Middle Bajocian A·mmonites from the Cook Inlet Region Alaska By Rf\LPH W. IMLAY JUR.ASSIC AMMONITES FROM SOUTHERN ALASKA GEOLOGICAL SURVEY PROFESSIONAL PAPER 418-B Desc"ription and illustrations of cephalopods of Middle Jurassic (middle Bajocian) age LIBRAR~ BUR!AU OF UfNEI '-IBRARV SPOkANl. NASH. Jl.I\J 3 1971 ...... .'4'f 0 ··±irtF ~ •.• f l S f R ET U R N ID liBRAIY UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 'l CONTENTS Page Page Abstract __________________________________________ _ B1 Comparisons with other faunas _____ - __ - ___ -_--------- B18 Introduction ________________ ·______________________ _ 1 Alaskan Peninsula _____________________________ _ 18 Biologic analysis ______________ - ________ -- ___ -- _____ _ 2 Queen Charlotte Islands, British Columbia _____ -- __ 19 Stratigraphic summary _____________________________ _ 6 Central British Columbia ____________________ -- __ 19 Tuxedni Group along northwest side of Cook Inlet __ 6 Western Interior of Canada _____________________ _ 19 Red Glacier Formation _____________________ _ 6 Western Interior of the United States _________ -- _- 19 Gaikema Sandstone ________________________ _ 8 East-central Oregon ___________ - __ - ___ ----------- 19 Fitz Creek Siltstone _____ -- _____ ---_- _______ - 8 Northern California __________________ -_-_-_----- 20 Cynthia Falls Sandstone ____________________ _ 9 Southern Caluornia ____________________________ _ 20 Tuxedni Formation in the Talkeetna Mountains ___ _ 9 Southern MexicO------------------------------- 20 South America ________________________________ _ Ages of the faunas _________ ------------------------- 10 20 Ages of the Tuxedni Group northwest of Cook Inlet_ 10 Indonesia and Australia _______ ------------------ 21 Europe _______________________________________ _ Red Glacier Formation _____________________ _ 10 21 Gaikema Sandstone ______ - _________________ - 12 Geographic distribution ______ - ____ ------------------- 21 Fitz Creek Siltstone ________________________ _ 12 Summary of results _______________ ------_----------- 27 Cynthia Falls Sandstone ________ - _____ -_-_-_- 14 Systematic descriptions ___________________ ----------- 31 Ages of the Tuxedni Formation in the Talkeetna Literature cited ___________________ ------------------ 55 Mountains----------------------------------- 14 Index--------------------------------------------- 59 ILLUSTRATIONS [Plates 1-29 follow Index] PLATE 1. Macrophylloceras and Holcophylloceras. 2. Sonninia and Phylloceras. 3. Sonninia. 4. Witchellia?, Sonninia?, and Lissoceras. 5. Witchellia? and Bradfordia?. 6. Sonninia, Pelekodites?, and Witchellia. 7. Witchellia. 8. Bradjordia and Oppelia. 9, 10. Labyrinthoceras. 11. Emileia. 12. Chondroceras. 13. Normannites. 14. Normannites (Itinsaites) and Otoites?. 15-19. Stephanoceras. 2Q-22. Stemmatoceras. 23. Lissoceras, Strigoceras, and Teloceras. 24. Teloceras and Zemistephanus. 25. Otoites and Zemistephanus. 26, 27. Zemistephanus. 28. Zemistephamts, Leptosphinctes, and Arkelloceras?. 29. Parabigotites. FIGURES 1-4. Index maps showing occurrences of middle Bajocian fossils. Page 1. In the Talkeetna Mountains ___________________________________________________ ---_-_-_------- B2 2. In the Tuxedni Bay area--------------------------------------------------------------------- 3 3. North of Chinitna Bay __ -----------------------------------------·--------------------------- 4 4. On the Iniskin Peninsula--------------------------------------------------------------------- 5 5. Correlation of spme Middle and Upper Jurassic formations and faunas in the Cook Inlet region ___ ------_- 7 m TABLES TABLE 1. Ammonite genera and subgenera in beds of middle Bajocian age in the Cook Inlet region showing biologic relationships and relatiye numbers available for study______________________________________________ B2 2. Thickness of the lower four formations of the Tuxedni Group along the northwest side of Cook Inlet________ 6 3. Early Bajocian ammonites in the lower part of the Red Glacier Formation along the northwest side of Cook Inlet----------------------------------------------------------------------------------------- 6 4-7. Middle Bajocian ammonites. 4. In the Red Glacier Formation along the northwest side of Cook Inlet______________________________ 11 5. In the Gaikema Sandstone along the northwest side of Cook Inlet_________________________________ 12 6. In the Fitz Creek Siltstone along the northwest side of Cook Inlet_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 13 7. In the Cynthia Falls Sandstone along the northwest side of Cook Inlet __________ ·- ______________ .___ 14 8. Stratigraphic distribution of middle Bajo'Cian ammonite species within the formations of the Tuxedni Group along the northwest side of Cook Inlet___________________________________________________________ 15 9. Stratigraphic distribution of certain Bajocian ammonite genera and subgenera within the Tuxedni Group along the northwest side of Cook Inlet___________________________________________________________ 16 10. European ranges of certain Bajocian ammonites present in the Tuxedni Group in the Cook Inlet region____ 17 11. Localities at which fossils of middle Bajocian age have been collected in the Cook Inlet region_____________ 22 12. Geographic distribution of middle Bajocian ammonites in the Talkeetna Mountains______________________ 27 13. Geographic distribution of middle Bajocian ammonites along the northwest side of Cook Inlet_ _ _ _ _ _ _ _ _ _ _ _ 28 IV JURASSIC AMMONITES FROM SOUTHERN ALASKA MIDDLE BAJOCIAN AMMONITES FROM THE COOK INLET REGION, ALASKA By RALPH w. IMLAY ABSTRACT Jurassic ammonites of middle Bajocian age occur in the stephanus and Parabigotites and the absence to· date of certain Tuxedni Group along the northwest side of Cook Inlet and in other genera, such as Dorsetensia. the Tuxedni Formation in the eastern part of the Talkeetna New species described herein include Holcophylloceras costi­ Mountains, Alaska. Numericaliy the dominant families are sparsum Imlay, Sonninia tuxedniensis Imlay, Witchellia adnata the Otoitidae and Stephanoceratidae. The familes Phyllocera­ Imlay, W.? aquilonia Imlay, Oppelia stantoni Imlay, Bradfordia tidae, Sonninidae, Oppelidae, and Perisphinctidae together costidensa Imlay, B.? caribouensis Imlay, Otoites? filicostatus compose only about one-third of the total specimens. Imlay, Emileia constricta Imlay, Labyrinthoceras glabrum Imlay, The Tuxedni Group has not furnished any ammonite genera Normannites kialagvikensis Imlay, N. variabilis Imlay, Stephe­ that characterize the European zone of Sonninia sowerbyi at noceras obesum Imlay, S. nelchinanum Imlay, S. (Skirroceras) the base of the middle Bajocian. It has, however, furnished juhlei Imlay, S. (Skirroceras) kirschneri Imlay, Stemmatoceras ammonites that characterize the next higher zones of Otoites ursinum Imlay, and Leptosphinctes evolutus Imlay. sauzei and Stephanoceras humphriesianum. The Otoites sauzei zone northwest of Cook Inlet is represented INTRODUCTION by an association of the genera Sonninia, S. (Papilliceras), Witchellia, Bradfordia, Otoites, Emileia, Stephanoceras, S. The ammonites described herein have been studied (Skirroceras), Stemmatoceras, and Parabigotites. These am­ partly as an aid to field geologists in dating the beds monites occur throughout most of the Red Glacier Formation of middle Bajocian age in the Cook Inlet region, Alaska, and some occur in the overlying Gaikema Sandstone of the partly to determine the sequence of faunas in the Mid­ Tuxedni Group. The presence of N ormannites in the upper dle Jurassic beds, partly as biological documentation third of the Red Glacier Formation suggests that this part correlates with only the upper part of the Otoites sauzei zone. of the genera and species present, and partly to estab­ T~e Otoites sauzei zone is also well represented throughout lish biologic and stratigraphic standards of reference. most of the Tuxedni Formation in the Talkeetna Mountains As a consequence, fragmentary or distorted ammonites by the same association of ammonite genera and by many of from other areas may now be colnpared readily with the species that occur in the Red Glacier Formation northwest well-preserved ammonites and age determinations can of Cook Inlet. With these in the Talkeetna Mountains occurs the ammonite Labyrinthoceras, which is typical of the Otoites be made with greater confidence. Such can be very sa~tzei zone in Europe. important in areas of poor exposures, of partly meta­ The Stephanoceras humphriesianum zone in the Cook Inlet morphosed rocks, or of complicated structures, such as region is represented by an association of the genera N ormannites, exist at many places in the Pacific coast States. Ch(mdroceras, Teloceras, Stephanoceras, Stemmatoceras, and The fossils from the middle Bajocian rocks of the Zemistephamts. These range through most of the Fitz Creek Siltstone and the lower fourth of the overlying Cynthia Falls Cook Inlet region, Alaska, were collected by A. A. Sandstone. In addition Chondroceras, a genus not known above Baker in 1921; Andrew Brown in 1904; R. L. Detterman the middle Bajo~ian, ranges through the lower two-thirds of in 1957 and 1958; L. F. Fay in 1954; C. N. Fenner in the Cynthia Falls Sandstone. The presence of a few specimens