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Characteristic Lower Cretaceous Megafossils from Northern Alaska

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Characteristic Lower Cretaceous Megafossils from Northern Alaska Characteristic Lower Cretaceous Megafossils From Northern Alaska GEOLOGICAL SURVEY PROFESSIONAL PAPER 335 Prepared in cooperation with the U.S. Department of the Navy^ Office of Naval Petroleum and Oil Shale Reserves Characteristic Lower Cretaceous Megafossils From Northern Alaska By RALPH W. IMLAY GEOLOGICAL SURVEY PROFESSIONAL PAPER 335 Prepared in cooperation with the U.S. Department of the Navy, Office of Naval Petroleum and Oil Shale Reserves UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1961 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library has cataloged this publication as follows : Imlay, Ralph Willard, 1908- Cliaracteristic Lower Cretaceous megafossils from north­ ern Alaska. Washington, U.S. Govt. Print. Off., 1960. iv, 74 p. illus., maps, tables. 30 cm. (U.S. Geological Survey. Professional paper 335) Part of illustrative matter in pocket. Prepared in cooperation with the U.S. Department of the Navy, Office of Naval Petroleum and Oil Shale Reserves. Bibliography: p. 66-69. 1. Paleontology Alaska. 2. Paleontology Cretaceous. I. U.S. Office of Naval Petroleum and Oil Shale Reserves. II. Title. (Series) For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, B.C. - Price $2.50 (paper cover) CONTENTS Page Page Abstract. ___-----_--____--_--__________ 1 Faunal zones and correlations Continued Introduction ___________________________ 1 Unnamed zone containing Cleoniceras tailleuri. Biologic analysis_ ____________________. 2 Gastroplites kingi zone______________________ 9 Stratigraphic relationships_______________ 3 Unnamed zone of possible late Albian age_____ 11 Beds of Berriasian to Valanginian age. 3 Comparisons with other faunas__________________ 12 Beds of Albian age___ ______ _________ 4 Ecological considerations_______________________ 12 Faunal zones and correlations ____________ 5 Geographic distribution_________________________ 17 Aucella okensis zone_________________ 5 Summary of results____________________________ 30 Aucella sublaevis zone__ ______________ 6 Systematic descriptions._____--_--_______--_____ 39 Aucella crassicollis zone._____________ 6 Literature cited..______________________________ 66 Colvillia crassicostata zone____________ 7 In dex_ _________-__-__-_-__-_-___-_-_------_- 71 Subarcthoplites belli zone._--________- ILLUSTRATIONS [Plates 1-20 follow index, 21-24 in pocket] PLATE 1. Chaetopod worms and scaphopods. PLATE 16. Subarctlioplites, Gastroplites and Xeno- 2. Chaetopod worms. helix? 3. Yoldia, Astarte, Solecurtus?, Gultellusf, 17. Gastroplites. and Tancredia. 18. Pseudopulcliellia, Paragastroplites, and 4. Dicranodonta and Tancredia. Cylindroteuthis? 5. Pleuromya and Panope. 19. Paragastroplites. 6. Thracia, MyopJiolas, Oxytoma, Veniella, 20. Cleoniceras. Arcticaf Flaventia?, Goniomya, Modiolus 21. Index map of northern Alaska showing Homomya, and Isognomonf Lower Cretaceous megafossil collection localities from outcrops. 7. Aucella. 22. Correlation of Lower Cretaceous forma­ 8. Aucella. tions in northern Alaska. 9. Inoceramus. 23. Stratigraphic distribution by areas of Al­ 10. Inoceramus, Camptonectes and. Placunopsis. bian megafossils in northern Alaska. 11. Entolium and Placunopsis. 24. Comparative Stratigraphic distribution of 12. Phylloceras. Albian megafossils in northern Alaska, Alberta, and British Columbia. 13. Lytoceras, Puzosia?, Colvillia, and Beudanticeras. Page 14. Beudanticeras. FIGURE 1. Index map of northern Alaska showing 15. Beudanticeras. location of test wells_________________ 2 in IV CONTENTS TABLES Page Page TABLE 1. Relative abundance of Lower Cretaceous TABLE 8. Geographic distribution of megafossils in the megafossils in northern Alaska. _________ Fortress Mountain and Torok formations 2. Succession of aucellan species in northern in northern Alaska._____________________ 31 Alaska ________________________________ 9. Geographic distribution of megafossils in the 3. Stratigraphic positions of fossils from the Ignek formation in northern Alaska._____ 31 Grandstand formation and equivalent beds 10. Geographic distribution of megafossils in the between the Tuktu and Ninuluk forma- Tuktu formation in northern Alaska_ ______ 32 tions_ _____________________________^___ 11 11. Geographic distribution of megafossils in the 4. Number of fossil occurrences in the Lower Kukpowruk formation in northern Alaska_ 34 Cretaceoiis (Albian) beds characterized by 12. Geographic distribution of megafossils in the Colvillia and Subarcthoplites. _____________ 14 Grandstand, Chandler and Corwin forma­ 5. Number of fossil occurrences in the Lower tions in northern Alaska.________________ 35 Cretaceous (middle Albian) zone of Gastro- 13. Test wells from which Lower Cretaceous fos­ plites kingi.. ___________________________ 14 sils have been obtained__________________ 35 6. Number of fossil occurrences in the Lower 14. Lower Cretaceous megafossils from well cores Cretaceous (Albian) beds above the Gas- 15 in northern Alaska,_____________________ 36 troplites kingi zone______________________ 7. Geographic distribution of aucellan species in the outcrops of the Okpikruak formation in northern Alaska__--_____---___-___-____ 30 CHARACTERISTIC LOWER CRETACEOUS MEGAFOSSILS FROM NORTHERN ALASKA By RALPH W. IMLAY ABSTRACT INTRODUCTION The megafossils from the Lower Cretaceous rocks of northern This study of the Lower Cretaceous megafossils from Alaska prove that only the Berriasian, Valanginian, and Albian northern Alaska, exclusive of echinoderms and brachio- stages are represented by strata. They prove that the lower pods, is based on collections made by E. de K. Leffing- Berriasian coincides with an erosional unconformity that lo­ cally truncates rocks of Jurassic, Triassic, and late Paleozoic well in 1911 and by field parties of the U.S. Geological age and that the Hauterivian, Barremian, and Aptian stages Survey since 1901. Most of the collections have been coincide with an angular unconformity involving mountain made since 1945. The writer visited some of the field building, overthrusting, and considerable erosion. They date parties in northern Alaska during the summer of 1950 the Okpikruak formation as being of Berriasian and Valangin­ to obtain background information on the stratigraphic ian ages and show that the earliest Cretaceous sea advanced over a hilly terrane, of which some high spots were not covered succession and has kept in close touch with the field until the middle Valanginian. They date the Fortress Moun­ geologists since 1948. They were consulted frequently tain formation, the Torok formation, and the overlying forma­ during the preparation of the chapters dealing with tions to the base of the Cenomanian Ninuluk formation as of stratigraphic relationships, faunal zones and correla­ Albian age only. This is rather astonishing considering that tions, and ecology in order to obtain pertinent data the sedimentary rocks involved, excluding the Fortress Moun­ tain formation, range in thickness from about 9,000 to 11,000 and opinions, or to make sure that all available strati- feet. The abrupt termination of the megafossil species at the graphic and paleontologic information was being top of the Albian strata indicates that some major geologic evaluated. These geologists, including R. S. Bickel, event occurred at the end of Albian time, either in Alaska or R. M. Chapman, R. L. Detterman, J. T. Dutro, George in the Boreal region. Gryc, A. S. Keller, B. H. Kent, M. D. Mangus, R. H. The Okpikruak formation of Berriasian to Valanginian age in Morris, W. W. Patton, Jr., H. N. Reiser, E. G. Sable, many places contains an abundance of the pelecypod Aucella, but otherwise contains very few fossils. The Aucellas belong I. L. Tailleur, and C. L. Whittington, have also checked to species that are common in the Boreal region and along the or rewritten all locality descriptions and have plotted west coast of North America. They permit dividing the Okpi­ the positions of the localities on figure 1. kruak formation into three faunal zones based on the strati- Great credit goes to the U.S. Navy for the financial graphic distribution of the species. The thick shells of the and logistic support given these geologists. Without Aucellas and their common occurrence in coarse detrital sedi­ that support most of the fossils described herein and mentary beds suggest that they lived in the shallowest part of the neritic zone or even partly in the littoral zone. the supporting field data would not have been obtained. The beds of Albian age in northern Alaska include more The echinoderms and brachiopods are being studied genera and species of marine megafossils than have ever been by other paleontologists and will be described else­ described previously from Albian beds in lands bordering the where. These classes are mentioned herein and are Arctic Ocean. Most of the fossils are from beds that are dated listed on distribution charts only in order to show as middle Albian. A scarcity of megafossils in the lower Al­ their strktigraphic distribution and faunal associ­ bian beds coincides with a scarcity of microfossils and is as­ cribed to exceedingly rapid sedimentation. A scarcity of ations. Such information may be useful to the field marine megafossils in the latest Albian beds is explained by the geologist, may give the biologist an impression of the fact that part of those beds are continental and much of the entire megafauna, and should not detract from the remainder
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