinge element. Hingement in left valve consists of two large, quadrate, anterior sockets; five ovoid anteromedian teeth; smooth median bar; five ovoid posteromedian teeth; and three small, quadrate, posterior sockets. Anteromedian and postero- median teeth form enlarged terminal portion of median bar. Median element formed by dorsal valve edge. Right valve hingement with dorsal margin enfolded to form accommoda- tion groove. Four large adductor muscle scars form inclined row; scars are close together. Dorsal scar is wedge-shaped; dor- somedian scar is elongate, subquadrate; ventromedian scar is |-shaped; ventral scar is elongate, subquadrate. Frontal scar irregular in shape, with dumbbell-shaped dorsal end and ovoid ventral end. Some small, ovoid dorsal scars above adductor row; prominent, elongate, dumbbell-shaped dorsal scars below median hinge element. Comparisons.—Cyther0pter0n vernritchiensis n. sp. differs from C. angulatum Brady and Robertson, 1872 (Qua— ternary, northeast Atlantic) by having a high, short valve shape; narrow, prolonged caudal process; weak ala with weak tubercle; small, numerous ornament pits; posterior ver- tical ridges; and anterior-bifurcating ala. C. vernritchiensis differs from C. pyramidale Brady, 1868 (Quaternary, north- east Atlantic) by having a small size; low, short valve out— line; posteroventral alar tubercle; large, numerous ornament pits; and oblique posterior ridges. C. vernritchiensis differs from C. nodosum Brady, 1868 (Quaternary, North Atlantic) by having a long, low valve outline; large, few ornament pits; strong posterodorsal cardinal angle; few, strong poste- rior ridges; and lack of a median depressed region bounded by two oblique ridges. 0ccurrence.—Cruise EGAL-75-KC, localities 39, 46, 141, 204, 263, 283, 289. Assemblages II, 111, V. Distribution—Pliocene and Pleistocene: central Japan. Pleistocene through Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf, Chukchi Sea, Pribilof Islands. Inner-middle sublittoral. Material.—Nine adult valves, three juvenile valves. Type specimens.—Holotype: USNM 408605, right valve (pl. 21, fig. 3), locality EGAL-75-KC-204, length 0.50 mm, height 0.33 mm. Paratypes: USNM 408606, left valve (pl. 22, fig. 14; pl. 23, fig. 2), locality EGAL-75-KC-263, length 0.45 mm, height 0.29 mm. USNM 408607, right valve (pl. 22, fig. 15; pl. 23, fig. 3), locality EGAL-75-KC-263, length 0.50 mm, height 0.30 mm. USNM 408608, left valve (pl. 23, fig. 1), locality EGAL-75-KC—30, length 0.48 mm, height 0.30 mm. USNM 408609, left valve (pl. 23, figs. 4, 5, 6), locality EGAL-75—KC—l4l, length 0.45 mm, height 0.28 mm. CYTHEROPTERON YAJIMAI Tabuki 1986 Plate 9, figures 5, 6; plate 8, figure 15; plate 10, figures 1—7, 9, 10; figures 38, 39 Cytheropteron yajimai Tabuki, 1986, p. 99—100, pl. 17, figs. 13—18; pl. 20, fig. 7; text-figs. 17—3, 17—4. Cytheropteron sp. E Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Diagnosis—Characterized by subtriangular lateral out- line; highly arched dorsum; concave anterodorsal corner; blunt anterior margin; sinuous venter with pronounced con- cavity; large, attenuated caudal process; prominent over- hanging ventral ala; ventral ridge is heavy, broad, strongly calcified; two oblique ridges trend toward posterodorsal and anterodorsal, forming anterior, posterodorsal, and median depressions; scattered small pits aligned in rows, follow ridge orientations. Description—Adult valves subtriangular in lateral View. Right valve with highly arched dorsal margin; antero- dorsal margin concave; anterior margin smoothly curved, somewhat blunted; ventral margin sinuous, with pronounced concavity; posterior margin with large, attenuated caudal process. Left valve differs in flattened, sinuous dorsum; con- vex anterodorsal margin; and broad, less pointed caudal pro- cess. Greatest length through caudal process; greatest height through middle of dorsal margin. Valve surface predominantly smooth, with pits and ridges. Prominent ventral ridge overhangs margin; ventral ridge is heavy, broad, strongly calcified. Ridge starts near caudal process, swings down to form arcuate alar structure, and bifurcates anteriorly, terminating at anterior. Strong, narrow dorsal sulcus. Two ridges proceed from posterior and anterior ends of ventral ridge to posterodorsal and anterodor- sal corners. Broad depressions between ridges, forming three pronounced depressed regions at anterior, posterodorsum, and median. Caudal process is smooth, flat. Small ovoid pits thinly scattered over surface; number and size of pits may vary among individuals. Pits occur in rows which follow ridge-depression orientation. Forty-six simple-type normal pores evenly distributed over surface, occurring within pits and on surface. Normal pores with light-colored marginal rim. Inner margin and line of concrescence coincide throughout; inner margin parallels valve outline. Inner lamella widest at anterior. Moderately developed selvage. 40 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 0.46 | | u: [140— — E I— ‘ o a LLI . E - g _ 3 O O. O :‘ ‘ .0 8 — E — 3 o — _ 030— . O. ':E ' 3'0 (3 — 0 - m . I - O — 0'20 | | l | i | | | i | | | l 0.3 0.4 0.5 0.6 LENGTH, IN MILLIMETERS Figure 38. Plot of length versus height for Cytheropteron yaji- mai. Dot may represent more than one specimen. Six radial pore canals, two false radial pore canals; most anterior. Radial pores straight, simple; radials short at pos- terior, long at anterior. Hingement in right valve consists of three rounded quadrate anterior teeth; four elongate quadrate anteromedian sockets; coarsely crenulate median groove; seven quadrate posteromedian sockets; and three rounded quadrate posterior teeth, with bifid posterior tooth. Anteromedian and postero- median sockets form terminally enlarged portions of median element. Dorsal edge of right valve enfolded to form accom- modation bar. Measurements.—X—Y plot based on 34 specimens (fig. 38). Comparisons.—Cyther0pter0n yajimai Tabuki, 1986 differs from C. sawanense Hanai, 1957 (upper Pliocene, northern Japan) by having a less arched dorsal margin; straight caudal process; lower ventral alar ridge; and oma- ment pattern with fewer, smaller, weaker pits that are irreg- ularly distributed. C. yajimai differs from C. nodosoalatum Neale and Howe, 1973 by having a higher dorsal margin, dif- ferent size, and differences in the size, number, and arrange- ment of ornament pits. 0ccurrence.——Assemblages II, III, V. Table 2; figure 39. Distribution—Pliocene and Pleistocene: central Japan. Pleistocene through Holocene: Cook Inlet, Kodiak Shelf, Gulf of Alaska. Middle-outer sublittoral. Material.—Two hundred forty-eight adult valves, two hundred eleven juvenile valves. Illustrated specimens.—USNM 408485, left valve (pl. 9, fig. 5), locality DC2—80—EG-195, length 0.52 mm, height 0.34 mm. USNM 408486, right valve (pl. 9, fig. 6), locality DC2-80—EG-l95, length 0.58 mm, height 0.35 mm. USNM 408487, left valve (pl. 8, fig. 15), locality DC2—80-EG-195, length 0.57 mm, height 0.38 mm. USNM 408488, right valve (pl. 10, fig. 1), locality DC2-80—EG-l95, length 0.52 mm, height 0.35 mm. USNM 408489, female left valve (pl. 10, figs. 2, 6), locality DC2-80-EG-195, length 0.55 mm, height 0.33 mm. USNM 408490, male right valve (pl. 10, figs. 3, 9), locality DC2-80-EG-l95, length 0.50 mm, height 0.30 mm. USNM 408491, male left valve (pl. 10, figs. 4, 10), locality DC2-80-EG-195, length 0.52 mm, height 0.31 mm. USNM 408492, female right valve (pl. 10, fig. 5), locality DC2—80— EG—195, length 0.51 mm, height 0.31 mm. USNM 408493, female right valve (pl. 10, fig. 7), locality DC2-80—EG-195, length 0.53 mm, height 0.32 mm. CYTHEROPTERON YAKUTATENSIS new species Plate 21, figure 4; plate 23, figures 7—13; figure 40 Cytheropteron sp. R Brouwers, 1981, p. 9; Brouwers, 1982a, p. 11; Brouwers, 1982b, p. 8; Brouwers, 1983. Etymology—After the town of Yakutat, southeast Alaska. Diagnosis—Characterized by subovoid lateral outline; arched, sinuous dorsum; sinuous venter with concavity; broad caudal process; oblique posterodorsal cardinal angle; ovoid pits in vertical rows; surface smooth between pits; strong, heavily calcified ventral ala, bifurcates at anteroven- ter. Description—Adult valves subovoid in lateral View. Dorsal margin arched, sinuous; anterior margin smoothly curved, with greatest width ventral of midline; ventral mar- gin sinuous with moderate concavity; posterior margin with broad, moderately developed caudal process. Oblique pos- terodorsal cardinal angle. Left valve with less arched dor- sum, less drawn-out anteroventral margin, and broad, blunt development of caudal process. Greatest length through mid- line; greatest height through anterior hinge element. Valve covered with ovoid pitting of various sizes; pits are large, ovoid, in vertical rows. Pitting smaller marginally. Valve surface smooth between pits. Strong, heavily calcified ventral ridge or ala originates at ventral caudal process, over- hangs margin, and bifurcates at anteroventral corner. Ridge strongly indented at posteroventral corner. Sixty—two simple-type normal pores evenly distributed over surface, most within pits. Normal pores with raised marginal rim. Inner margin and line of concrescence coincide throughout. Inner lamella widest at anterior, even width at posterior and venter. Inner margin parallels valve outline. Well-developed selvage. Seven radial pores, three false radial pores, most anterior; pores straight, short, simple. Hinge in left valve consists of four ovoid anterior sock- ets; crenulate median bar which thickens, enlarges termi- nally into five elongate-quadrate anteromedian teeth and nine rectangular posteromedian teeth; three posterior quad- rate sockets. Median bar formed by dorsal valve edge. Right valve hingement with dorsal edge enfolded to form accom- modation groove. SYSTEMATIC PALEONTOLOGY 41 NUMBER OF VALVES l ‘l‘lU DEPTH, IN METERS 130 150 170 190 Figure 39. Plot of abundance versus water depth for Cytheropteron yajimai. Four adductor muscle scars in row, inclined posterodor- sally. Dorsal scar is semicircular; dorsomedian scar is elon- gate, with inflated anterior; ventromedian scar is sinuous; ventral scar is ovoid. Frontal scar split into larger, kidney- shaped posterior scar and small, round, anterior scar. Large crescentic fulcral point. Measurements.—X—Y plot based on 19 specimens (fig. 40). C0mparis0ns.-—Cytheropteron yakutatensis n. sp. dif- fers from C. pararcticum Whatley and Masson, 1979 (Pleis- tocene, northeast Atlantic) by having a high, short valve outline; sinuous venter; sinuous ala with posteroventral tubercle; and large, few ornament pits. C. yakutatensis dif- fers from C. angulatum Brady and Robertson, 1872 (Quater- nary, North Atlantic) by having a short, high valve outline; median, wide caudal process; sinuous venter; sinuous, over- hanging ala; and small, numerous ornament pits. C. yakutat- ensis differs from C. nodosoalatum Neale and Howe, 1973 (Quaternary, North Atlantic) by having a sinuous venter; sin- uous ala with strong posteroventral incurving; more ornament pits; weak, broad median caudal process; and lack of posterior ridges. 0ccurrence.—Cruise EGAL-75-KC, localities 58, 86, 87, 157, 174. Cruise DC2-87-EG, locality 195. Assem- blages II, 111, V. Distribution—Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf. Inner-middle sublittoral. Material.——Fifty—five adult valves, twenty-two juvenile valves. Type specimens.—Holotype: USNM 408610, right valve (pl. 21, fig. 4), locality EGAL-75-KC—204, length 0.58 mm, height 0.35 mm. Paratypes: USNM 408611, left valve (pl. 23, figs. 7, 9, 12), locality DC2-80-EG—195, length 0.65 mm, height 0.33 mm. USNM 408612, right valve (pl. 23, fig. 8), locality EGAL-75-KC-32, length 0.51 mm, height 0.29 mm. USNM 408613, left valve (pl. 23, fig. 10), locality DC2-80—EG—195, length 0.58 mm, height 0.33 mm. USNM 408614, left valve (pl. 23, figs. 11, 13), locality DC2—80-EG-195, length 0.59 mm, height 0.30 mm. 42 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 C YTHEROPTERON Sp. J Plate 14, figure 1 Cytheropteron sp. J Brouwers, 1982a, p. 11; Brouwers, 1983. Diagnosis—Characterized by subtriangular lateral out- line; highly arched dorsum; sinuous venter with subtle con- cavity; wide, short caudal process; smooth valve surface; and broad, arcuate, overhanging ventral ridge. Occurrence—Cruise EGAL-75—KC, locality 421. Cruise DC1-79—EG, locality 46. Cruise DC2-80-EG, local- ity 73. Distribution.—Holocene: Gulf of Alaska. Material—Two adult valves, one juvenile valve. Illustrated specimen.——USNM 408529, left valve (pl. 14, fig. 1), locality EGAL-75-KC-421, length 0.54 mm, height 0.30 mm. CYTHEROPTERON sp. V Plate 11, figure 6 Cytheropteron sp. V Brouwers, 1981, p. 9; Brouwers, 1983. Diagnosis—Characterized by subtriangular to semicir— cular lateral outline; broadly arched dorsum inclined sharply toward posterior; blunt posterior; weak, obtuse posterodorsal cardinal angle; reticulate ornament with polygonal fossae, arranged concentrically at anterior; massive, heavily calci- fied, overhanging ventral ridge; and shallow, crescentic pos- terior vestibule. Occurrence—Cruise EGAL-75-KC, locality 11. Distribution.—Pleistocene: Gulf of Alaska. Material—Five adult valves, one juvenile valve. Illustrated specimen.—USNM 408521, left valve (pl. 11, fig. 6), locality EGAL-75-KC-11, length 0.39 mm, height 0.25 mm. Genus S WAINOCYTHERE Ishizaki, 1981 Type species.—Swainocythere chejudoensis Ishizaki, 1981 (Type by original designation). S WAINOCYTHERE CHEJUDOENSIS Ishizaki, 1981 Plate 21, figure 5; plate 23, figures 14, 15 Swainocythere chejudoensis Ishizaki, 1981, p. 59—60, pl. 12, figs. 12a, 13—15; pl. 13, figs. 17, 18; pl. 15, figs. 12, 13. Swainocythere chejudoensis Ishizaki. Wang and others, 1988, pl. 54, figs. 11—12. Cytherura sp. I Brouwers, 1982b, p. 9; Brouwers, 1983. Description—Valves elongate, subtriangular in lateral View. Dorsal margin with convex median portion and con- cave anterior and posterior portions. Rounded, obtuse anterodorsal cardinal angle extends high above dorsum. Smoothly curved anterior margin; ventral margin with subtle 0.4 I I | l | I I I I I I I l _ . _ U) Q: T . — E o o 0 LL, — _ E . . . .. . j — _ =' . 203— .: O — z O O F I _ a 9 Lu I — _ 0.2 I I I I I I I I I i I I I 0.4 0.5 0.5 0.7 LENGTH, IN MILLIMETERS Figure 40. Plot of length versus height for Cytheropteron yaku- tatensis. Dot may represent more than one specimen. concavity; posterior margin drawn-out, with sharp, pro- nounced caudal process. Greatest length through caudal pro- cess; greatest height through anterior hinge element. Valve covered with ridges and pitting. Dominant ridge extends from anterodorsal corner, loops parallel to anterior margin, curves around to follow ventral margin, and loops back vertically to posterodorsal corner. Series of discontinu- ous, horizontal ridges; ridges most pronounced near margins and weaken toward median valve area. Regions between ridges contain ovoid pits, which occur in groups of two to three pits or as rows between ridges. Posterior and anterior margins have wide, flat region lacking primary ornament; marginal regions covered by secondary fine ridges and punc- tation. Secondary ridges in anterodorsal corner form series of lines parallel to valve outline. Sixteen simple-type normal pores, most anterior. Normal pores with highly visible light- colored marginal rim. Inner lamella and line of concrescence coincide at pos- terior; deep, crescentic anterior vestibule and sinuous ventral vestibule. Inner margin parallels valve outline; inner lamella widest along anterior. Moderate selvage, best developed at anterior. Six radial pore canals, two false radial pore canals; most anterior. Radial pores few, straight, simple. Three adductor muscle scars reflected exteriorly by row of three elongate pits. Remarks.—Swainocythere chejudoensis Ishizaki, 1981 was originally described from the East China Sea; four local- ities contained the species, at lat 31° N., long 127° E. (east of the Yangtze River and north of Okinawa). Fine sand to mud substrates predominated in water depths of 105—1 14 m. The East China Sea marks the geographic zone delimiting sub- tropical southern Japanese faunal elements from the tropical Indo-Pacific realm. The presence of the warm-water Swainocythere cheju- doensis was difficult to explain in Quaternary sediments of the Gulf of Alaska because the species did not have a docu— mented range in the temperate realm. One explanation that I REFERENCES CITED 43 invoked for the presence of this rare taxon was that it was weathering out of Pliocene or older sediments of the Yakat- aga Formation, reflecting past warmer climates. The four localities in which Swainocythere occurs are on Tarr Bank, with exposures of Pleistocene and older lithified sediments of the lower part of the Yakataga Formation. Until recently, the only known occurrences of Swain- ocythere were the Gulf of Alaska and the East China Sea. I speculated that the taxon either (a) migrated up the Japanese coast to the Kuril Islands and crossed the Bering Sea or moved along the south side of the Aleutian Islands into the Gulf of Alaska or (b) was carried via floating debris across the Pacific Ocean along the Kuroshio Current (Ishizaki, 1981). W.M. Briggs Jr. has recovered several species of Swainocythere in the Arctic Ocean (oral communication, 1993). Even more recently, Correge and others (1993) illus- trated Swainocythere nansem’ from deep water samples around Australia; S. mmseni was originally described as Cytheropteron nansem' Joy and Clark from the central Arctic Ocean. Occurrence—Cruise EGAL—75-KC, localities 105, 150, 153, 154. Distribution—Pliocene (7), Holocene: East China Sea, Gulf of Alaska. Material.—One adult valve, five juvenile valves. Illustrated specimens.—USNM 408615, left valve (pl. 21, fig. 5), locality EGAL-75-KC-154, length 0.28 mm, height 0.15 mm. USNM 408616, left valve (pl. 23, figs. 14, 15), locality EGAL-75-KC—105, length 0.28 mm, height 0.14 mm. FAMILY LOXOCONCHIDAE Swain and Gilby, 1974 Type species.—Palm0c0ncha laevimarginata Swain and Gilby, 1974 (Type by original designation). PALMOCONCHA KRAUSEI Brouwers, 1993 Plate 1, figure 7', plate 4, figures 1—5; figure 41 Eucytherura sp. B Brouwers, 1981, p. 10; Brouwers, 1983. Palmoconcha krausei Brouwers, 1993, pl. 13, figs. 5, 6; pl. 14, figs. 13—15; pl. 15, figs. 1—3, 6; text-fig. 33. Diagnosis—Characterized by a short, squared, sub- quadrate lateral outline; truncated, convergent posterior; low reticulation network with large, subovoid pits arranged con- centrically at anterior; series of parallel anterior and poste- rior marginal ridges; large eye tubercle; and anterior and posterior marginal flanges. Measurements.—X—Y plot based on eight specimens (fig. 41). Occurrence.—Cruise EGAL-75-KC, localities 17, 421. Cruise DC1-79-EG, locality 46. Cruise DC2-80—EG, locality 195. 0.30 I I I I | I I I I I I I I I I I I I I - 0 3’2 — o o — E 0.25 ~ 0 — ”J .— 2 _ 2| — O O — E _ _ g — _ F o 20 — O — I _ Q _ Lu — - I 0.15 — _.. I I I I l I I I I l I I I I l I I I I 0.30 0 35 0 0,45 0.50 . .40 LENGTH, IN MILLIMETERS Figure 41. Plot of length versus height for Palmoconcha krausei. Distribution—Holocene: Gulf of Alaska, Cook Inlet, Kodiak Shelf. Material—Nine adult valves, one juvenile valve. Illustrated specimens.—-USNM 408423, female left valve (pl. 1, fig. 7), locality EGAL-75-KC-421, length 0.36 mm, height 0.23 mm. USNM 408424, left valve (pl. 4, figs. 1, 3), locality EGAL-75-KC-17, length 0.39 mm, height 0.25 mm. USNM 408425, right valve (pl. 4, figs. 2, 5), locality DC2-80—EG—195, length 0.33 mm, height 0.23 mm. USNM 408426, right valve (pl. 4, fig. 4), locality DC2-80-EG—195, length 0.35 mm, height 0.20 mm. ACKNOWLEDGMENTS I would like to extend my thanks to Michael Ayress and Ryoichi Tabuki for reviewing this report; their com- ments improved the manuscript considerably. John Neale provided comments on an early draft. I would like to thank Richard Forester and Don Eicher for encouraging me to finish this work. REFERENCES CITED Baird, W., 1838, The natural history of the British Entomostra- ca—Pan 4: Magazine of Zoology and Botany, v. 2, no. 8, p. 132—144. Bonaduce, G., Ciampo, G., and Masoli, M., 1975, Distribution of Ostracoda in the Adriatic Sea: Pubblicazioni della Stazione Zoologica di Napoli, v. 40, suppl. 1, p. 1—154. Brady, G.S., 1867, A synopsis of the Recent British Ostracoda: The Intellectual Observer, V. 12, no. 2, p. 110—130. Brady, G.S., and Robertson, D., 1872, Contributions to the study of Entomostraca, Number 6—On the distribution of the British 44 SYSTEMATIC PALEONTOLOGY OF QUATERNARY OSTRACODE ASSEMBLAGES, GULF OF ALASKA, PART 3 Ostracoda: Annals and Magazine of Natural History, Series 4, v. 9, p. 48—70. Brouwers, E.M., 1981, Tabulation of the ostracode assemblages and associated organisms from selected bottom grab samples taken in the northeast Gulf of Alaska, F.R.S. Townsend Cromwell cruise EGAL-75-KC, 1975: US. Geological Survey Open- File Report 81—1314, 134 p. 1982a, Tabulation of the ostracode assemblages and asso- ciated fauna and flora from Van Veen samples taken in the northeast Gulf of Alaska, R/V Discovery cruise DC2-80-EG, June, 1980: US. Geological Survey Open-File Report 82—390, 68 p. 1982b, Tabulation of the ostracode assemblages and associ— ated organisms from selected bottom grab samples taken in the northeast Gulf of Alaska, F.R.S. Townsend Cromwell cruise EGAL-75-KC, 1975, Part II: US. Geological Survey Open- File Report 82—949, 92 p. 1982c, Re—evaluation of the cytheracean ostracode species identified by Painter (1965) from localities in the northeastern Pacific Ocean and Chukchi Sea: US. Geological Survey Open-File Report 82—736, 36 p. 1983, Occurrence and distribution chart of ostracodes from the northeast Gulf of Alaska: US. Geological Survey Miscel- laneous Field Studies Map MF—1518. 1988, Palaeobathymetry on the continental shelf based on examples using ostracods from the Gulf of Alaska, in De Deck- ker, P., Colin, J .—P., and Peypouquet, J .P., eds., Ostracoda in the Earth Sciences: Amsterdam, Elsevier, p. 55—76. 1990, Systematic paleontology of Quaternary ostracode assemblages from the Gulf of Alaska, Part 1—Families Cytherellidae, Bairdiidae, Eucytheridae, Krithidae, Cushmani- deidae: US. Geological Survey Professional Paper 1510, 43 p. 1993, Systematic paleontology of Quaternary ostracode assemblages from the Gulf of Alaska, Part 2—Fami1ies Trachyleberididae, Hemicytheridae, Loxoconchidae, Para- cytherideidae: US. Geological Survey Professional Paper 153 1, 82 p. Correge, T., Ayress, M.A., and Drapula, V., 1993, On Swain- ocythere nansem' (Joy and Clark): Stereo-Atlas of Ostracod Shells, V. 19, no. 25, p. 107—110. Cronin, T.M., 1981, Paleoclimatic implications of late Pleistocene marine ostracodes from the St. Lawrence Lowlands: Micropa- leontology, v. 27, no. 4, p. 384—418. 1988, Paleozoogeography of postglacial Ostracoda from Northeastern North America, in Gadd, N.R., ed., The Late Quaternary development of the Champlain Sea Basin: Geolog- ical Association of Canada Special Paper 35, p. 125—144. Elofson, 0., 1941, Zur kenntnis der marinen Ostracoden Schwedens, mit besonderer Berucksichtigung des Skagerraks: Zoologiska Bidrag fran Uppsala, v. 19, p. 215—534. Hanai, T., 1957, Studies on the Ostracoda from Japan; 3. Subfami— lies Cytherurinae, G.W. Mueller (Emend. G.O. Sars, 1925) and Cytheropterinae N. Subfam.: Journal of the Faculty of Science, University of Tokyo, Section 2, v. 11, pt. 1, p. 11—36. 1959a, Studies on the Ostracoda from Japan; 5. Family Cytherinae Dana, 1852 (emend.): Journal of the Faculty of Sci- ence, University of Tokyo, Section 2, V. 11, pt. 4, p. 409—418. 1959b, Studies on the Ostracoda from Japan; Historical Review with bibliographic index of Japanese Ostracoda: Journal of the Faculty of Science, University of Tokyo, Sec- tion 2, v. 11, pt. 4, p. 419—439. 1961, Studies on the Ostracoda from Japan—Hingement: Journal of the Faculty of Science, University of Tokyo, Section 2, V. 13, pt. 2, p. 345—377. Ishizaki, K., 1968, Ostracodes from Uranouchi Bay, Kochi Prefec- ture, Japan: Science Reports of the Tohoku University, Second Series (Geology), v. 40, no. 1, p. 1—45. 1981, Ostracoda from the East China Sea: Science Reports of the Tohoku University, Second Series (Geology), v. 51, nos. 1—2, p. 37—65. Ishizaki, K., and Gunther, F.J., 1974, Ostracoda of the Family Cytheruridae from the Gulf of Panama: Science Reports of the Tohoku University, Series 2 (Geology), V. 45, no. 1, p. 1—50. Ishizaki, K., and Matoba, Y., 1985, Akita (Early Pleistocene cold, shallow water Ostracoda): Guidebook Excursions, Excursion 5, 9th International Symposium on Ostracoda, Shizuoka Uni— versity, p. 1—12. Kajiyama, E., 1913, The Ostracoda of Misaka, Part 3: Zoological Magazine of Japan (Dobutsugaku-zasshi), v. 25, p. 1—16 [in Japanese]. Lev, O.M., 1972, Bionomicheskiye i paleogeograficheskiye uslov— iya morskikh neogen—chetvertichnykh basseynov severa SSSR po fauna ostrakod, in N oveyshaya mineral’nykh resursov: Len- ingrad, Nauchno Issledovatel’skiy, Institut Geologii Arktiki, Trudy, p. 15—20. Mueller, G.W., 1894, Die Ostracoden des Golfes von Neapel und der angrenzenden Meeres-Abschnitte: Fauna und Flora des Golfes von Neapel, V. 21, p. 1—404. Mueller, OF, 1785, Entomostraca seu Insecta Testacea, Quae in aquis Daniae et Norvegiae Reperit, Descripsit et Iconibus Illustravit: Lipsiae et Havniae, p. 1—135. Neale, J .W., and Howe, H.V., 1973, New cold water Recent and Pleistocene species of the ostracod genus Cytheropteron: Crus— taceana, v. 25, no. 3, p. 237—244. 1975, The marine Ostracoda of Russian harbor, Novaya Zemlya and other high latitude faunas, in Swain, F.M., ed., Biol- ogy and paleobiology of Ostracoda: Bulletins of American Paleontology, V. 65, no. 282, p. 381-431. Norman, A.M., 1865, Report on the Crustacea of the deep sea dredg- ing on the coasts of Northumberland and Durham: Transactions of the Natural History Society of Northumberland, Durham and Newcastle-upon-Tyne, v. 1, no. 1, p. 12—29. Okubo, Y., 1980, Recent marine Ostracoda in the Inland Sea, J apan—15 ; Six species of the Subfamily Cytherurinae Mueller, 1894, in the Inland Sea, Japan (Ostracoda): Publications of the Seto Marine Biological Laboratory, v. 25, no. 1/4, p. 7—26. Sars, GO, 1866, Oversigt af Norges marine Ostracoder: Forhan- dlinger I Videnskabs—Selskabet I Christiania, 130 p. Swain, F.M., 1963, Pleistocene Ostracoda from the Gubik Forma- tion, Arctic Coastal Plain, Alaska: Journal of Paleontology, v. 37, p. 798—834. 1967, Ostracoda from the Gulf of California: Geological Society of America Memoir 101, 139 p. REFERENCES CITED 45 Swain, F.M., and Gilby, J.M., 1974, Marine Holocene Ostracoda from the Pacific coast of North and Central America: Micro- paleontology, V. 20, no. 3, p. 257—352. Tabuki, R., 1986, Plio-Pleistocene Ostracoda from the Tsugaru Basin, North Honshu, Japan: Bulletin of College of Education, University of the Ryukyus, No. 29, pt. 2, p. 27—160. Valentine, RC, 1976, Zoogeography of Holocene Ostracoda off western North America and paleoclimatic implications: US. Geological Survey Professional Paper 916, 47 p. Wagner, C.W., 1957, Sur les Ostracodes du Quatemaire Recent des Pays—Bas et leur utilisation dans 1’etude geologique des depots Holocene: S’Gravenhage, Mouton and C0,, 259 p. Wang, P.-X., Zhang, J., Zhao, Q.-H., Min, Q., Bian, Y., Zheng, L., Cheng, X., and Chen, R., 1988, Foraminifera and Ostracoda in bottom sediments of the East China Sea: Beijing, Ocean Press, 438 p. Published in the Central Region, Denver, Colorado Manuscript approved for publication December 27, 1993 Edited by Lorna Carter Graphics prepared by Gayle M. Dumonceaux Photocomposition by Carol A. Quesenberry Whatley, R., Chadwick, J ., Coxill, D., and Toy, N., 1988, The Ostra- cod Family Cytheruridae from the Antarctic and south-west Atlantic: Revista Espanola de Micropaleontologia, v. 20, no. 2, p. 171—203. Whatley, RC, and Masson, D.G., 1979, The ostracod genus Cytheropteron from the Quaternary and Recent of Great Britain: Revista Espanola de Micropaleontologia, v. 11, no. 2, p. 223—277. Yajima, M., 1982, Late Pleistocene Ostracoda from the Boso Pen- insula, central Japan, in Hanai, T., ed., Studies on Japanese Ostracoda: Bulletin, University Museum, University of Tokyo, v.20, p. 141—227. 1988, Preliminary notes on the Japanese Miocene Ostracoda, in Hanai, T., Ikeya, N., and Ishizaki, K., eds., Evolutionary biol- ogy of Ostracoda: Proceedings of the Ninth International Sym- posium on Ostracoda, Kodansha Ltd., Tokyo, Japan, p. 1073—1085. PLATES 1—23 Contact photographs of the plates in this report are available, at cost, from US. Geological Survey Library, Denver Federal Center, Denver, CO 80225 Figure l. PLATE 1 [All figures are camera lucida drawings] Cytherura sp. H (p. 5). Exterior left valve, length 0.44 mm, height 0.20 mm. USNM 408412. Locality EGAL-75-KC-157. Cythemra burroughsensis n. sp. (p. 2). Exterior left valve, length 0.43 mm, height 0.23 mm. USNM 408413, holotype. Locality EGAL-75-KC-202. Cytherura sp. J (p. 5). Exterior left valve, female, length 0.54 mm, height 0.28 mm. USNM 408416. Locality EGAL—75-KC-69. Semicytherura tauronae n. sp. (p. 14). Exterior right valve, female, length 0.58 mm, height 0.33 mm. USNM 408419, holotype. Locality EGAL-75-KC—144U. Cytherura sp. G (p. 4). Exterior left valve, female, length 0.53 mm, height 0.30 mm. USNM 408418. Locality EGAL-75-KC-39. Cytherura wachusettensis n. sp. (p. 4). Exterior right valve, male, length 0.53 mm, height 0.25 mm. USNM 408422, holotype. Locality EGAL-75-KC-1 l. Palmoconcha kmusei Brouwers, 1993 (p. 43). Exterior left valve, female, length 0.36 mm, height 0.23 mm. USNM 408423. Locality EGAL—75-KC-421. Eucytherura ishizakii n. Sp. (p. 6). Exterior left valve, female, length 0.40 mm, height 0.28 mm. USNM 408431, holotype. Locality EGAL-75-KC-284. U.S‘ GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 1 e. n / ”MT \ \ z ., ..,, I, .3) “‘1’” a 0 —— U.) u T“ . a” CYTHERURA, SEMICYTHERURA, PALMOCONCHA, EUCYTHERURA PLATE 2 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 1—2. 5—7, 9—10, 13; bar scale equals 10 micrometers for figs. 3, 4, 8, 11, 12, 14] Figures 14. Cytherura burroughsensis n. sp. (p. 2). 1. 2. 3. 4. Exterior left valve. USNM 408414, paratype. Locality EGAL-75—KC-6. Exterior right valve. USNM 408415, paratype. Locality EGAL-75-KC-6. Close—up view of secondary ornament. USNM 408414. Close-up View of secondary ornament. USNM 408415. 6. Semicytherura miurensis (Hanai, 1957) (p. 12). Exterior left valve. USNM 408417. 5, 7, 8. Semicythemra tauronae n. sp. (p. 14). 5. 7. 8. Interior left valve. USNM 408420, paratype. Locality EGAL—75-KC-144U. Exterior right valve. USNM 408421, paratype. Locality EGAL-75-KC-144U. Close-up view of ornament, normal pore. USNM 408421. 9—14. Eucytherura hazeli n. sp. (p. 5). 9. 10. 11. 12. 13. 14. Exterior left valve. USNM 408427, holotype. Locality DC2-80—EG—l95. Exterior right valve. USNM 408428, paratype. Locality DC2-80-EG- 195. Close-up view of ornament, normal pores. USNM 408429. Close—up view of ornament. USNM 408427. Interior right valve. USNM 408429, paratype. Locality DC2-80—EG-195. Close-up view of central muscle-scar field. USNM 408429. US, GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 2 CYTHERURA, SEMICYTHERURA, EUCYTHERURA Figure 1. 2, 3. 5, 6. 7, 8. PLATE 3 [All figures are camera lucida drawings] Eucythemra ishizakii n. sp. (p. 6). Exterior left valve, male, length 0.41 mm, height 0.26 mm. USNM 408432, paratype. Locality EGAL-75—KC-284. Hemicytherum dageletensis n. sp. (p. 7). 2. Exterior left valve, length 0.40 mm, height 0.24 mm. USNM 408438, holotype. Locality DC2-80-EG-195. 3. Exterior right valve, length 0.41 mm, height 0.26 mm. USNM 408439, paratype. Locality DC2-80-EG—195. Hemicythemra lemesuriensis n. sp. (p. 8). Exterior left valve, length 0.35 mm, height 0.20 mm. USNM 408442, holotype. Locality DC2-80—EG- 195. Hemicytherura sitakadayensis n. sp. (p. 10). 5. Exterior left valve, length 0.46 mm, height 0.23 mm. USNM 408445, holotype. Locality DC2-80-EG-l95. 6. Exterior right valve, length 0.47 mm, height 0.27 mm. USNM 408446, paratype. Locality DC2—80-EG-195. Semicytherura sp. E (p. 14). 7. Exterior left valve, length 0.35 mm, height 0.19 mm. USNM 408458. Locality EGAL-75—KC-l 1. 8. Exterior right valve, length 0.35 mm, height 0.20 mm. USNM 408459. Locality EGAL-75-KC—1 1. U‘S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 3 EUCYTHERURA, HEMICYTHERURA, SEMICYTHERURA PLATE 4 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 1—2, 4, 7—8, 10—11, 13; bar scale equals 10 micrometers for figs. 6, 9, 12, 14—15; bar scale equals l micrometer for figs. 3, 5] Figures 1—5. Palmoconcha krausei Brouwers, 1993 (p. 43). 1. Exterior left valve. USNM 408424. Locality EGAL-75-KC—17. 2. Exterior right valve. USNM 408425. Locality DC2-80-EG—195. 3. Close-up view of normal pore. USNM 408424. Locality EGAL-75-KC- 17. 4. Interior right valve. USNM 408426. Locality DC2—80-EG—195. 5. Close—up view of pore. USNM 408425. 6—13. Eucytherura ishizakii n. sp. (p. 6). 6. Close-up view of ornament. USNM 408433. 7. Exterior left valve. USNM 408434, paratype. Locality EGAL-75-KC-268. 8. Exterior right valve. USNM 408433, paratype. Locality EGAL—75-KC-268. 9. Close-up view of normal pore, seta. USNM 408433. 10. Exterior right valve. USNM 408435, paratype. Locality EGAL-75—KC-268. 11. Interior left valve. USNM 408436, paratype. Locality EGAL-75-KC-268. 12. Close-up view of ornament, normal pores with seta. USNM 408435. 13. Interior right valve. USNM 408437, paratype. Locality EGAL-75-KC-268. 14—15. Eucytherura hazeli n. sp. (p. 5). 14. Central muscle-scar field. USNM 408429, paratype. Locality DC2-80-EG-195. 15. Close-up View of ornament. USNM 408430, paratype. Locality DC2—80-EG-195. U‘S, GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 4 PALMOCONCHA, E UC YTHERURA PLATE 5 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 1—2, 4—5, 7—8, 10—11, 13—14, 16, 18; bar scale equals 10 micrometers for figs. 3, 6, 9, 12, 15, 17] Figures 1—3. Hemicytherura dageletensis n. sp. (p. 7). 1. Exterior left valve. USN M 408440, paratype. Locality DC2-80—EG-195. 2. Exterior right valve. USNM 408441 , paratype. Locality DC2-80-EG-195. 3. Close—up View of ornament, pore. USNM 408440. 4—6. Hemicytherura lemesuriensis n. sp. (p. 8). 4. Exterior right valve, female. USNM 408443, paratype. Locality DC2-80-EG-195. 5. Interior left valve, female. USN M 408444, paratype. Locality DC2-80-EG-195. 6. Close—up view of central muscle-scar field. USNM 408444. 7—14. Hemicytherura sizakadayensis n. sp. (p. 10). 7. Exterior left valve, female. USNM 408447, paratype. Locality DC2—80—EG- 195. 8. Exterior right valve, female. USNM 408448, paratype. Locality DC2-80-EG-195. 9. Close-up view of ornament, pores. USNM 408449. 10. Exterior left valve, male. USNM 408449, paratype. Locality DC2—80—EG-195. 11. Exterior right valve, male. USNM 408450, paratype. Locality DC2-80—EG—l95. 12. Close—up view of central muscle-scar field. USNM 408451. 13. Interior right valve, female. USNM 408452, paratype. Locality DC2-80-EG-l95. 14. Interior left valve, male. USNM 408451, paratype. Locality DC2—80—EG- 195. 15—18. Semicytherura balrogi n. sp. (p. 11). 15. Close-up view of ornament, pores. USNM 408455. 16. Exterior left valve. USN M 408456, paratype. Locality DC2-80—EG-195. 17. Close-up view of ornament, pores. USNM 408456. 18. Exterior left valve. USNM 408455, paratype. Locality DC2-80-EG-195. US‘ GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 5 HEMICYTHERURA, SEMICYTHERURA Figures 1, 2. 3, 4. 7, 8. PLATE 6 [All figures are camera lucida drawings] Semicytherura balrogi n. sp. (p. 11). 1. Exterior left valve, female, length 0.35 mm, height 0.20 mm. USNM 408453, holotype. Locality DC2—80—EG- 195. 2. Exterior right valve, female, length 0.35 mm, height 0.20 mm. USNM 408454, paratype. Locality DC2~80-EG-195. Semicytherura henryi n. sp. (p. 12). 3. Exterior left valve, length 0.36 mm, height 0.18 mm. USNM 408460, holotype. Locality EGAL—75-KC-18. 4. Exterior right valve, length 0.38 mm, height 0.18 mm. USNM 408461, paratype. Locality EGAL-75-KC—18. Semicytherura skagwayensis n. sp. (p. 13). Exterior left valve, length 0.65 mm, height 0.32 mm. USNM 408464, holotype. Locality DC2-80—EG-195. Cytherura sp. I (p. 5). Exterior left valve, female, length 0.41 mm, height 0.25 mm. USNM 408469. Locality G4. Semicytherura sp. F (p. 14). 7. Exterior left valve, length 0.51 mm, height 0.27 mm. USNM 408470. Locality EGAL-75-KC— 1 1. 8. Exterior right valve, length 0.51 mm, height 0.26 mm. USNM 408471. Locality EGAL-75-KC-11. PROFESSIONAL PAPER 1544 PIATE 6 US. GEOLOGICAL SURVEY SEMICYTHERURA, CYTHERURA PLATE 7 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 1, 4—5, 7, 9—1 1, 13—15, 17; bar scale equals 10 micrometers for figs. 2—3, 6. 8, 12; bar scale equals 1 micrometer for figs. 16, 18] Figures 1—3, 6. Semicytherura balrogi n. sp. (p. 11). 1. Exterior right valve. USNM 408457, paratype. Locality DC2-80—EG-195. 2. Close-up view of ornament. USNM 408457. 3. Close-up view of ornament. USNM 408457. 6. Close—up view of ornament. USNM 408457. 4—5, 7—8. Semicytherura henryi n. sp. (p. 12). 4. Exterior left valve. USNM 408462, paratype. Locality EGAL-75-KC-4. 5. Exterior right valve. USNM 408463, paratype. Locality EGAL—75-KC-4. 7. Close—up View of posterior ornament. USNM 408462. 8. Close—up View of ornament. USNM 408463. 9—16. Semicytherura skagwayensis n. sp. (p. 13). 9. Exterior left valve. USNM 408465, paratype. Locality DC2-80—EG—195. 10. Exterior left valve. USNM 408466, paratype. Locality DC2—80—EG-195. 11. Exterior right valve. USNM 408467, paratype. Locality DC2-80-EG- 195. 12. Close-up view of pore. USNM 408467. 13. Interior right valve. USNM 408468, paratype. Locality DC2-80—EG-195. 14. Close—up View of right valve hingement. USNM 408468. 15. Close—up view of posterior inner lamella. USNM 408468. 16. Close-up view of pore. USNM 408465. 17—18. Semicytherura sp. F (p. 14). 17. Exterior right valve. USNM 408472, paratype. Locality EGAL—75-KC- 1 1. 18. Close-up view of pore. USNM 408472. US. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 7 SEMICYTHERURA PLATE 8 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 1—2, 4, 7—8, 10, 13—15; bar scale equals 10 micrometers for figs. 3, 5—6, 9, 11—12] Figures 1—6. Cytheropteron dimlingtonensis Neale and Howe, 1973 (p. 19). 1. Exterior left valve. USNM 408474. Locality EGAL-75-KC-123. Exterior right valve. USNM 408475. Locality EGAL-75—KC-123. Close—up View of simple pore. USNM 408474. Interior left valve. USNM 408476. Locality EGAL—75-KC-320. Central muscle-scar field. USNM 408476. 6. Close-up View of pore with seta. USNM 408475. 7—1 1. Cytheropteron brokenoarensis n. sp. (p. 15). 7. Exterior left valve. USNM 408478, paratype. Locality EGAL-75—KC-52A. ' 8. Exterior right valve. USNM 408479, paratype. Locality EGAL-75-KC-52A. 9. Close-up view of ornament pits, simple pores with setae. USNM 408478. 10. Interior left valve. USNM 408480, paratype. Locality EGAL—75-KC—52A. 11. Central muscle-scar field. USNM 408480. 12—14. Cytheropteron carolae n. sp. (p. 17). 12. Close-up view of ornament pits, simple pores. USNM 408483. 13. Exterior right valve. USNM 408483, paratype. Locality EGAL-75-KC-52A. 14. Interior right valve. USNM 408484, paratype. Locality EGAL-75—KC-l41. 15. Cyzheropteron yajimai Tabuki, 1986 (p. 39). 15. Exterior left valve. USNM 408487. Locality DC2—80-EG-195. 5"???) 8 E w P 4. A. 5 1 R E m P L A N D S S E F O R P US. GEOLOGICAL SURV Y CYTHEROPTERON Figure 1. 3, 4. 5,6. 7, 8. PLATE 9 [All figures are camera lucida drawings] Cytheropteron dimlingtonensis Neale and Howe, 1973 (p. 19). Exterior left valve, length 0.57 mm, height 0.34 mm. USNM 408473. Locality EGAL-75—KC-127. Cytheropteron brokenoarensis n. sp. (p. 15). Exterior left valve, length 0.52 mm, height 0.32 mm. USNM 408477, holotype. Locality EGAL-75-KC-52A. Cytheropteron carolae n. sp. (p. 17). 3. Exterior right valve, female, length 0.53 mm, height 0.35 mm. USNM 408481, holotype. Locality EGAL-75-KC—68A. 4. Exterior right valve, male, length 0.50 mm, height 0.33 mm. USNM 408482, paratype. Locality EGAL-75—KC-68A. Cytheropteron yajimai Tabuki, 1986 (p. 39). 5. Exterior left valve, length 0.52 mm, height 0.34 mm. USNM 408485. Locality DC2-80-EG-195. 6. Exterior right valve, length 0.58 mm, height 0.35 mm. USNM 408486. Locality DC2-80-EG-195. Cytheropteron chichagofensis n. sp. (p. 18). 7. Exterior left valve, length 0.58 mm, height 0.35 mm. USNM 408495, holotype. Locality DC2—80—EG—67. 8. Exterior right valve, length 0.55 mm, height 0.35 mm. USNM 408496, paratype. Locality DC2—80—EG—67. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 9 C YTHEROPTERON PLATE 10 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 145 7— 8, 11, 14~17; bar scale equals 10 micrometers for figs 6, 9—10, 12— 13] Figures 1 —7, 9—10 Cytheropteron yajimai Tabuki, 1986 (p 39). 1. Exterior right valve. USNM 408488. Locality DC2— 80- EG- 195. 2. Exterior left valve female. USNM 408489. Locality DC2-80-EG-195. 3. Exterior right valve, male. USNM 408490. Locality DC2-80-EG—195. 4. Exterior left valve, male. USNM 408491. Locality DC2—80—EG- 195. 5. Exterior right valve, female. USNM 408492. Locality DC2—80-EG-195. 6. Close-up view of ornament pitting, simple pores with setae. USNM 408489. 7. Interior right valve, female. USNM 408493. Locality DC2—80-EG-195. 9. Close-up view of secondary ornament, simple pores with setae. USNM 408490. 10. Close-up View of simple pores with simple bifurcating setae. USN M 408491. 11—13. Cytheropteron chichagofensis n. sp. (p. 18). 11. Exterior right valve. USNM 408497, paratype. Locality EGAL—75-KC- 141. 12. Close-up view of ornament pits, simple pores with setae. USNM 408497. 13. Close—up View of secondary ornament. USNM 408497. 8, 14—18. Cytheropteron tsugaruense Tabuki, 1986 (p. 37). 8. Close-up view of hinge. USNM 408504. Locality DC2-80-EG-195. 14. Exterior left valve, female. USNM 408500. Locality DC2—80—EG—195. 15. Exterior right valve, female. USNM 408501. Locality DC2-80-EG-195. 16. Exterior left valve, male. USNM 408502. Locality DC2-80-EG-l95. 17. Exterior right valve, male. USNM 408503. Locality DC2-80—EG-195. 18. Close-up View of secondary ornament. USNM 408500. 0 1 E W P 4 4 5 1 R E M P L A N D S S E F O R P U.S. GEOLOGICAL SURVEY CYTHEROPTERON Figures 1, 2. PLATE 11 [All figures are camera lucida drawings] Cytheropteron tsugaruense Tabuki, 1986 (p. 37). 1. Exterior left valve, length 0.49 mm, height 0.31 Locality DC2-80-EG-l95. 2. Exterior right valve, length 0.49 mm, height 0.3 Locality DC2-80—EG- 195. mm. USNM 408498. 0 mm. USNM 408499. Cytheropteron nodosoalatum Neale and Howe, 1973 (p. 32). Exterior right valve, length 0.65 mm, height 0.43 mm. USNM 408505. Locality DC2—80-EG-195. Cytheropteron eremitum Hanai, 1959 (p. 23). Exterior left valve, length 0.48 mm, height 0.26 mm. Locality BFM-78- l. Cytheropteron discoveria n. sp. (p. 20). Exterior left valve, length 0.45 mm, height 0.26 mm. Locality DC2—80-EG- 195. Cytheropteron sp. V (p. 42). Exterior left valve, length 0.39 mm, height 0.25 mm. Locality EGAL—75-KC- l 1. Cytheropteron drybayensis n. sp. (p. 21). Exterior right valve, length 0.55 mm, height 0.38 mm Locality EGAL-75-KC-95. Cytheropteron eicheri n. sp. (p. 22). Exterior right valve, length 0.56 mm, height 030 mm Locality EGAL-75-KC-77. USNM 40851 1. USNM 408516, holotype. USNM 408521. . USNM 408522, holotype. . USNM 408526, holotype. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 1 1 U" 00 on u .2 1": 4, ’ n a x n , om n CYTHEROPTERON PLATE 12 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 1—2, 4—8, 10—1 1, 15-16; bar scale equals 10 micrometers for figs. 3, 9, 12—14, 17] Figure l. Cytheropteron tsugaruense Tabuki, 1986 (p. 37). Interior right valve. USNM 408504. Locality DC2-80-EG-l95. 2—7. Cyzheropteron nodasoalatum Neale and Howe, 1973 (p. 32). 2. 3. 4. 5 6 7. Exterior left valve. USNM 408506. Locality DC2-80-EG—63. Close-up View of ornament, pores. USNM 408506. Exterior left valve. USNM 408507. Locality DC2-80—EG-l95. Exterior right valve. USN M 408508. Locality DC2-80-EG-263. Interior left valve. USNM 408509. Locality DC2-80—EG-l95. Interior right valve. USNM 408510. Locality DC2-80-EG—195. 8—17. Cytheropteron eremitum Hanai, 1959 (p. 23). 8. 9. 10. ll. 12. l3. 14. 15. 16. 17. Exterior right valve, female. USNM 408512. Locality BFM—78-l. Close-up View of ornament, external reflection of central muscle scars. USNM 408512. Exterior left valve. male. USNM 408513. Locality BFM—78-1. Exterior right valve, male. USNM 408514. Locality BFM—78-l. Close-up view of ornament, external reflection of central muscle scars. USNM 4085 l 3. Close-up View of normal pore. USNM 408513. Close-up View of ornament, pore. USNM 408512. Interior left valve, male. USNM 408515. Locality BFM-78—l. Close—up View of hingement. USNM 408515. Close-up View of central muscle scars. USNM 408515. US. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 12 C YTHEROPTERON PLATE 13 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 2, 4—8, 10, 14; bar scale equals 10 micrometers for figs. 3, 9, 11—13, 15] Figures 1—6, 9. Cytheropteron discoveria n. sp. (p. 20). 1. 2. 3. 4. 5. 6. 9 Exterior left valve. USN M 408517, paratype. Locality DC2-80—EG- 195. Exterior right valve. USNM 408518, paratype. Locality DC2-80—EG-195. Close-up view of ornament, pore. USNM 408517. Exterior left valve. USNM 408519, paratype. Locality EGAL-75-KC— 150. Interior right valve. USNM 4085 20, paratype. Locality DC2-80-EG- l 86. Close-up view of hingement. USNM 408520. Close-up View of central muscle scars. USNM 408520. 7—8, 10—15. Cytheropteron drybayensis n. sp. (p. 21). 7. 10. 11. 12. 13. 14. 15. Exterior left valve. USNM 408523, paratype. Locality EGAL-75-KC-128. Exterior right valve. USNM 408524, paratype. Locality DC2—80-EG-186. Interior right valve. USNM 408525, paratype. Locality EGAL—75-KC-128. Close—up view of ornament, pores. USNM 408524. Close—up view of pore. USNM 408524. Close-up view of ala. USNM 408525. Close-up view of hingement. USNM 408525. Close-up view of central muscle scars. USNM 408525. US. GEOLOGICAL SURV PROFESSIONAL PAPER 1544 PLA E 13 CYTHEROPTERON Figure 1. 2, 3. 4,5. PLATE 14 [All figures are camera lucida drawings] Cytheropteron sp. J (p. 2). Exterior left valve, length 0.54 mm, height 0.30 mm. USNM 408529. Locality EGAL—75-KC-421. Cytheropteron haydenensis n. sp. (p. 25). 2. Exterior left valve, length 0.45 mm, height 0.25 mm. USNM 408530, holotype. Locality EGAL-75-KC-46. 3. Exterior right valve, length 0.45 mm, height 0.25 mm. USNM 408531, paratype. Locality EGAL-75-KC-46. Cytheropteron lordi n. sp. (p. 30). 4. Exterior left valve, length 0.35 mm, height 0.20 mm. USNM 408537, holotype. Locality DC2-80-EG—l95. 5. Exterior right valve, length 0.35 mm, height 0.19 mm. USNM 408538, paratype. Locality DC2-80-EG—195. Cytheropteron hopkinsi n. sp. (p. 27). Exterior right valve, length 0.53 mm, height 0.33 mm. USNM 408546, holotype. Locality EGAL-75-KC-1 1. Cytheropteron drybayensis n. sp. (p. 21). Exterior right valve, length 0.55 mm, height 0.35 mm. USNM 408552, holotype. Locality EGAL-75-KC—6. Cyzheropteron champlainum Cronin, 1981 (p. 17). Exterior left valve, length 0.55 mm, height 0.36 mm. USNM 408553. Locality EGAL—75-KC-6. US. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 14 C YTHEROPT ERON PLATE 15 [All figures are scanning electron photomjcrographs. Bar scale equals 100 micrometers for figs. 1—2, 4—5, 7—8, 10, 13—15; bar scale equals 10 micrometers for figs. 3, 6, 9, 11—12] Figures 1—5. Cytheropteron eicheri n. sp. (p. 22). 1. 2. 3. 4. 5 Exterior right valve. USNM 408527, paratype. Locality EGAL—75-KC-30. Close—up view of ala. USNM 408528. Close—up view of pores. USNM 408527. Exterior left valve. USNM 408528, paratype. Locality EGAL—75-KC-30. Close—up View of hingement. USNM 408528. 6—15. Cytheropteron haydenensis n. sp. (p. 25). 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. Close-up view of posterior ornament. USNM 408532. Exterior left valve. USNM 408532, paratype. Locality EGAL-75-KC-46. Exteriorrightvalve. USNM408533, paratype. Locality EGAL—75-KC-46. Close-up view of ornament, pores. USNM 408532. Exterior left valve. USNM 408534, paratype. Locality EGAL—75-KC—46. Close-up view of posterior ornament. USNM 408534. Close-up View of secondary ornament papillae. USNM 408534. Interior right valve. USNM 408535, paratype. Locality EGAL—75-KC—46. Interior left valve. USNM 408536, paratype. Locality EGAL-75-KC—46. Close-up view of hingement. USNM 408535. 5 1 E m P 4 4 5 1 R E M P L A N D $ E F O R P U ‘S‘ GEOLOGICAL SURVEY C YTHEROPTERON PLATE 16 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 1—2, 4—5, 7—8, 10—11, 13, 16—17; bar scale equals 10 micrometers for figs. 3, 6, 9, 12, 14—15, 18] Figures 1—9. Cylheropteron lordi n. sp. (p. 30). l. >°9°>‘9‘ Exterior left valve, female. USNM 408539, paratype. Locality DC2-80-EG-286. Exterior right valve, female. USNM 408540, paratype. Locality DC2-80-EG— 195. Close-up view of pores. USNM 408540. Exterior left valve, male. USNM 408541, paratype. Locality DC2—80—EG-l95. Exterior right valve, male. USNM 408542, paratype. Locality DC2-80-EG—195. Close-up view of hingement. USNM 408543. Interior right valve. USNM 408544, paratype. Locality DC2-80-EG-286. Interior left valve. USNM 408543, paratype. Locality DC2—80-EG-286. Close—up View of central muscle scars. USNM 408545, paratype. Locality DC2-80-EG-195. 10—17. Cytheropteron hopkinsz' n. sp. (p. 27). 10. ll. l2. l3. 14. 15. l6. 17. Exterior left valve, female. USN M 408547, paratype. Locality EGAL-75-KC—5. Exterior right valve, female. USNM 408548, paratype. Locality EGAL—75—KC-263. Close-up view of ornament, pores. USNM 408548. Exterior left valve, male. USNM 408549, paratype. Locality EGAL—75—KC-333. Close—up view of ornament. USNM 408549. Close-up view of secondary ornament and pores. USNM 408547. Interior right valve. USNM 408550, paratype. Locality EGAL-75-KC—333. Close-up view of hingement. USNM 408551, paratype. Locality EGAL-75—KC—6. l8. Cytheropteron champlainum Cronin, 1981 (p. 17). Close-up view of ornament. USNM 408554. Locality EGAL-75-KC-6. U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PIATE 16 CYTHEROPTERON PLATE 17 [All figures are scanning electron photomjcrographs. Bar scale equals 100 micrometers for figs. 1—2, 4—5, 7, 10—1 1, 13—14, 16—17; bar scale equals 10 micrometers for figs. 3, 6, 8—9, 18] Figures 1—6. Cytheropteron champlainum Cronin, 1981 (p. 17). 1. .U‘PPJN 6. Exterior left valve. USNM 408554. Locality EGAL-75-KC-6. Exterior right valve. USNM 408555. Locality EGAL-75-KC-6. Close-up View of ornament, pores. USNM 408554. Exterior left valve. USNM 408556. Locality EGAL-75-KC-6. Interior left valve USNM 408557 Locality EGAL- 75- KC- 6. Close- -up view of central muscle- -scar field. USNM 408557. 7—12. Cytheropteron drybayensisn. sp. (p. 21). 7. 8. 9. 10. 11. 12. Exter1or left valve. USNM408559, paratype. Locality EGAL- 75- KC- 123. Close- -up view of ala. USNM 408559. Close-up View of ornament, pores. USNM 408559. Interior left valve. USNM 408560, paratype. Locality EGAL-75-KC- 106. Close—up view of hingement. USNM 408560. Close-up view of central muscle-scar field. USNM 408560. 13—18. Cyzheropzeronforeszeri n. sp. (p. 24). l3. 14. 15. 16. 17. 18. Exterior left valve, female. USNM 408563, paratype. Locality EGAL- 75— KC— 432. Exterior right valve, female. USNM 408564, paratype. Locality EGAL- 75- KO 432. Close—up View of ala. USNM 408563. Exterior left valve, male. USNM 408565, paratype. Locality EGAL-75-KC-432. Exterior right valve, male. USNM 408566, paratype. Locality EGAL-75-KC-432. Close-up view of pore. USNM 408564. 7 1 E m P 4 4 5 1 R E w“ P L A N D S S E F O R P U .S. GEOLOGICAL SURVEY C YTHEROPTER ON Figure l. 2, 3, 6. 4,5. 7, 8. PLATE 18 [All figures are camera lucida drawings] Cytherapteron drybayensis n. sp. (p. 21). Exterior left valve, length 0.65 mm, height 0.38 mm. USNM 408558, paratype. Locality EGAL-75-KC-124A. Cytheropteronforesteri n. sp. (p. 24). 2. Exterior left valve, female, length 0.51 mm, height 0.30 mm. USNM 408561, holotype. Locality EGAL-75-KC—432. 3. Exterior right valve, male, length 0.54 mm, height 0.30 mm. USNM 408562, paratype. Locality EGAL-75-KC-432. 6. Exterior right valve, length 0.50 mm, height 0.31 mm. USNM 408586, paratype. Locality EGAL-75-KC-117. Cytheropteran suzdalskyi Lev, 1972 (p. 35). 4. Exterior left valve, female, length 0.56 mm, height 0.33 mm. USNM 408579. Locality BFM-78-l. 5. Exterior left valve, male, length 0.53 mm, height 0.29 mm. USNM 408580. Locality BFM-78— 1. Cytheropteron squirei n. Sp. (p. 34). 7. Exterior left valve, female, length 0.45 mm, height 0.25 mm. USNM 408588, holotype. Locality EGAL-75-KC-52A. 8. Exterior left valve, male, length 0.50 mm, height 0.29 mm. USNM 408589, paratype. Locality DC2-80-EG-l95. PROFESSIONAL PAPER 1544 PLATE 18 US GEOLOGICAL SURVEY CYTHEROPTERON PLATE 19 [All figures are scanning electron photoxnicrographs. Bar scale equals 100 micrometers for figs. 1—2. 4, 6—7, 9—14; bar scale equals 10 micrometers for figs. 3, 5, 8] Figures 1—4. Cytheropleronfaresteri n. sp. (p. 24). 1. Interior right valve, female. USNM 408567, paratype. Locality EGAL-75-KC-432. 2. Interior left valve, female. USNM 408568, paratype. Locality EGAL-75—KC-432. 3. Close-up View of central muscle-scar field. USNM 408568. 4. Close-up view of hingement. USNM 408568. 5—7, 9. Cytheropteron lituyaensis n. sp. (p. 28). 5. Close-up View of pore. USNM 408571. 6. Exterior right valve. USNM 408571, holotype. Locality EGAL-75-KC—17. 7. Interior right valve. USNM 408572, paratype. Locality EGAL-75-KC- 17. 9. Close—up View of hingement. USNM 408572. 8, 10—14. Cytheropteron midtimberensis n. sp. (p. 31). 8. Close—up view of pore. USNM 408575. 10. Exterior left valve. USNM 408575, holotype. Locality DC2-80-EG—l95. 11. Exterior right valve. USNM 408576, paratype. Locality DC2-80-EG—195. 12. Exterior left valve. USNM 408577, paratype. Locality DC2-80-EG—195. 13. Interior left valve. USNM 408578, paratype. Locality DC2-80-EG—195. 14. Close-up View of hingement. USNM 408578. US. GEOLOGICAL SUR Y PROFESSIONAL PAPER 1544 PLATE 19 C YTHEROPTERON PLATE 20 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 1—2, 4—5, 7—8, 10, 13~14, 16—17; bar scale equals 10 micrometers for figs. 3, 6, 9, 11] Figures 1—9. Cytheropteron suzdalskyi Lev, 1972 (p. 35). 1 Exterior left valve female USNM 408581. Locality BFM— 78— 1. Exterior right valve, female. USNM 408582. Locality BFM— 78— 1. Close-up View of secondary ornament, pores. USNM 408582. Exterior left valve, male. USNM 408583. Locality BFM-78-l. Exterior right valve, male. USNM 408584. Locality BFM-78-1. Close-up view of secondary ornament, pores. USNM 408584. Interior left valve. USNM 4085 85. Locality BFM-78-1. Close— —up View of hingement. USNM 408585. 9. Close— up View of central muscle- scar field. USNM 408585. 10—1 1. Cytheropteron foresteri n. sp. (p. 24). 10. Exterior left valve. USNM 408587, paratype. Locality DC2—80—EG- 195. 11. Close-up View of normal pores. USNM 408587. 12—18. Cytheropleron squirei 1'1. sp. (p. 34). 12. Close—up View of normal pores. USNM 408590. 13. Exterior left valve, female. USNM 408591, paratype. Locality EGAL-75-KC-32. 14. Exterior right valve, female. USNM 408592, paratype. Locality DC2-80—EG- 195. 15. Close-up View of ornament, surface boring. USNM 408593. 16. Exterior left valve, male. USNM 408594, paratype. Locality DC2-80—EG— 195. 17. Exterior right valve, male. USNM 408590, paratype. Locality DC2—80—EG- 1 95. 18. Close—up View of ornament. USNM 408590. POFP‘P‘PWN. 0 2 E W P 4 4 5 1 R E M P L A N D S S E F O R P U .S. GEOLOGICAL SURVEY C YTHEROPTERON Figure 1. PLATE 21 [All figures are camera lucida drawings] Cytheropteron tarrensis n. sp. (p. 36). Exterior left valve, length 0.54 mm, height 0.33 mm. USNM 408597, holotype. Locality EGAL-75-KC-6. Cytheropteron elaem' Cronin, 1988 (p. 23). Exterior left valve, length 0.43 mm, height 0.28 mm. USNM 408602. Locality EGAL-75-KC- 159. Cytheropteron vernritchiensis n. sp. (p. 38). Exterior right valve, length 0.50 mm, height 033 mm. USNM 408605, holotype. Locality EGAL-75-KC-204. Cytheropteron yakutatensis n. sp. (p. 40). Exterior right valve, length 0.58 mm, height 0.35 mm. USNM 408610, holotype. Locality EGAL—75-KC—204. Swainocythere chejudoensis Ishizaki, 1981 (p. 42). Exterior left valve, length 0.28 mm, height 0.15 mm. USNM 408615. Locality EGAL-75-KC-154. U.S, GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 21 (>01) 0 w 0 \ ~ 0 ‘5’ n u " o “ “ . 3 u I) u o 0 / ‘ a a 0 “o 0‘ " \ " u , .1 , u / / , . 0 on / / ”u 0 l / / / / " CYTHEROPTERON, SWAINOCYTHERE PLATE 22 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 1—2, 4—5, 7—8, 10—1 1, 14—15; bar scale equals 10 micrometers for figs. 3, 6, 9, 12; bar scale equals 1 micrometer for fig. 13] Figures 1—3. Cytheropteron squirei n. sp. (p. 34). 1. Interior right valve. USNM 408595, paratype. Locality DC2-80-EG—195. 2. Interior left valve. USNM 408596, paratype. Locality DC2—80-EG-195. 3. Close-up view of central muscle scars. USNM 408596. 4—10. Cytheropteron tarrensis n. sp. (p. 36). 4. Exterior left valve. USNM 408598, paratype. Locality EGAL-75-KC-6. Exterior right valve. USNM 408599, paratype. Locality EGAL-75-KC—6. Close-up view of ornament, pores. USNM 408599. Exterior left valve. USNM 408600, paratype. Locality EGAL-75-KC-6. Interior left valve. USNM 408601, paratype. Locality EGAL—75—KC-6. 9. Close-up view of central muscle—scar field. USNM 408601. 10. Close-up view of hingement. USNM 408601. 11—13. Cytheropteron elaem' Cronin, 1988 (p. 23). 11. Exterior left valve. USNM 408603. Locality EGAL-75—KC-55. 12. Close-up view of ornament. USNM 408603. 13. Close-up view of normal pore. USNM 408603. 14—15. Cytheropteron vernritchiensis n. sp. (p. 38). 14. Exterior left valve. USNM 408606, paratype. Locality EGAL-75-KC-263. 15. Exterior right valve. USNM 408607, paratype. Locality EGAL-75-KC-263. 53°89)?" US. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 22 CYTHEROPTERON PLATE 23 [All figures are scanning electron photomicrographs. Bar scale equals 100 micrometers for figs. 1, 4—5, 7—8, 10—1 1, 14; bar scale equals 10 micrometers for figs. 2—3, 9, 12—13; bar scale equals 1 micrometer for fig. 15] Figures 1—6. Cytheropteron vernritchiensis n. sp. (p. 38). 1. Exterior of left valve. USNM 408608, paratype. Locality EGAL—75-KC-30. 2. Close-up view of ornament and pores. USNM 408606. 3. Close—up view of secondary ornament and pores. USNM 408607. 4. Interior of left valve. USNM 408609, paratype. Locality EGAL-75-KC- 141. 5. Close-up View of hingement. USNM 408609. 6. Close-up view of central muscle-scar field. USNM 408609. 7—13. Cytheropteron yakutazensis n. sp. (p. 40). 7. Exterior of left valve. USNM 408611, paratype. Locality DC2—80-EG— 195. 8. Exterior of right valve. USNM 408612, paratype. Locality EGAL-75—KC-32. 9. Close—up view of ornament and pores. USNM 408611. 10. Interior of left valve. USN M 408613, paratype. Locality DC2-80—EG-195. 11. Close-up view of hingement. USNM 408614, paratype. Locality DC2—80—EG-195. 12. Close-up view of surface borings. USNM 408611. 13. Close-up view of central muscle-scar field. 14—15. Swainocythere chejudoensis Ishizaki, 1981 (p. 42). 14. Exterior of left valve. USNM 408616. Locality EGAL—75-KC-105. 15. Close-up view of normal pore. USNM 408616. US. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1544 PLATE 23 C YTHEROPTERON, SWAINOCYTHERE a5 75 P6 PROFESSIONAL PAPER 1544 TABLES 1 AND 2 US. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY TABLE 1.—Latitude, longitude, and water depth of samples TABLE 2.—Occurrence of ostracode species in the samples considered in this report. considered in this report. Sample Latitude (°N.) Longitude (°W.) Water depth EGAL-75-KC Number (meters) EGAL-75-KC 2 22 9303031 232323233 2 2 2 32 25 41 46 53 54 55 58 59 8 69 7O 71 72 73 242 27 323 156111718192 C th erura H the h a s C therura s C therura H Crulse EGAL-75-KC h a u 2 herura s J C therura s G J G 1 59° 39.3' 147° 40.1' unknown h 5 59°36.5' 147° 32.8‘ unknown c 9""3 “Chuse 9" S c ""3 "3° "5" e" s 6 59° 32.3‘ 147° 21.1' 143 Euc therura S - B Euc therura s . B 11 59° 55.9' 147° 25.4' 49 Euc therura hazeli Euc therura hazeli 17 59° 38.1' 146° 43.5' 97 h ura ish akii h ura ishizakii 18 590 335. 146°32.4' “3 emic h ra da ele Iensis e {c th ra da eIetIens:s 19 590 31.8’ 146° 51.0’ 113 Hemic h ura emesu :en 5 Hem1c herura Iemesu :en 20 59°28.5' 146° 41.8' 88 emi h u a S ak en 5 '"i h ’8 5 “3°" 5 24 60° 01.2' 147° 15.0' 143 mi i s emi m n 26 59° 56.6' 147° 06.1’ 205 emic therura balro ,- emic therura balro i ' ' h s E 27 59°53.8' 146°59.2' 163 emI:c therura s EI emIrc t erura . 32 590 28.7’ 146°29.1' 53 Sem:c h a henr : Semrc h r a henr : 39 59028.0' 145°59.7' 148 emic h ra r n e emic h a a n e 41 60° 09.1’ 1470 07.2’ 212 emic therura ska wa ensis emic herura ska wa ensis 46 60°00.0‘ 146° 45.5' 126 emic henna s , H emic h u a s . H - m'c u a s F 52A 59°59.0' 146° 27.5' 71 m "’a s I:- . e n, r ' ' 53 60° 07]. 146° 52.8’ 156 ther eron d mlln tonensm t ero or n d mIIn tonens:s 54 60°06.1' 146°49.4’ 112 h e n k noa en h e " k "03 e" 55 60°14.5' 146° 50.6' 220 to n a o! e teron 3 ol e 58 60°13.8' 146° 44.3' 221 c thero teron a imai C thero teron a imai h' h h e n chich of ns s 59B 60°11.8’ 146° 41.5' 183 e " ° '° °f "8 s e 63B 60°01.8' 146° 14.6' 64 " a e" e a 9" 68A 59° 425' 146°15.0’ 31 h o teron nodosoa C h eron nodosoa a um 69 60° 16.6” 146° 14.6' 49 th 0 ran eremitum C h eron eremitum 70 60°12.6’ 146°15.3’ 108 eron scoveria eron scoveria o h n s V h n s V ;; 2301(5); 12:: (1)33, 84 thero teron dr ba ensis thero teron dr ba ensis 73 60° 10:5. 146° 01:4. 3.2 ro teron eicheri teron eicheri 74 60°09.2’ 146°O1.5' 9o " e 0" 5 J " e "s J 75 60° 07.4’ 146° 02.3' 84 h :7 ha denensis h e n ha d nensis 0 her 9 d her e Z? 230223! 1353?? 22 h e " ho km" n e n o kinsi 78 596515. 146o 00:9. 101 her teron ch inum her teron ch a:nI m 80 59°46.7' 145°59.5' 91 n 8!” mani n auffmam 83 59° 39.0’ 145° 59.5' 91 hero ter n faresteri her eron foresteri ther ter n Iitu aensis h r teron Iitu aensis 84 59° 32.2' 145° 59.5’ 157 . , _ . . . 86 60014.0. 1450 34.5. 48 h eron MIdIIMbereHSIS h eron mldtIMbe’ensIS 87 60° 06.9' 145° 34.4' 126 h or n 51’2" k her eron suzd k 88 59° 59.2' 145° 34.0' 88 eron s S eron s S 90 59° 52.6’ 145° 34.5' 88 th ro teron s uirei thero teron s uirei 91 59°50 5' 145039 6' 97 he” tem" ”wens“ hero teron tarrensis ' ' ‘ h n e aen' 94 60°07.7' 145° 21.0' 97 " °’°" e’ae’I" . I am am I I: . . 95 60° 03.3' 145° 19.8’ 132 yther teron vernr:tch:ens:s ther teron vernr:tch:ens:s 96 59° 59.2 145°19.3 119 there teron akutatensis thero teron akutatensis 97 59° 55-7' 1450195 ‘01 wainoc there che udaensis wainoc there che udaensis 98 59° 52.5' 145° 19.8' 101 104 60° 08.1' 144° 54.9’ 53 105 59° 57.1' 144° 55.4' 183 106 59° 57.0' 144° 57.4' 192 . EGAL-75-KC EGAL-75-KC DC1—79-EG 107 590 46.5' 145° 03.2' 185 74 75 76 77 78 so 83 84 86 87 88 9o 91 94 95 96 97 98 4 34 4 2 42 42 42 1 5 e 7 1o 12 13 17 23 25 28 108 59°44.2' 144°56.2' 192 C therura H c therura H 109 59° 43.4' 144° 52.7' 102 her r u hsen s h 110 59° 41.5' 144° 47.2’ 97 herura s J J 111 59°38.9’ 144°41.0' 148 c therura s G :"was G 112 59°37.6' 144°37.0' 145 C t 9""3 s C "W3 wachuse en s C erura wachuse en s 113 59°34.9' 144°3o.0' 139 Euc therura s - B Euc therura s . B 115 59° 46.0' 144° 47.7' 64 Euc therura hazeli Euc therura hazeli 117 59: 43.0' 144: 38.1' 119 h ura ishizakii h ura ish akii 12g 53°38’144°3:133'6g7 emic th ura da eletensis e ic h ura da eletensis ' ‘ emic h ra Iemesu ien s Hemic h r ra emes iens s 122A 59°55.6’ 1440314 55 em” " '3 s "a" 5 mi :1 ura s ak er: s 123 59° 56.7' 144° 40.2' 210 e i mi n s e mi "S s I 0 r . . 124B 59:57.5 1440432 234 emic therura balro , emic therura balm i 124A 59 57.5 144 43.2 234 emic them”, 8 E , 125 59° 59 8' 1440 44 0' 232 em:c herura s E ' I Semic h ra henr i semic h a h I". i 127 60°02.8' 144°43.5' 21o em“ " a " e emic h ra a n e 128 60° 00.6' 144° 40.0' 227 therura ska W3 enSis emic therura ska wa ensis 0 - o . _ 130 600 07.8 1440395 31 h ura s . H emic h u a s _ H 138 59 38.2' 145 50.4 168 - ",3 s ,.- F 141 60° 06.8’ 146° 14.5‘ 71 . . m c ura s C eron d’m'" tonens:s C ther ter n dmlin tonensis 144u 59°57.3' 146°19.6' 64 " " e" :1 e n noa en 145 59°37.4' 146° 09.0' 101 C ""0" °_’ e_ to n o! 146 59° 35.6’ 145° 54.8' 143 C thero teron a Imal C thero teron a imai 147 59° 34.2' 145° 45.7’ 165 e n chich ofens s ' 149 60°03.2’ 145°34.5' 104 3 en 9 " e " °’"°" °f "3 s n u 8 en 9 150 60°10.4‘ 145° 34.5’ 104 h ro teron nodosoa a um eron nod sea a m 153 60:12.5: 1452270: 137 h o teron eremitum eron eremitum 154 59 51.4 145 28.5 95 e on scoveria e on scoveria 155 59:55.2 145°42.0' 82 ,, ,, s _ v n n s v 157 60 01.4 146°08.5 73 hem teron d, be ensis hero teron d, ba ”sis 158 60° 06.0’ 146° 40.5' 117 “'0" “Che” teron eicheri 159 60°10.2' 146°52.1' 165 h e on s J h e n s J 162 60' 19.2' 146°13.2' 24 h n ha denensis ' 173 60’10.4’ 145°13.6' 24 ,, , d h " ”a “"9"” 174 60‘ 09.6' 145° 06.4' 35 . . be e d h e n ho kms: e n o kinsi 181 60‘ 01.0' 144°24.0' 33 "'9’ “’0" °" ’" '" her teron ch ain m 184 59[ 54.8’ 144° 54.6' 188 auffmani '- 0 I O : . 202 590 31.4I 144° 36.6 187 hero teron forester: thero teron foresteri 204 59 34.8 144 35.8 141 - - . 205 590 37 0' 144° 35 3, 145 ther eron Iltu aens:s ther te n I, u aensis ' ' h eron midtimbe ensis eron midtimb ensis 209 59° 35.1' 144°31.7' 139 ’7 "SUN k n e nsuzd k 210 59: 36.9' 144°3o.5' 146 h eron s S :r eron s s I 0 I . . 211 590 40.1I 1440 284 146 there teron s u:re: thero teron s uirei 212 59 46.4 144 33.1 91 hero teron tarrensis _ o . o . hero teron tarrens:s 215 59 42.9 144 27.0 134 . hero eron elaen: hero teron elaeni 216 59° 42.1' 144°23.0' 152 themp'emn “mmcmens's therapteron vernritchiensis 219 59°36.3’ 144°17.4' 475 1 cm teron akutatensis thero teron akutatensis 221 59° 50.1’ 144° 27.4' 29 wainoc there che udaensis - ' 223 59° 52.4‘ 144° 18.7‘ 51 walnoc there che udaens:s 224 59° 50.0’ 144° 16.0' 64 225 59° 46.2' 144° 11.5' 101 0 . 0 - 14 :32 53°53; 14:“333 11131 15 1‘ 1‘ 12 1:2 23 1; 1: 25127 28 3 38““ 145 4614 14 1 155 57 53 59 52 73 31 2 36 38 41 42 43 44 45 46 47 G4 60 62 63 67 70 73 82 86 94 97 68 70174 233 59°51.6’ 143°5313' 106 C ”WW3 H c therura H 1 the u hsen s ",9 1 246 59: 41.9' 142: 55.8’ 198 herura s J herura s J 247 590 52.2 143020.3' 214 c then,” s G c therura s G 249 59 58.4' 143 23.0' 152 C erura wachuse en is c h a w chu et en s 251 59° 44.5' 142° 54.0' 188 or r a s 256 59°48.2’ 142° 46.2’ 190 5” “'e’m' ‘ ' B 5“ them” 5 ' B Euc therura hazeli Euc therura hazeli 257 59° 57.3' 142° 46.5' 119 h ura ishizakii h ura ishizakii 258 59: 57.5: 142° 41.2: 108 emic th ura da eletensis e ic he ura da ele ensis :2: 230333.123232': :; Hemic he ura emesu en s emic h ura leme u en s 263 59°5o.8' 142° 31.0 95 ””' " ’3 s “a" 5 mi h ura s akaen s 264 59°49 5' 142° 30 0' 134 e i n e i n” n s 266 59°42.5' 142° 34.0' 262 e"”_° “'"u’a ba”° ’ emrIc therura balro : 268 59°40.7' 142°21.6' 174 em": ”WW3 5 E emrc therura s E 282 59° 54.5' 142° 20.0' 82 Semic h a henr i Semic h a henr i 283 59°51.0' 142°14.5' 84 emic h a a n e emic h a a n e emic therura ska wa ensis m'c th 3 ska wa ens's 284 59°50.o' 142°14.2' 86 mic :1 "”3 s . H emgc h°’:’a s H ' 285 59° 47.4' 142° 14.4' 115 , ' 286 59°43.0' 142° 13.1' 157 °”"° "’3 s - F em U a S F 289 59° 53.1' 142° 03.8' 55 0 them er n dmlin 10" "sis c thero teron dmlin tonensis 296 59° 45.5' 141° 43.5' 49 h e n kenoa r: h e n k noa en 0 . o I teron a olae C teron a o! e 297 59032.9 141046.7I 165 c the", ten," 3 imai c them teron almai 307 59 28.9 141 27.8 165 h n ch'ch of us s _ 308 59°25.8' 141°21.1' 201 e ' e e " chm” 0' "5 s 314 59° 28.5' 141° 06.3’ 311 n a en e n a en e 320 59° 36.4' 140° 50.5' 163 hero eron "0d 503 C h r er I: nod oa a m o o the teron eremitum C the eron eremitum 324 590 32.3’ 140014.0' 192 r eron scoveria e on scoveria 3:: 22:22. 122011;. 13; . . .. v . .. v 328 59°4322' 144°33:6' 134 h ’° “5”" ”I” baIens’s c hero teron dr ba ensis 331 59° 56.1' 143° 53.4' 66 teron eiche" c teron eicheri ’7 e n S J C h eron s J 332 59° 54.3’ 143° 53.2’ 73 n he d nensis h I: ha denensis 333 590 47.1' 143° 51.5' 128 e d C h r e d 338 60° 01.0’ 143°09.3' 101 k' . . . 339 60°00.8’ 142°56.6' 102 " e " ° :ner e n 0 “HS! 341 59° 57.7' 143° 04.7’ 137 hero teron Ch In In her teron ch am m uf mani auffmani 344 59: 992: 142° 222: 21° hero 19’0" ’0’951'9’1' C thero teron foresteri 10 22 39 9 11 336 Eggs-3' 111: 3193'; :23 the’ ’°" ”t" “"3” C h e n u aensis 2 2 420 59° 55.1' 141° 32.9' 64 " °’°" ’"id'im‘w’enm :1 e on midtimberensis 421 59° 55.2' 141° 34.4' 59 he er " suzd k n eron suzd k eron s S h teron s S 422 59° 55.8' 141;J 35.6’ 68 thero teron s uirei thero teron s uirei 0 r : 425 590 56.7. 141° 35.1I 59 hero teron tarrensis her IGIOH tarrensis 426 59 56.1 141 33.5 71 h teron elaeni h n elaeni 427 59° 55.5' 141° 32.7' 71 I I I ro ero I I I 428 590 54.7' 1410 30.1' 49 ytheropteron vernr:tch:ens:s yther teron vernr:tch:ensrs thero teron akutatensis thero teron akutatensis 429 59° 55.5’ 141° 30.6‘ 60 wainoc there che udaensis wainoc there che udaensis 430 59° 56.0’ 1410 31 .6’ 59 431 59° 56.5' 141° 33.3’ 59 432 59° 57.2' 141'J 31 .6' 68 433 59°57.5' 141°30.8’ 68 EGAL-75-KC _ _ 434 59° 57.1' 141° 29.6' 68 DC2 8° EG 74 18118 0 2 1 21 21 21 21 21 22 22 24 22 22 22 23 2 4 251 56 25 258 177 831 8 Crulse DC1'79-EG C therura H c therura H the u a r the u hsen s 1 59° 05.0' 138° 39.9‘ 77 h a s J C herura s J 5 58°152.1' 138°58.6‘ 205 C therura S G c therura s G 6 58° 46.8’ 138959.7' 220 C herura wachuset er: s C erura wachuse en s 7 58:48.2: 1392079: 188 Euc therura s . B Euc therura s . B 10 58 44.9 139 19.1 183 Euc therura haze“- Euc therura haze". 12 58°39.0’ 139°22.3' 251 _ " ”’a ”h’zak“ . E h "'3 is" 3k" 13 58° 45.21 138° 38.4' 108 e IC the ura da eletensrs e ic he ura da eletensis 17 58: 26.4' 138° 26.4' 123 Hemic herura emesu ions 3 Hemic he ”,3 lemesu ien 23 58 26.0' 137° 48.3' 167 emic h a s akaen 3 mi h ura s ak er: s 25 58° 13.9’ 138° 01.9' 138 e i ”"- , e m: 28 58°11.2' 137°39.1' 161 em"? "'e’wa ba’” ’ Semic therura balm i 31B 58°18.6' 137° 08.2’ 154 emic therura 5 E emic therura s E 328 58° 10.9' . 137° 19.8' 121 Semic h ru 3 henr i Semic h a he", ,- 36 58°21.7' 137° 00.7' 111 emic h a a n e en". h a a n e 38 58° 20.2’ 137° 02.3' 159 - - emrc therura ska wa ens:s emic therura ska a ensis 41 58°15.7' 137° 00.4' 187 em'c ” ”’ a s ' H emic h ru a s . H 42 58°13.6' 136° 58.9’ 174 6’" u a S F em u a s F :2 23:12.; 13$ 57.9' 185 c ther er :1 dmlin tonensis c the", e, n dmlin to" n s . ’ 13 57.3' 183 e n n ens h e n e a en 45 58°14.6' 136° 47.8’ 119 ,e ,, a o, e te n a o, e 46 58°13.7' 136°50.1' 93 C the” 'e’°" aI'ma' c thero teron a imai 47 58012.6, 136° 532. 133 h e n ch:ch of ns s e n chich of ns s o 0 en e n en e BFM-78-1 60 17.0' 148 21.0' unknown C her teron nodosoa a um h eron nodosoa m C th ro eron eremitum h o ron eremitum Cruise DC1-80—EG e on scoveria e on scoveria h '7 s V h e n s V 60 59°28.5' 139°48.0’ 58 he” ”’0" d’ ”3 ens" hero teron dr ba ensis 62 59° 28.5’ 139° 48.4' 64 teron eicheri teron eicheri 63 59°28.2’ 139°48.9' 62 h er n s J h e, ,, s J 67 59°28.0‘ 139°49.3' 82 n n ha denensis . 70 59°28.9' 139°49.8' 98 " " "a d ”"5” h r r n d h r d 73 59°27.7' 139°5o.2' 104 h e " 0 k "3" n e n ho kinsi 82 59° 28.2’ 139° 48.4' 74 her teron Ch inum her teron ch ain m 86 59° 27.5’ 139° 50.5' 110 n auf mani u mani 0 1 o - , g; :30 3?: 12:50 2310' :8 hero teron forester: hero teron fol-esten' ‘ ' her or n Ii u aensis ther e n u aensis 168 59° 40.1' 141° 21.6‘ 68 h eron midtimberensis h eron mid imb ensis 170 59° 38.1' 141° 22.5' 84 e n suzd k e s d k 174 59°37.2' 141° 23.1' 91 e n s s h "z 0 . o 1 ’° h eron s S 177 59 36.1 141 23.5 102 there teron s uirei _ _ 183 59° 34.4” 141° 25.1' 121 I thero teron s urrel he” "”0" ta”e"s'5 hero teron tarrensis :22 23232-2: 12122:: :2: .. ,., .. 192 590 31:2, 1410 26:8' 150 ther teron vernritchlenIs:s her teron vernritchiensis 195 59°36.5' 14o°19.2' 82 “'9” ‘°’°" ““3""5’3 t ero teron akutatensis wainoc there che udaensis wainoc there che udaensis LOCALITY AND WATER DEPTH OF OSTRACODE SAMPLES, AN) OCCURRENCE OF SPECIES, GULF OF ALASKA By E. M. Brouwers 1994 Depositional Framework and Regional Correlation of Pre—Carboniferous Metacarbonate Rocks of the Snowden Mountain Area, Central Brooks Range, Northern Alaska Cover: Massive carbonate rocks chiefly of the Mathews River unit, Chandalar D—6 quadrangle, central Brooks Range, northern Alaska. The image is a digital enhancement of the photograph (fig. 4) on page 7. Design and layout by Sunne Rinkus, 1994. Depositional Framework and Regional Correlation of Pre-Carboniferous Metacarbonate Rocks of the Snowden Mountain Area, Central Brooks Range, Northern Alaska By J .A. Dumoulin and Anita G. Harris U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1545 Lithofacies, conodont biostratigraphy and biofacies, and depositional environments of pre-Carboniferous metacarbonate rocks, correlation with other sequences across northern Alaska, and paleogeographic and paleotectonic implications UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON Z 1994 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY GORDON P. EATON, Director For sale by U.S. Geological Survey, Information Services Box 25286, Federal Center, Denver, CO 80225 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Published in the Eastern Region, Reston, Va. Manuscript approved for publication August 17, 1993. Library of Congress Cataloging in Publication Data Dumoulin, Julie A. Depositional framework and regional correlation of pre-Carboniferous metacarbonate rocks of the Snowden Mountain area, central Brooks Range, northern Alaska / by J .A. Dumoulin and Anita G. Harris. p. cm.—(U.S. Geological Survey professional paper ; 1545) “Lithofacies, conodont biostratigraphy and biofacies, and depositional environments of pre—Carboniferous metacarbonate rocks, correlation with other sequences across northern Alaska, and paleogeographic and paleotectonic implications.” Includes bibliographical references. Supt. of Docs. no. : I 19.1621545 l. Rocks, Carbonate—Alaska—Snowden Mountain Region. 2. Conodonts— Alaska—Snowden Mountain Region. 3. Stratigraphic correlation. I. Harris, Anita G. II. Title. III. Series. QE471 . 15 .C3D86 1994 552’.58—dc20 93—21361 CIP CONTENTS Abstract ........................................................................................... Acknowledgments .............................................................................. Introduction .......................................................................... ‘ ............ Geologic Setting ................................................................................ Previous Work .................................................................................. Stratigraphic Nomenclature ................................................................... Methods .......................................................................................... Metacarbonate Succession—Cambrian (and older?) to Middle Devonian Metasedimentary Rocks .............................................................. Cambrian Rocks .......................................................................... Lithologies ........................................................................... Age and Biofacies .................................................................. Distribution .......................................................................... Depositional Environment ......................................................... Middle Ordovician Rocks ................................................................. Lithologies ........................................................................... Age and Biofacies .................................................................. Distribution .......................................................................... Depositional Environment ......................................................... Upper Ordovician and Silurian Rocks ................................................ Lithologies ........................................................................... Age and Biofacies .................................................................. Distribution .......................................................................... Depositional Environment ......................................................... Lower and (or) Middle Devonian Rocks ............................................. Metacarbonate Rocks of Uncertain Age .............................................. Wiehl Mountain Area .............................................................. Dillon Mountain Area .............................................................. Snowden Mountain Massif ........................................................ Table Mountain Area .............................................................. Summary of the Metacarbonate Succession in the Snowden Mountain Area ................................................................................ Devonian Metaclastic Rocks .................................................................. Beaucoup Formation ..................................................................... Carbonate Lithologies .............................................................. Age and Biofacies .................................................................. Distribution .......................................................................... Depositional Environment ......................................................... Hunt Fork Shale .......................................................................... Carbonate Lithologies .............................................................. Age and Biofacies .................................................................. Distribution .......................................................................... Depositional Environment ......................................................... Nutirwik Creek Unit ..................................................................... Carbonate Lithologies .............................................................. Age and Biofacies .................................................................. Distribution .......................................................................... Depositional Environment ......................................................... Summary of Devonian Metaclastic Rocks in the Snowden Mountain Area ................................................................................ owWNNr—‘H OOOOQQGQ 8 10 14 14 l4 l6 17 20 21 21 22 23 23 24 25 25 26 28 28 28 30 30 30 31 31 31 31 32 33 33 34 34 34 34 III IV CONTENTS Regional Relationships ......................................................................... 35 Pre—Carboniferous Metacarbonate Successions ...................................... 35 Eastern Baird Mountains Metacarbonate Succession ......................... 37 Proterozoic and (or) Cambrian Rocks ..................................... 37 Lower and Middle Ordovician Rocks ..................................... 39 Upper Ordovician to Devonian(?) Rocks ................................. 40 Comparison of the Snowden Mountain and Eastern Baird Mountains Metacarbonate Successions .............................................. 40 Other Pre-Carboniferous (Meta)sedimentary Successions ................... 42 Western Baird Mountains ................................................... 42 York Mountains ............................................................... 44 Shublik and Sadlerochit Mountains ........................................ 47 Doonerak Window ............................................................ 47 Devonian Siliciclastic Units ............................................................. 48 Devonian Siliciclastic Units in the Baird Mountains ......................... 48 Nakolik River Unit ........................................................... 48 Unit qus ...................................................................... 48 Hunt Fork Shale .............................................................. 49 Comparison of Snowden Mountain and Baird Mountains Devonian Siliciclastic Units .......................................................... 49 Discussion .................................................................................. 50 Comparative Microfacies Analysis .............................................. 51 Paleobiogeography .................................................................. 53 Conclusions ...................................................................................... 57 References Cited ................................................................................ 57 ‘ Appendix ......................................................................................... 62 l PLATES [Plates follow appendix] Ordovician conodonts from the Snowden Creek unit. . Late Ordovician and Silurian conodonts from the Mathews River unit. 3. Latest Givetian and Frasnian conodonts from the Beaucoup Formation, Hunt Fork Shale, and Nutirwik Creek unit. Ny—n FIGURES H Index map showing location of Snowden Mountain study area, northern Alaska ................................. 2 Map showing generalized distribution of geologic units in the Snowden Mountain area ........................ 4 Index map showing geographic names and location of measured sections and lithologic and fossil collections ....................................................................................................................... 5 Photograph showing massive metacarbonate rocks of the Mathews River unit ..................................... 7 Diagram showing lithologic and paleontologic symbols used in this report ......................................... 8 9 0 5”!" Columnar section showing metacarbonate succession in the Snowden Mountain area ............................ Photographs of the Snowden Mountain unit and overlying strata ..................................................... 1 Columnar section showing fossil distribution in the metacarbonate succession in the Snowden Mountain area ............................................................................................................................... 1 1 Photographs of sedimentary features of the Snowden Creek unit ..................................................... 12 10. Photomicrographs of clasts in calcareous turbidite, Snowden Creek unit ............................................ 14 @995”? _~o 11—15. 16. 17. 18. 19. 20. 21. 22. 23. 24—26. 27. 28. 29. 30. [Qt—a CONTENTS Photographs showing— 11. Sedimentary features of the Mathews River unit ................................................................... 12. Sedimentary features and megafossils of the Mathews River unit .............................................. 13. Fossils and sedimentary features of the Mathews River unit .......................... . .......................... 14. Aligned sticklike organic forms in Emsian or Eifelian metalimestone ......................................... 15. Sedimentary features of metacarbonate rocks of uncertain age .................................................. Chart showing hypothetical stratigraphic position of units of uncertain age within the metacarbonate succession in the Snowden Mountain area ................................................................................ Photographs showing features of the Beaucoup Formation ............................................................. Photographs showing sedimentary features of the Hunt Fork Shale .................................................. Schematic columnar sections showing lithofacies, conodonts, and age relations of the Beaucoup Formation, Hunt Fork Shale, and Nutirwik Creek unit ................................................................. Index map of northern Alaska showing distribution of pre-Carboniferous (meta)carbonate rocks .............. Columnar section showing lithofacies and fossil distribution in the metacarbonate succession in the eastern Baird Mountains ...................................................................................................... Photographs showing sedimentary features of meatacarbonate succession in the eastern Baird Mountains Diagram showing correlation of pre-Carboniferous rocks in the Snowden Mountain area and eastern Baird Mountains ...................................................................................................... Columnar sections showing— 24. Lithofacies and conodont distribution, metacarbonate succession in the western Baird Mountains ....... 25. Lithofacies and conodont distribution, carbonate succession in the York Mountains ........................ 26. Lithofacies and fossil distribution, carbonate succession in the Shublik and Sadlerochit Mountains ................................................................................................................. Photographs showing sedimentary features of the Nakolik River unit, western Baird Mountains ............... Chart showing correlation and depositional environments of (meta)carbonate successions in the York, Baird, Snowden, and Shublik and Sadlerochit Mountains .............................................................. Diagram showing schematic reconstruction of pre-Carboniferous carbonate successions in northern Alaska ............................................................................................................................ Diagram showing global plate tectonic reconstruction for part of Late Ordovician time ......................... TABLES Names of fossils shown in figures 8, 19, 21, and 24—26 ............................................................... . Paleobiogeographic affinities of faunas from Cambrian and Ordovician (meta)carbonate successions in northern Alaska ................................................................................................................ METRIC CONVERSION FACTORS For readers who wish to convert from the metric system of units to the inch-pound system, the conversion factors are listed below. Multiply By To obtain Length micrometer (um) 0.0039 inch millimeter (mm) 0.039 inch centimeter (cm) 0.394 inch meter (m) 3.281 foot kilometer (km) 0.621 mile 17 19 20 23 24 27 29 32 36 37 41 43 45 46 49 52 54 57 15 55 Depositional Framework and Regional Correlation of Pre-Carboniferous Metacarbonate Rocks of the Snowden Mountain Area, Central Brooks Range, Northern Alaska By J .A. Dumoulin and Anita G. Harris ABSTRACT A succession of chiefly metacarbonate rocks in the Snowden Mountain area of the central Brooks Range includes strata of Cambrian (and older?) to Devonian age, structurally intercalated with dominantly siliciclastic rocks of Devonian age. Both carbonate and siliciclastic rocks are deformed and metamorphosed to greenschist facies, but locally preserved primary textures and environmentally diagnostic conodont assemblages allow interpretation of depositional environments. Rocks of the Snowden Moun- tain area are the first pre-Carboniferous metacarbonate succession from the central Brooks Range for which detailed sedimentologic and biofacies data are available. Massive metacarbonate rocks at Dillon Mountain may be Cambrian and (or) older in age, contain coated grains and stromatolites, and formed in a peritidal environment. Phyllite and lesser sandy metalimestone (Snowden Moun- tain unit) yield early Middle Cambrian trilobites with Siberian biogeographic affinities and were deposited on an outer shelf or slope. Carbonaceous phyllite, metachert, and metalimestone (Snowden Creek unit) produce cosmopoli- tan, cool—water conodonts of Middle Ordovician (late Aren- igian to early Caradocian?) age. These strata accumulated chiefly in a slope to basinal setting, but the vertical sequence indicates a shallowing-upward depositional regime. Middle Ordovician rocks are succeeded by Upper Ordovician and Silurian dolostone and metalimestone (Mathews River unit) that contain conodonts of Edenian and Maysvillian, Richmondian, Llandoverian and early Wen— lockian, and Wenlockian and Ludlovian ages. Late Ordo- vician conodonts include Siberian and North American faunal elements; Silurian conodonts are chiefly cosmopoli- tan. The Mathews River unit is characterized by shallowing-upward peritidal cycles and was deposited in a range of warm, shallow-water environments; it is locally overlain by Lower and (or) Middle Devonian (Emsian and (or) Eifelian) metalimestone bearing two-hole crinoid columnals. Thrust slices of metacarbonate rocks in the Wiehl Mountain area, the Snowden Mountain massif, and the Table Mountain area retain some primary features similar to those of the Mathews River unit but are less well dated and may be of Ordovician to Devonian age. The dominantly metacarbonate succession is structur- ally juxtaposed with metasiliciclastic rocks of the Beaucoup Formation, Nutirwik Creek unit, and Hunt Fork Shale. These units contain layers and lenses of metalimestone that yield latest Middle and early Late Devonian (latest Givetian and Frasnian) conodonts. Thicker limy layers formed as bioherrnal buildups and ooid or bioclastic shoals; thinner limy layers are tempestites or turbidites derived from shelf or platform carbonate deposits. Metasedimentary rocks of the Snowden Mountain area have some faunal and lithologic similarities to coeval strata in the Baird Mountains (western Brooks Range), the Shub- lik and Sadlerochit Mountains (eastern Brooks Range), and the York Mountains (Seward Peninsula). The chiefly metacarbonate succession correlates particularly well with Ordovician and Silurian strata in the eastern Baird Moun- tains; Devonian siliciclastic units correspond to Middle and Upper Devonian rocks in the Baird Mountains. Available biogeographic and lithologic data from northern Alaska are best explained by postulating that the pre-Carboniferous carbonate successions accumulated on a single continental margin or platform that had faunal exchange with both Siberia and North America, rather than on a series of discrete platforms juxtaposed by later tectonic events. ACKNOWLEDGMENTS We thank our colleagues on the Brooks Range segment of the Trans—Alaska Crustal Transect program for logistical support and useful geologic discussions, particularly Alison 2 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA Area of C figure 1 R \‘, - 0'95 0 100 200 KILOMETERS o c Prudhoe 5 141° W. Figure 1. Location of Snowden Mountain study area in Chandalar, Philip Smith Mountains, and Wiseman quadrangles (l:250,000), northern Alaska. B. Till. We appreciate the careful technical reviews pro- vided by Godfrey S. Nowlan, Geological Survey of Can- ada, and James G. Clough, Division of Geological & Geophysical Surveys, State of Alaska. INTRODUCTION This paper describes pre-Carboniferous metacarbonate rocks that crop out along the Dalton Highway through the central Brooks Range (fig. 1). In this area, bedrock consists largely of intercalated thrust sheets of calcareous and siliceous metasedimentary rocks. Our study concentrates on a succession of chiefly carbonate rocks, which are Cam- brian (and older?) to Devonian in age, and on subordinate limy layers within three Devonian siliciclastic units. The focus of this study is the Snowden Mountain area, about 300 km south of Prudhoe Bay. The area investigated in detail extends from south of Sukakpak Mountain north to Atigun Pass and includes parts of the Chandalar, Philip Smith Mountains, and Wiseman 1:250,000-scale quadran- gles (figs. 1—3). The pre-Carboniferous stratigraphy of northern Alaska is only beginning to be unraveled. Bedrock geology is dominated by a Jurassic to Cretaceous orogenic belt, which extends more than 1,000 km from the Seward Peninsula through the Brooks Range. Outcrops of pre-Carboniferous metacarbonate rocks occur throughout this belt, but their origin and tectonic significance are uncertain. Did these rocks once constitute a single carbonate platform, like that formed by the chiefly Carboniferous Lisbume Group, which has since been tectonically dismembered? Or are they parts of several discrete platforms, derived from disparate continental margins, that have been juxtaposed by later tectonic events? Rocks of the Snowden Mountain area are the first pre-Carboniferous carbonate succession from the central Brooks Range for which detailed sedimentologic and bio- facies data are available, and these data permit comparison with better known lower and middle Paleozoic rocks in the western and eastern Brooks Range and Seward Peninsula. Detailed lithologic and faunal similarities between strata in these areas suggest that, like the Lisbume Group, older carbonate rocks display relative stratigraphic continuity across northern Alaska. GEOLOGIC SETTING During the Jurassic to Cretaceous Brooks Range orog- eny, rocks of the central Brooks Range were complexly folded, thrust faulted, and underwent syntectonic regional metamorphism; contrasting structural levels are now exposed from south to north, the direction of tectonic transport (Moore and others, 1991). Several schemes have been proposed by various authors to describe these contrast— ing levels; bedrock has been divided into belts, terranes and subterranes, and domains and allochthons. These diverse STRATIGRAPHIC NOMENCLATURE 3 approaches all recognize the existence of distinct linear zones within the orogen that are characterized by rocks of contrasting metamorphic grade and structural style. All of the metacarbonate succession and most of the siliciclastic rocks described in this paper occur within a region variously designated as the central belt (Till and others, 1988; Till and Moore, 1991), the Hammond subter- rane of the Arctic Alaska terrane (Moore and others, in press), or the Skajit allochthon (Oldow and others, 1987). Central belt rocks are markedly less deformed and meta- morphosed than the pelitic and calcareous rocks of the schist belt (Coldfoot subterrane) to the south; schist belt _ rocks are penetratively deformed and have undergone high- pressure metamorphism (Till and Moore, 1991). However, central belt rocks are more deformed and metamorphosed than rocks of the Endicott Mountains allochthon (Endicott Mountains subterrane) to the north, and the stratigraphy of central belt rocks is less well understood (Oldow and others, 1987). The precise location and nature of boundaries between the schist belt, central belt, and Endicott Mountains alloch- thon are controversial (Oldow and others, 1991; Moore and others, 1991; Till and Moore, 1991), and the northernmost thrust sheets of Devonian siliciclastic rocks discussed in this paper are considered part of the Endicott Mountains alloch- thon by some authors. These rocks are included here because their lithofacies, conodont faunas, and levels of thermal alteration are similar to those of Devonian silici- clastic rocks within the central belt. All the rocks described in this report have been dismembered by thrust faults and metamorphosed to greenschist facies; they contain cono— donts that have color alteration indices (CAIs) of 5 or higher, indicating that the host rocks reached at least 300°C (Epstein and others, 1977). However, microfossils, mega- fossils, and primary sedimentary textures are locally well preserved; these features allow reconstruction of original stratigraphic relationships and depositional environments and provide a basis for regional correlation. PREVIOUS WORK The geology of much of the central Brooks Range is still relatively poorly known, and pre-Carboniferous car- bonate rocks in this area have received little attention. Reconnaissance geologic mapping and resource assessment of this part of the Brooks Range was initiated by Mertie (1925, 1929); later, more detailed geologic maps of the Chandalar, Wiseman, and Philip Smith Mountains quadran- gles were published by Brosgé and Reiser (1964, 1971), Brosgé and others (1979), and Dillon and others (1986, 1988). Oldow and others (1987) presented a generalized geologic map of the central Brooks Range as well as balanced cross sections along two north-south transects, one of which bisects the‘ Snowden Mountain area. All of these maps include brief lithologic descriptions of the metacar- bonate rocks described in this report. Brosgé and others (1962) described the general Pale- ozoic sequence in the eastern half of the Brooks Range and assigned most metacarbonate rocks in the Snowden Moun- tain area to the Skajit Limestone of Middle(?) and Late Devonian age. Palmer and others (1984) first recognized rocks of early Paleozoic (Cambrian) age in the Snowden Mountain area, and Dillon and others (1987a, 1988) docu— mented the occurrence of rocks of Ordovician and Siluri- an(?) age in this region. The latter two reports summarize lithologic and age data that were available from the Snow- den Mountain area prior to 1986 but contain little specific biostratigraphic or sedimentologic information. The present study combines detailed petrologic data, results of more than 60 productive conodont collections made during the 1989 and 1990 field seasons, and a reassessment of all previous fossil collections available from the study area in order to characterize the sedimentology, stratigraphy, and regional relationships of pre-Carboniferous metacarbonate rocks in the Snowden Mountain region. STRATIGRAPHIC NOMENCLATURE Previous workers assigned most metacarbonate rocks in the Snowden Mountain area to the loosely defined Skajit Limestone and considered these rocks to be of Devonian age on the basis of rare, poorly preserved megafossils (Brosgé and others, 1962). Metasedimentary, chiefly silici- clastic rocks (for example, units Dsg, Dl, Dls, and Ds of Brosgé and Reiser, 1964)1 spatially associated with these massive carbonate bodies were thought to stratigraphically overlie the Skajit Limestone and were also interpreted as Devonian in age. Later publications (Brosgé and others, 1979, and Dillon and others, 1988) referred some fine- grained metaclastic rocks in the Wiseman and Philip Smith Mountains quadrangles to the Upper Devonian Hunt Fork Shale. Dutro and others (1979) proposed a new Upper Devonian stratigraphic unit, the Beaucoup Formation, to encompass intercalated clastic and carbonate rocks in the Philip Smith Mountains, Chandalar, and Arctic quadran- gles; this unit was considered to unconformably overlie the Skajit Limestone and conformably underlie the Hunt Fork Shale. Rocks previously assigned to unnamed units, such as units D1, Dls, and Ds of Brosgé and Reiser (1964) in the Chandalar quadrangle, were reassigned, in part, to the Beaucoup Formation. In the middle 1980’s, conodont and megafossil collec- tions made by field parties of the Alaska State Division of Geological & Geophysical Surveys in the Wiseman and leg, Devonian siltstone and grit; D1, Devonian limestone; Dls, Devonian calcareous and noncalcareous phyllite, grit, and silty limestone; Ds, Devonian slate. 4 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA 150°00' 149°30' 10 KILOMETERS Lfijgj 68000' Snowden Mountain P15 6745' Mountain Grotto Mountain J/ \\ \ \_ AMountain/ I .. ASukak'pak \ / Mountain Pzw ‘ y/ ‘\ my Wiehl / fl/ 4 EXPLANATION [MAP UNITS DISCUSSED IN THIS REPORT] DEVONIAN METACLASTIC ROCKS Dh Hunt Fork Shale (Devonian) Dn Nutirwik Creek unit (Devonian) Db Beaucoup Formation (Devonian) PRE-CARBONIFEFIOUS METACARBONATE SUCCESSION SOm Mathews River unit (Silurian and Ordovician) Os Snowden Creek unit (Ordovician) Pit Metacarbonate rocks of Table Mountain area (Paleozoic) PzW Metacarbonate rocks of Wiehl Mountain (Paleozoic) P28 Metacarbonate rocks of Snowden massif (Paleozoic)--lncludes Snowden Mountain unit PzEd Metacarbonate rocks of Dillon Mountain area (Paleozoic and (or) Proterozoic) OTHER MAP UNITS [PM] Lisburne Group (Pennsylvanian and Mississippian)--|ncludes Lower Mis- sissippian Kekiktuk Conglomerate and Kayak Shale MDk Kanayut Conglomerate (Missis- sippian? and Devonian) Fzmu Metasedimentary rocks, undivided (Paleozoic) lemd Metasedimentary and metavolcanic rocks in Mount Doonerak window :' // A. i / szu (lower Paleozoic) “/ k \ / Z/ 05 ‘9 ‘ ‘ 7. / _ _ _? Contact-Dashed where inferred; ' I W / e. l queried where uncertain Figure 2. Generalized distribution of geologic units in the Snowden Mountain area, based on preliminary compilations (1992) by personnel of the Trans-Alaska Crustal Transect Program; a geologic map of this area was not available for our use. Most contacts of geologic units are thrust faults, and many units are internally imbricated. Map units may include areas underlain by rocks of other units too small to show at the scale of this map. Chandalar quadrangles revealed that at least some of the massive carbonate bodies included in the Skajit Limestone, and some of the associated metaclastic rocks assigned to the Beaucoup Formation or to unnamed Devonian map units by previous workers, are of Silurian and older age. Dillon and others (1987a, 1988) proposed a new stratigraphy to encom- pass these findings. They defined a sequence of unnamed lower Paleozoic map units, including several units of Cambrian(?) and Cambrian(?) to Ordovician(?) age, two Middle Ordovician units (Om, Obpm),2 and an Upper Ordovician and Silurian unit (unit SOmZ; designated as unit 2Om, Ordovician marble; Obpm, Ordovician black phyllite and metalimestone; SOm, Ordovician to Silurian marble. STRATIGRAPHIC NOMENCLATURE 5 150°00' l EXPLANATION Biostratigraphically and (or) lithologically significant locality 0 Locality 4 g. Measured section Auxiliary lossil collection Q Ordovician I Devonian O$$ 10 KILOMETERS (9% 0 5 68°00' 67°43 Grotto Mountain 149°30’ A\‘ ble Mou I tain k J Figure 3. Geographic names and location of measured sections and lithologic and fossil collections in the Snowden Mountain area. See figure 2 for distribution and identification of geologic units; see appendix 1 for geographic coordinates and key faunal components and lithologies for numbered localities. 08111 by Dillon and others, 1987a, 1988). These workers retained the Skajit Limestone, Beaucoup Formation, and Hunt Fork Shale, considered all three units to be of Devonian age, but restricted their geographic extent within the northern Wiseman-Chandalar area. In addition, they proposed a series of new Devonian units, such as the rocks of Whiteface Mountain, which were distinguished on the basis of different proportions of metasedimentary versus metavolcanic rocks. Our work indicates that most of the massive carbonate rocks previously assigned to the Skajit Limestone in the Snowden Mountain region are of pre-Devonian age. How- 6 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA ever, at least some massive carbonate rocks in this area are Devonian in age, and other strata are Silurian or Devonian. Reliable lithologic criteria that allow discrimination of pre-Devonian from Devonian carbonate rocks have not yet been established. Contacts between the massive carbonate rocks and the associated metaclastic rocks are generally faults, but, locally, contacts appear to be gradational and stratigraphic. The various Devonian metaclastic rock units, as presently defined, are also difficult to discriminate in the field (for example, Hunt Fork Shale versus Beaucoup Formation). Our present state of knowledge is sufficient to indicate problems with previously established stratigraphic nomenclature but is not yet adequate to support the defini- tion of a series of new formal unit names. Hence, in this paper, established stratigraphic names are used where they are consistent with our new lithologic and faunal data. Elsewhere, map-unit designations or informal names employed during recent mapping are used, and the relation— ship of these names to the older stratigraphic nomenclature is indicated. METHODS The metacarbonate rocks described in this report were observed and sampled in a series of traverses and partial measured sections east and west of the Dalton Highway; locations of measured sections and key lithologic and fossil collections are shown in figure 3 and described in appendix 1. Petrographic descriptions are based on field studies of lithology and sedimentary structures as well as on exami- nation of about 50 polished slabs and 400 thin sections. Sections were measured using Jacob’s staff, Brunton com- pass, and tape; identification of calcite and dolomite was made on selected samples using the Alizarin Red-S and potassium ferricyanide staining technique of Dickson (1966). Carbonate rocks in which original texture is not obscured by metamorphism, deformation, or diagenesis are classified following Dunham (1962); when descriptive modifiers are employed, they are listed in order of increas- ing abundance. Metalimestone is used to indicate rocks that are partially recrystallized but retain some relict primary textures; marble is used to describe rocks that are totally recrystallized. Biostratigraphy relies largely on conodont faunas from our measured sections and spot samples, but data from previous megafossil collections (particularly cor- als and trilobites) are included where appropriate. Interpre- tations of depositional environments are based on deposi- tional models for carbonate rocks outlined in Wilson (1975); the environmental implications of conodont assem- blages (for example, Sweet and Bergstrom, 1971; Clark, 1984) are also used to constrain our interpretations. METACARBONATE SUCCESSION— CAMBRIAN (AND OLDER?) TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS Bedrock in the Snowden Mountain area consists mostly of large masses of metacarbonate rocks associated with subordinate thinner intervals of carbonaceous phyllite (fig. 4). Deformation and metamorphism have obscured the original depositional patterns of these rocks, but compila- tion of a number of partial, but overlapping, measured sections allows reconstruction of a generalized stratigraphy (figs. 5, 6). The oldest dated strata are of early Middle Cambrian age; these rocks are fault bounded, and their stratigraphic relationship to the other units discussed here is uncertain. Rocks of Late Cambrian and Early Ordovician age have not been recognized in the Snowden Mountain area, but Middle Ordovician strata are widely distributed and comprise a variety of carbonaceous, chiefly fine- grained lithofacies laid down in a shallowing-upward dep- ositional regime. These rocks are structurally intercalated with, and locally grade up into, massive metacarbonate rocks. Many exposures of this lithology are of Late Ordo- vician and Silurian age, but some are Devonian, and other metacarbonate masses in the study area may be of Cambrian or older age. The reconstructed stratigraphic column shown in figure 6 is undoubtedly incomplete; it does not include lithologic units in the Snowden Mountain area (such as units szu and lemd in fig. 2) that are of unknown or uncertain age. However, it portrays our present understanding of the relative stratigraphic position, age range, and minimum thickness of well-dated lithologic units known to be pre- Late Devonian in age in the Snowden Mountain area. A more speculative column including units of less well con- strained age is presented and discussed below (see “Sum- mary of the Metacarbonate Succession in the Snowden Mountain Area,” p. 26). CAMBRIAN ROCKS The oldest well—dated rocks in the study area are a thin interval of phyllite and subordinate metalimestone, about 3 km in lateral extent, that discontinuously underlies massive marble on the north side of Snowden Mountain (fig. 3, 10c. 20). These rocks constitute unit Cl (Cambrian marble) of Dillon and others (1988) and are here referred to as the Snowden Mountain unit. Ten to twenty meters of continu- ous section are relatively well exposed directly below the massive marble along a small north-facing ridge; additional phyllitic strata discontinuously exposed on the steep north- ern side of this ridge also belong to this unit but are inaccessible and were not examined during the course of this study. The entire phyllite and metalimestone interval is no more than a few hundred meters thick. METACARBONATE SUCCESSION—CAMBRIAN TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS 7 Figure 4. Massive metacarbonate rocks chiefly of the Mathews River unit, Chandalar D—6 quadrangle. The Snowden Mountain unit overlies a thick section of metasedimentary rocks, including calcschist and metacon- glomerate; the nature of the contact between these units is uncertain but was thought to be a normal stratigraphic contact by Dillon and others (1988) (see further discussion below). The upper contact of the Snowden Mountain unit has been interpreted as an unconformity (Dillon and others, 1987a, 1988), but where observed during the course of this study it appears to have undergone at least some faulting. The basal meter of strata directly overlying the phyllite and metalimestone interval consists of dominantly clast— supported, calcareous conglomerate (fig. 7A), which grades upward into massive, cliff-forming gray marble. Clasts are 1 mm to 15 cm in diameter, subrounded to angular, and generally well aligned. Most clasts consist of medium-gray, finely crystalline marble; rare pebbles and cobbles of tan, fine—grained, dolostone(?) and white, coarse-crystalline marble also occur. This conglomeratic layer could represent a basal lag developed along an unconformity surface, but it (and the immediately overlying gray marble) is locally strongly sheared, brecciated, and iron stained, thus indicat- ing at least some deformation along the upper contact of the Snowden Mountain unit. LITHOLOGIES The dominant lithology in the Snowden Mountain unit is noncalcareous, gray to silver phyllite. Thin layers and lenses of slightly recrystallized, sandy metalimestone make up 5 to 10 percent of the section and are thicker and more abundant in the upper part of the section. The top 2 m of strata are orange—weathering, dark-gray, bioclastic wacke- stone to packstone, with phyllitic partings and layers spaced 4 to 10 cm apart. The wacke-packstone consists of locally abundant whole and fragmentary trilobites and phosphatic brachiopods, as well as echinoderrn and other fossil debris, peloids, and a few to 10 percent angular, fine sand- to silt-sized quartz grains in a matrix of lime mud; thin seams of dolomite euhedra occur locally (fig. 7B). AGE AND BIOFACIES Limy layers in the uppermost part of the Snowden Mountain unit contain trilobites of early Middle Cambrian age, including many specimens of Kounamkites cf. K. frequens Chernysheva, less common specimens of Chon- 8 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA dranomocare cf. C. speciosum M. Romanenko, and frag- ments of indeterminate olenellids (Palmer and others, 1984; Dillon and others, 1988) (fig. 8). The fauna has strong Siberian biogeographic affinities and is typical of open- shelf facies (Palmer and others, 1984). DISTRIBUTION Dillon and others (1987a, p. 337) suggested that strata “thought to be stratigraphically below and on strike with those at the trilobite locality” within the Chandalar D—6 quadrangle are also of Cambrian age. These rocks consist of units €cq, Ccs, and parts of 060, OCvc, and O€vp (Dillon and others, 1988)3 and include interlayered tan- to orange-weathering, calcareous schist and quartzite, sand- stone and granule conglomerate, sandy marble, and gray, green, and purple phyllite. Dillon and Reifenstuhl (in press) extended this stratigraphy south of the Snowden Mountain area on the basis of lithologic correlation and considered additional, widely distributed strata in the Chandalar C—5 and C—6 quadrangles to be of Cambrian age. Thus far, no fossils have been found in any of these rocks to confirm a Cambrian age; 10 samples taken for microfossils from these units are barren, and a single productive sample from the Chandalar C—6 quadrangle contains a conodont fragment of post-Cambrian age. In addition, at least some of the units assigned a Cambrian age by Dillon and others (1988) have strong lithologic similarities to rocks of known Devonian age, and contacts considered to be stratigraphic by Dillon and others (1988) have been reinterpreted as faults by later workers (T.E. Moore, US Geological Survey, written commun., 1991). In this paper, only the Snowden Moun- tain unit (unit CI of Dillon and others, 1988) is considered to be of Cambrian age; it has been recognized in only one locality, along the north side of Snowden Mountain (fig. 3, 10c. 20). DEPOSITIONAL ENVIRONMENT Sedimentary features of the Snowden Mountain unit suggest deposition in an outer shelf or slope setting. The fine grain size and lack of current structures characteristic of most of the section imply deposition in a quiet setting, below fair-weather wave base. Lenses of quartzose lime wackestone and packstone intercalated in the phyllite prob- ably represent storm deposits, and the increased abundance of such lenses in the upper part of the section suggests a 3ch, Cambrian chlorite quartz schist; Ccs, Cambrian calc-schist; OCc, Cambrian(?) to Ordovician(?) calcareous elastic rocks; OCvc, Cambrian(?) to Ordovician(?) volcanic conglomerate; OCvp, Cambrian(?) to Ordovician(?) interlayered volcanic rocks and phyllite. EXPLANATION FOR STRATIGRAPHIC COLUMNS [Figures 6, 8, 16, 19, 21, 23— 26, and 29] ROCK TYPES SEDIMENTARY STRUCTURES Metasandstone 5 Bioturbation or uartzite q \\\_ Cross lamination Silty shale or N Fenestral fabric and (or) SlltY phyllite ‘ cryptalgal lamination Shale or ll Vertical fenestral fabric phyllite FOSSILS AND GRAIN TYPES Limestone or metalimestone s Bioclast Argillaceous limestone O Coated grain or metalimestone a v lntraclasl Dolomitic limestone or Eflflmfiflfll Tuff Slromatolite . =° Peloid metalimestone o Brachiopod Dolostone l’ Bryozoan a Crinoid ossicle Marble . 512% Colonial coral 69 Dasycladacean alga A A A Chertormetachert A A A WE? Solitarycoral /n\ ”s“ Slromatoporoid Melabasife — Boundary— C, conformable; U, unconformable; F, fault; F/U, fault and (or) unconformity V v V V ' Mafic dike 554‘ Figure 5. Lithologic and paleontologic symbols used in this report. shallowing-upward depositional regime. The trilobite- brachiopod—echinoderm fauna contained within the limy lenses is characteristic of normal marine conditions and moderate water depths (Palmer and others, 1984). MIDDLE ORDOVICIAN ROCKS Middle Ordovician strata are widely distributed in the Snowden Mountain area and consist primarily of phyllite, metachert, metalimestone, and marble (fig. 6). These rocks were originally included in units Dsk (Skajit Limestone) and D1 (limestone) by Brosgé and Reiser (1964) and were considered by them to be of Devonian age. Dillon and others (1987a, 1988) recognized the presence of Middle Ordovician conodonts in these strata and assigned them to their units Obpm (black carbonaceous phyllite and crinoidal metalimestone) and Om (gray to black crinoidal marble bodies of mappable extent included within unit Obpm). METACARBONATE SUCCESSION—CAMBRIAN TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS SNOWDEN MOUNTAIN AREA SYSTEM/ SERIES/SUBSERIES/ $2335 SERIES STAGE/SUBSTAGE UNIT DEVONIAN EIFELIAN AND (OR) EMSIAN W LUDLOVIAN AND WENLOCKIAN a E s o F/ U SILURIAN METERS WLELwhODcOf/UEKQIQED SD lo ES /V F 300— Ian/oN/Mofl : 5/ / s 2 ° 0 N a f’R’z F / . /. D o /o / N RICHMONDIAN E “1 w/ E l, (INCLUDES MINOR 2 -m! 0: LOWER SILURIAN(?) 0: e " / f5 7 25° _ uJ STRATA) m D. g o N a w s v E -- N 2 [:3/ s] I | L fé/ fi’f/ 200 — MAYSVILLIAN w; g ° 2 AND EDENIAN ° 9 o it s j 5 , F/C? g l . ; I I > 8 150— n: I:. O E LOWER x CARADOCIAN(?) Lu AND LLANDEILIAN '5'5' LU O 5' z 100— .0. LU 2 E o ———————— z (D LLANVIRNIAN 50— UPPER E E ARENIGIAN g I; E F/U O :> D CAMBRIAN LOWER MIDDLE z 0 o m 2 F Figure 6. Generalized composite stratigraphic column for metacarbonate succession in the Snowden Mountain area, based on a number of overlapping, partial measured sections with good biostratigraphic control. Thicknesses are minima, particularly for Upper Ordovician and Silurian rocks. European series names are used for intervals containing dominantly cosmopolitan faunas, whereas North American series and (or) stage names are used for intervals containing chiefly North American Midcontinent Province faunas (NAMP). See figure 5 for explanation of symbols. 9 10 PRE—CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA Figure 7. A, Carbonate-clast conglomerate directly overlying Snowden Mountain unit; layer could be a lag developed along an unconformity surface or a fault breccia (fig. 3, 100. 20) (pencil, 14 cm long). B, Photomicrograph of bioclastic peloidal packstone, Snowden Mountain unit (fig. 3, 10¢. 20); dark ovoids are peloids, and other grains are bioclasts, including echinoderm and trilobite fragments. The basic unit concept established by Dillon and others (1987a, 1988) is used here, and these rocks are referred to as the Snowden Creek unit. However, our map distribution of the Snowden Creek unit (fig. 2) differs somewhat from that of unit Obpm (Dillon and others, 1987a, 1988), and the unit as defined here includes a slightly broader array of rock types. In addition, our interpretation of the stratigraphic context of these rocks differs from that of Dillon and others (1987a, 1988). These authors stated that unit Obpm uncon- formably(?) overlies calcareous metasedimentary rocks, which they believed to be of Cambrian age, and is in turn overlain by “Skajit Limestone of Devonian age” (Dillon and others, 1987a, p. 337). Our studies indicate that the basal contact of most exposures of the Snowden Creek unit is a fault, and a stratigraphic relationship to rocks of definite Cambrian age has not been established. The upper contact of this unit is also generally a fault, but locally (for example, fig. 3, loc. 11) a gradational and apparently conformable contact with Upper Ordovician and Silurian massive metacarbonate rocks of the Mathews River unit is observed. The Snowden Creek unit is at most a few hundred meters thick. Exposed sections range from about 10 to 100 m thick and are typically strongly folded; some sections may have been structurally thickened. A generalized com- posite stratigraphy (fig. 6) has been pieced together from a number of overlapping partial measured sections, particu- larly those at localities 22, 24, 28, 29, and 36 (fig. 3). LITHOLOGIES Carbonaceous, fine-grained siliciclastic and calcareous rocks characterize the Snowden Creek unit and are inter- layered on a scale of a few centimeters to tens of meters. Calcareous material dominates some sections but makes up less than 5 percent of others (Dillon and others, 1987a) (fig. 9A); these differences reflect both temporal and spatial fluctuations in carbonate input. Elongate lenses of light- colored calcite marble (equivalent to unit Om of Dillon and others, 1987a, 1988) occur locally within the Snowden Creek unit. Siliciclastic lithologies in the Snowden Creek unit include phyllite, metachert, and rare metasandstone. Phyllite-rich intervals are poorly exposed and crop out best in streamcuts such as the headwaters of Snowden Creek (fig. 3, 10c. 24). More commonly, phyllite forms subordi- nate layers a few millimeters to a few meters thick within sections of metachert or metalimestone. Phyllite is black to silvery gray, generally carbonaceous, and locally calcare- ous; foliation planes are spaced a few millimeters to 3 cm apart. Reddish-brown- to brown-weathering, gray to black metachert occurs in intervals of 2 to 30 m; it weathers into irregular slabs, 0.5 to 5 cm thick, which may contain millimeter— to centimeter-scale laminations of mica, pyrite, or carbonaceous material. In some outcrops, this small- scale compositional layering is so pronounced that the rocks are rhythmically color-banded (for example, fig. 3, 10c. 29). Local lenses, 15 to 30 cm thick, of brown-weathering, black dolostone occur throughout the metachert intervals. Both metachert and dolostone are fine grained; crystal size is 20 to 100 um in metachert and 20 to 50 um in dolostone. Both lithologies contain spheroids and ovoids, 50 to 400 um (mostly 100—200 um) in diameter, that are probable radiolarian ghosts. In the metachert layers, these ghosts are made of quartz crystals that are slightly coarser than those in the surrounding matrix. Ghosts in the dolomitic lenses consist of crystalline calcite or dolomite; concentrations of carbonaceous material preserve details of the original test in some specimens. Radiolarian ghosts generally are rare (a few percent) and disseminated but reach abundances of 5 to METACARBONATE SUCCESSION—CAMBRIAN TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS 11 SYSTEM/ SERIES/SUBSERIES/ 5,129.15 56 113 SNOWDEN MOUNTAIN AREA SERIES STAGE/SUBSTAGE UN” 6 EXPLANAHON DEVONIAN EIFEUAN ANDmeMSIAN F L.J 36 65 Number of samples that LUDLOVIAN AND WENLOCKIAN /. K&] g 47 yielded a species SILURIAN WENLOCKIAN AND E 94 m association METERS LLANDOVERIAN F .————— fl . 1 48 C325 300 — . K (3:5 45 O 3 E 56 @1343 :a 6 C 5 RICHMONDIAN 35 (INCLUDES MINOR 2 a: LOWER SILURIAN(?) II 25° — E STRATA) m a. 3 3 “I” '2 2 20° — MAYSVILLIAN 2 AND EDENIAN S $2 5 150— D E E 2 O LOWER x CARADOCIAN(?) E AND LLANDEILIAN 0: Lu 0 _l D Z 100 — 9 Lu 2 S o _______ Z ' U) LLANVIRNIAN 50 -— ——————— Z Z UPPER uDJ 2 ._ ARENIGIAN ; 5 E O D D CAMBRIAN LOWER MIDDLE g g Figure 8. Generalized composite stratigraphic column showing fossil distribution in the metacarbonate succession in the Snowden Mountain area; selected fossils (chiefly conodonts) of biostrati— graphic, paleogeographic, and (or) paleoecologic significance are shown at appropriate points adjacent to the lithologic column. Thicknesses are minima, particularly for Upper Ordovician and 25 percent in some samples and may be concentrated into irregular laminae. Some metachert layers contain small knots of chloritoid. Metasandstone is less abundant in the Snowden Creek unit than the finer grained siliciclastic lithologies described above but may form 20 to 30 percent of some outcrops. It occurs intercalated with phyllite in graded, poorly sorted layers, 2 to 25 cm thick, which weather pink, greenish gray, 116 Redeposited Late Cambrian and (or) Early v a Ordovician conodonts Silurian rocks. European series names are used for intervals containing dominantly cosmopolitan faunas, whereas North Amer- ican series and (or) stage names are used for intervals containing chiefly North American Midcontinent Province (NAMP) faunas. See figure 5 and table 1 for explanation of symbols and numerical identification of fossils, respectively. or brownish gray. Most layers are semischistose, and some are slightly calcareous; grain size ranges from very fine to very coarse. Clasts are rounded to subangular and consist of 15 to 30 percent quartz, lesser amounts of plagioclase, and abundant lithic grains in a recrystallized matrix of mica, chlorite, and calcite. Lithic clasts are primarily sedimentary (chert, siltstone, dolostone) and metamorphic (schist, phyl- lite). Heavy minerals include tourrnaline and garnet. 12 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA Figure 9. Sedimentary features of the Snowden Creek unit. A metasandstone (fig. 3, loc. 22). B, Section consisting chiefly of calcareous turbidites (fig. 3, Ice. 28); arrow marks turbidite shown in C (hammer, 40 cm long). Limy layers are found throughout the Snowden Creek unit, but, as noted above, the kind and amount of calcareous material vary strikingly from section to section. The major carbonate rock types are thinly layered, carbonaceous metalimestone and massive, light-colored calcite marble. Carbonaceous metalimestone is most abundant in the lower part of the Snowden Creek unit. It occurs as contin- uous sequences, 10 to 100 m thick, that dominate some sections and as subordinate layers, a few millimeters to 1 In thick, in sections made mostly of phyllite and (or) meta- chert. In both settings it forms couplets, 0.5 to 10 cm thick, defined by a contrast in color, grain size, and (or) noncar- bonate components (fig. 9B—D). The finer grained upper part of the couplet is dark gray to black, weathers brown or black, and may contain abundant mica and (or) carbona- ceous material. The lower part of the couplet is generally thicker, lighter in color, and may contain abundant quartz. Most contacts between the two parts of a single couplet are gradational, whereas those between adjacent couplets are , Section consisting chiefly of noncalcareous phyllite and lesser sharp. In the least deformed and recrystallized outcrops of carbonaceous metalimestone, details of original bedform and composition are preserved. Most couplets are even to slightly undulatory, laterally continuous, and parallel lam— inated; some form lenses, 0.5 to 1. 5 m long, with scoured bases. The amount of noncarbonate material in the couplets varies greatly from outcrop to outcrop. Some couplets contain few noncarbonate grains and consist mostly of calcareous bioclasts and (or) calcareous lithiclasts and lime mud. At locality 28 (fig. 3), at least 40 m of relatively pure metalimestone overlies several meters of black metachert. Carbonate couplets here consist of skeletal packstone grad- ing up to lime mudstone and are separated by 1 cm or less of calcareous phyllite; bioclasts are almost exclusively echinoderm debris (crinoid columnals) (fig. 9B—D). The basal centimeter of a typical 8-cm-thick couplet at this outcrop contains columnals that average 2 mm in diameter, as well as 5 to 10 percent rounded grains of quartz silt and METACARBONATE SUCCESSION—CAMBRIAN TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS 13 fine sand, in a matrix of fine-crystalline (200 um) calcite. The upper part of the couplet contains rare columnals that average 0.5 mm in diameter, and less than 1 percent quartz silt, in a matrix of microcrystalline (20—40 um) calcite. At other outcrops (for example, fig. 3, loc. 19), couplets contain 20 to 30 percent rounded to angular carbonate lithic clasts (fig. 10A, B) in addition to echinoderm debris. These clasts include lime mudstone, peloidal wackestone and grainstone, bioclastic packstone and grainstone, and fine— grained dolostone with disseminated radiolarian ghosts. The largest clasts are as much as 1.5 cm in diameter but in general are coarse to very coarse sand sized. Other metalimestone intervals include abundant non— carbonate material. At locality 30 (fig. 3), just 3 km southeast of locality 28, 100 m of quite impure metalime— stone overlies 5 m of black metachert. The coarse lower parts of couplets at this site contain 20 to 80 percent quartz, as well as calcite and subordinate white mica. Elsewhere, rounded phosphatic grains and phosphatic skeletal frag- ments make up as much as 25 percent of the coarse fraction of some metalimestone couplets. Distinctive, light-colored carbonate bodies (unit Om of Dillon and others, 1987a, 1988) occur locally within Figure 9.—Continued. C, Sawed slab of turbidite showing well-developed graded bed- ding. D, Photomicrograph of lower part of turbidite in C; rock consists primarily of crinoid ossicles, C, in a matrix of fine- crystalline calcite and minor amounts of quartz silt. the Snowden Creek unit. These bodies are typically elon— gate lenses, 10 to 100 m thick and a few hundred meters to several kilometers long, which are white to light gray and weather white to beige. Most are massive, fine— to medium— crystalline, calcite marble in which original texture has been obliterated. Locally, however, original fabric can be discerned and consists of peloidal-skeletal packstone or grainstone. These white marble bodies are most common in the upper part of the section. At several outcrops, carbonaceous metalimestone grades upward through an interval of a few tens of meters into massive white marble. At locality 28 (fig. 3), 2 m of black metachert with minor thin layers of black metalime- stone is overlain by about 40 m of metalimestone couplets. At the base of the metalimestone sequence, couplets are dark gray to black, 3 to 5 cm thick, and typically separated by about a centimeter of calcareous phyllite. A few meters higher, couplets are medium gray, 5 to 10 cm thick, and separated by at most a few millimeters of phyllite. In the uppermost part of the sequence, light-gray, flaggy meta— limestone grades up into white, sugary, fine crystalline marble. Changes in microtexture occur throughout this sequence as well. The lowest metalimestone layers (those 14 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA Figure 10. A and B, Photomicrographs of clasts in calcareous turbidite, Snowden Creek unit (fig. 3, Ice. 19). C, crinoid ossicle; M, carbonaceous mudstone clast; P, peloidal grainstone clast. intercalated with the metachert) are strongly carbonaceous and contain radiolarian ghosts. The metalimestone couplets consist primarily of echinoderrn packstone, micrite, and minor detrital quartz and become less carbonaceous and more quartzose upward. The marble consists of 5 percent crinoid columnals in a matrix of anhedral calcite. AGE AND BIOFACIES Conodonts have been obtained from 22 samples, which represent 16 localities and several lithologies in the Snowden Creek unit (fig. 3 and app. 1, locs. 18, 19, 22, 24, 25, 28, 30—32, 35, 36), and provide relatively good age control for these strata. Dolostone lenses in metachert, thin metalimestone couplets intercalated with phyllite, and thick sequences of pure and impure metalimestone have all yielded conodonts (fig. 8; table 1; app. 1). Key species, including Periodon flabellum, Tripodus laevis, Pygodus serra, Py. anserinus, Prattognathus rutriformis, and E0- placognathus elongatus transitional to Polyplacognathus sp. (fig. 8; pl. 1, figs. 1, 2, 5, 6, 9—12, 17, 18), indicate an age of late Arenigian to at least Llandeilian and probably to early Caradocian (early to middle Middle Ordovician) for this unit (USGS collns. 10728—CO, 99l3-CO, 99ll—CO, 10851—CO); the highest beds (USGS colln. 9909—CO) contain Periodon aculeatus (pl. 1, fig. 8) and are thus no younger than early Caradocian (middle Middle Ordovi- cian). The most precisely dated parts of the unit represent intervals within the serra Zone (USGS colln. 10728—CO) and Baltom'odus variabilis Subzone to lowermost B. gerdae Subzone of the Amorphognathus tvaerensis Zone (USGS colln. 10851—CO) of late Llanvimian and latest Llandeilian age to earliest Caradocian age, respectively. The oldest beds thus far sampled are very late Arenigian in age (USGS collns. 10826—CO and 10827—CO); these strata also contain redeposited Late Cambrian and (or) Early Ordovician con- odonts (fig. 8; pl. 1, figs. 21—24). Conodonts from the Snowden Creek unit are chiefly cosmopolitan, deep- and (or) cool-water species of the protopanderodid-periodontid biofacies. DISTRIBUTION The Snowden Creek unit is exposed primarily in several west- to southwest-trending linear outcrop belts. The southernmost belt lies south of Sukakpak and Wiehl Mountains; age control is provided by a single sample (fig. 3, 100. 36). The central belt is the best dated and most studied; it consists of at least three discrete fault slices and can be traced from south of Snowden Mountain west across the Dalton Highway to Grotto Mountain. Two smaller exposures occur north and northeast of Snowden Mountain (fig. 3, locs. 11 and 18—19). DEPOSITIONAL ENVIRONMENT Sedimentary features and conodont biofacies of the Snowden Creek unit indicate that deposition took place chiefly in a slope to basinal setting, and the vertical sequence of lithologies suggests a shallowing-upward dep- ositional regime. The carbonaceous siliceous lithology is interpreted as metachert because of its lithologic association and the presence of radiolarian ghosts and fine-scale lami- Table 1. Names of fossils shown in figures 8, 19, 21, and 24—26. METACARBONATE SUCCESSION—CAMBRIAN TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS 15 No. Conodonts No. Conodonts 1 Ancyrodella gigas 61 Paroistodus originalis 2a Ancyradella lobata 62 Paroistodus proteus 2b Ancyrodella nadosa 63 Paroistodus cf. P. proteus 3 Ancyrodella sp. indet. 64 Pelekysgnathus dubius 4 Ancyrognathus cf. A. coeni 65 Pelekysgnathus sp. indet. 5 Ancyrognathus aff. A. triangularis 66 Periodon aculeatus 6 Aphelognathus aff. A. divergens 67 Periodon flabellum 7 Aspidognathus cf. A. sp. B of Mannik (1983) 68 Phakelodus tenuis 8 Astrapentagnathus irregularis 69 Phragmodus n. sp. (= Ph. n. sp. of Barnes, 1974) 9 Aulacognathus bullatus 70 Plectodina? tunguskaensis 10 Belodina sp. 71 Plectodina? cf. PL? dolbaricus 11 Chosonodina rigbyi 72 Plegagnathus? repens 12 Clavohamulus densus 73 Polonodus sp. 1-3 Clavohamulus n. Sp. 74 Polygnathus evidens 14 Cordylodus angulatus 75 Polygnathus gronbergi 15 “Cordylodus” harridus 76 Polygnathus inversus 16 Cordylodus intermedius 77 Polygnathus linguiformis 17 Cordylodus proavus 78 Polygnathus pacificus 18 Culumbodina? cf. C. occidentalis 79 Polygnathus planarius 19 Dapsilodus? similaris 80 Polygnathus samueli 20 Diaphorodus delicatus 81 Polygnathus webbi 21 Distomodus? dubius 82 Polygnathus of the Po. xylus group 22 Drepanodus arcuatus 83 Polygnathus sp. indet. 23 Eoplacognathus elongatus transitional to Polyplacognathus sp. 84 Prattognathus rutriformis 24 Erraticodan balticus 85 Prioniadus elegans 25 Fahraeusodus marathonensis 86 Proconodontus muelleri 26 Fryxellodontus? n. sp. 87 Protopanderodus graeai 27 Histiodella n. sp. 88 Protopanderodus insculptus 28 Icriodella? sp. indet. 89 Protopanderodus liripipus 29 Icriadus symmetricus 90 Protopanderadus varicostatus 30 Icriodus taimyricus 91 Protoprioniodus aranda 31 Icriadus sp. indet. 92 Pseudobelodina adentata 32 Juanognathus variabilis 93 Pseudobelodina vulgaris vulgaris 33 Jumudontus gananda 94 Pterospathodus aff. P. cadiaensis 34 Klapperina ovalis 95 Pygodus anserinus 35 Kockelella amsdeni 96 Pygodus serru 36 Kockelella sp. indet. 97 Pygodus sp. indet. 37 Macerodus n. sp. 98 Rossodus manitouensis 38 Mesotaxis falsiovalis 99 Rossodus n. sp. 39 Oepikodus communis 100 Rossodus sp. 4O Oistodus lecheguillensis 101 Scolopodus bolites 41 Oistodus multicarrugatus 102 Scolopadus flaweri 42 Oneotodus costatus 103 Scalopodus leei 43 Oulodus? n. Sp. 104 Spinodus ramosus 44 Oulodus sp. 105 Stereoconus corrugatus 45 Ozarkodi‘na cf. 0. cadiaensis 106 Teridontus nakamurai 46 Ozarkodina confluens 107 Variabiloconus bassleri 47 Ozarkodina excavata 108 Walliserodus australis 48 Ozarkodina aff. 0. oldhamensis 109 Walliserodus ethingtoni 49 Ozarkodina remscheidensis remscheidensis 50 Ozarkodina n. sp. cf. 0. remscheidensis OTHER FOSSILS 51 Ozarkodina n. sp. 110 Chancelloria sp. (spongelike forms) 52 Palmatolepis plana 111 Acrotretid brachiopods 53 Palmatolepis proversa 112 Tcherskidium n. sp. of Blodgett and others (1988) (brachiopod) 54 Palmatolepis sp. indet. 113 Pelagiella sp. (primitive mollusk) 55 Paltodus subaequalis 114 Homagnostus sp. (agnostid trilobitomorph) 56 Panderodus sp. 115 Hystricurus? sainsburyi (trilobite) 57 Pandorinellina exigua philipi 116 Kaunamkites cf. K. frequens (trilobite) 58 Pandorinellina expansa 117 Plethometopus armatus (trilobite) 59 Pandorinellina insita 118 Two-hole crinoid columnal 60 Paracordylodus gracilis 16 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA nation. Metachert and phyllite dominate the lower part of the unit and indicate a relatively quiet, starved basin setting; the highly carbonaceous nature of these rocks and the lack of an indigenous benthic fauna suggest that the basin was poorly oxygenated. Rare graded metasandstone layers are probable turbidites. Metalimestone layers occur throughout the Snowden Creek unit but are thicker and more abundant in its upper part. Sedimentologic and fauna] evidence demonstrate that most metalimestone layers are also probable turbidites, which were deposited against a “background” accumulation of fine-grained siliceous material (now metachert) and clay (now phyllite). Most calcareous layers are distinctly graded and form partial Bouma (1962) sequences (typically ABDE or BDE); the lack of a well-developed C division is common in carbonate turbidites (Scholle, 1971; Dumoulin, 1992). Composition of the carbonate turbidites suggests their derivation from a variety of intrabasinal and extrabasinal sources and some changes in provenance with time. Lithic clasts include grains indicative of a deep—water origin, such as black phyllite and dolostone with radiolarian ghosts, and lithologies typical of a shallow-water carbonate-platform source, such as peloidal mudstone and bioclastic grain- stone. Some clasts are rounded and irregular; these were probably still soft when deposited and thus derived from contemporaneous, intrabasinal strata. Other clasts are angu- lar and contain calcite veins; these were fully lithified when eroded and infer an extrabasinal origin. Fauna] evidence (discussed below) demonstrates that older, extrabasinal rocks have been eroded, reworked, and included in these turbidites. Calcareous extrabasinal sources appear to have been most important in the early history of the Snowden Creek unit; samples from lower in the unit contain more carbonate lithic clasts, whereas those in the upper part of the unit consist mostly of skeletal (echinoderm) debris and contain more quartz. Paleoenvironmental interpretation of the elongate white marble bodies in the Snowden Creek unit is problem- atic because most retain little primary texture. Where original fabric can be discerned, it is typical of shallow- water sedimentary environments (peloidal-skeletal pack- stone or grainstone), and there are no structures, such as graded bedding, indicative of redeposition. Previous studies of metacarbonate rocks in northern Alaska (Dumoulin and Harris, 1987a, 1992) have demonstrated that shallow-water accumulations of skeletal grainstone are particularly suscep- tible to recrystallization and obliteration of primary texture. The marble bodies are much less carbonaceous than the rest of the Snowden Creek unit, are generally in gradational contact with intervals of darker metalimestone (turbidites), and occur predominantly in the uppermost part of the unit. Most of the marble bodies probably represent carbonate banks or shoals formed in situ on local highs that developed within the basin. Their concentration in the upper part of the unit suggests a shallowing-upward depositional regime. Small, shallow-water carbonate buildups, which pass later- ally and vertically into basinal bituminous pelagic sedi- ments, have been described from the Cretaceous of Mexico and the Middle East (Jenkyns, 1980; Wilson, 1975). Conodont biofacies analysis supports the environmen- tal interpretations outlined above. Conodonts from the Snowden Creek unit represent the protopanderodid- periodontid biofacies, which is characteristic of a cool- and (or) deep—water depositional environment. Assemblages from dolostone lenses in metachert (for example, fig. 3, 10c. 31) include complete and well-preserved fragile ele- ments; such elements could not have survived post-mortem transport and were probably deposited by simple settling from within the water column to the basin floor. Most conodonts from the Snowden Creek unit, however, come from carbonate turbidites; these assemblages are hydrauli- cally sorted, and some include elements of anomalous age or biofacies introduced by redeposition. The coarser grained parts of these turbidites yield mostly large, robust protopan- derodids (pl. 1, figs. 3, 4), whereas finer grained layers produce more delicate periodontids (pl. 1, figs. 8, 15). Several early Middle Ordovician faunas collected northeast of Snowden Mountain (fig. 3, 10c. 18) include reworked conodonts of Late Cambrian and (or) Early Ordovician age, such as Phakelodus tenuis, Cordylodus spp., Rossodus manitouensis, and “Scolopodus” gracilis (fig. 8; pl. 1, figs. 21—24). In addition, although conodonts of cool-water biofacies dominate the Snowden Creek unit, some samples include a few forms typical of warmer, shallower water, such as belodinids (fig. 3, 10c. 35), plectodinids, and Prattognathus rutriformis (fig. 3, 10c. 22; pl. 1, fig. 6), that were transported seaward into a deeper water setting. All samples from the elongate marble bodies are barren. Thus, Middle Ordovician strata in the Snowden Moun- tain area were deposited primarily in a poorly oxygenated, off—platform setting that received minor fine-grained silici- clastic detritus, as well as pulses of allodapic calcareous material derived from contemporaneous and older carbonate deposits rimming the basin. Carbonate input varied across the basin, but, in general, increased through time. Eventu- ally, water depths shallow enough for in situ accumulation of calcareous shoals were achieved locally. UPPER ORDOVICIAN AND SILURIAN ROCKS The carbonaceous Middle Ordovician strata discussed above are structurally intercalated with, and locally grade up into, massive metacarbonate rocks (fig. 11A) assigned to the Skajit Limestone by previous workers (for example, Brosgé and Reiser, 1964). Dillon and others (1987a, 1988) reported the presence of Late Ordovician and Silurian(?) microfossils and megafossils from several thrust slices of “Skajit Limestone” north of Snowden Mountain and METACARBONATE SUCCESSION—CAMBRIAN TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS 17 Figure 11. reassigned these rocks to their unit SOm. This unit was described as consisting of “massive gray marble and orange dolomite with local replacement bodies of black chert” (Dillon and others, 1988). Other massive carbonate out- crops in the Snowden Mountain area were still considered to represent the Skajit Limestone of Devonian age, however, which was described by Dillon and others (1988) as consisting mostly of “massive gray marble and dolomite,” and subordinate carbonate conglomerate and minor pelitic, quartzose, and volcanic layers. Thus, discrimination of these two units on lithologic grounds is difficult. Our studies confirm the Late Ordovician and Silurian age of unit SOm but also identify Late Ordovician and Silurian fossils in strata both north and south of Snowden Mountain that had been referred to the Skajit Limestone (Dsk) by Dillon and others (1987a, 1988). In addition, our collections produced fossils of definite and possible Devo- nian age from some occurrences of the Skajit Limestone (as mapped by Dillon and others, 1988). Various lines of evidence (discussed below) suggest that other outcrops of the Skajit Limestone may be pre-Late Ordovician in age. Massive carbonate bodies in the Snowden Mountain area probably represent dismembered pieces of a long—lived carbonate platform; individual thrust slices differ in age and the degree to which primary fabric has been preserved. In this paper, distinctive dolomitic metacarbonate rocks north and south of Snowden Mountain, including unit 80m and parts of unit Dsk of Dillon and others (1987a, 1988), are referred to as the Mathews River unit. All rocks assigned to this unit have yielded some fossils of Late Ordovician and (or) Silurian age. Massive metacarbonate rocks in which the distinctive lithologic features of the Mathews River unit have not been found are shown in figure 2 as PzEd, st, Pzw, or Pzt. Some of these strata may be facies equivalents of the Mathews River unit or parts of the Mathews River unit that have lost their distinctive lithologic features Sedimentary features of the Mathews River unit. A, Typical cliff—forming outcrops of massive dolostone and metalimestone located in the Chandalar D—6 quadrangle. B, Dark-weathering, fossiliferous, burrowed metalimestone overlain by light-weathering, thinly laminated dolostone (lens cap, 6 cm in diameter) (fig. 3, loc. 12). Bioturbated metalimestone beds produce more conodonts than other lithologies in this unit. through metamorphism and (or) deformation. Other strata may be older or younger than the Mathews River unit. These rocks are discussed below as “Metacarbonate Rocks of Uncertain Age.” Most sections of the Mathews River unit are fault bounded as well as internally faulted and folded. A com— posite of several partial measured sections (fig. 3, locs. 6, 12, and 16) shows the unit to be at least 150 m thick. Stratigraphic relationships with other units may be dis— cerned in the northern outcrop belt. At locality 11 (fig. 3), rocks of the Mathews River unit gradationally and appar- ently conforrnably overlie rocks of the Snowden Creek unit. At locality 6 (fig. 3), a thin layer of Devonian carbonate rocks overlies the Mathews River unit; the contact appears to be an unconformity but could be a fault. Carbonate rocks lithologically similar to these Devonian strata, but which have not yet been dated, overlie the Mathews River unit at several other localities. LITHOLOGIES Massive cliffs of orange and gray dolostone and metalimestone and lesser amounts of marble make up the Mathews River unit (fig. 11A). Some dolostone forms irregular masses that crosscut bedding, but most occurs as even, laterally continuous beds, which alternate with darker weathering metalimestone to produce the decimeter- to meter-scale color-banding characteristic of this unit (fig. 118). Black chert constitutes l to 10 percent of some outcrops; it replaces skeletal material and forms irregular bands and stringers a few centimeters thick. Much of this unit is notably fetid, particularly those sections dominated by dolostone. Where original textures are best preserved, the Mathews River unit consists of four main lithologies, interbedded on a scale of a few centimeters to tens of 18 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA meters. These lithologies are bioturbated metalimestone, parallel-laminated metalimestone, fossiliferous dolostone, and algal-laminated dolostone. The first lithology is gray— to brown-weathering, medium-gray to black, locally dolomitic metalimestone, which forms slightly undulatory to nodular beds, 2 to 50 cm (mostly 5—15 cm) thick, separated by orange-weathering argillaceous partings (fig. 12A). Most beds show mega- scopic and microscopic evidence of bioturbation, ranging from an irregularly mottled fabric to a network of discrete burrows (fig. 12B). Mottled fabric typically consists of irregular ovoids and cylinders, one to a few centimeters across, in a darker matrix. Discrete burrows are light colored, a few millimeters in diameter, and subvertical; most have a Chondrites- or Trichichnus-like form. Both mottles and burrows are less dolomitic, less carbonaceous, and coarser grained than the surrounding material. Within a single bed, mottled fabric generally grades upward into an array of discrete burrows, which in turn decrease upward in size and abundance. Bioturbated metalimestone is mostly skeletal wacke- stone and lesser packstone and mudstone, which may alternate on a scale of centimeters or decimeters. Matrix consists of micrite, locally slightly recrystallized (crystals 2—14 um). Skeletal material constitutes 15 to 25 percent of most samples but reaches 60 to 80 percent and shows overly close packing in some millimeter- to centimeter- thick layers. Fossils in wackestone and mudstone intervals are mostly whole skeletons; shells are articulated and many are coated with and (or) partially replaced by pyrite. Bioclasts in packstone layers are commonly 3 mm or less in diameter, broken, abraded, and (or) disarticulated. Shelter porosity, filled with sparry calcite cement, and biogenic geopetal fabric (fig. 12C) are locally well developed in this lithology. A relatively diverse fauna characterizes the bioturbated metalimestone intervals. Corals are locally abundant and include Catem'pora sp. aff. C. rubra (T.E. Bolton, Geo- logical Survey of Canada, written commun., 1992) (fig. 12D), halysitids, favositids (fig. 12E, F), and syringopo- rids (R.B. Blodgett and WA. Oliver, Jr., US. Geological Survey, written commun., 1991). Most corals occur as isolated specimens, and biohermal concentrations were not observed. Other fossils include echinoderm debris, brachi- opods (including pentamerids), mollusks, and bryozoans. A second distinctive lithology is tan- to gray- weathering, gray metalimestone in even, parallel-laminated beds 2 to 5 cm thick; it forms subordinate intervals as much as 30 cm thick within intervals of bioturbated metalime- stone. These beds consist of packstone and grainstone made up of silt- to fine-sand-sized skeletal material, peloids, and a few percent detrital quartz. Bioclasts are mostly broken, abraded, and not specifically identifiable. Laminae are made of concentrations of peloids alternating with bioclasts; peloidal layers are generally somewhat dolomitic. Orange- to light-brown-weathering, dark-gray to black, locally calcitic dolostone in even, massive beds 20 cm to 3 m (typically 50 cm to 1 m) thick constitutes the third lithology. Most samples consist largely of euhedral to subhedral dolomite crystals 40 to 100 um in size. Relict microtextures indicate that these rocks were sparsely bio- clastic lime wackestone and mudstone prior to dolomitiza- tion (fig. 13A); a few to 20 percent silt- to sand-sized bioclasts are disseminated in the fine-grained matrix. In some samples, skeletal material has not been dolomitized; elsewhere, bioclast outlines are preserved as concentrations of organic material that crosscut dolomite crystal bound- aries. Identifiable skeletal material in these beds consists mostly of ostracodes, including Leperditia sp. (Dillon and others, 1988), gastropods, dasycladacean algae (fig. 133), and rare halysitid coral fragments. Locally, bioclasts have been bored or partly to completely micritized. A few to 10 percent disseminated peloids and oncoids occur in some samples. Peloids are ellipsoidal and average 0.2 mm in diameter; oncoids are oval, irregularly laminated, range from 0.5 to 2.0 mm in size, and are commonly partially pyritized. The fourth lithology is beige-, pink-, orange-, or tan-weathering, light- to medium—gray, dolostone to dolo- mitic limestone; it forms even to slightly irregular beds 2 cm to 2 m (mostly 10—40 cm) thick. Many samples are finely laminated (fig. 13C) and contain fenestral fabric. Laminae are 0.2 to 1.0 mm thick, crinkled and irregular, form small-scale hummocks with as much as 0.5 cm of relief, and are interpreted as cryptalgal in origin. Fenestrae vary from horizontal, laminar forms to more irregular shapes; most are 2 to 3 mm in diameter. Sheet cracks, 0.5 to 2 mm by l to 2 cm, occur locally. Both fenestrae and sheet cracks are filled with relatively coarse, sparry calcite or dolomite. Most of this lithology consists of finely crystalline (25—80 um) dolomite, but some intervals are undolomitized or partially dolomitized and display excellently preserved original microtexture. Fenestrae in these rocks are sur- rounded by lime mud or fine-grained peloids; the peloids have locally coalesced into a flocculent, clotty mass (struc— ture grumeleuse) in which individual grain outlines are difficult to discern (for example, Bathurst, 1976). The peloids are made of fine-grained calcite (crystals 2—20 um), Figure 12. Sedimentary features and megafossils of the V Mathews River unit. A, Nodular-bedded, bioturbated meta- limestone overlying parallel-laminated metalimestone (fig. 3, Ice. 10) (hammer, 40 cm long). B, Mottled fabric produced by bioturbation (fig. 3, 100. 12) (pen tip, 3 cm long). C, Shelter porosity in bioclastic wackestone (fig. 3, Ice. 6); gastropod shell (arrow) is filled with a thin layer of lime mudstone (dark) overlain by sparry calcite cement (light). D—F, Slabs of colonial corals in bioturbated metalimestone: D, Catenipora sp. aff. C. rubra (primitive halysitid coral) (fig. 3, loo. 6); E and F, Favositoid corals (fig. 3, locs. 12 and 16, respectively). 20 PRE—CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA Figure 13. Fossils and sedimentary features of the Mathews River unit. A, Photomicrograph of typical texture of fossiliferous dolostone; bioclasts float in matrix of peloidal carbonate mud (fig. 3, Ice. 12). B, Photomicrograph of dasycladacean algae in fossiliferous dolostone (fig. 3, 10c. 13). C, Cryptalgal lamination in dolostone (fig. 3, Ice. 8 grainstone containing subordinate bioclasts, B (fig. 3, 10c. 34). have maximum diameters of 100 to 160 um, and are uniformly ellipsoidal. Laminae in this lithology are produced by alternations of lime micrite and fine-crystalline dolomite or by subtle variations in dolomite color or crystal size. Some samples contain a few percent disseminated bioclastic debris. In addition, relatively coarse grained peloidal and (or) bioclas- tic grainstone and packstone form local layers a few millimeters to several centimeters thick. Peloids in these layers are irregular to oval and are 0.1 to 0.8 mm in diameter (fig. 13D). Recognizable bioclasts include ostra- codes and dasycladacean algae. AGE AND BIOFACIES The age of the Mathews River unit is constrained largely by conodonts, obtained from 26 samples at 17 localities (fig. 3; app. 1,10cs. 6, 8—10, 12, 13, 16, 17, 34); ) (entire pencil, 14 cm long). D, Photomicrograph of peloidal, P, 5 coral faunas from 4 localities provide additional age control. All four lithologies described above yield cono- donts, but burrowed metalimestone is the most productive rock type. Conodont collections from all parts of this unit are dominated by the long-ranging genus Panderodus, which merely indicates a Middle Ordovician through Mid- dle Devonian age. It is the sole constituent of five samples but elsewhere occurs with species that allow more precise age assignments. The oldest conodont samples (fig. 3, locs. 6, 8—10, 13; app. 1) contain Phragmodus n. sp. (fig. 8; pl. 2, figs. 20—24; =Phragm0dus n. sp. of Barnes, 1974) and fewer Plectodina? cf. P.? dolboricus and are of Edenian to Maysvillian (early Late Ordovician) age. Two samples yield slightly younger faunas. One collection (fig. 3, 10c. 12) consists exclusively of abundant, broken specimens of Aphelognathus aff. A. divergens and is Richmondian in age (fig. 8; pl. 2, fig. 16). A sample of peloidal dolostone (fig. 3, 10c. 9) yielded Ozarkodina aff. 0. oldhamensis and oulodontids (fig. 8; pl. 2, figs. 7—14) and is of very latest METACARBONATE SUCCESSION—CAMBRIAN TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS 21 Ordovician to Early Silurian age. The youngest conodont collections are Silurian in age; both Llandoverian to early Wenlockian (fig. 8; pl. 2, figs. 1—4) (fig. 3, locs. 16, 17) and Wenlockian to Ludlovian (pl. 2, figs. 5, 6) (USGS collns. 12069—SD, 12070—SD) faunas were found. Silurian sam- ples contain rare pterospathodids, icriodellid fragments, oulodids, and ozarkodinids (including 0. excavata and 0. cf. 0. cadiaensis), as well as ramiforrn and coniform elements of Kockelella and Pelekysgnathus, respectively (pl. 2, figs. 1—6). Coral collections from the Mathews River unit include Catenipora sp. aff. C. rubra of probable early Late Ordovician age (T.E. Bolton, written commun., 1992), Tetradium(?) sp. and halysitids of Late(?) Ordovi- cian age, and Mesofavosites? sp. of probable Late Ordovi- cian or Silurian age (Dillon and others, 1988). Conodonts from the Mathews River unit represent warm, shallow-water biofacies. Late Ordovician collections are dominated by provincial forms, but Edenian to Mays- villian faunas have slightly different biogeographic affini- ties than Richmondian faunas. Edenian to Maysvillian collections consist mostly of Siberian-northem North Amer- ican province elements (Phragmodus n. sp. and Plectodina? cf. P.? dolboricus). The single Richmondian sample is a monospecific collection of a western North American form, Aphelognathus aff. A. divergens. DISTRIBUTION The Mathews River unit crops out in several thrust sheets north, east, and southeast of Snowden Mountain. These sheets are intercalated with Devonian siliciclastic rocks, and, in the south, with metasedimentary rocks of uncertain age (fig. 2). Conodont collections demonstrate that some sections of the Mathews River unit have been tectonically thickened, and other sections contain fault slices of younger units. At locality 9 (fig. 3), peloidal dolostone of latest Ordovician or Early Silurian age underlies crinoidal marble of early Late Ordovician age; sedimentologic criteria indicate that these strata are not overturned. At locality 12 (fig. 3), peloidal and algal-laminated dolostone of Richmondian age under- lies at least 20 m of Frasnian metalimestone (Nutirwik Creek unit), which in turn underlies metalimestone and dolostone of Middle and Late Ordovician age. DEPOSITIONAL ENVIRONMENT The Mathews River unit was deposited in normal marine to slightly restricted, moderate to very shallow water environments. Sedimentologic and faunal evidence indicate that the major lithologies described above formed in spe- cific settings on the middle to inner shelf. Bioturbated metalimestone and parallel-laminated metalimestone were deposited in open-marine conditions at moderate to shallow water depths. Fossiliferous dolostone accumulated in a somewhat restricted, shallower water environment. Algal- laminated dolostone formed in the most restricted and shallowest water setting. Bioturbated metalimestone and subordinate beds of parallel-laminated metalimestone formed primarily below fair-weather wave base. These lithologies have features such as variable bed thickness, nodular bed form, abundant carbonate mud, and argillaceous partings that are charac- teristic (Wilson and Jordan, 1983) of middle shelf deposits. They contain a stenohaline macrofauna of corals, bryozo- ans, echinoderms, and brachiopods, indicating that open circulation and normal marine salinity prevailed during deposition. Bioturbated metalimestone is mostly “whole fossils wackestone” (usage of Wilson, 1975); the lime mud matrix and intact, unabraded skeletal material in these beds indicate deposition in relatively quiet water lacking “cur— rents of removal” (Dunham, 1962). Mud-poor beds of bioclastic packstone and parallel—laminated metalimestone (containing broken and abraded skeletal debris, peloids, and quartz) most likely accumulated during storms and (or) in local shoals. Fossiliferous dolostone formed in a shallower, more restricted environment than the rocks just described, prob- ably on the inner shelf. The abundance of lime mud (now dolomitized) indicates a quiet depositional setting like that inferred for the bioturbated metalimestone, but the macro- fauna includes few forms characteristic of normal marine conditions and is dominated by biota tolerant of restricted circulation (Wilson, 1975) such as ostracodes, gastropods, and dasycladacean algae. Some bioclasts are micritized, a process that most commonly occurs in the photic zone as a result of boring by endolithic algae (Bathurst, 1976). Local occurrence of oncoids and peloids in this lithology further supports the interpretation of a shallow-water, somewhat hypersaline depositional setting. Oncoids are biogenic encrustations, typically formed on soft substrates in moderate-energy environments (Wilson, 1975', Fliigel, 1982). Oncoids disseminated in a micritic matrix, as well as pelleted mudstone and wackestone, typically occur in pro- tected, somewhat restricted environments such as marine shelf lagoons (Wilson, 1975). Sedimentary structures and fauna of the algal- laminated mudstone lithology indicate deposition in shallow subtidal to supratidal environments on the inner shelf (Wilson, 1975; Shinn, 1983; James, 1984). The association of algal mats, fenestral fabric, and sheet cracks is best developed and most commonly preserved in intertidal to supratidal settings (James, 1984). Modern and ancient shallow subtidal sediments consist largely of gray (reduced) pelleted muds that have been thoroughly bioturbated and lack primary sedimentary structures; storms introduce such sediments onto tidal flats, where they form layers a few millimeters to several centimeters thick that alternate with 22 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA algal laminite (Shinn, 1983). Most peloids in the Mathews River unit are similar in size and shape to modern fecal pellets, but some grains are larger and (or) quite irregular and may be skeletal particles that are completely micritized (Bathurst, 1976). The sparse biota of the algal-laminated dolostone is consistent with deposition in an inner shelf setting. Megafossils are limited to ostracodes and algae, forms that are tolerant of restricted circulation and shallow water depths (Wilson, 1975). Interpretations of the depositional environments of the Mathews River unit suggested by conodont biofacies agree with those outlined above that are based on sedimentary features. Collections from bioturbated metalimestone and fossiliferous dolostone contain variably abundant Pandero— dus associated with Phragmodus n. sp., Plectodina? cf. P. ‘? dolboricus, and belodinids in Ordovician strata and with pterospathodids, icriodellid fragments, oulodids, ozarkodi- nids, and ramiform and coniform elements of Kockelella and Pelekysgnathus in Silurian strata. These assemblages indicate deposition in warm, relatively shallow water set- tings. Samples of clast-rich skeletal packstone and parallel- laminated metalimestone also produce Phragmodus n. sp. but consist chiefly of abraded, incomplete conodont frag- ments typical of high—energy depositional environments. Algal—laminated dolostone yields monospecific faunas of Panderodus sp. or Aphelognathus aff. A. divergens that are characteristic of warm, shallow-water, intermittently restricted environments. Sedimentologic and paleontologic evidence indicates that fossiliferous dolostone and algal-laminated dolostone were deposited in shallow to very shallow water with locally restricted circulation, and this depositional setting probably accounts for the pervasive dolomitization of these lithologies. Dolomite in the algal-laminated lithology may be detrital and (or) authigenic; both types of dolomite are common on modern tidal flats (Shinn, 1983). Subtidal sediments in the Mathews River unit may have been dolomitized by reflux of Mg-rich surficial brines produced in nearby supratidal environments; this mechanism has been invoked by many authors to explain dolomitization of a variety of modern and ancient sediments. The four major lithologies described and interpreted above occur throughout the Mathews River unit, but there is some spatial and temporal variation in their abundance. For example, bioturbated metalimestone is most abundant in the lower Upper Ordovician part of the unit, whereas fossilif- erous dolostone and algal-laminated dolostone predominate in uppermost Ordovician and Silurian strata. Sedimentary features and conodont biofacies suggest that the shallowest, most restricted conditions prevailed during Richmondian time. The Mathews River unit also contains small-scale lithologic cycles in both Ordovician and Silurian strata. A typical cycle is 50 cm to 5 m thick and consists of 20 cm to a few meters of burrowed, fossiliferous metalimestone overlain by a similar thickness of massive, sparsely fossil- iferous dolomitic wackestone. The wackestone grades up into a thinner interval of algal-laminated, peloidal dolostone with fenestral fabric, which is in turn overlain by another bed of fossiliferous metalimestone. The cycles appear to have formed under shallowing-upward (regressive) condi- tions because transitions from bioturbated metalimestone to dolomitic wackestone, and from dolomitic wackestone to cryptalgal dolostone, are generally gradational, whereas those from cryptalgal dolostone to fossiliferous metalime- stone are commonly abrupt. LOWER AND (OR) MIDDLE DEVONIAN ROCKS Rocks of confirmed Early or Middle Devonian age are rare in the study area, but Emsian and (or) Eifelian marble and metalimestone crop out 4.5 km east of Nutirwik Creek (fig. 3, loo. 6). At this locality, a small lens, 10 to 15 m thick, of Lower and (or) Middle Devonian strata uncon- formably overlies, or is faulted above, carbonate rocks of the Mathews River unit. These Devonian rocks are strongly deformed, lineated, and flattened, but relict sedimentary textures are locally preserved. Devonian rocks at locality 6 consist of yellow- weathering, cliff-forming marble with layers 50 cm to 2 m thick of dark-gray to black metalimestone and rare pink- to orange-weathering, medium-gray dolostone. Relict textures preserved in metalimestone include peloidal-bioclastic packstone and wackestone; bioclasts are chiefly crinoid columnals and coral debris. The most distinctive relict texture occurs near the base of the section and consists of packstone rich in aligned sticklike forms that do not branch and are probably amphiporid stromatoporoids (fig. 14). Individual sticks are 1 to 4 mm in diameter, as much as 3 cm in length, and contain an internal network of 0.2-mm pores; details of original wall structure have been destroyed by recrystallization. Similar packstone, rich in sticklike forms and crinoids, structurally (and stratigraphically?) overlies the Mathews River unit at several other sites (fig. 3, locs. 7, 8, and 14) and may be correlative with packstone at locality 6. Fossils and sedimentary structures in all these strata indicate a shallow-water depositional environment. Two-hole crinoid columnals in the rocks at locality 6 restrict their age to the Emsian and (or) Eifelian (late Early and (or) early Middle Devonian) (R.B. Blodgett, oral commun., 1990). These rocks are more likely of Emsian than Eifelian age. Our experience in northern Alaska indicates that two-hole crinoid columnals most often occur in rocks of Emsian age and are unlikely to occur in rocks younger than early Eifelian in age. Conodonts from local— ity 6 (USGS colln. 12064—SD) merely indicate a Silurian through Middle Devonian age. Samples taken for conodonts from the other localities noted above yielded only Pandero- dus sp. (Middle Ordovician to Middle Devonian) or were barren. METACARBONATE SUCCESSION—CAMBRIAN TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS 23 METACARBONATE ROCKS OF UNCERTAIN AGE Massive metacarbonate rocks that lack the lithologic characteristics of the Mathews River unit crop out through- out the study area; they occur in fault slices in the vicinity, from south to north, of Wiehl, Dillon, Snowden, and Table Mountains (Pzw, PzEd, Pm, and Pzt, fig. 2). These rocks are undated or contain fossils indicative of a relatively broad age range; some may be correlative with the Mathews River unit, but others may be older or younger. Some of these rocks possess distinctive sedimentary features, but most have retained little primary fabric. Lithologic and age information for these rocks is summarized by geographic area below. WIEHL MOUNTAIN AREA Metacarbonate rocks at Wiehl Mountain are lithologi- cally similar to the Mathews River unit and yield fossils permissive, but not diagnostic, of correlation with the Mathews River unit. But the Wiehl Mountain area meta- carbonate rocks are locally intercalated with noncarbonate lithologies not seen in the Mathews River unit and so are discussed separately here. Metacarbonate rocks make up the main massif of Wiehl Mountain and continue east at least 10 km. They are in thrust contact with calcschist to the east, other metacar- bonate rocks to the northwest, and the Snowden Creek unit and other metasedimentary rocks to the south. Marble is the major lithology; it is white to dark gray, white to orange to gray weathering, fine to medium crystalline and forms prominent cliffs. Local color lamination on a millimeter to centimeter scale reflects variation in purity and crystal size; darker laminae contain more mica and carbonaceous mate- rial and are finer grained. Layers of pink- to orange- weathering, light- to dark-gray dolostone a few centimeters to several meters thick form recessive zones or saddles. Figure 14. Aligned sticklike organic forms (proba- ble amphiporid stromatoporoids) in Emsian or Eifel- ian metalimestone (fig. 3, 10¢. 6). A, Slab. B, View of thin section in reflected light. Relict sedimentary textures are preserved in some metalimestone and dolostone layers. Lime packstone and wackestone containing peloids and (or) bioclasts occur at several localities on the west and north sides of Wiehl Mountain; identifiable skeletal debris in these rocks consists of echinoderm and brachiopod fragments. Color mottling, probably produced by bioturbation, characterizes some dolostones. Other dolomitic layers preserve cryptalgal lam- ination and fenestral fabric. These sedimentary structures are like those found in the Mathews River unit and indicate a shallow subtidal to peritidal depositional environment. Several types of metaigneous rocks are intercalated with the massive metacarbonate rocks at Wiehl Mountain. Brosgé and Reiser (1964) noted four elongate bodies of albite-epidote—chlorite-muscovite schist (Dgs) on the east side of the mountain. Dillon and others (1987b) reported bimodal volcanic rocks in this area; their “Llama Creek” sequence includes felsic flows, tuffs, and breccias, as well as mafic greenschists. These authors obtained a U—Pb isotopic age of 396 Ma (middle Early Devonian, based on Bally and Palmer, 1989; Harland and others, 1990) from a felsic flow on Wiehl Mountain and suggested that mafic and felsic rocks in this region are coeval. We observed both felsic and mafic metavolcanic rocks intercalated with the metacarbonate rocks at Wiehl Moun- tain (fig. 15A). Rubble of gray metarhyolite, containing phenocrysts of potassium feldspar and plagioclase, was found at one locality. Elsewhere, reddish-brown to green altered tuff forms centimeter— to meter-thick layers in marble; these layers consist mostly of fine-grained, felty masses of mica, clay, and carbonate that retain relict shard textures. Larger bodies (to 40 m thick) of green to greenish- gray, andesitic to basaltic metavolcanic rocks are locally schistose but elsewhere preserve diabasic textures and chilled margins. 24 PRE—CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA Figure 15. Sedimentary features of metacarbonate rocks of uncertain age. A, Marble, M, intercalated with, B, basaltic metavolcanic rocks, northeast side of Wiehl Mountain. B and C, Slabs showing coated grains and intraclasts with cryptalgal laminae, I, in dolomitic metalimestone, metacarbonate rocks of Dillon Mountain area (fig. 3, loc. 37). Conodonts indicate an age of Middle Ordovician to Middle Devonian for the metacarbonate rocks at Wiehl Mountain. Black peloidal dolostone on the southwest side of the mountain produced Panderodus sp. and a fragment of Ozarkodina? sp. indet., denoting a Late Ordovician to Middle Devonian age and a normal-marine, shallow-water depositional environment (USGS colln. 11961—SD). A sample of dolomitic marble taken 1.5 km to the northeast yielded only Panderodus sp., indicating a Middle Ordovi- cian to Middle Devonian age (field no. 89AD14A). Two other samples from the Wiehl Mountain metacarbonate rocks were barren. DILLON MOUNTAIN AREA Metacarbonate rocks that crop out in the vicinity of Dillon Mountain have certain lithologic features that distin- guish them from all other rocks in the study area. They occur in a northeast-trending fault slice that extends at least 15 km from Sukakpak Mountain east to the Mathews River and that is imbricated with metacarbonate rocks to the south and east and calcschist to the north and west. Stratigraphic thickness of this sequence appears to be several hundred meters, but the section may have been tectonically thick- ened. The rocks are strongly deformed; isoclinal folds are obvious in outcrop. . Major lithologies are marble, dolomitic marble, and dolostone, with rare, meter-thick layers of orange- or green-weathering, calcareous or chloritoid-bearing, quartz- ose metasedimentary rocks. Most marble is light-gray weathering, white, medium crystalline, and relatively pure; it forms massive cliffs cut by irregular, flaggy foliation planes. Some intervals are distinctly color-banded on a scale of a few millimeters to several meters; the banding is produced by layers of dark-gray micaceous or dolomitic marble, or of orange or gray dolostone. Relict primary features are rare in marble and consist mainly of local parallel to low—angle cross lamination defined by quartz- rich laminae a few millimeters to 2 cm thick. However, sedimentary textures are preserved in many dolomitic lay- ers; these layers consist of grainstone to wackestone made up of a variety of coated grains (fig. 153, C). METACARBONATE SUCCESSION—CAMBRIAN TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS 25 Coated grains occur in layers 0.5 to 5 cm thick and consist both of ooids and oncoids (usage of Fliigel, 1982). Ooids in these rocks are relatively homogeneous in size (average diameter 1.0 mm) and shape (spherical to ellipsoi— dal) and contain smooth, multiple, concentric laminae. Oncoids vary in size (0.5—3 mm), are more irregular in form, characterized by uneven laminae, and include some composite grains with multiple nuclei. Both sorts of coated grain generally occur in grain support, but some layers contain 20 percent or fewer grains floating in a finely crystalline matrix. Most of the coated grains in these rocks consist of polycrystalline dolomite in a calcite matrix; locally, both grains and matrix are dolomite. Concentric lamination within these dolomite masses is preserved as a palimpsest texture that crosscuts individual dolomite crys- tals. Coated-grain—bearing layers are most abundant in the lower third of the Dillon Mountain section (for example, fig. 3, 100. 37). A few layers in this interval contain crinkly, hummocky lamination of probable cryptalgal (stromatolitic) origin; cryptalgal laminite also occurs as elongate intraclasts in some coated-grain-rich layers (fig. 153, C). Preserved sedimentary features indicate a peritidal depositional environment for the Dillon Mountain area metacarbonate rocks. Ooids form through inorganic chem- ical precipitation in warm, wave-agitated saline or hyper- saline waters; oncoids are produced by biogenic encrusta— tion, typically by algae or cyanobacteria (Wilson, 1975; Flfigel, 1982). Modern ooids and oncoids form in warm, shallow shelf areas of moderate to high wave and current activity; oolitic sands generally occur in waters less than 10 m deep (Choquette, 1978). As noted above, algal mats are most common in intertidal to supratidal settings (James, 1984), particularly in Paleozoic or younger rocks. Other than oncoids and cryptalgal laminae, no organic structures have been found to constrain the age of the Dillon Mountain area metacarbonate rocks. Several samples were taken for conodonts, but all were barren. Similar carbonate sequences containing abundant coated grains (ooids and oncoids) and stromatolites but lacking other organic remains occur in the western Brooks Range (unnamed units described by Dumoulin, 1988) and in the northeastern Brooks Range (Katakturuk Dolomite; Clough, 1989; Clough and others, 1990). These rocks are thought to be of Late Proterozoic and (or) earliest Paleozoic age in the western Brooks Range (Dumoulin, 1988) and of Protero- zoic age in the northeastern Brooks Range (Blodgett and others, 1986). SNOWDEN MOUNTAIN MASSIF Massive metacarbonate rocks make up the main massif of Snowden Mountain and are in probable fault contact with Cambrian rocks (Snowden Mountain unit) to the northwest, Upper Ordovician and Silurian metacarbonate rocks (Mathews River unit) to the northeast, Middle Ordovician phyllite and metalimestone (Snowden Creek unit) to the southwest, and metacarbonate rocks of uncertain age (Dil- lon Mountain area metacarbonate rocks) to the south (fig. 2). Little sedimentologic or paleontologic information has been recovered from the Snowden Mountain massif meta— carbonate rocks, at least in part because the steep and rugged terrain has limited helicopter access. No lithologic or biostratigraphic data yet obtained permit definitive cor- relation of these rocks with any of the metacarbonate units described above; available fossil collections indicate that strata of several ages are present. Most of the Snowden Mountain massif metacarbonate rocks examined are light-gray-weathering, white to light- gray, fine- to medium—crystalline marble exposed in sheer cliff faces. Some marble is color laminated and contains rare echinoderrn debris. Subordinate intervals of pink- to beige-weathering, medium— to dark-gray dolostone preserve relict sedimentary features, including sheet cracks and fenestral fabric. No megafossil-based ages are reported from massive metacarbonate rocks making up the Snowden Mountain massif, and samples taken for conodonts have been mostly unproductive. Dillon and others (1988) reported three collections from the southern, central, and northern parts of the massif, as well as two barren samples. The southem- most collection was made along Snowden Creek in massive metacarbonate rock 7 m from the contact with black phyllite of the Snowden Creek unit; it yielded a meager fauna of probable late Early through early Middle Ordovician (mid- dle Arenigian through Llanvirnian) age (USGS colln. 9905—CO; fig. 3, 10c. 24; 10c. 13 of Dillon and others, 1988). A sample of marble about 2 km to the northwest, however, produced a single deformed conodont of Silurian through Mississippian morphotype (fig. 3, 10c. 23; 10c. 16 of Dillon and others, 1988). The northernmost collection came from massive dolostone 5 m above the contact with Cambrian rocks and consists of a single fragment of Ordovician through Triassic age (fig. 3, Ice. 21; loc. 20 of Dillon and others, 1988). Three samples taken from the massif during the present study were barren. TABLE MOUNTAIN AREA Massive metacarbonate rocks in the Table Mountain area have some lithologic similarities to the Mathews River unit but include little or no dolostone and have produced no fossils diagnostic of a Silurian or older age. These rocks crop out from the Hammond River northeast to Table Mountain (fig. 3) and make up several thrust sheets imbri- cated with Devonian siliciclastic rocks (fig. 2). Table Mountain area metacarbonate rocks are mostly cliff-forming, light- to medium-gray marble and lesser 26 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA medium- to dark-gray metalimestone; relict sedimentary textures are rare and consist of skeletal—peloidal wackestone and packstone. Recognizable bioclasts are chiefly echino- derm columnals but include brachiopods, ostracodes, and stromatoporoid and bryozoan fragments. Peloids range from 30 to 200 um in diameter and are rounded to ellipsoidal. Few fossils have been found to constrain the age of these rocks. Megafossils are poorly preserved; collections from two localities east and southeast of Table Mountain are of Silurian or Devonian age (Brosgé and Reiser, 1964, their locs. 9 and 10). Conodonts are scarce and nondiagnostic. Of seven samples taken during our study, two produced fragments indicative of an Ordovician through Permian or Triassic age (field localities 89TM290A and 90TM468C, respectively), and five were barren. Dillon and others (1988) reported three barren samples from these rocks (their locs. 45, 49, and 62). SUMMARY OF THE METACARBONATE SUCCESSION IN THE SNOWDEN MOUNTAIN AREA The massive metacarbonate rocks and subordinate associated lithologies described above represent a pre- Carboniferous stratigraphic succession that has been meta- morphosed, deformed, and dismembered by thrust faults. This succession encompasses distinct lithologic units of relatively well—constrained ages, as well as other units of uncertain age. Figures 6 and 8 summarize stratigraphic relationships of well-dated units in the Snowden Mountain area; figure 16 attempts to integrate units of uncertain age within this framework and presents several alternative stratigraphic hypotheses. Well-dated units in the Snowden Mountain area meta- carbonate succession are the Snowden Mountain unit (Middle Cambrian), the Snowden Creek unit (Middle Ordovician), the Mathews River unit (Upper Ordovician through Silurian), and unnamed Lower and (or) Middle Devonian metalimestone. Most contacts between these units are faults, but some contacts between the Snowden Creek and Mathews River units may be depositional, and the contact between the Mathews River unit and overlying Lower and (or) Middle Devonian metalimestone may be an unconforrnity. Units of uncertain age but that, by virtue of spatial association and lithologic correlation, also appear to be part of the Snowden Mountain area metacarbonate succession are the metacarbonate rocks of the Wiehl Mountain area, the Dillon Mountain area, the Snowden Mountain massif, and the Table Mountain area. All of these units (with the possible exception of Snowden Mountain massif strata) are fault bounded. All consist of massive metacarbonate rocks generally similar to, but not as dolomitic as, those that make up the Mathews River unit, and all contain some organic remains. Stratigraphic integration of these units within the Snowden Mountain area metacarbonate succession is attempted in figure 16 and is constrained by fossils, lithologic considerations, and local and regional relationships. The Dillon Mountain area metacarbonate rocks have produced no organic remains other than algal structures (stromatolites, oncolites). Such forms are known from strata of Archean to Holocene age but are most common in Proterozoic rocks (Krumbein, 1983). Both algal lamination and coated grains are found in Paleozoic strata in the Snowden Mountain area; stromatolites occur in tidal-flat facies of the Upper Ordovician through Silurian Mathews River unit, and coated grains (ooids) make up one bed in the Upper Devonian Hunt Fork Shale (discussed below). How- ever, these occurrences also include other fossil debris; algal laminites in the Mathews River unit contain local ostracodes and are interlayered with coral-bearing meta- limestone, and ooid grainstone in the Hunt Fork Shale contains brachiopod and echinoderm fragments in addition to coated grains. Strata elsewhere in northern Alaska that contain only algal forms and no other fossils, such as the Katakturuk Dolomite in the northeastern Brooks Range and unnamed rocks in the western Brooks Range, are thought, on the basis of regional relationships and isotopic data, to be of Proterozoic age in the northeastern Brooks Range (Blodgett and others, 1986; Clough and others, 1990) and Late Proterozoic age and (or) Early Cambrian age in the western Brooks Range (Dumoulin, 1988; Till, in press). We propose that the Dillon Mountain area metacarbon- ate rocks correlate with other stromatolitic, coated—grain- bearing units in the Brooks Range and infer an age of Proterozoic and (or) Early Cambrian for them. If this inference is correct, the Dillon Mountain area metacarbon— ate rocks predate the Middle Cambrian Snowden Mountain unit and constitute the basal part of the Snowden Mountain area metacarbonate succession. The Snowden Mountain unit has so far been recognized in only one area, more than 10 km north of the northernmost outcrops of the Dillon Mountain area metacarbonates, so the original stratigraphic relationship between these two units cannot directly be assessed. Did strata of the Snowden Mountain unit origi- nally accumulate on the Dillon Mountain area metacarbon- ate rocks? Or did spatially associated rocks of unknown age, such as the calcschist exposed north and west of Dillon Mountain (included in unit szu, fig. 2), originally overlie the metacarbonate rocks and underlie the Snowden Moun- tain unit? Further mapping and structural analyses are needed to resolve this problem. Metacarbonate rocks of the Snowden Mountain massif retain little relict texture and have yielded few fossils. Meager conodont collections of (from north to south) Ordovician through Triassic, Silurian through Mississip- pian, and late Early through early Middle Ordovician age are known (fig. 3, locs. 21, 23, and north end of 24). The METACARBONATE SUCCESSION—CAMBRIAN TO MIDDLE DEVONIAN METASEDIMENTARY ROCKS 27 SNOWDEN MOUNTAIN SYSTEM/ SERIES/SUBSERIES/ (3539,11; ”2:592:38?!“ SERIES STAGE/SUBSTAGE UNIT DEVONIAN EIFELMN AND (OR) EMSIAN § ‘ ‘ LUDLOVIAN AND WENLOCKIAN g f 5 Flu SILUFIIAN WENLOCKIAN AND _ s METERS LLANDOVERIAN 5‘21 I s a F 400 _ . , N N ., . I: I: E "~ 'r ? II 7 . / N RIOHMONDIAN m i ,K/ ‘ , (INCLUDES MINOR 2 7 is t I: LOWER SILURIAN(?) ‘1 “ 'g' '1’” 35° _ 3f STRATA) g M % uJ l s . 1: I s '2 IL. ~ 2 21‘.— f / ”NV 300 — MAYSVILLIAN ' we . X... 2 AND EDENIAN ”fl" 5 ‘ _ ’ . F/C'? <_J . > O 250 — E I: O § LOWER x CARADOCIAN(?) ”I; AND LLANDEILIAN 0: u.| O -‘ z 200 — 8 I3 5 3 O _______ Z (I) LLANVIRNIAN 150 —— UPPER E E '_ p— _ _ ARENIGIAN gg E . FIE \ CAMBRIAN LOWER MIDDLE g g 100 F LOWER CAMBRIAN 5° — AND (OR) PROTEROZOIC 0 / DILLON SNOWDEN WIEHL TABLE MOUNTAIN MOUNTAIN MOUNTAIN MOUNTAIN AREA MASSIF AREA AREA HI-l-ll ”-I—I | | | I I I I l | | | | | I I I I I | I | I I l | I / / / / LOWER ORDOVICIAN O 0 Figure 16. Hypothetical stratigraphic position of units of uncertain age within the metacarbonate succession in the Snowden Mountain area. Parts of columns with symbols indicate preferred correlation. Thicknesses are minima, particularly for Upper Ordovician and Silurian rocks. European series names are used for intervals containing dominantly cosmopolitan faunas, whereas North American series and (or) stage names are used for intervals containing chiefly North American province faunas. See figure 5 for explanation of symbols. Snowden Mountain massif metacarbonate rocks structurally overlie Middle Cambrian rocks of the Snowden Mountain unit to the north and structurally underlie Middle Ordovi— cian rocks of the Snowden Creek unit to the south, but the exact nature of these contacts is disputed. Dillon and others (1988) included the Snowden Mountain massif metacarbon- ate rocks in their Skajit Formation, which they considered to be of Devonian age, and interpreted the northern contact as an unconformity and the southern contact as a fault. However, T.E. Moore (written commun., 1991) suggested that the southern contact may be depositional, and we observed some evidence (discussed above) that the northern contact is a fault; The stratigraphic position of the metacarbonate rocks of the Snowden Mountain massif is thus uncertain, and it is possible that rocks of several ages are included within this unit. Two hypotheses are most compatible with the avail- able data. In the first, the Snowden Mountain massif metacarbonate rocks depositionally overlie Middle Cam- brian rocks, depositionally underlie Middle Ordovician strata, young from north to south, and are of Early to earliest Middle Ordovician age. In this interpretation, the lower age of the unit is limited by the Ordovician-Triassic conodont fragment obtained just above the contact with Middle Cambrian rocks, the upper age is constrained by the late Early through early Middle Ordovician age of the fauna 28 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA collected just below the contact with Middle Ordovician rocks, and the Silurian-Mississippian collection must be attributed to a fault sliver of younger rocks. A second possibility is that the Snowden Mountain massif metacarbonate rocks are a facies equivalent of the Mathews River unit and are of Late Ordovician through Silurian age; they could also be Devonian in age, as suggested by Dillon and others (1988). In this interpreta— tion, the northern contact could be a fault or an unconform- ity, but the southern contact must be a fault. This hypothesis is compatible with two of the three fossil collections from these strata; conodonts of late Early through early Middle Ordovician age from locality 24 (fig. 3) must be reworked or produced by a sliver of the Snowden Creek unit. The metacarbonate rocks in the Wiehl Mountain and Table Mountain areas have some lithologic similarities to the Mathews River unit and contain rare fossils of Ordovi- cian to Devonian and Silurian to Devonian age. These data are compatible with, but not diagnostic of, correlation with the Mathews River unit and assignment of a Late Ordovi- cian and Silurian age. Available evidence also permits the interpretation that these rocks are, at least in part, of Devonian age, and they could be entirely younger than the Mathews River unit. Metaigneous rocks like those interca— lated with the Wiehl Mountain area metacarbonate rocks have not been noted in the Mathews River unit or in any of the other metacarbonate units discussed above. The Table Mountain area metacarbonate rocks occur north of all other metacarbonate units and are intimately associated with Devonian siliciclastic rocks, particularly those of the Nutir- wik Creek unit. Thus, the Snowden Mountain area metacarbonate suc- cession includes rocks of Middle Cambrian, Middle Ordo- vician, Late Ordovician, Silurian, and Early and (or) Middle Devonian ages; less well dated parts of the succes- sion may be Proterozoic and (or) Early Cambrian and Early Ordovician in age. Shallow-water shelf or platform depo- sition occurred during Proterozoic and (or) Early Cambrian, Early Ordovician(?), Late Ordovician and Silurian, and Early and (or) Middle Devonian time; outer-shelf to basinal environments prevailed during Middle Cambrian and Mid- dle Ordovician time. Fauna] and lithologic evidence indi— cate that the deepest water (most basinal) settings existed during the early Middle Ordovician, whereas the shallow- est, most restricted depositional regimes existed in the latest Ordovician. Fossils with specific biogeographic affinities found in this succession include Middle Cambrian trilobites and early Late Ordovician conodonts with Siberian affini- ties, an early Late Ordovician cateniporid coral with Cana- dian Arctic affinities, and latest Ordovician conodonts with western North American affinities. Fossils of Middle Ordo- vician, Silurian, and Devonian ages (mainly conodonts) are chiefly cosmopolitan. DEVONIAN METACLASTIC ROCKS The pre-Carboniferous Paleozoic metacarbonate rocks described above are structurally juxtaposed with Devonian metaclastic rocks throughout the Snowden Mountain area (fig. 17A). These metaclastic rocks consist of the Hunt Fork Shale (Chapman and others, 1964), the Beaucoup Forma- tion (Dutro and others, 1979; Dillon and others, 1988), and the Nutirwik Creek unit (Aleinikoff and others, 1993). All three units consist chiefly of fine-grained siliciclas- tic rocks with subordinate layers and lenses of metalime- stone and include distinctive subordinate lithologies. The units are further distinguished by characteristic carbonate lithofacies and conodont biofacies. Conodonts obtained from limy layers demonstrate that the three metaclastic units are at least in part correlative and in part of Frasnian age. Our study concentrated on metalimestone intervals within the metaclastic units and was less detailed than our work on the metacarbonate sequence. The descriptions below are based on reconnaissance outcrop observations and petrologic and paleontologic analyses of spot samples; sections were not measured in the metaclastic units. BEAUCOUP FORMATION In the Snowden Mountain area, the Beaucoup Forma- tion consists chiefly of gray slate and phyllite with lesser amounts of quartz-muscovite schist and local mafic intru- sions. Limy layers are relatively abundant and constitute 5 to 30 percent of most sections; they are more abundant in outcrops in the southern part of the study area. Some metalimestone bodies are tens of meters thick and as much as 6 km long (Dillon and others, 1988), but most are smaller (2—30 m thick, a few tens of meters long) and distinctly lens shaped. CARBONATE LITHOLOGIES The most southerly exposures of the Beaucoup Forma- tion in the study area, in the vicinity of the sharp bend in the Hammond River (figs. 2 and 3), are strongly recrystallized and retain little relict texture. Carbonate layers in these rocks consist of fine- to medium-crystalline marble with minor amounts of detrital quartz and rare brachiopod fragments. Elsewhere in the Snowden Mountain area, original textures of the Beaucoup Formation are better preserved, and carbonate bodies consist of two main types. The first is mostly gray-weathering, dark—gray to black, fine-grained lime mudstone, wackestone, and lesser packstone, in mound-shaped lenses 3 to 30 m thick (fig. 178). These rocks are generally massive but contain irregularly spaced gray to orange phyllitic partings and local mottled zones produced by bioturbation. Most bodies are texturally and compositionally heterogeneous and tend to be darker, finer DEVONIAN METACLASTIC ROCKS 29 Figure 17. Features of the Beaucoup Formation. A, Beaucoup Formation, including phyllite, gabbro, and Frasnian metalimestone, overlies massive metacarbonate rocks (photograph by T.E. Moore). B, Thick, mound-shaped layer of fossiliferous metalimestone (fig. 3, loc. 27); a sample from this locality (USGS colln. 11966—SD) produced conodonts of latest Givetian or early Frasnian age (pl. 3, figs. 3, 4). C, Deformed corals in metalimestone (field loc. 89ATi39). grained, richer in clay, and less recrystallized toward the periphery. The predominant lithology is slightly recrystallized lime mudstone. Most samples contain 2 to 10 percent bioclasts and peloids disseminated in a matrix of calcite crystals 8 to 25 mm in diameter. Bioclasts, locally bored and micritized, include echinoderm columnals and spines, ostracodes, and bryozoans. Peloids are ellipsoidal, 40 to 160 mm in diameter, and organic rich. Some samples are couplets, a few centimeters thick, of relatively pure lime mudstone grading up into finer grained, phyllitic lime mudstone. Bioclastic—peloidal wackestone and packstone form zones a few centimeters to several meters thick within these muddy mounds. Bioclasts here are chiefly corals, stroma- toporoids, and fewer brachiopods and echinoderms. Fossils are not uniformly distributed; some patches are rich in corals or stromatoporoids, for example, whereas others contain mostly brachiopods. Corals are tabulate forms and solitary and colonial rugosans (fig. 17C). Coral genera 30 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA include Alveolites? sp., Cladopora? sp., Macgeea sp., Spongophyllum? sp., and Thamnopora sp.; stromatoporoids include Amphipora sp. and massive forms (Dillon and others, 1988). Articulated brachiopod shells and articulated crinoid columnals occur locally and indicate relatively quiet water conditions. The second type of carbonate body consists of buff- to orange-weathering, gray lime packstone to grainstone in relatively elongate lenses 2 to 10 m thick. Some intervals appear thoroughly bioturbated, and discrete Chondrites— type burrows occur locally. Clasts, mostly skeletal material and peloids, range from very fine to coarse sand sized; individual samples are fairly well sorted. Bioclasts are generally broken and abraded, and many are micritized. Identifiable biotic grains consist of crinoid columnals and fewer brachiopod fragments, foraminifers, and algal onco- lites. Peloids in these bodies are more irregular in size and shape than those in the muddy mounds; they range from 50 to 700 mm in diameter, and at least some may be micritized skeletal grains. Most samples also contain 1 to 25 percent disseminated, angular, quartz silt and sand. Euhedral rhombs of dolomite, 30 to 50 um in diame- ter, occur locally in all of the calcareous lithologies described above. They are most common in mudstones and grain—poor wackestones and constitute 5 to 30 percent of some samples. Silicification of skeletal material is rare but was noted at a few outcrops. AGE AND BIOFACIES Conodonts indicate that the Beaucoup Formation in the study area is of latest Givetian and Frasnian (latest Middle and early Late Devonian) age. Megafossils in these rocks are chiefly poorly preserved corals, stromatoporoids, brach- iopods, and mollusks of Middle through early Late Devo- nian age (Brosgé and Reiser, 1964, locs. 2 and 3; Brosgé and others, 1979, locs. 136 and 143; Dillon and others, 1988, locs. 2, 3, 11,28, 51, 60, 61). Conodonts have been obtained from 19 collections at 17 localities (fig. 3, locs. 3, 15, 26, 27, 33). Some conodont collections merely indicate a broad Middle to Late Devonian age, but others are more diagnostic. Four collections are latest Givetian to early Frasnian in age (fig. 3, 1005. 15 , 26, 27, 33), one represents an interval within the early Frasnian (upper part of transi- tans Zone into lower part of Upper hassi Zone; USGS colln. 12078—SD, about 30 km east of the study area, listed in app. 1 and not shown on fig. 3), and another is long-ranging within the Frasnian (Upper hassi Zone to linguiformis Zone; fig. 3, loo. 3). Map distribution of these diagnostic samples suggests that younger parts of the Beaucoup Formation are exposed to the north. Conodonts from the Beaucoup For- mation mostly represent a polygnathid-icriodid biofacies, which typifies normal-marine, relatively shallow-water, and locally high-energy depositional environments. DISTRIBUTION The Beaucoup Formation occurs in largethrust sheets throughout the Snowden Mountain area (fig. 2). It is tectonically interleaved with the Hunt Fork Shale and Nutirwik Creek unit in the north and with the Mathews River unit, the Snowden Creek unit, and metasedimentary rocks of uncertain age to the south. DEPOSITIONAL ENVIRONMENT Siliciclastic strata predominate throughout the Beau— coup Formation, indicating that conditions suitable for carbonate accumulation were only locally or occasionally achieved. Lithologic and fauna] evidence demonstrates that limy layers in this unit accumulated in situ as shallow-water bioherms and bioclastic shoals. Turbidity strongly inhibits primary carbonate production (for example, Wilson, 1975); thus, limy strata formed only in times and (or) places of reduced Siliciclastic influx. The two types of carbonate bodies described above formed in slightly different settings. We interpret mudstone-wackestone “mounds,” locally rich in corals, stromatoporoids, and other fossils, as biohermal buildups; the abundance of mud and the presence of articulated brachiopods and crinoid columnals suggest deposition in quiet water below fair-weather wave base. The fauna is predominantly stenohaline and denotes open circulation and normal-marine salinity. Peloids in these rocks resemble modern fecal pellets. Thinner layers of packstone and grainstone accumulated in shallower and (or) higher energy settings, as demonstrated by abraded, size—sorted grains and rarity of mud. Some layers were probably deposited in carbonate sand shoals; others may be grain-rich lags derived from bioherms through current winnowing. Peloids in these rocks are most likely micritized grains; micritization is most common in the shallow photic zone where it is mediated by algae (Bathurst, 1976). Different lithologies in the Beaucoup Formation pro- duce distinct conodont assemblages. Samples from muddy biohermal buildups produce few conodonts; those that occur represent chiefly the polygnathid-icriodid biofacies, with or without pandorinellinids (pl. 3, figs. 1—4). More diverse and abundant faunas are found in bioclastic packstone- grainstone layers. Polygnathids dominate these collections but occur with ancyrodellids, Mesotaxis, and rare icriodon- tids and Klapperina (pl. 3, figs. 5—11). It appears that Pandorinellina, Icriodus, and polygnathids lived over the biohermal buildups, whereas Ancyrodella, Mesotaxis, and DEVONIAN METACLASTIC ROCKS 31 many polygnathids lived over and peripheral to grain-rich bioclastic shoals and aprons surrounding the buildups. HUNT FORK SHALE The Hunt Fork Shale consists of as much as 1,000 m of dark—gray to black shale, slate, and phyllite with lesser amounts of fine- to medium-grained sandstone, siltstone, calcareous sandstone, and ferruginous fossiliferous lime- stone (Brosgé and others, 1979; Nilsen, 1981; Moore and Nilsen, 1984) (fig. 18A). The unit was defined by Chapman and others (1964) from exposures in the Killik River quadrangle, 150 km west of Snowden Mountain but has since been recognized throughout the Brooks Range. It is the basal formation of the Endicott Group (Tailleur and others, 1967) and grades upward into marginal marine and nonmarine clastic rocks (Noatak Sandstone and Kanayut Conglomerate). In the Philip Smith Mountains quadrangle, the Hunt Fork Shale is at least 700 m thick and comprises quartzite, calcareous sandstone, limestone, shale, and wacke members (Brosgé and others, 1979). The limestone member consists of lenticular beds, 1 to 15 m thick, that occur mostly in a persistent zone as much as 50 m thick about 200 to 300 m below the top of the formation. In addition, minor thin limy beds occur in other members. Most calcareous layers examined for this study are part of the shale member of Brosgé and others (1979). CARBONATE LITHOLOGIES In the Snowden Mountain area, the Hunt Fork Shale contains fewer, thinner limy layers than does the Beaucoup Formation. Calcareous beds make up 5 percent or less of most sections and are generally 5 cm to 1.5 In thick; rare carbonate intervals as much as 100 m thick occur at some outcrops. Many limy layers in the Hunt Fork Shale contain a mixture of calcareous and siliciclastic grains. In the descriptions below, calcarenite describes rocks that include more than 10 percent noncarbonate detrital clasts. Thinner calcareous beds in the Hunt Fork Shale are graded (fig. 18B), locally bioturbated, and consist mostly of orange-weathering, medium-gray to black bioclastic grain- stone, lesser packstone, and calcarenite composed of fossil debris (5—70 percent), carbonate lithic clasts (1—30 per- cent), and siliciclastic detritus (1—80 percent) (fig. 18C, D). Most samples are poorly sorted and contain coarse bioclasts (a few millimeters to several centimeters in diam— eter) in a matrix of fine to very fine carbonate and siliciclastic sand cemented by sparry calcite or (rarely) silica. Muddy rip-up clasts are locally abundant, and many bioclasts are filled and (or) coated with mud. Fossils include corals (solitary and colonial rugosans), brachiopods, echin- oderrns, bryozoans, gastropods, ostracodes, foraminifers, ichthyoliths, and hydraulically sorted, reworked conodonts of mixed biofacies (pl. 3, figs. 12—15). Carbonate clasts are primarily lime mudstone and peloidal packstone; most are rounded to irregular and of probable intrabasinal origin, but some are angular, contain calcite veins truncated at the clast margin, and are most likely extrabasinal. Noncarbonate grains are angular to subangular and consist chiefly of monocrystalline quartz, less abundant chert, and minor amounts of plagioclase feldspar, phyllite, white mica, chlorite, phosphate, and opaques. Dark-gray, medium-bedded oolitic grainstone (fig. 18E) forms a 30-cm-thick bed in the Hunt Fork Shale 2 km south of Atigun Pass (fig. 3, 10c. 1). Ooids average 0.5 mm in diameter, display both concentric and radial lamination, and occur in a matrix of sparry calcite cement; many have quartz silt nuclei. Other grains make up less than 5 percent of this bed and consist of brachiopod and echinoderm debris, quartz sand, and intraclasts of oolitic packstone. Rare, thicker (2—100 rn) carbonate intervals in the Hunt Fork Shale consist of nodular bedded to massive, bioclastic-peloidal lime wackestone and mudstone. These rocks contain corals, stromatoporoids, bryozoans, and gas- tropods dispersed in a matrix of peloids and slightly dolomitic lime mud. AGE AND BIOFACIES Megafossils indicate a Frasnian and Famennian (early and late Late Devonian) age for the Hunt Fork Shale in the Philip Smith Mountains quadrangle (Brosgé and others, 197 9). Frasnian corals, brachiopods, pelecypods, mollusks, and plants have been obtained from the limestone, calcar- eous sandstone, and shale members of the formation, but the uppermost wacke member yields Famennian brachio- pods and pelecypods. In the Snowden Mountain area, conodont assemblages from limy layers in the Hunt Fork Shale are dominated by polygnathids and suggest a middle to late Frasnian age (pl. 3, figs. 12—15). Nine samples from eight localities yielded conodonts (fig. 3, locs. 1, 2). Collections are more abun- dant than those from the Beaucoup Formation, and poly- gnathids are more diverse; they are chiefly Polygnathus pacificus (pl. 3, fig. 13), P. aequalis, P. evidens (pl. 3, fig. 12), and P. samueli (pl. 3, fig. 14). Some of these species have previously been reported only from late Frasnian rocks of the Hay River area, southwestern Northwest Territories, Canada (Klapper and Lane, 1985), and southeast Alaska (Savage, 1992). Most collections represent a post-mortem biofacies mixture derived from normal—marine, relatively shallow to moderately deep shelf environments. DISTRIBUTION The Hunt Fork Shale crops out only in the northem- most part of the study area in the vicinity of Atigun Pass 32 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA Figure 18. Sedimentary features of the Hunt Fork Shale. A, Typical outcrop of phyllite containing subordinate layers of metasiltstone and metasandstone (hammer, 40 cm long). B, View of thin section (reflected light) showing graded metalimestone bed; coarse grains at base of sample are coral fragments (field loc. 90TM527). C, Photomicrograph of thin calcareous bed containing abundant detrital quartz grains, as well as, M, mudstone clasts and skeletal debris (fig. 3, Ice. 1). D, Photomicrograph of thin calcareous bed made chiefly of carbonate bioclasts such as, C, crinoid ossicles (field 10c. 90TM570). E, Photomicrograph of oolitic grainstone (fig. 3, loc. 1). (fig. 2). It forms several large fault sheets thrust above the Beaucoup Formation to the south and the Kanayut Con— glomerate to the north. DEPOSITIONAL ENVIRONMENT The Hunt Fork Shale, like the Beaucoup Formation, accumulated in a marine regime dominated by silici- clastic influx. But Hunt Fork limy layers are thinner and rarer than those in the Beaucoup Formation and indicate a depositional environment even more inimical to in situ carbonate production. Previous workers observed that the Hunt Fork Shale grades upward from deep- to shallow-marine facies (for example, Nilsen, 1981; Moore and Nilsen, 1984). Most of the unit accumulated in a low—energy, relatively deep (below fair-weather wave base) depositional environment such as a prodelta slope, but the uppermost wacke member records delta progradation across a shallower (outer shelf?) setting (Moore and Nilsen, 1984). The lower part of the Hunt Fork Shale contains thin, graded beds of siliciclastic sandstone and siltstone that increase in abundance upward. Some of these beds contain partial Bouma sequences and are probably turbidites, whereas others may have formed through vertical settling from storm-generated overflows (Nilsen, 1981). Sandstone bodies in the upper part of the Hunt Fork represent shoals, channel-mouth bars, and sub- merged linear ridges (Nilsen, 1981). DEVONIAN METACLASTIC ROCKS 33 Sedimentologic and faunal evidence indicate that most limestone layers of the Hunt Fork Shale in the study area were not generated in place but were redeposited by storm waves and (or) turbidity currents. A tempestite origin may best explain many of the thin calcareous beds. They do not display sedimentary structures characteristic of Bouma sequences, such as parallel and cross lamination, but do possess typical storm deposit features (Fliigel, 1982), including grading, shale rip-up clasts, a variety of carbonate lithoclasts, and a mix of fossils derived from various shallow-water biofacies. The condition and composition of conodont collections from these layers support the interpre- tation of redeposition. Assemblages consist chiefly of robust elements, and most specimens are broken and abraded. Platform elements are usually incomplete, and very few ramiform elements are recognizable to morpho- type, indicating post—mortem, relatively high energy hydraulic transport. A few carbonate layers in the Hunt Fork Shale appear to have formed in place in relatively shallow water. Oolitic grainstone most likely accumulated in local high-energy shoals, and rare thick layers of bioclastic-peloidal wacke— stone and mudstone probably represent muddy biohermal buildups like those in the Beaucoup Formation. The scarcity of limestone in the Hunt Fork Shale relative to the Beaucoup Formation could reflect several factors. The Hunt Fork may have been deposited in deeper and (or) colder water; in situ carbonate production is highest in warm, shallow seas (Wilson, 1975; Flugel, 1982). Alternately, or additionally, conditions during Hunt Fork Figure 18. ——Continued. deposition may have been too turbid to allow establishment of much neritic carbonate production; siliciclastic input may have been greater and more continuous than during accu- mulation of the Beaucoup Formation. NUTIRWIK CREEK UNIT The Nutirwik Creek unit consists of purple and green phyllite with subordinate volcaniclastic metasandstone, pebble conglomerate, and felsic igneous rocks (Aleinikoff and others, 1993). Some purple and green phyllite sections contain minor calcareous black phyllite and metalimestone, which we here provisionally include within the Nutirwik Creek unit. These limy layers appear to be in the upper part of the unit (T.E. Moore, written commun., 1991). Rocks presently assigned to the Nutirwik Creek unit were consid- ered part of the Beaucoup Formation and (or) the rocks of Whiteface Mountain (informal unit) by previous authors (Brosgé and others, 1979; Dillon and others, 1988). Most exposures of the Nutirwik Creek unit occur in the Table Mountain area, where the rocks are intercalated with massive metacarbonate rocks (Pzt) (fig. 2). CARBONATE LITHOLOGIES Limestone is even less common in the Nutirwik Creek unit than in the other Devonian siliciclastic units discussed above; it occurs intercalated with recessive intervals of 34 PRE—CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA slightly calcareous black phyllite and makes up at most a few percent of the overall section. Most calcareous beds are 3 to 20 cm thick and consist of finely laminated, carbona- ceous, dark-gray to black, medium- to dark-gray- weathering lime mudstone to wackestone. Bioclasts are chiefly pelagic fossils such as tentaculitids and calcitized radiolarians, as well as, less commonly, echinoderm debris. Other silt— and sand—sized grains in these predominantly fine-grained rocks include peloids and minor amounts of detrital quartz. A few limy beds consist of redeposited, grain-rich packstone like that found in the Hunt Fork Shale. These beds are thicker (as much as l m), weather orange, and contain a mix of bioclasts, calcareous lithic clasts, and minor amounts of lime mud. Fossils include coral, bryo- zoan, and echinoderm fragments; carbonate clasts consist of lime mudstone or skeletal wackestone. AGE AND BIOFACIES Limestone layers included in the Nutirwik Creek unit yield megafossils and conodonts of Middle to early Late Devonian age. Megafossils (Dillon and others, 1988, locs. 47, 49, and 50) include solitary and colonial rugose corals, tabulate corals (Cladopora? sp.), and stromatoporoids (Amphipora? sp.) of early Late Devonian and Middle to early Late Devonian age and brachiopods (Mucrospirifer sp.) of Middle(?) Devonian age. Four samples from the Nutirwik Creek unit yielded conodonts; the most diagnostic collections are of middle Frasnian (early Late Devonian) age (fig. 3, locs. 4, 5, 12; pl. 3, figs. 16—21). Skeletal packstone (fig. 3, loc. 5) produced abundant and diverse conodonts indicative of the upper part of the Lower hassi Zone. Bioclastic limestone (fig. 3, loc. 4) yielded conodonts of the Upper hassi Zone to Lower rhenana Zone. These assemblages, unlike those obtained from the Beaucoup Formation and the Hunt Fork Shale, are not dominated by polygnathids. Instead they commonly contain ancyrodellids and palmatolepids, as well as lesser numbers of Ancyrognathus spp., icriodids, and polygnathids. Most of these conodonts represent the polygnathid-ancyrodellid-palmatolepid biofacies and are characteristic of an outer shelf or slope environment. Two metafelsite samples from the Nutirwik Creek unit produced Early Devonian zircon ages (393 i 2 and about 385—390 Ma) (Aleinikoff and others, 1993). These ages, together with the paleontologic data, suggest that the Nutirwik Creek unit was formed by a long-lived deposi— tional regime that existed from at least Early to Late Devonian time. Alternatively, the unit could represent a heterogeneous assemblage of fault slices of various Devo- nian ages. Thus far, limestone layers we include in the Nutirwik Creek unit have yielded chiefly Late Devonian (Frasnian) fossils. DISTRIBUTION The Nutirwik Creek unit crops out in the north-central part of the study area (fig. 2), where it forms several large thrust sheets intercalated with massive metacarbonate rocks. Metacarbonate rocks and the Nutirwik Creek unit are also intercalated on a smaller scale. At locality 12 (fig. 3), a 20-m-thick, fault-bounded layer of the Nutirwik Creek unit is structurally overlain and underlain by Upper Ordo- vician massive metacarbonate rocks of the Mathews River unit. The Nutirwik Creek unit at this locality consists of black phyllite with fewer carbonaceous lime wackestone beds that yield Frasnian conodonts (fig. 3, loc. 12). DEPOSITIONAL ENVIRONMENT Lithologic and fauna] evidence suggest that calcareous layers in the Nutirwik Creek unit accumulated in a more offshore and (or) deeper water environment than that postulated for limestone in the Beaucoup Formation or the Hunt Fork Shale. Most of the Nutirwik Creek limy beds are fine-grained, laminated, carbonaceous, and contain rare, chiefly pelagic fossils. These beds are interpreted as distal turbidites, derived from bioherms or other carbonate depos- its on an adjacent platform or shelf, and deposited in quiet water at some distance from the original source. Less abundant, thicker layers of skeletal packstone probably reflect the passage of rare, high-magnitude hydraulic events, such as unusually large turbidity currents and (or) storm waves. In situ shallow-water carbonate deposits, such as the muddy bioherms and ooid grainstone that occur in the Beaucoup Formation and Hunt Fork Shale, have not been observed in the Nutirwik Creek unit. Conodont biofacies analysis supports the conclusions outlined above. Conodont assemblages from the Nutirwik Creek unit show evidence of hydraulic breakage and sorting and include a mix of shallow and deeper water species. However, most conodonts obtained from this unit are characteristic of an outer shelf or slope environment (polygnathid-ancyrodellid-palmatolepid biofacies). Thus, Nutirwik Creek conodont assemblages formed through post-mortem transport of moderate- to shallow-water cos- mopolitan species into a deeper water setting. SUMMARY OF DEVONIAN METACLASTIC ROCKS IN THE SNOWDEN MOUNTAIN AREA Three metaclastic units of Devonian age are recog- nized in the Snowden Mountain area: the Beaucoup Forma- tion, the Hunt Fork Shale, and the Nutirwik Creek unit. Each of these units consists chiefly of fine-grained silici- clastic rocks and includes subordinate amounts of meta- limestone. However, the units contain distinctive subordi- REGIONAL RELATIONSHIPS 35 nate lithologies; mafic intrusions are apparently restricted to the Beaucoup Formation, quartzose metasandstone beds are most abundant in the Hunt Fork Shale, and the association of purple and green phyllite, volcaniclastic sandstone, and felsic igneous rocks distinguishes the Nutirwik Creek unit. Previous authors (for example, Dutro and others, 1979) proposed that rocks here included in the Beaucoup Formation and Nutirwik Creek unit depositionally overlie massive metacarbonate rocks of Devonian and older age (Snowden Mountain area metacarbonate succession of this paper) and are themselves overlain by the Hunt Fork Shale. Other workers suggested that most boundaries between these elastic units and the Snowden Mountain area meta- carbonate succession are faults. The Beaucoup Formation and Nutirwik Creek unit are widely distributed throughout the study area and are closely associated with rocks of the Snowden Mountain area metacarbonate succession, but the Hunt Fork Shale occurs only in the northernmost part of the map area and is nowhere in contact with the metacarbonate succession (fig. 2). Our work indicates that characteristic carbonate lithol- ogies and conodont biofacies distinguish the three metaclas- tic units, but all the units are in part correlative and in part of Frasnian age (fig. 19). Metalimestone is most abundant in the Beaucoup Formation and accumulated mainly in relatively shallow water (shelf or platform environment) as in situ muddy bioherrns and bioclastic shoals. Calcareous material is less abundant in the Hunt Fork Shale and is chiefly redeposited. Most limy layers in this unit are tempestites or turbidites; such deposits can form in a variety of settings, but tempestites are most common in inner to outer shelf environments. In situ bioclastic-ooid shoals and bioherrnal buildups are also found in the Hunt Fork Shale and suggest midshelf or shallower conditions. Metalime- stone is least abundant in the Nutirwik Creek unit and occurs mostly as fine-grained, distal turbidites. Lithologic and faunal evidence infer a more offshore and (or) deeper water environment (outer shelf or slope) for this unit. Available fossil data suggest that limy layers in the Beaucoup Formation are in part older than limy layers in the other two metaclastic units, whereas limy layers in the Hunt Fork Shale are in part younger, but all three units include some strata of middle(?) Frasnian age. The oldest well- dated beds in the Beaucoup Formation yield latest Middle to earliest Late Devonian (latest Givetian to earliest Frasnian) conodonts, but other intervals are early Frasnian and middle to early late Frasnian in age. The most diagnostic conodont collections from the Nutirwik Creek unit are middle Fras— nian in age, but Middle(?) Devonian brachiopods are also reported from this unit. Limy layers in the Hunt Fork Shale contain conodonts of middle to late Frasnian age, but the upper (wacke) member of this unit yields Famennian brachiopods. Some of the conodont species found in the Hunt Fork Shale have previously been noted only in northern Canada (Northwest Territories) and southeast Alaska; specific biogeographic affinities have not been suggested for other faunal elements of the metaclastic units. REGIONAL RELATIONSHIPS Pre-Carboniferous (meta)carbonate4 rocks are widely distributed across northern Alaska (fig. 20), but the litho— facies, biostratigraphy, and interrelationships of these sequences are only beginning to be deciphered. In many areas, such as the Arctic quadrangle in the eastern Brooks Range and the Survey Pass and Ambler River quadrangles in the west, pre-Carboniferous metacarbonate successions are known to occur (Dumoulin and Harris, 1988 and unpub. data), but they have not yet been closely studied. However, stratigraphic successions that correlate at least in part with rocks in the Snowden Mountain area have been described in relative detail from several localities: the Doonerak Window just west of the study area (Dutro and others, 1976, 1984a, 1984b; Repetski and others, 1987; Julian, 1989), the Baird Mountains in the western Brooks Range (Dumoulin and Harris, 1987a, 1987b; Dumoulin, 1988; Karl and others, 1989; Till, in press), the Shublik and Sadlerochit Mountains in the eastern Brooks Range (Blodgett and others, 1986, 1988, 1992a), and the York Mountains on the Seward Peninsula (Sainsbury, 1969, 1972', Till and Dumoulin, in press). Of the sections known in detail, metacarbonate rocks of the Snowden Mountain area are lithologically and fau— nally most similar to strata of the Baird Mountains, 400 km to the west (fig. 20). The Proterozoic(?) to Devonian metacarbonate succession of the Snowden Mountain area correlates best with rocks in the eastern Baird Mountains, whereas the Devonian siliciclastic units correlate with rocks exposed in the eastern and western Baird Mountains. PRE-CARBONIFEROUS METACARBONATE SUCCESSIONS The overall progression of lithofacies, depositional environments, conodont faunas, and biofacies in the eastern Baird Mountains succession is strikingly similar to that in the Snowden Mountain area. In the sections that follow, metacarbonate rock units in the eastern Baird Mountains are briefly described and compared with correlative units in the Snowden Mountain area. Other pre-Carboniferous sedimen- tary successions in northern Alaska are then summarized and compared in turn with Snowden Mountain area rocks. 4(Meta)carbonate is used for successions of pre-Carboniferous rocks that include metamorphosed and nonmetamorphosed carbonate rocks. 36 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA I: z D x LU LlJ I: o E in. E I I I: II |I||I||IIIIIIIIIIIIIIIIIIIIIIIIII IIIII 3 I IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIlI “lllI 0- Z IIIIIIIIIIIIIIIIIIIII'I IIII I: LLI ._l < I m x cc 8 a a '2 . - ' {III '. III .’II “IIIIIIIIIIIIEJI IIIIIIIIII IIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIII g EIIIII l§:|I!II| IIIIIIIIIIII,JIIIIIIIIIIIICD fIIIIIlllIIIIIIIIIIIIZIIIIIIIIIIIIIl -1 m -'IIIII lIlIIlf‘lIllIll o |I|IIII|I|I|_|lIll g as: I: ~ < . 2 E a m '— O co u_ . CL 8 0 @fi 8 2 I II I L“ IIIIIIII III I9 Imu: III» IIIIIIm IIIIIIIIlfi ’IIIIII IIIIII Ia IIIIwm II “0 §II 'I"I'I"I§II/IIIII I wIIlII III'IIIIII Mb IIIiI 'III I II I IIII I “III I'IIII'I I'IIII’I II'IIIIII 'I'iIIII 'IIIIIII EOVLSHDS ' eons ”“3332???“ -: NVINSVHd 3100M EIIIEICIfiéfé’IWSSI‘Ié‘I‘ VINO/El 31 Cl saluas (.LHVdINVINOAElCI Haddn ,1 N Gijaddfi'W warms (1.8le NVINOAEICI to right), and published descriptions), selected conodonts (relative abundance decreases from left nit. Only the calcareous part of the Nutirwik Creek unit is shown. See figure 5 and , conodont biostratigraphy, Figure 19. Schematic sections (based on field observations table 1 for , Hunt Fork Shale, and Nutirwik Creek u explanation of symbols and numerical identification of fossils, respectively. and age relations of the Beaucoup Formation REGIONAL RELATIONSHIPS 37 ”YORK MTNS. _ a: ’ SEWARD PENINSULA 200 KILOMETERS SADLEROCHIT 141° W- MTNS. \ SHUBLIK M MTNS. A N G R Philip Smith Mtns. Deonerak nowde Mountain area Chandalar Figure 20. quadrangle and geographic names referred to in text. EASTERN BAIRD MOUNTAINS METACARBONATE SUCCESSION Carbonate rocks in the eastern Baird Mountains, like those in the Snowden Mountain area, have been deformed, metamorphosed (to blueschist and greenschist facies), and yield conodonts with CAIs of 5 or higher (Dumoulin and Harris, 1987a). In the eastern Baird Mountains (Mt. An- gayukaqsraq area), dolostone and marble of Proterozoic and (or) Cambrian age contain stromatolites and coated grains and are overlain by fossiliferous Middle and Upper Cam- brian carbonate rocks. These strata are succeeded by a condensed Lower and lower Middle Ordovician section of carbonaceous phyllite, rare radiolarian chert, and carbon- ate turbidites, which shallows upward into Upper Ordovi- cian to Devonian(?) dolostone and metalimestone deposited in warm, locally restricted marine environments. The lithologic and biostratigraphic summary of the eastern Baird Mountains metacarbonate succession given below is taken chiefly from Dumoulin and Harris (1987a, b), Dumoulin (1988), Harris and others (1988), Karl and others (1989), and Till (in press) and includes some of our previously unpublished data. PROTEROZOIC AND (OR) CAMBRIAN ROCKS The basal unit in the eastern Baird Mountains meta- carbonate succession is at least 100 m thick and consists of cliff-forming, orange— to light-gray—weathering, dark— to Map of northern Alaska showing general distribution of pre-Carbonife rous (meta)carbonate rocks (gray pattern) and light-gray dolostone, metalimestone, and marble with sub- ordinate layers of quartz-rich metasedimentary rocks and metabasite (unit Cszc of Till, in press; unit PzEcb of Karl and others, 1989)5 (fig. 21). Original sedimentary textures are locally well preserved; major carbonate lithologies include stromatolitic boundstone and cross-laminated grain- stone composed of ooids, oncoids, composite grains, and rare pisoids. Stromatolitic morphologies range from tabular sheets to club-shaped mounds as much as 15 cm high. Regional relationships suggest that these rocks are of Proterozoic and (or) Cambrian age; the assemblage of sedimentary features indicates an intertidal to shallow subtidal depositional environment. The massive dolostone unit appears to grade upward and laterally into a section at least 90 m thick of orange- and gray—weathering, variously impure metalimestone, marble, and dolostone, and lesser gray to green phyllite and calcar- eous and chloritic schists (unit €Eic of Till, in press; subunit one of unit O€c of Karl and others, 19895). Prominent lithologies include quartzose and (or) chloritic calcarenite and packstone and grainstone containing 5CEvc, Proterozoic and (or) Cambrian dolostone, conglomerate, and mafic volcanic rocks; CEic, Proterozoic and (or) Cambrian impure marble and phyllite; Cc, Cambrian dolostone and metalimestone; 0pc, Ordovi— cian phyllite, metalimestone, dolostone, and marble; DOc, Devonian(?) to Upper Ordovician marble and dolostone unit of Till (in press). Pchb, Paleozoic and (or) Proterozoic carbonate rocks and metabasite; OCc, Ordovician and Cambrian carbonate rocks; DOc, Devonian(?) to Ordovi- cian carbonate rocks units of Karl and others (1989). SERIES/STAGE/ SYSTEM SUBSTAGE D Z < EE LOWERMOST METERS 350-— O UPPER AND D a: MIDDLE O _ _ _ __ m _. LLANDEILIAN 300— D Q 2 LLANVIFINIAN 1255:5155 LOWER :E—_—:E??1:f: UPPER \‘R VA 250— ‘2: 5 VA 5 g o —‘- “ _ 2 MIDDLE _ _ _ < _ _ O 7 _ 200 LOWER(.) ______ : ____ 150i 5 .- c.) CAMBRIAN 100— AND (OR) PROTEROZOIC 50— V V V v V V v v V U of, v t.) EASTERN BAI RD MOUNTAINS EXPLANATION Number of samples that yielded a species association 0 1 O 3 O 5 "tam; EEK (99 fits tiers F’ — . Z; 90 $9 _F 1%g@§0§?x70 6 ' 66 I I @ 0 ea 1 e 68 1 10 1 13 114 Figure 21. Generalized composite stratigraphic column and distribution of fossils in the metacarbonate succession in the eastern Baird Mountains; selected fossils (chiefly conodonts) of biostratigraphic, paleogeographic, and (or) paleoecologic significance are shown at appropriate points adjacent to the lithologic column. Rocks of Early Ordovician and early Llanvimian age contain an abundant graptolite succession (see Carter and Tailleur, 1984; other data from Dumoulin, 1988; Dumoulin and Harris, 1987a, b, and unpub. data; Karl and others, 1989; Till, in press). Thicknesses are minima. European series names are used for intervals containing dominantly cosmo- politan faunas, whereas North American series and (or) stage names are used for intervals containing chiefly North American province faunas. Letter symbols are map units of Till (in press): CEVC, Proterozoic and (or) Cambrian dolostone, conglomerate, and mafic volcanic rocks; CEic, Prot- erozoic and (or) Cambrian impure marble and phyllite; Cc, Cambrian dolostone and metalimestone; 0pc, Ordovician phyllite, metalimestone, dolostone, and marble; DOc, Devonian(?) to Upper Ordovician marble and dolostone. See figure 5 and table 1 for explanation of symbols and identification of fossils, respectively. Vertical black bar indicates samples too closely spaced to show separately. REGIONAL RELATIONSHIPS 39 Figure 22. Sedimentary features of metacarbonate succession in the eastern Baird Mountains. A, Middle Ordovician carbonate turbidites (Opc, Ordovician phyllite and carbonate of Till, in press; lens cap, 6 cm in diameter). B, Upper Ordovician shallowing—upward cycles of dark-weathering bioturbated pack—grainstone and light-weathering cryptalgal laminite (lower part of DOc unit of Till, in press). locally abundant coated grains. Some layers are graded, contain parallel and cross lamination, and are interpreted as turbidites. No fossils have been found in this unit, but map relations suggest that it is a deeper water facies equivalent of the upper part of unit CBVC and the lower part of unit €c (see below and footnote 5). Rocks of definite Cambrian age overlie both units CBvc and €Eic and make up a section at least 60 m thick (unit Cc of Till, in press; subunit two of unit 060 of Karl and others, 1989). The basal part of this section is massive marble; it grades up into thin-bedded, platy metalimestone and then into thin couplets of bioturbated metalimestone and laminated dolostone interpreted as shallowing-upward peritidal deposits. Protoconodonts, chancellorid sclerites, hyolithids, and phosphatized steinkerns of monoplacopho- ran mollusks indicate a maximum age of Early (but not earliest) Cambrian for the lower part of this unit; acrotretid brachiopods and agnostid arthropods demonstrate Middle (probably late Middle) and Late Cambrian ages, respec- tively, for the middle and upper parts of the unit (fig. 21). Fossils and sedimentary features infer that most of the section was deposited in a shallow subtidal to supratidal environment; the fauna is cosmopolitan and suggests no specific paleogeographic affinities. LOWER AND MIDDLE ORDOVICIAN ROCKS A condensed Lower and lower Middle Ordovician section at least 50 to 100 m thick overlies rocks of Middle and Late Cambrian age in the eastern Baird Mountains (unit 0pc of Till, in press; subunits three and four of unit O€c of Karl and others, 1989; see footnote 5). Carbonaceous phyllite with rare layers of radiolarian—bearing metachert and fine—grained metalimestone makes up the basal part of the sequence. Calcareous layers increase in thickness and abundance upward. Thin graded beds of metalimestone, separated by phyllitic partings (fig. 22A), pass up into thicker bedded, bioturbated, bioclastic packstone and grain- stone. The unit contains an excellent Arenigian to Llanvir- nian graptolite succession (Carter and Tailleur, 1984) and cosmopolitan, chiefly cool-water conodonts of Llanvimian, 40 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA latest Llanvirnian to Llandeilian, and late Llandeilian to earliest Caradocian(?) age (fig. 21). Lithologic and biostrat- igraphic criteria indicate a shallowing-upward depositional regime; basinal phyllite grades up into shelf—margin carbon- ate turbidites and then into mid- to inner-shelf bioclastic grainstones. The turbidites contain a mix of warm- and cool-water conodont species. UPPER ORDOVICIAN TO DEVONIANC’) ROCKS Lower and Middle Ordovician strata in the eastern Baird Mountains are succeeded by more than 200 m of Upper Ordovician, Silurian, and Devonian(?) dolostone and less abundant metalimestone (unit DOc of Karl and others, 1989 and Till, in press; see footnote 5). The lower part of this section forms steep cliff exposures; the upper strata crop out as rubble-covered hills. The lower interval is distinctively color banded on a scale of one-half to several meters; the bands represent cyclic alternations of dark-gray to black, bioturbated pack-grainstone and light-gray crypt- algal laminite with fenestral fabric (fig. 228). Similar lithologies occur in the upper part of the section, along with layers of bioclastic packstone and wackestone that contain corals, stromatoporoids, and pentamerid brachiopods. Conodonts and brachiopods (Tcherskidium n. sp.) constrain the age of this unit. The cliff-forming lower part of the section is of Late Ordovician age; the basal beds contain Protopanderodus insculptus and the Siberian- northem North American conodont Plectodina? cf. P.? dolboricus and may be as old as middle Maysvillian, but most strata yield chiefly Aphelognathus divergens, a west— ern North American Midcontinent Province (WNAMP) conodont, and are Richmondian (latest Ordovician). The rubble-forming upper strata are mostly Llandoverian to Ludlovian in age (Early and Late Silurian); the uppermost beds are no younger than Early Devonian and could be as old as latest Silurian. Fossils and sedimentary structures indicate a warm, shallow-water depositional environment for these rocks; the shallowest, most restricted conditions prevailed during Richmondian time. COMPARISON OF THE SNOWDEN MOUNTAIN AND EASTERN BAIRD MOUNTAINS METACARBONATE SUCCESSIONS The Snowden Mountain metacarbonate succession (used hereafter for the Snowden Mountain area metacarbon- ate succession) has many lithologic and faunal similarities to the succession in the eastern Baird Mountains. Ordovi- cian and Silurian strata in the two areas correlate particu- larly well, but points of correspondence exist throughout both metacarbonate successions (fig. 23). Both the Snowden Mountain and the eastern Baird Mountains metacarbonate successions include strata of Cambrian and possible Proterozoic age. Massive metacar- bonate rocks of the Dillon Mountain area are lithologically similar to and may correlate with unit CEvc (fig. 23) in the eastern Baird Mountains. The major carbonate lithologies in both units are crossbedded, coated-grain grainstone and algal (stromatolitic) boundstone; both units contain layers of quartzose metasedimentary rocks and were deposited in peritidal environments. Stromatolites are more abundant and display a wider range of morphologies in the eastern Baird Mountains strata, but this difference may reflect a preservational bias; stromatolites are best preserved in the dolomitic parts of unit €Evc, and dolostone is relatively uncommon in the Dillon Mountain area. Unit CEvc also differs from the metacarbonate rocks in the Dillon Mountain area because it contains layers of metabasite and is spatially associated with rocks of known Cambrian age. Correspondence between other pre-Ordovician units in the two areas is less precise. The Snowden Mountain unit may correlate with the upper part of unit CEic or, less likely, with the lowermost part of unit Cc. Lithologically, the Snowden Mountain unit is more like unit €Eic. Both units include gray phyllite, impure metalimestone, and quartzose metalimestone, and both accumulated in an outer shelf or slope setting. The well-dated uppermost part of the Snowden Mountain unit is of early Middle Cambrian age, older than part of unit Cc, and the shallow-water deposi- tional environment inferred for unit 6c is at odds with the setting proposed for the Snowden Mountain unit. No rocks have yet been found in the Snowden Mountain area that correlate with the Upper Cambrian part of unit Cc. Proof that strata of this age once existed in this region, however, is provided by the presence of redeposited Late Cambrian conodonts in basal parts of the Snowden Creek unit. Cambrian faunas in the Snowden Mountain area may have been more provincial than those in the eastern Baird Mountains; Snowden Mountain unit trilobites have Siberian biogeographic affinities, whereas the biota of unit €c is cosmopolitan. Such paleobiogeographic interpretations remain preliminary, however, because the Cambrian fauna thus far recovered from the Snowden Mountain area is much more limited than that found in the eastern Baird Mountains, and strictly comparable forms with well- defined Cambrian provinciality (for example, trilobites) have not been obtained from the eastern Baird Mountains. Ordovician strata in the Snowden Mountain area and the eastern Baird Mountains correlate well. Lithofacies and biofacies of the Snowden Creek unit correspond closely with those of unit Opc. Lower parts of both sections consist of carbonaceous phyllite with layers of radiolarian meta- chert and allodapic metalimestone; higher strata are pre- dominantly calcareous and comprise dark, thin—bedded turbidites grading up into lighter colored, thicker bedded bioclastic pack-grainstone. Both units accumulated in REGIONAL RELATIONSHIPS 41 EASTERN BAIRD MOUNTAINS <—-———400 KM—-——————) SNOWDEN MOUNTAIN AREA shallowing-upward depositional regimes that evolved from poorly oxygenated basins to shallow subtidal carbonate shoals, and turbidites in both units contain hydraulically sorted conodont assemblages, which include a mixture of warm- and cool-water species. Conodonts represent chiefly cosmopolitan forms of the protopanderodid-periodontid biofacies and indicate that deposition of the two sections SERIES/STAGE, gm; SERIES/SUBSERIES/ SYSTEM/ SYSTEM SUBSTAGE UNIT STAGE/SUBSTAGE SERIES EIFELIAN AND C 5 (omemsm DEVONIAN 5‘2: C C LUDLOVIAN AND ‘2‘ E LOWERMOST c WENLOCKIAN SILURIAN METERs - DEV0N|AN(?) W-—— METERS 550_ E 3 AND UPPER C C LLANDOVERIAN _400 E o SILURIAN : o E: a E E C RICHMONDIAN m (INCLUDES MINOR LUDLOV'AN c :u LOWER SILURIAN('?) % __35° 50°_ - STRATA) 1; 2 g m E LUDLOVIAN I 3 AND (OR) 3 WENLOCKIAN C E u: C :4 c C MAYSVILLIAN _ 450 — LLANDOVERIAN AND 300 0 cs EDENIAN o I! 8 C < I: RICH- 6 Lu 0 U) .— 400— a: MONDIAN g 32> _250 D c 5 LOWER z c P” c CARADOCIAN(?) < 2 AND 5 MAVSVILLIANU’) C O C LLANDEILIAN : _ :3 _ > "” U —— 200 35°— 0 UPPER AND V; c E D MIDDLE c I z E _____ 0 — -c II c uJ ‘3 LLANVIRNIAN 5' LLANDEILIAN — 150 300— Q c ______ 2 LLANVIRNIANC E g C UPPER _ J; E g g ARENIGIAN —( U LOWER G 32’ :2 T LOWER MIDDLE CAMBRIAN P c, ,T 250— Z fli— z 100 s o T. E s 3 5 <2: MIDDLE .E E O E g 8 LOWER CAMBRIAN LOWER(?) m g 2 AND (OR) — 5° 20° > o 3 PROTEROZOIC E I11 I S 8 Z x "’ o 150- 100— 03:11:23: Figure 23. Correlation of pre-Carboniferous rocks in the Snowden Mountain area PROTEROZOIC and eastern Baird Mountains. Letters indicate the position of precisely dated samples: __ C, conodonts; G, graptolites; T, trilobites and trilobitomorphs; and S, other shelly fossils. Correlation lines are solid where well controlled and dashed where approxi- 50__ v mate. Letter symbols in stratigraphic column for the eastern Baird Mountains are map U V V . . . . - . . g: V 0" V 0V0 un1ts of T111 (in press). Thicknesses are minima. European series names are used for o w . . . . . . . Q 0 1ntervals contalnlng dominantly cosmopolitan faunas, whereas North American ser1es V V v V v and (or) stage names are used for intervals containing chiefly North American 0 V V V V Midcontinent Province faunas. See figure 5 for explanation of symbols. was essentially coeval', the lowest exposed beds of unit 0pc are slightly older than the oldest dated strata in the Snowden Creek unit. Middle Ordovician strata display subtle compositional differences between the eastern Baird Mountains and the Snowden Mountain area that appear to reflect local varia- tions in depositional environment and turbidite provenance. 42 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA The lower part of the Snowden Creek unit is more siliceous and less phyllitic than the lower part of unit Opc. Grapto- lites have not been found in the Snowden Creek area, but this may be an artifact of preservation—cleavage must parallel bedding in phyllitic rocks in order for graptolites to be observed. Siliciclastic turbidites are rare in both sections but slightly more common in the Snowden Creek unit, and Snowden Creek calcareous turbidites are in general more impure than those in unit Opc. Rare reworked conodonts of anomalous (older) age occur in Snowden Creek turbidites but have not yet been found in any turbidites of unit 0pc. Upper Ordovician and Silurian strata in the Snowden Mountain area and eastern Baird Mountains also correlate well. The Mathews River unit is lithologically and faunally similar to unit DOc. Both are massive, dolomitic, and characterized by meter-scale color bands; the bands reflect shallowing-upward peritidal cycles of bioturbated, bioclas— tic and,(or) peloidal carbonate deposits overlain by crypt- algal laminite. Both units contain similar mega- and micro- faunas and were deposited in warm, shallow-water depositional environments that were shallowest and most restricted during Richmondian time. Some Upper Ordovi- cian strata in both areas produce conodonts characteristic of Siberian-northem North American faunas, whereas latest Ordovician assemblages are dominated by WNAMP fau- nas, and Silurian faunas are predominantly cosmopolitan. Devonian rocks are rare in the Snowden Mountain meta— carbonate succession and rare or absent in the eastern Baird Mountains succession. OTHER PRE-CARBONIFEROUS (META)SEDIMENTARY SUCCESSIONS Several other (meta)sedimentary successions in north- ern Alaska are at least in part coeval with the Snowden Mountain area strata and have been described in sufficient detail for sedimentologic and biostratigraphic comparisons to be made. (Meta)carbonate successions in the western Baird Mountains, the York Mountains, and the Shublik and Sadlerochit Mountains have similarities to the metacarbon— ate succession in the Snowden Mountain area but differ in some particulars. Most notably, these successions contain a relatively thick sequence of Lower Ordovician platform carbonate rocks. Lower Paleozoic metasedimentary rocks are also exposed in the Doonerak window; these strata are chiefly siliciclastic and volcaniclastic but include minor amounts of carbonate that may have been derived from the Snowden Mountain metacarbonate succession (Julian, 1989). WESTERN BAIRD MOUNTAINS Description. —Pre—Carboniferous metacarbonate rocks are widespread in the western Baird Mountains; these rocks constitute the Baird Group. In this paper, we restrict the Baird Group to metacarbonate rocks of Ordovician through Middle Devonian age in the western Baird Mountains; we do not include partly coeval metacarbonate rocks of the Maiyumerak Mountains and eastern Baird Mountains or impure carbonate rocks of Middle and Upper Devonian age (for example, Eli Limestone). Like the metacarbonate succession in the eastern Baird Mountains, these strata have been metamorphosed to greenschist and blueschist facies and contain conodonts with CAIs of 5 or higher. But overall stratigraphic successions in the two areas differ in detail (Dumoulin and Harris, 1987a, b, and unpub. data; Harris and others, 1988; Karl and others, 1989). Rocks of pre—Ordovician age have not been recognized in the western Baird Mountains; the metacarbonate succes- sion begins with a relatively thick (at least 400 m) interval of Lower and Middle Ordovician carbonate strata deposited chiefly in restricted to normal marine, very shallow to deeper water platform environments (fig. 24). These rocks comprise two distinct, roughly coeval facies: dolostone with abundant fenestral fabric and bioturbated to laminated, argillaceous metacarbonate rocks. Conodonts indicate that these strata were deposited during early Early to early Middle Ordovician time (Rossodus manitouensis Zone to Histiodella altzfrons Zone of the NAMP conodont zona- tion); the bulk of both facies accumulated during early Fauna D time. Conodont faunas include chiefly WNAMP and some Siberian-Alaskan (SAP) province endemics. One sample of argillaceous metalimestone contains reworked conodonts of Late Cambrian age, in addition to Early Ordovician conodonts (fig. 24). A thin layer of dark, fine-grained metalimestone occurs in the lower part of the argillaceous metacarbonate section, and similar layers overlie the section. These layers contain cool-water cono- donts of middle Early and early Middle Ordovician age, respectively; that is, slightly older than the oldest dated strata of unit 0pc in the eastern Baird Mountains, and equivalent in age to the middle beds of unit 0pc. Younger Ordovician rocks appear to be rare in the western Baird Mountains and are of uncertain thickness. Middle Middle Ordovician dolostone contains Siberian province conodonts indicative of a very restricted, warm, shallow-water, innermost platform environment. A single locality of definitively Upper Ordovician marble contains a Figure 24. Generalized composite stratigraphic section and b selected conodonts of the metacarbonate succession in the western Baird Mountains (data from Dumoulin and Harris, 1987a, b, and unpub. data; Karl and others, 1989). Thick- nesses are minima. European series names are used for intervals containing dominantly cosmopolitan faunas, whereas North American series and (or) stage names are used for intervals containing chiefly North American province faunas. See figure 5 and table 1 for explanation of symbols and identification of fossils, respectively. REGIONAL RELATIONSHIPS 43 SYSTEM/ SERIES/STAGE, STRAU WESTERN BAIRD SUBSTAGE GRAPHIC METERS SER'ES (ZONE/FAUNA) UNIT MOUNTA'NS 600— UJ s 2 5' EIFELIAN s 9 _______ 5 LEI ' n: 550 _ U>J Lg EMSIAN I . D O A g) 75 30 57 z 500 — Z O: s S 33 5 0 CE 0- .4 O O 3 D 0 w =1 3 g 450 — <0 50 E 65 21 a WENLOCKIAN o E GAMACHIAN TO 35%? F . @E’N‘ % M. MAYSVILLIAN 400 — F Q $5 35 (C. sweeti Zone?) . "'" ##1## I I 88 _l 8 N F o — (H. altifrons N 350 — E Zone) LL u "u 105 g ‘41 :> _ __ O 66 90 l 7°; 0: 1 n 7 u I O N N N ~ ~ , (D 300 — E “ I fig 20 E D “N ‘L’ E E 0 Q a 11 Z 9 < % I: (:9 33 250 — E m u “ o (MIDDLE W, I _ z FAUNA D) > <_( I aff 200 — O (2'3 N 42 D u: a: E 3:: 9 O E 1 0 9 (LOW + 5 N ‘1 86 N \ FAUNA W ‘ 99 63 . 100 — + \ Redeposited D) (e w 50 85 g. T \ a Late Cambrian !\ ' g 3 . %. 62 \\ . speCIes Q s q: _ \_ , . § + E 37 26 fl. < E I(H.manitou- / I / T 3413 A O E ensis Zone) I / I I I // 102 101 14 98 44 PRE—CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA cosmopolitan conodont fauna that includes some North American forms; these strata are equivalent in age to the lower part of the Mathews River unit in the Snowden Mountain area and the lowest part of unit DOc in the eastern Baird Mountains and appear to have been deposited in a middle to outer shelf setting. Silurian strata are lithologically and biostratigraphi- cally similar to those in the eastern Baird Mountains but are more restricted in age (Llandoverian rocks have not been recognized) and areal distribution; the section may be several hundred meters thick. Lower and Middle Devonian (Emsian and Eifelian) carbonate strata, rare or absent in the Snowden Mountain area and eastern Baird Mountains, are widely distributed and were deposited in a variety of shelf and platformal environments. These rocks contain chiefly shallow-water, cosmopolitan conodonts, as well as repre- sentatives of a more provincial form, Icriodus taimyricus, a Siberian-northem North American endemic. The section is at least 60 m (and probably more than 100 m) thick and contains locally abundant amphiporid stromatoporoids, cor- als, bryozoans, gastropods, and brachiopods. Correlation. —The metacarbonate succession in the western Baird Mountains has some points of correspon- dence with the metacarbonate succession in the Snowden Mountain area but has other notable differences. Cambrian conodonts reworked into Lower Ordovician carbonate deposits testify that pre-Ordovician sediments once existed in the western Baird Mountains, but no strata similar to the Dillon Mountain area metacarbonate rocks, or the Cambrian Snowden Mountain unit, have been found in the western Bairds. On the other hand, the thick, widely distributed Lower Ordovician section in the western Baird Mountains has no established counterpart in the Snowden Mountain area. No lithologic equivalent of the basinal Middle Ordo- vician Snowden Creek unit is known in the western Bairds, although brief episodes of cooler and (or) deeper water produced a few thin dark carbonate layers. Upper Ordovi- cian and Silurian strata are lithologically similar in the two regions, but rocks of definite Early Silurian age are not known in the western Bairds. Lower and Middle Devonian metacarbonate rocks are widespread in the western Bairds but appear to be rare in the Snowden Mountain area. YORK MOUNTAINS Description.——The (meta)carbonate succession in the western Baird Mountains is similar in many ways to that in the York Mountains on the western Seward Peninsula (fig. 20). The York Mountains carbonate succession consists of more than 1 km of Ordovician, Silurian, and Devonian(?) limestone, argillaceous limestone, and dolostone deposited in predominantly shallow water environments (Sainsbury, 1969, 1972; Till and Dumoulin, in press; Dumoulin and Harris, unpub. data; Harris and others, 1988; Vandervoort, 1985). It is largely unmetamorphosed; most conodonts have CAIs of 2 to 4. Ordovician rocks predominate in the York Mountains carbonate succession (fig. 25). The oldest dated rocks are Early Ordovician and comprise two lithofacies, units Cal and 016 of Sainsbury (1969). Unit Oal consists of at least 350 m of dolomitic, locally argillaceous, limestone. Unit 01 is primarily micritic limestone and is at least 450 m thick. Both units are characterized by 8- to 15-m-thick, shallowing-upward cycles (Vandervoort, 1985) deposited in a range of subtidal to supratidal environments; the overall section accumulated in a deepening-upward regime. Units Cal and 01 produce chiefly tropical, cosmopolitan cono- donts of early Arenigian (low Fauna D) age and yield some WNAMP and some SAP elements. The uppermost beds of unit 01 contain early middle Arenigian, cooler and (or) deeper water conodonts of the Baltoscandic Province, and trilobites very similar to forms described from Novaya Zemlya, northern Siberia (Ormiston and Ross, 1976). Unit 01 is overlain, apparently conformably, by 7 to 30 m of black, graptolitic shale with minor interbedded black limestone, which grades upward into flaggy, thin-bedded limestone with shale partings (unit Olsh6 of Sainsbury, 1969). The lower limestone beds contain calcified radiolar- ians; higher beds are graded and allodapic. Unit Olsh is at least 300 m thick; it yields cool-water, pandemic conodonts of latest Arenigian and earliest Llanvirnian age and accu- mulated in a shallowing-upward regime. A fault-bounded section of dark limestone (unit 0le of Sainsbury, 1969) yields cephalopods of late Llanvirnian to early Llandeilian age and probably accumulated in middle to outer shelf conditions. Upper Ordovician and Silurian strata (unit 30le of Sainsbury, 1972) are at least 340 m thick in the York Mountains. Upper Ordovician beds are slightly dolomitic, fossiliferous limestone; rugose corals (Bighornia) indicate a possibly Richmondian age. Conodonts from these strata include pandemic forms, WNAMP elements, and some SAP elements (Plectodina? tunguskaensis) and are charac— teristic of a warm, relatively shallow-water biofacies. These rocks also contain the trilobite Monorakos, a form known previously only from the Siberian and Kolyma platforms (Ormiston and Ross, 1976), and brachiopods and gastro- pods with Siberian affinities (Potter, 1984; Blodgett and others, 1992b). Silurian rocks are chiefly dolostone, contain 5- to 8-m-thick shallowing—upward cycles, and are of Ludlovian age. The youngest rocks known in the York Mountains carbonate succession are of probable late Lud- lovian to Early Devonian age (Allan Pedder, Geological Survey of Canada, oral commun., 1988). 6Oal, Ordovician argillaceous limestone and limestone; Ol, Ordovi- cian limestone and argillaceous limestone; Olsh, Ordovician limestone and shale; Odl, dark limestone; SOdl, Silurian and Ordovician limestone and dolomitic limestone. REGIONAL RELATIONSHIPS SYSTEM/ SERIES/STAGE/ YORK MOUNTAINS SERIES SUBSTAGE (FAUNA) 7 LOWER UPPER DEVONIAN TO a)? UPPER SILURIAN I r I‘D] I F I —~ M . UJ — METERS 2 & LUDLOVIAN 1% I Q “’50— E 3 if ”a :F . ° ' [E 46 a: WENLOCKIAN m [/57 W F @9135 3 ‘I . M ° 64 51 65 __I LU " 3 G g 21 a, o LLANDOVERIAN o S Y 900— ° 0: _ 70 93 N GAMACHIAN TO ‘_. 72 @ g RICHMONDIAN n— Q72 F NOYOUNGER "‘ o THAN LLANDEILJAE E5 F § & 750- ------ 24 s s . 5 LOWERMOST f o LLANVIRNIAN S 66 \ 9 AND 2 91 600 — E O _ __ _ - - z UPPERMOST — o ARENIGIAN < o 450_ > UPPER 5 O _.MI.PQ.L§_ 5 67 D s s m s s l 300 O _ A t z 1: 525 D . ‘ LU ; 3 575 s 53 O ”J 3 s s I _.l c: < < ” 4? 3 M3 x». ' .126 150— 9 W W o ' ‘ Ii 55 V A . of. I 0 am a N ’~" A 103 0-1 N "N“ l 13 101 0 Figure 25. Generalized composite stratigraphic section and selected conodonts of the carbonate succession in the York Mountains (data from Sainsbury, 1969, 1972; Till and Dumoulin, in press; Dumoulin and Harris, unpub. data). Letter symbols represent map units of Sainsbury (1969, 1972): Cal, Ordovician argillaceous limestone and lime- stone; Ol, Ordovician limestone and argillaceous limestone; Olsh, Ordovician limestone and shale; Odl, dark limestone; SOdl, Silurian and Ordovician limestone and dolomitic 27 102 limestone. All thicknesses are minima, based on partial sections measured by the authors; Sainsbury (1969) reports greater thicknesses for most of these units, but his estimates probably include structural repetitions. European series names are used for intervals containing dominantly cosmo— politan faunas, whereas North American series and (or) stage names are used for intervals containing chiefly North Amer— ican province faunas. See figure 5 and table 1 for explana- tion of symbols and identification of fossils, respectively. S 5 E m a: SHUBLIK AND SADLEROCHIT I 55 Egg g MOUNTAINS 76 5§ g m e 118 METERS . I 2 5 112 3900 _ § 3 g 27‘, :7, g m 69 LL! - o 2 “J 0 Q Q .1 Lu m D— t - ! ! v 0 ‘0 U 6 — .1 ,‘3 E’ o o @812 g: 5 .cf. ° @cf yafi — g i 5 . 2 ’9 N 9 N u? z 0 Q o a 0 ° 3700 — <_): E 5 s a a Q E: 9 o 0 o o _ > D o . I s o . O O _ é Go a o cf. ZQ32 ‘ O E l 0 I ° 39 3 °l I ° 1 ° 3500— 9 s 1 a I 1 s : — . o 0 ° 12 _ <2: 6 °‘ l l l 0° & (g _ 0: ° . _ o S o a g 33 i , ‘3'” 115 awe—2 % w ”1 ‘ 1 '° 2% < ° ° 0 E . a U 117 _ g I //| // _ g / / / _l ‘ / 3100 — X / 9 <2: 0 N m 9 Z _ O 2 o < / CE <1: N Z u.1 o O / _ 1. o: a: 8 UJ E / / 2900 — Q E g / / _ m S D. / I o z 95 / / _ z < CL / s 5% / _ I LU m m .1 E / 2 D O 2700‘ < 9 _ 0 5 / f / a / /5 l S l. l - — —I a. I0 1 [—1— 2500 M U ’— m a o 0 2 ”/0. _ A. 0_ 3 0 9 I“: —,— 4-w— Q Q 2 g X 2’1°°M_NOTSHOWN Figure 26. Generalized composite stratigraphic sec- E a —_ 1 tion and fossil distribution in the carbonate succession in 3 I..- I I _—_ the Shublik and Sadlerochit Mountains (data from O a E l; 1:“ A : Blodgett and others, 1986, 1988, 1992a; Robinson and IE 0 R4 0 others, 1989; J.G. Clough, 1989, and written commun., :6: o / W 1992; and AG. Harris, unpub. data). See figure 5 and o 0 table 1 for explanation of symbols and identification of 0 ° ° fossils, respectively. REGIONAL RELATIONSHIPS 47 Correlation—Differences between the York Moun- tains and Snowden Mountain (meta)carbonate successions are most marked in pre-Middle Ordovician rocks. No definitively Cambrian or older strata are known in the Yorks, but Lower Ordovician rocks are thick and widely distributed. Middle Ordovician and younger rocks in the two areas correspond better. The lower part of unit Olsh correlates lithologically and faunally with part of the Snow- den Creek unit, which suggests that basins existed in both regions during early Middle Ordovician time. The Snowden Mountain area basin received more siliciclastic input and persisted longer than its counterpart in the York Mountains. Upper Ordovician and Silurian strata are also similar in the two areas, but Richmondian rocks in the York Mountains formed in slightly more normal marine and deeper water than coeval Snowden Mountain area strata. Definitively Devonian carbonate rocks are rare or absent in the York Mountains and appear to be uncommon in the Snowden Mountain metacarbonate succession. SHUBLIK AND SADLEROCHIT MOUNTAINS Description. ——A carbonate platform succession some- what similar to that in the western Baird and York Moun- tains occurs in the Shublik and Sadlerochit Mountains in the northeastern Brooks Range (Clough, 1989; Blodgett and others, 1986, 1988, 1992a; Clough and others, 1988, 1990). These rocks are not metamorphosed and yield conodonts with a CAI of 4. The succession comprises the Katakturuk Dolomite (at least 2,500 m thick), the Nanook Limestone (about 1,200 m thick), and the Mount Copleston Limestone (71 m thick) (fig. 26). The Shublik-Sadlerochit Mountains carbonate succes- sion (as used herein) is distinguished by a thick sequence of pre-Ordovician carbonate rocks. The Katakturuk Dolomite consists of a variety of carbonate lithologies deposited in shallow subtidal to supratidal settings; it includes abundant stromatolites and coated grains and is considered to be of Proterozoic age. The overlying Nanook Limestone also contains a variety of shallow-water carbonate lithofacies; the lower two-thirds of the formation have yielded no body fossils (although the basal part of the unit contains burrows) and is thought to be chiefly Proterozoic or Early and Middle(?) Cambrian in age. These unfossiliferous strata are overlain by at least 160 m of Upper Cambrian peloidal pack-grainstone, which yields trilobites with North Ameri- can paleobiogeographic affinities. The upper part of the Shublik-Sadlerochit Mountains carbonate succession is Ordovician (upper one-third of the Nanook Limestone) and Devonian (Mount Copleston Lime— stone) in age. Lower Ordovician strata are as much as 300 m thick and consist chiefly of peloidal pack-grainstone. These rocks yield trilobites with affinities to the Bathyurid Province, which occupied low-paleolatitude sites in North America, Greenland, northeastern Russia, and Kazakhstan, and locally abundant Clavohamulus densus, a NAMP con- odont that indicates a warm, partly restricted, very shallow water depositional environment. Clavohamulus densus is diagnostic of the Rossodus manitouensis Zone of early Early Ordovician age. An interval of Middle and (or) Late Ordovician age, as much as 120 m thick, lies between definitive Lower and Upper Ordovician strata. The upper- most 44 m of the Nanook Limestone are definitively Late Ordovician in age, consist of interbedded dolostone and lime mudstone, and yield a relatively diverse gastropod fauna, as well as other mollusks and ostracodes and the pentamerid brachiopod Tcherskidium sp., which has Sibe- rian biogeographic affinities. Upper Ordovician strata pro- duce conodont faunas similar to those from the eastern Baird Mountains, including the Siberian-northern North American element Phragmodus n. sp. but having a greater diversity of WNAMP species such as Aphelognathus aff. A. divergens, Culumbodina occidentalis, and Pseudobelodina vulgaris vulgaris. Locally, in the Shublik Mountains, the Mount Copleston Limestone of Emsian (late Early Devo— nian) age disconformably overlies the Nanook Limestone. This Devonian unit is mostly lime mudstone with local banks of pentamerid brachiopods and lagoonal deposits rich in amphiporid stromatoporids; other fossils include two- hole crinoid columnals and conodonts of the gronbergi to serotinus Zones, inclusive. Correlation. —-The carbonate succession in the Shublik and Sadlerochit Mountains differs considerably from that in the Snowden Mountain area. The Shublik-Sadlerochit pre- Ordovician section is much thicker than known or suspected coeval rocks in the Snowden Mountain area; well-dated Cambrian strata are younger than the Middle Cambrian Snowden Mountain unit and include faunas with North American, not Siberian, biogeographic affinities. The rela- tively thick, Lower Ordovician part of the Nanook Lime- stone has no dated equivalents in the Snowden Mountain area, and the basinal, Middle Ordovician Snowden Creek unit has no lithologic counterpart in the Shublik—Sadlerochit carbonate succession. Upper Ordovician strata in the upper part of the Nanook correspond lithologically and faunally with coeval rocks in the Snowden Mountain metacarbonate succession, but Silurian strata are missing in the Shublik and Sadlerochit Mountains. The Emsian Mount Copleston Limestone is lithologically similar to, and may correlate with, Emsian and (or) Eifelian metalimestone in the Snow- den Mountain area. Both units contain the distinctive two-hole crinoid columnals. DOONERAK WINDOW Description—Lower Paleozoic rocks, informally named the Apoon assemblage (Julian, 1986), are exposed in a structural high near Mount Doonerak, about 40 km northwest of Snowden Mountain (fig. 20). The assemblage 48 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA consists of black slate and argillite, green and gray phyllite, volcaniclastic conglomerate, mafic tuff and pyroclastic breccia, massive basalt, and minor marble; it is severely deformed and metamorphosed to lowest greenschist facies (Julian, 1986, 1989). Structural complexity precludes deter- mination of stratigraphic thickness; structural thickness of the assemblage exceeds 3,000 m (Julian, 1989). The age of the Apoon assemblage is poorly constrained but appears to be early Paleozoic. A few fossils have been recovered from metasedimentary rocks in the western part of the Doonerak window. North of Frigid Crags (about 15 km southwest of Mount Doonerak), dark-gray phyllite contains Early Silurian (Llandoverian) graptolites and Silu- rian conodonts, and siliceous volcaniclastic rocks produced Ordovician, probably Middle Ordovician, conodonts (Repetski and others, 1987). In the hills south of Wolf Creek (about 30 km southwest of Mount Doonerak), sandy metalimestone contains Middle (probably early Middle) Cambrian trilobites, as well as protoconodonts, hyolithids, and acrotretid brachiopods; the fauna has Siberian biogeo- graphic affinities (Dutro and others, 1984a, 1984b). Two marble bodies in this area produced protoconodonts of Middle Cambrian to Early Ordovician age (Dutro and others, 1984a). Mafic dikes and sills in the Apoon assem— blage have been dated by K—Ar and Ar-Ar techniques and yield ages of about 470 and 350 Ma (Dutro and others, 1976); these values fall within the early Middle Ordovician and late Early Mississippian, respectively (based on Har- land and others, 1990; Bally and Palmer, 1989). The Apoon assemblage is interpreted as a subduction- related magmatic arc complex, deposited in a back-arc basin (Julian, 1989). An undated marble body in the eastern Doonerak area locally preserves a limestone breccia texture, contains shale-rip-up clasts, and is thought to be a carbonate debris-flow deposit (Julian, 1989). Cambrian metacarbon- ate layers from the Wolf Creek area contain calcareous lithiclasts (Dumoulin, unpub. data) and could also have been redeposited. Correlation. —Julian (1989) suggested that limy debris-flow deposits within the Apoon assemblage were derived from a carbonate platform in the Snowden Mountain area. However, no lithologic or faunal data have yet been found to confirm this suggestion because dated metacarbonate layers in the Apoon assemblage are older (Middle Cambrian to Early Ordovician) than the main period of platform carbonate deposition at Snowden Moun- tain (Late Ordovician and Silurian). DEVONIAN SILICICLASTIC UNITS Metasedimentary rocks that are at least in part correl- ative with Devonian siliciclastic units in the Snowden Mountain area occur in the western (and possibly, in the eastern) Baird Mountains. The Baird Mountains units are briefly described below (description based on data in Karl and others, 1989) and then compared to the Snowden Mountain units. DEVONIAN SILICICLASTIC UNITS IN THE BAIRD MOUNTAINS NAKOLIK RIVER UNIT The Nakolik River unit is an informal name proposed by Karl and others (1989) for metasedimentary rocks that crop out in the western Baird Mountains. Two subunits are distinguished, units Dnl and Dnu.7 Unit Dnl consists of metalimestone and marble intercalated with subordinate (20—40 percent) quartzose metaclastic rocks (fig. 27A). Metalimestone intervals are a few to several tens of meters thick, contain locally abundant corals (fig. 273), stroma- toporoids, and brachiopods, and formed as biohermal build- ups on a shelf or platform subject to periodic influx of siliciclastic material. Other limy layers consist of quartzose calcarenite deposited by storms or in high-energy shoals. Unit Dnl yields rare conodonts of latest Givetian and Frasnian age that represent the polygnathid-icriodid biofa— cies. Unit Dnu consists primarily of green, gray, and maroon phyllite, as well as lesser amounts of metalime- stone, quartzose metasandstone, and metaconglomerate; it is laterally gradational to, and locally gradationally over- lies, unit Dnl. Metalimestone layers are similar to those in unit Dnl but are generally less than 10 In thick. Conodonts obtained from these layers are of Frasnian age; polygnathids dominate the assemblages, but minor ancyrodellids and palmatolepids occur and suggest an outer shelf depositional environment. The N akolik River unit is gradationally overlain by the Hunt Fork Shale; the base of the unit is not exposed. The unit is transitional in time and space between the Lower and Middle Devonian carbonate platform sequence of the upper part of the Baird Group to the south and the dominantly elastic, mostly Upper Devonian Endicott Group to the north. UNIT qus Unit qus8 of Karl and others (1989) crops out in the northeastern Baird Mountains and consists of quartz-pebble metaconglomerate, quartzose, locally calcareous metasand- stone, and green, maroon, and black (carbonaceous) phyl- lite. Coarse-grained metaclastic rocks are primarily quartz- ose but include some volcanic rock fragments, and the unit 7Dnl, Devonian limestone of Nakolik River; Dnu, Devonian phyllite, carbonate, and elastic rocks of Nakolik River, undivided. 8F’zqs, Paleozoic quartz conglomerate, sandstone, and siliceous phyllite. REGIONAL RELATIONSHIPS 49 A Metasandstone ’ Metasiltstone and phyllite Metalimestone and marble containing corals and stromatoporonds V Figure 27. Sedimentary features of the Nakolik River unit, western Baird Mountains. A, Outcrops of the Nakolik River unit. B, Colonial coral in fossiliferous metalimestone. is “intimately associated” (Karl and others, 1989, p. 33) with siliceous volcanic rocks (metarhyolite). No fossils have been recovered from unit qus, but the unit is thought to be Middle and Late Devonian in age on the basis of regional relationships (Karl and others, 1989). Unit qus overlies the Devonian(?) and older eastern Baird Mountains metacarbonate succession described above. In most places the contact is a fault, but a depositional contact has been reported from one locality (Karl and others, 1989). The unit is overlain by gray phyllite assigned to the Hunt Fork Shale; this contact is covered and may be structural and (or) stratigraphic . HUNT FORK SHALE Rocks referred to the Hunt Fork Shale by Karl and others (1989) crop out in both the eastern and western Baird Mountains. These strata have been metamorphosed to lower greenschist facies and consist of gray to green or black phyllite and subordinate siliceous or calcareous metasilt- stone and metasandstone. Metasandstone layers are graded, as much as 1 m thick, and interpreted as turbidites; some contain transported fossil debris. In both its eastern and western outcrop areas, the Hunt Fork Shale is intruded by massive mafic sills and dikes; at one western locality, the unit contains a 30-m-thick section of pillowed(?) mafic flows. No fossils have been found in this unit in the eastern Baird Mountains, but western outcrops yield brachiopods and mollusks of late Frasnian or early Famennian age. Karl and others (1989) suggest a prodelta, outer shelf or slope depositional setting. COMPARISON OF SNOWDEN MOUNTAIN AND BAIRD MOUNTAINS DEVONIAN SILICICLASTIC UNITS Like the Snowden Mountain area, the Baird Mountains contain several siliciclastic units of Devonian age that are structurally intercalated with older metacarbonate rocks. The lithology, fauna, age, and general depositional setting of the Nakolik River unit are similar to those of the Beaucoup Formation and Nutirwik Creek units in the Snowden Mountain area. Unit Dnl and the Beaucoup Formation contain fine- and coarse-grained siliciclastic rocks, biohermal buildups, redeposited calcarenite layers, and conodonts of the polygnathid-icriodid biofacies. Unit Dnl is more calcareous than the Beaucoup Formation and appears to be, in part, older; the oldest faunas known from unit Dnl are Eifelian or early Givetian in age, whereas well-dated samples from the Beaucoup Formation are no older than latest Givetian. Unit Dun and the Nutirwik Creek unit consist primarily of purple and green phyllite but include some conglomerate and minor metalimestone; limy layers produce Frasnian conodonts, including some forms 50 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA typical of deeper water (outer shelf or slope) settings. Unit qus is also lithologically similar to much of the Nutirwik Creek unit; both include pebble conglomerate, maroon, green, and black phyllite, and volcanic material. Limestone lenses have not been noted in unit qus, however, and its age is poorly constrained. Unit qus, the N akolik River unit, and the Nutirwik Creek unit are spatially associated with, and may have been deposited on, older metacarbonate successions. Age, lithology, and depositional setting of the Hunt Fork Shale are similar in both the Baird Mountains and Snowden Mountain area, although the unit appears to contain less limestone and is consequently less well dated in the Baird Mountains. The Hunt Fork Shale is thought to depositionally overlie the N akolik River unit in the western Baird Mountains (Karl and others, 1989), but all contacts between the Hunt Fork Shale and the Beaucoup Formation and Nutirwik Creek units in the Snowden Mountain area appear to be faults. Finally, mafic igneous rocks intrude the Beaucoup Formation in the Snowden Mountain area but are intercalated with and intrude the Hunt Fork Shale in the Baird Mountains. DISCUSSION The present configuration of pre-Carboniferous rocks in northern Alaska is a result of Mesozoic tectonism; the original configuration of these rocks is unknown. Paleo- geographic reconstruction of northern Alaska remains con- tentious because fundamental tectonic questions are unre- solved. In particular, the cause and effects of Devonian orogeny in the Brooks Range, and the position of northern Alaska prior to Mesozoic opening of the Canada basin, are poorly understood (Nelson and others, 1993; Lawver and Scotese, 1990). Most workers interpret pre-Carboniferous carbonate strata of northern Alaska as a platform or continental margin assemblage formed on continental crust, but the Paleozoic position of this crust is poorly constrained. Proposed Paleozoic configurations include northern Alaska as a northwest-protruding extension of the North American craton (Churkin and others, 1984, 1985) or as an isthmus connection between North America and Siberia (Churkin and Trexler, 1981; Rowley and others, 1985). Other authors have hypothesized that northern Alaska and the Chukotka region of northeastern Siberia constituted a dis- crete continental block with a Paleozoic kinematic history distinct from that of North America (for example, Sweeney, 1982). Alternatively, pre-Carboniferous strata now found in northern Alaska may have accumulated along several dis- parate continental margins and then juxtaposed by later tectonic events. Grantz and others (1991) suggested that the Brooks Range is underlain by Siberian and North American crustal fragments assembled during early Paleozoic conver- gence. These authors interpret rocks with “Siberian” fau- nas, such as pre-Devonian strata in the Snowden Mountain area, as Siberian crustal fragments and metavolcanic rocks in the Doonerak window as remnants of the arc formed during this convergent event. ' Various techniques can be used to test the models for origin of pre-Carboniferous carbonate strata in northern Alaska discussed above. Approaches include ( 1) establish- ing displacement histories of carbonate successions through paleomagnetic studies, (2) identifying structures and (or) rock associations (such as ophiolite assemblages or volcanic arc deposits) that mark suture zones between carbonate successions, (3) using microfacies analyses to assess the degree of lithologic and biotic similarity between individual (meta)carbonate successions, and (4) comparing paleobio- geographic affinities of faunas in distinct (meta)carbonate successions. Reliable primary magnetic components have not been obtained from Paleozoic rocks of the Brooks Range or the Seward Peninsula (Plumley and Tailleur, 1987; Plumley and Reusing, 1984), but the other three methods have been used to investigate the origin of pre- Carboniferous strata of northern Alaska. Identifying boundaries between Paleozoic crustal frag- ments is hindered by the masking effects of younger tectonic events on older structures and the difficulty of recognizing and precisely dating ancient suture assem- blages. Metavolcanic rocks of early Paleozoic age in the Doonerak window, and of Early and Late Cambrian age in the northeastern Brooks Range, have been interpreted as possible remnants of oceanic crust trapped during a pre- Carboniferous continental collision (Moore, 1987; Grantz and others, 1991) (fig. 20). These rocks yield ambiguous geochemical signatures, however, and could also have formed along the North American continental margin (Moore, 1987). Deep-water carbonate rocks are another lithology that might occur along suture zones between continental carbon- ate terranes, but these strata could also accumulate in intracratonic basins. Slope and basinal carbonate rocks of Cambrian to Devonian(?) age occur on the northeastern and southeastern Seward Peninsula (Dumoulin and Till, 1985; Till and others, 1986; Ryherd and Paris, 1987; Dumoulin and Harris, unpub. data), and carbonate turbidites of Silurian and (or) Devonian age crop out in the Ambler River and Wiseman quadrangles (Dumoulin and Harris, 1988 and unpub. data) (fig. 20). Nothing is known, however, about the type of basement (oceanic or continental) on which these sequences were deposited. Zones where disparate continental fragments may have been juxtaposed are marked by suture assemblages, but distinguishing the fragments requires detailed stratigraphic comparisons. Comparative lithofacies analysis and paleo- biogeography have been used in the Appalachians (Williams and Hatcher, 1983) and the North American REGIONAL RELATIONSHIPS 51 Cordillera (Monger and Ross, 1984) to recognize “exotic” Paleozoic terranes thought to have been displaced great distances before accretion to the North American continen- tal margin. Application of such techniques to the pre- Carboniferous strata of northern Alaska has been limited, however, because relatively detailed paleontologic and sedimentologic data have only recently been obtained from much of this region. These data are summarized below, and their implications for the Paleozoic history of northern Alaska are briefly explored. COMPARATIVE MICROFACIES ANALYSIS One approach that could help identify “exotic” conti- nental fragments in northern Alaska is comparative analysis of microfacies in the pre-Carboniferous (meta)carbonate successions. Carbonate rocks deposited along the same margin or platform should show similar successions of lithofacies, biofacies, and depositional environments. Coeval rocks formed on separate continents, in contrast, could differ greatly, because they might have different sediment sources, paleoclimates, and (or) subsidence his— tories. Distinction between these end—member cases is not necessarily straightforward, however. Intracratonic basins can develop within a single continental block and give rise to a variety of dissimilar but coeval facies. Alternatively, global changes such as eustatic shifts could produce uni— form effects on disparate continental margins. Similarities and differences between the (meta)carbon- ate successions of northern Alaska are summarized below and in figure 28. The metacarbonate succession in the Snowden Mountain area correlates best, lithologically and faunally, with the metacarbonate succession in the eastern Baird Mountains, but also has similarities with (meta)car- bonate successions in the western Baird, York, and Shublik and Sadlerochit Mountains. Differences between these (meta)carbonate successions could reflect origins in several discrete carbonate platforms but also could be explained through variation in subsidence rates, erosion, and elastic input along a single continental margin. Strata of Proterozoic and Cambrian age are thickest in the Shublik and Sadlerochit Mountains and have not been observed in the York and western Baird Mountains. Rela- tively deep-water facies (deposited in outer shelf and (or) slope settings) of Middle Cambrian and older(?) age are known in the eastern Baird and Snowden Mountain meta— carbonate successions and may also occur in Doonerak window rocks. Relatively shallow-water facies of Late Cambrian age are recognized in the eastern Baird and Shublik-Sadlerochit (meta)carbonate successions. Lower Ordovician platform carbonate rocks are widely distributed in the York, western Baird, and Shublik and Sadlerochit Mountains. The western sections are thicker and differentiated into at least two distinct lithofacies; the Shublik-Sadlerochit section appears relatively uniform. Carbonate platform rocks of Early Ordovician age have not been identified in the eastern Baird Mountains or Snowden Mountain area; instead, basinal facies (carbonaceous phyl- lite, siltstone, and metachert) appear to have accumulated during this time. Middle Ordovician strata in the eastern Baird and Snowden Mountain metacarbonate successions consist chiefly of deep—water slope to basinal facies; both sections shallow upward and contain abundant fine-grained silici- clastic detritus. The Middle Ordovician section in the York Mountains is similar but contains less siliciclastic material and a larger proportion of somewhat shallower (outer to middle shelf) facies. Other Middle Ordovician sections are dominated by platform. carbonate rocks; deep-water facies of Middle Ordovician age appear to be a minor part of the western Baird metacarbonate succession and have not been reported from the Shublik and Sadlerochit Mountains. Global sea level was high during the Llanvirnian; relatively deep—water facies characterize many Llanvimian sections worldwide. Carbonate strata of Late Ordovician through Middle Devonian age are generally similar across northern Alaska; variations appear to reflect differential erosion during Early Silurian and (or) post-Early Devonian time. Upper Ordovi- cian strata were deposited in a shallowing-upward shelf or platform setting; this pattern has been documented in all successions with the exception of the western Baird Moun- tains, where Upper Ordovician strata appear to be scarce. Lower and Upper Silurian strata occur in the York, eastern and western Baird, and Snowden Mountain (meta)carbonate successions. No Silurian rocks have been found in the Shublik and Sadlerochit Mountains. Meter—scale shallowing-upward cycles have been noted in Upper Ordovician strata in the eastern Baird and Snowden Mountain metacarbonate successions and in Silu- rian strata in the York, western Baird, eastern Baird, and Snowden Mountain (meta)carbonate successions. Carbon— ate facies and depositional patterns in Ordovician and Silurian strata in northern Alaska correlate well with pub- lished eustatic curves for the early Paleozoic. Global sea level was high at the base of the Ashgillian and then fell sharply throughout the remainder of the Late Ordovician (Ross and Ross, 1988). The Silurian eustatic curve is marked by a number of short-term rises and falls (Ross and Ross, 1988) so small-scale depositional cycles are not surprising in strata of this age. Lower and Middle Devonian carbonate rocks appear to be rare in the Snowden Mountain area, are rare or absent in the eastern Baird and York Mountains, and are only locally present in the Shublik and Sadlerochit Mountains. The thickest and most widely distributed section of Lower and Middle Devonian carbonate rocks occurs in the western Baird Mountains. Global sea level was relatively low during PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA 52 8 83A 258 358 new w2=2wanw ..9_Eo_on_ xEExmfix A593 .6 .mao.w 52m $53 $886 ..2m3-awmo OlOZOHEiOHd A5 83 €82.28 5 :95 SEE . : E 83 255 53 A. / mcfimhflflwwfi .5::: 358% 583-30:me m8 cm mm .0 «EB § . _ A. wowmxom. 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AE o 3 328E532 mcofimE=EwE O 98 9.28.8 mqDQE W V Ewan—D N memm szzmwwfiQO $5 ”#252302 952302 3596 DZ< v=l_mDIw z_<._.ZDO_2 2w0>>Ozm Om= \EmIHOZOm REGIONAL RELATIONSHIPS 53 the Early Devonian but began to rise in the Eifelian (Ross and Ross, 1988). Carbonate-siliciclastic rocks of Middle and Late Devo- nian age occur in the Snowden Mountain area and western Baird Mountains; carbonate content is higher in the Baird Mountains units. Possibly correlative sequences that con- tain little carbonate material crop out in the eastern Baird Mountains. No strata definitively of this age are known in the York or Shublik and Sadlerochit Mountains. Thus, carbonate platform development started as early as the latest Proterozoic in at least some parts of northern Alaska and had ended by the Early or Middle Devonian in all of the (meta)carbonate successions discussed above. Clastic influx and (or) Devonian orogeny may have caused the demise of early Paleozoic carbonate platforms in north- ern Alaska. Successions of mixed carbonate and siliciclastic material (with carbonate generally subordinate) of Middle and Late Devonian age are widely distributed across north— ern Alaska. A depositional relationship between older carbonate platform successions and younger carbonate- clastic units has been postulated by some workers but has not been proven in most areas. The best case for such a relationship can be made in the western Baird Mountains, where a continuous Devonian succession of Emsian, Eifel- ian, Givetian, Frasnian, and possibly Famennian age is present. The Emsian to Eifelian cessation of carbonate platform deposition in most of northern Alaska appears to roughly coincide (about 390 Ma; Aleinikoff and others, 1993) or slightly predate (370 t 30 Ma; Nelson and others, 1993; Dillon and others, 1987b) intrusion of granitic plu- tons. These ages fall within the Early Devonian and Frasnian, respectively (based on Harland and others, 1990', Bally and Palmer, 1989). Lithologic data from the pre-Carboniferous (meta)car- bonate successions of northern Alaska could be explained through origin on three discrete carbonate platforms. The Snowden Mountain and eastern Baird metacarbonate suc- cessions are distinguished from other northern Alaska (meta)carbonate successions by well-developed basinal assemblages of chiefly Middle Ordovician age and the apparent absence of Lower Ordovician shallow-water car- bonate rocks. The York and western Baird (meta)carbonate successions are characterized by a thick section of Lower Ordovician platforrnal carbonates and by relatively minor amounts of Middle Ordovician deeper water facies. The Shublik—Sadlerochit carbonate succession is similar to the York and western Baird (meta)carbonate successions but 4 Figure 28. Correlation and depositional environments of (meta)carbonate successions in the York, western and eastern Baird, Snowden, and Shublik and Sadlerochit Mountains. All rocks shown in the western Baird Mountains column are part of the Baird Group. Number in parentheses indicates thickness of unit. includes a thick section of Proterozoic and Cambrian strata not known in the west. An alternate explanation of the available data is that the pre-Carboniferous carbonate successions described above formed along a single continental margin that was near, and shared some faunal elements with, both the North American and Siberian continents (fig. 29). During Early and Middle Ordovician time, an intracratonic basin devel— oped along part of the north Alaskan margin (eastern Baird and Snowden Mountain metacarbonate successions) while carbonate platform deposition continued elsewhere (York, western Baird, and Shublik-Sadlerochit (meta)carbonate successions). By Late Ordovician time, shallow-water car- bonate deposition had spread again across the north Alaska margin, and these conditions persisted, with some interrup- tions, through at least the Early Devonian. PALEOBIOGEOGRAPHY Paleobiogeographic analysis is another technique that can shed light on the Paleozoic configuration of northern Alaska. “Siberian” and “North American” biogeographic affinities have been reported for various fossils from the pre-Carboniferous (meta)carbonate successions described above. The biogeography of Cambrian trilobites has attracted the most attention (Palmer and others, 1984; Dutro and others, 1984a, b', Grantz and others, 1991), but provin- ciality has also been noted in Ordovician trilobites, cono- donts, brachiopods, gastropods, and corals. Silurian and Devonian faunas in northern Alaska appear relatively cosmopolitan. The biogeographic affinities of Cambrian and Ordovi- cian faunas from northern Alaska are summarized in table 2. Late Cambrian trilobites in the Shublik—Sadlerochit carbonate succession have North American affinities (Blodgett and others, 1986); Early Cambrian trilobites found in limy beds in the Marsh Fork volcanic rocks (informal unit of Moore, 1987), 50 km south of the Shublik Mountains, also have North American affinities (Dutro and others, 1972). Middle Cambrian rocks in the Doonerak window and at Snowden Mountain yield trilobites with Siberian affinities (Palmer and others, 1984). Lower Ordo- vician strata in the Shublik-Sadlerochit carbonate succes- sion produce trilobites with affinities to the Bathyurid Province, which occupied low-paleolatitude sites in North America, northeastern Russia, Kazakhstan, and Greenland (Blodgett and others, 1986). Early and Late Ordovician trilobites from the York Mountains carbonate succession have Siberian affinities (Orrniston and Ross, 1976). Late Ordovician brachiopods and gastropods with Siberian affin- ities occur in the York, eastern Baird, and Shublik- Sadlerochit (meta)carbonate successions (Blodgett and oth- ers, 1988', Potter, 1984; Blodgett and others, 1992b). Some corals from the York Mountains (Oliver and others, 1975; 54 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA WEST YORK BAIRD MOUNTAINS MOUNTAINS WESTERN MIDDLE DEVONIAN TO LATE EAST SNOWDEN SHUBLIK AND EASTERN MOUNTAIN SADLEROCHIT AREA MOUNTAINS ORDOVICIAN MIDDLE AND EARLY ORDOVICIAN ' CAMBFllAN AND LATE PROTEROZOIC ? EXPLANATION Shallow-water shelf or platform carbonate deposits (Cambrian and Late Proterozoic) Shallow-water shelf or platform carbonate deposits (Middle and Early Ordovician) Figure 29. Schematic reconstruction of pre-Carboniferous car— bonate successions in northern Alaska. During Late Proterozoic and Cambrian time, chiefly shallow-water carbonate facies accu- mulated in the eastern Baird Mountains, Snowden Mountain area, and Shublik and Sadlerochit Mountains; rocks of this age have not been found in the York Mountains or western Baird Mountains. During Early and Middle Ordovician time, chiefly shallow-water R.J. Elias, University of Manitoba, written commun., 1986) and Snowden Mountain area (T.E. Bolton, written commun., 1992) have North American affinities. Provinciality has also been noted in Ordovician cono- dont faunas from northern Alaska; species typical of WNAMP and SAP have been identified. Lower Ordovician strata in the York and western Baird (meta)car- bonate successions yield chiefly tropical cosmopolitan (for example, Acanthodus lineatus, Variabiloconus bassleri, Protopanderodus leei, Rossodus floweri, Scolopodus bolites, and “S. ” gracilis ) and pandemic species (Drepan- odus arcuatus, Drepanoistodus forceps, Paltodus subae- qualis, and Paroistodus parallelus) together with fewer WNAMP (Clavohamulus n. sp., Rossodus n. sp., and Deep-water, outer shelf, slope. or basin deposits (Middle and Early Ordovician) Shallow-water shell or platform carbonate deposits (Middle Devonian to Late Ordovician) carbonate facies were deposited in the York Mountains and western Baird Mountains, basinal facies accumulated in the eastern Baird Mountains and Snowden Mountain area, and only shallow-water carbonate facies formed in the Shublik-Sadlerochit Mountains. During Late Ordovician to Middle Devonian time, neritic carbonate deposits accumulated across northern Alaska. See figure 5 for explanation of symbols. Histiodella n. sp.) and SAP (Fryxellodontus? = Acodina? bifida of Abaimova, 1975) elements. Lowermost Ordovi- cian beds in the Shublik and Sadlerochit Mountains yield NAMP conodonts (Clavohamulus densus). Middle Ordovi- cian rocks in all of the northern Alaskan (meta)carbonate successions contain chiefly cosmopolitan forms, with the exception of some intervals in the western Baird metacar- bonate succession; lowermost Middle Ordovician strata in this area contain NAMP elements and middle Middle Ordovician beds are dominated by SAP species (mostly acanthocodinids and stereoconids) (fig. 24). Upper Ordo- vician strata reveal a relatively complex pattern of conodont fauna] affinities. Early Late Ordovician collections in the eastern Baird, Snowden, and Shublik—Sadlerochit 55 REGIONAL RELATIONSHIPS A: ANFQ .0550 :5 2:5 25:82 :55 :o .53 :0— om :55 .500: 250:3 50m 552 5 55:05 505:5 552 550550 ”80525 .5: .50 “2:52.80 ”3555005..“— AS 85— £550 :5 55 35:55 55000550 ”555—8 55:35:: :5 55:05 5550050052 .6 Cum:— AO awe :55500 55:3 £550 :5 5555 555:5 555m 3530M 3.5 5:8 54:05550 5:050 ”50553:. 5:55:55 :5..55< 2:52 .00 Gwfl £550 :5 A: Antwa— .5.5: :5 5.55:8 “Haw—00.5 555:5 505:5 552 5:8 5505550 5:055 5:550 ”555:; 5:55: :5 55:05 555055052 554 .30 35:55 m> 3:50 550:0 KC mE>15_::0E:0_M |A855555E :5 5.5552 :5 53.9 5555‘: 552 3.550 ”3:05:00 ”3:05:00 5 C mE>|55555E 5500 omowE 550m .Amv 3&0— .m5:5 :5 AC Aga— ..:=:=:00 53:3 .523: 5:05:00 AS .SNQE .5550. :5 5355 55550 55505 5552:5535 .muC 558 5050.2. 552 :5552 A: 55:55 5:35 5505550 5050: :5 855:5: sumo: .5090 55505 5:35 553050 “500055.. :5 5005:05m 5550 550—00 5:005:55 5:0:050 5:25.55» :5 50555.5 Q53 55.552 :05 :5552 :o:30:m 5555: 55m 5350 55552 55m 5353 55552 55> ow< :5005—5W :5 553a . . . . . . 255:5: :55£m 2: :0 500: 50555.: 530— 50.: 5:05:00 .53 55:55 5:05 55: 552 5253 £3223 ”£5550 8:305 55550052 555:5 552 £32 Z :305 5 :3: 5 5559 5:05:00 00:30.3 5:52-555m mam ”3:05:00 8:305 55550052 5055< 3 5355 50 :8: 5553 5 505:: 555:5 3:5 530:3 55:52 45:2 55 :5 n50:00:00 335m 35280 .3: so: 0% 853:5: .55 :25 5 :3. .05: E5 5 ME“: .05: :25 5 5585 .35: m5: 5 5850 5:3: :25 5 8:0 as: as 5% 2888 :3 .552 :555: 5 w 555005 5550505550 553050 :5 5:550 :53 5:5: 5 5:55: 05550550005: .N 2.5:. 56 PRE-CARBONIFEROUS METACARBONATE ROCKS, NORTHERN ALASKA (meta)carbonate successions are dominated by Siberian— northern North American forms, whereas latest Ordovician faunas in these areas contain WNAMP conodonts (predom- inantly aphelognathids). Upper Ordovician strata in the York Mountains yield WNAMP and SAP conodonts; the single known locality of Upper Ordovician rocks in the western Baird Mountains produced cosmopolitan conodonts. Specific elements of the paleobiogeographic pattern outlined above have been used to infer the presence of “exotic” continental fragments in northern Alaska. The occurrence of Cambrian trilobite faunas with Siberian affinities in the Doonerak-Snowden Mountain area, and with North American affinities in the Shublik and Sadlero- chit Mountains, has been cited as evidence that the Brooks Range is underlain by “Siberian” and “North American” crustal fragments (Grantz and others, 1991). The Siberian affinities of Ordovician trilobites in the York Mountains led Ormiston and Ross (1976) to conclude that the Seward Peninsula was part of a Siberia-Kolyma continent during the early Paleozoic and was not connected to the rest of Alaska and North America until the Mesozoic. Long-distance translation of tectonic blocks is not the only mechanism that can produce “anomalous” faunal distributions, however. Modern biogeographic patterns are controlled by many variables, including global circulation, continental configuration, and larval ecology. Position of the paleoequator relative to northern Alaska during the Paleozoic is one factor that may have affected faunal distributions. The biogeography of the present-day Great Barrier Reef demonstrates the importance of continental configuration. The reef occurs along the eastern margin of the Indian-Australian plate and is oriented roughly perpen- dicular to the equator; it is more than 2,000 km long and extends through 15° of latitude. Distinct biotic zones occur within the reef as a direct result of pronounced latitudinal variations in temperature and salinity (Davies and others, 1987). Recent paleogeographic reconstructions (for exam- ple, Scotese, 1986) have positioned northern Alaska at a moderate angle to the paleoequator during the early Paleo— zoic, so biotic differentiation in pre-Carboniferous strata may reflect, at least in part, latitudinally controlled ecologic variation. Larval ecology also influences biogeography. Many modern marine organisms produce pelagic larvae that are able to survive long-distance transport by ocean currents; such dispersal results in pantropic species distributions. Studies of comparative larval morphology suggest that some ancient species also had teleplanic larvae (Smith and others, 1990). The occurrence of “Tethyan” species in Paleozoic faunas of the North American Cordillera may reflect pantropic dispersal of certain species rather than large—scale tectonic displacements (Newton, 1988). Such dispersal mechanisms also may have affected faunal distri- butions in northern Alaska. The most precise biogeographic studies compare fos- sils of the same age and depositional environment and consider all elements of a given fauna. The “Siberian” trilobites in the central Brooks Range are of Middle Cam— brian age, whereas the “North American” trilobites in the northeastern Brooks Range are Early and Late Cambrian in age. Trilobites of exactly the same age have not been found in the two areas, and conclusions based on noncoeval species may be misleading. Middle Cambrian trilobites of “Siberian” aspect have recently been reported from rocks in southwestern Alaska that are considered part of the North American continental margin (Babcock and Blodgett, 1992). The Middle Cambrian may have been a time when faunal exchange between Alaska and Siberia was particu- larly pronounced. Ordovician conodont faunas also show temporal variations in biogeographic affinities; in most northern Alaskan (meta)carbonate successions, “Siberian” faunal elements in lower Upper Ordovician strata give way to “North American” faunal elements in upper Upper Ordovician rocks. Analogous temporal variations in the proportion of “Tethyan” species occur in Paleozoic and Mesozoic Cordilleran faunas and are attributed to climate- related pulses of larval distribution (Newton, 1988). It is also important to consider the biogeographic implications of as many fossil groups as possible within a given fauna. Potter (1984) studied brachiopods, corals, and trilobites in Upper Ordovician strata of the York Mountains and suggested that the biogeographic affinities of the entire fauna indicated faunal exchange between the York Moun- tains area, the North American continent, Chukotka, the Siberian platform, and Kazakhstan. The distribution of a variety of Late Ordovician brachiopod and gastropod spe- cies led Blodgett and others (1992b) to argue that, in early Paleozoic time, Arctic Alaska, the Seward Peninsula, and Chukotka formed a single tectonic block with faunal ties to the Kolyma region. In our View, the available biogeographic data from northern Alaska are best explained by postulating that pre-Carboniferous carbonate successions accumulated on a single continental margin or platform that had faunal exchange with both Siberia and North America. If northern Alaska represented a collage of distinct crustal fragments, one would expect to find “Siberian” faunas throughout one carbonate succession and “North American” faunas throughout another. This pattern is not observed. Rather, both “Siberian” and “North American” faunal affinities occur at different times and in different fossil groups within all of the (meta)carbonate successions discussed above. “Siberian” influences are particularly noteworthy in Middle Cambrian and early Late Ordovician time. This interpreta- tion agrees well with the Phanerozoic plate tectonic recon- structions of Scotese (1986) and Scotese and McKerrow (1990) (fig. 30). They treat northern Alaska-Chukotka as a discrete continental block that lay between Siberia and North America throughout the early Paleozoic. Their recon- REFERENCES CITED 57 60° NORTH ERN ALASKA / CHUKOTKA 300 _, A t! 00 30° Late Ordovician (Ashgillian) Figure 30. Global plate tectonic reconstruction for part of Late Ordovician (Ashgillian) time, showing relative proximity of northern Alaska, Siberia, and North America (modified from Scotese and McKerrow, 1990). structions indicate particular proximity between Siberia and Alaska during Middle Cambrian and Late Ordovician time. CONCLUSIONS Pre-Carboniferous rocks of the Snowden Mountain area consist of a dominantly metacarbonate succession of Proterozoic(?) through Early or Middle Devonian age that has been structurally dismembered and intercalated with predominantly metaclastic rocks of chiefly early Late Devo— nian age. Ordovician through Silurian rocks constitute the most precisely dated and best studied part of this metacarbonate succession. Middle Ordovician strata are mainly carbona- ceous phyllite, metachert, and allodapic metalimestone deposited in a slope or basinal environment; their vertical sequence indicates a shallowing-upward depositional regime. These strata are succeeded by Upper Ordovician and Silurian metacarbonate rocks that were deposited in warm, shallow-water environments. Devonian metaclastic units contain subordinate meta- limestone that yields late Givetian(?) and Frasnian cono- donts. Thicker limy layers formed as in situ shallow-water buildups; thinner layers are mostly calcarenite redeposited by storms and (or) turbidity currents. The metacarbonate succession in the Snowden Moun- tain area correlates best, lithologically and biostratigraphi- cally, with metacarbonate rocks in the eastern Baird Moun— tains and also has similarities with (meta)carbonate successions on the Seward Peninsula and in the western and eastern Brooks Range. Detailed comparisons of the lithol- ogy, biofacies, and biogeographic affinities of pre- Carboniferous carbonate successions across northern Alaska suggest that these rocks represent a single carbonate platform or continental margin dismembered by later tec- tonic events, rather than a collage of “exotic terranes.” REFERENCES CITED Abaimova, GP, 1975, Early Ordovician conodonts of the middle fork of the Lena River: Trudy Sibirskogo Nauchno- Issledovatelskogo Instituta, Geologii, Geofiziki i Mineral- nogo Sirya (SNIGGIMS), no. 207, 129 p. Aleinikoff, J .N. , Moore, T.E., Walter, Marianne, and Nokleberg, W.J., 1993, U-Pb ages of zircon, monazite, and sphene from Devonian metagranites and felsites, central Brooks Range, Alaska, in Dusel-Bacon, Cynthia, and Till, A.B., eds., Geologic studies in Alaska by the US Geological Survey during 1992: US. Geological Survey Bulletin 2068, p. 59—70. 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Key faunal components and lithologies Fossil age CAI 1 (Dh) 90ABd37A 68°06.9’/l49°32.5’ Skeletal wacke-packstone early Late Devonian (Frasnian) 5 (120674D) Polygnathus evidens (pl. 3, fig. 12) Polygnathus of the P0. xylus group (Dh) 90ABd37B 68°06.9’/149°32.5’ Oolitic grainstone interbedded with 90ABd37A. 2 (Dh) 9OABd34 68°06.8'/149°32.2’ Quartzose skeletal grainstone early Late Devonian (Frasnian, 5 (12065—SD) Polygnathus pacificur (pl. 3, fig. 13) probably late Frasnian). Polygnathus aff. P0. planarius Polygnathus samueli (pl. 3, fig. 14) 3 (Db) 9OTM529A 68°04.l’/ l49°12.3' Skeletal grainstone early Late Devonian (middle to late 5—5.5 (12082—SD) Ancyrodella nodosa (pl. 3, fig. 8) Frasnian; Upper hassi Zone to Palygnathus aff. P0. pacificus linguiformis Zone). 4 (Dn) 84DN199 68°00.l’/149°34.5’ Crinoidal marble early Late Devonian (middle 5.5 (11083—SD) Ancyrodella gigas Frasnian; Upper hassi Zone to Ancyradella lobata (pl. 3, fig. 19) Lower rhenana Zone). Ancyrognathus aff. A. triangularis (pl. 3, fig. 21). Icriadus symmetricus (pl. 3, fig. 1) 5 (Dn) 90TM453B 67°59.2’/ l49°21.7' Intraclast—skeletal packstone early Late Devonian (middle 5 (12076—SD) Ancyrodella sp. Frasnian; upper part of Lower Ancyrognathus cf. A. caem' (pl. 3, fig. hassi Zone). 20). Icriodus sp. Palmatolepis plamz (pl. 3, fig. 16) Palmatolepir proversa (pl. 3, figs. 17, 18). 6 (50m) 90AD20G 67°54.8’/l49°31 .4’ Peloidal-skeletal packstone early Late Ordovician (Edenian to 5 (10828—CO) “Belodina” spp. Maysvillian). Panderodus spp. Phragmodus n. sp. (= Ph. new species of Barnes, 1974). Plectodina? cf. PL? dolboricus (SOm) 9OAD20H 67°54.8’/ 149°31.4’ Coralline wackestone probably early Late Ordovician Coral: Catenipora sp. aff. C. rubra2 (Devonian lime- 90ABd31 67°54.8’/149°3l.4’ Skeletal pack-wackestone (containing late Early to early Middle stone outcrop (l2064—SD) probable amphiporid stromatoporids) Devonian (Emsian to Eifelian). too small to overlying 90AD2OH. show on map) Panderodur sp. Ozarkodina of Silurian-Middle Devo- nian morphotype. Echinoderms: two-hole crinoid ossicles3 7 (80m and 89ATi75 67°53.4’/149°32.7’ Bioturbated dolomitic metalimestone Devonian? lime- (SOm) overlain by skeletal wacke- stone) stone containing probable amphiporid stromatoporoids; wackestone is litho- logically similar to 90ABd31 and may be Devonian. lSamples collected by RB. Blodgett (ABd), J .A. Dumoulin (AD), A.G. Harris all US. Geological Survey; J.T. Dillon (DN) and D.N. Solie (DNS), 2Identified by T.E. Bolton, Geological Survey of Canada. 3Identified by RB. Blodgett, U.S. Geological Survey. (7—84), T.E. Moore (TM), George P1afl