Late Jurassic Ammonites From the Western Sierra Nevada, California GEOLOGICAL SURVEY PROFESSIONAL PAPER 374-D Late Jurassic Ammonites From the Western Sierra Nevada, California By RALPH W. IMLAY SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 374-D Ammonites furnish correlations with Jurassic rocks elsewhere on the Pacific coast and with the standard European stages UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1961 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 25, D.C. CONTENTS Page Page Abstract,__________________________________________ D-l Comparisons with other faunas Continued Introduction. ______________________________________ D-l Taylorsville area, California______________________ D-9 Biologic analysis--_--_-__-_----____--__-__-__--_____ D-2 Central Oregon_______________________-_________ D-10 Stratigraphic summary______________________________ D-2 Southwestern Oregon__________________________ D-10 Ages and correlations______________________________ D-3 Western British Columbia _______________________ D-10 Alaska Peninsula and Cook Inlet regions, Alaska. __ D-ll Cosumnes formation. ___________________________ D-3 Mexico-...-._______._--__-________-__-______ D-12 Logtown Ridge formation______________________ D-6 Geographic distribution___________________________-__ D-13 Colfax formation of Smith, 1910_._______.____-_-. D-6 Summary of results___________________-_____________ D-13 Mariposa formation._----______-_-_______--_--__ D-7 Systematic descriptions_-____-__-_-__-_-_-_____-_-_ D-19 Monte de Oro formation_____-___________--__-__- D-8 Literature cited.__________________________________ D-27 Comparisons with other faunas_______________________ D-9 Index.__________________-___-__.______-___-__--_ D-29 ILLUSTRATIONS [Plates 1-6 follow index] PLATE 1. Kepplerites, Gowericeras, and Taramelliceras. 2. Pseudocadoceras, Amoeboceras (Amoebites), and Grossouvria. 3. Perisphinctes (Discosphinctes) and Grossouvria. 4. Perisphinctes (Dichotomosphinctes). 5. Subdichotomocerasf', Perisphinctest, Dichotomosphinctesf, Idoceras, and Buchia. 6. Peltoceras (Metapeltocerast). Page FIGURE 1. Correlation of the Late Jurassic formations in the Pacific coast region. ______ D-4 2. Correlation of the Late Jurassic faunas in the Pacific coast region.__________ D-5 3. Index map of Jurassic localities in the western Sierra Nevada, Calif. ________ D-l 5 TABLES Page TABLE 1. Ammonite genera and subgenera from late Jurassic beds in the western Sierra Nevada, Calif. D-2 2. Geographic distribution of the Late Jurassic megafossils in the western Sierra Nevada, Calif_ D-l 4 3. Descriptions of the Late Jurassic fossil localities in the western Sierra Nevada, Calif________ D-16 m SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY LATE JURASSIC AMMONITES FROM THE WESTERN SIERRA NEVADA, CALIFORNIA By RALPH W. IMLAY ABSTRACT with pronounced angular unconformity by beds of middle to The ammonites from the Jurassic strata in the western part of late Portlandian age (Riddle formation), the middle Kimmeridg­ the Sierra Nevada represent the Callovian, Oxfordian, and the ian to early Portlandian time appears to be represented, at lower part of the Kimmeridgian stages of the Upper Jurassic. least in part, by the unconformity. There is no faunal evidence for the presence of any older Jurassic The affinities of the Callovian ammonites in the Sierra Nevada rocks, although the lower and middle parts of the Cosumnes are mainly boreal as indicated by the presence of such ammo­ formation have not furnished any fossils and could be in part nites as Cadoceras, Paracadoceras, Pseudocadoceras, Kepplerites, older than the Callovian. The upper part of the Cosumnes and Gowericeras. The affinities of the late Oxfordian ammo­ formation has furnished one fragmentary ammonite indicative nites are mostly with ammonites in Mexico and Cuba but partly of a Callovian age. The lower part of the overlying Logtown with those in Alaska. The early Kimmeridgian ammonite Ridge formation has furnished many ammonites of early to Amoeboceras indicates boreal affinities as the genus is rare in the middle Callovian age not older than the European zone of Tethyan region. These affinities indicate that the seas in Cali­ Sigaloceras calloviense. Because the formations grade into each fornia were connected freely northward with Alaska and south­ other, the part of the Cosumnes formation that contains the ward with southern Mexico. Callovian ammonite must be of early Callovian age older than that zone. INTRODUCTION The early Callovian is definitely represented by the ammonites Kepplerites (Seymourites) and K. (Gowericeras) obtained near This study of the Late Jurassic ammonites from the Colfax, Calif. These indicate an age slightly older than the western part of the Sierra Nevada, Calif., is based ammonites in the lower part of the Logtown Ridge formation mainly on collections made by field parties of the U.S. on the Cosumnes River. The late Callovian is represented by Geological Survey since 1884. It includes, also, 4 a large specimen of Peltoceras obtained near Indian Creek in specimens from Leland Stanford Junior University Amador County, presumably from the Logtown Ridge formation. There is no faunal record of the early Oxfordian in California. furnished by Siemon Win. Muller, 1 specimen from The late Oxfordian to early Kimmeridgian is represented by the the University of California furnished by Wyatt ammonite Idoceras obtained near the top of the Logtown Ridge Durham and Joseph H. Peck, Jr., and 1 specimen from formation on the Cosumnes River. The late Oxfordian is the Museum of Comparative Zoology at Harvard represented in the Mariposa formation by species of Perisphinctes furnished by Bernhard Kummel. It does not include (Dichotomosphinctes) and P. (Discosphinctes) that are virtually identical with species in Mexico and Cuba. These ammonites any fossils from the Taylorsville, Downieville, or show that the lower part of the Mariposa formation and similar Sailors Canyon area in the eastern part of the western slatey units are locally of the same approximate age as the Sierra Nevada metamorphic belt. upper part of the Logtown Ridge formation on the Cosumnes The description of the ammonites is a byproduct of River. paleontological assistance to Lorin D. Clark, of the The early Kimmeridgian is represented in the Mariposa formation by Amoeboceras (Amoebites) and probably by Sub- Geological Survey, in his comprehensive analytical dichotomoceras in association with the pelecypod Buchia con- studies of the geology of the western Sierra Nevada. centrica (Sowerby). The assistance mainly involved determining the age The late Oxfordian to early Kimmeridgian is represented limits of the rock units that Clark had mapped. This in the Monte de Oro formation by an ammonite, Perisphinctes appeared at first to be a difficult task because of the (Dichotomosphinctes) cf. P. elisabethaeformis Burckhardt, and by two crushed specimens of Buchia cf. B. concentrica (Sowerby). wretched preservation of most of the fossils. After a The Mariposa and Monte de Oro formations have not fur­ little study, however, it was found that some of the nished any fossils that are younger than the early Kimmeridg­ fossils belonged to well-known genera and species ian. The same is true of the Galice formation of southwestern from Alaska, Mexico, and Cuba and that rather Oregon and northwestern California which is lithologically precise dating of the rock units was locally possible similar to the Mariposa and likewise is characterized by the presence of Perisphinctes (Dichotomosphinctes} and Buchia by comparisons with the faunal successions in those concentrica (Sowerby). As the Galice formation is overlain areas. Such faunal dating is useful in making corre- D-l D-2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY lations with Jurassic rocks elsewhere on the Pacific restricted by J. P. Smith (1910, chart facing p. 217) to coast, in unraveling complex stratigraphic and struc­ the slate and associated rocks in the metamorphic tural problems, and in interpreting the history of Gold Belt (mother lode) area that are characterized by Jurassic sedimentation in California. the pelecypod Buchia (formerly called Aucella) and by the ammonite now referred to Amoeboceras dubium BIOLOGIC ANALYSIS (Hyatt). The Late Jurassic ammonite specimens from the For the rocks in the southwestern part of the Colfax western part of the Sierra Nevada that are available quadrangle that had been called Mariposa slate by for study number about 200. Of these, 150 belong to Becker, Smith (1910, p. 217) proposed the term Colfax the Cardioceratidae, 29 to the Perisphinctidae, and 13 formation. These rocks, as described by Lindgren to the Kosmoceratidae. Most genera and subgenera (1900), consist of interbedded shale, slate, sandstone, are represented by 1 to 4 specimens. Ammonites are tuff, and conglomerate. He noted that most of the actually more difficult to find in the area than these slate is not very fissile, which feature is a possible dis­ figures suggest, considering that 1 locality (Mesozoic tinction from the slates of the Mariposa formation. loc. 27317) accounts for 120 specimens, and 3 localities In naming the Colfax formation, Smith appears to (Mesozoic Iocs. 719, 901, and 27313) account for have been influenced by the lack of the pelecypod another 45 specimens. The biological distribution