Downloaded from gsabulletin.gsapubs.org on November 18, 2014 Geological Society of America Bulletin Mount Jura Investigation C. H. CRICKMAY Geological Society of America Bulletin 1933;44, no. 5;895-926 doi: 10.1130/GSAB-44-895 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geological Society of America Bulletin Permission request click http://www.geosociety.org/pubs/cop yrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms to further education and science. This file may not be posted to any Web site, but authors may post the abstracts only of their articles on their own or their organization's Web site providing the posting includes a reference to the article's full citation. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Notes © 1933 Geological Society of America Downloaded from gsabulletin.gsapubs.org on November 18, 2014 BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA V O L . AA, PP. 895-926. PLS. 23-34 OCTOBER 31. 1933 MOUNT JURA INVESTIGATION 1 BY C. H . CRICKMAY (Presented before the Geological Society, December 30,1982) CONTENTS Page Introduction ................................ 895 Acknowledgments ...................... 895 General and structural geology 895 Stratigraphie summary 896 Description of species. 903 Explanation of plates. 915 I ntroduction Since 1927 the writer has been engaged in a study of the stratigraphy, structure, and paleontology of Mount Jura, California, undoubtedly the finest Jurassic section in North America. Elucidation of the stratigraphy has been made extremely difficult by the complexity of the geologic struc­ ture of the mountain. The work is now complete, however, and a mono­ graph on the geology and paleontology is being written. Since it may be some years before that monograph can be issued, this article is published as an advance summary of results. A cknowledgments The writer is under deep obligations to the University of California and to the National Research Council for generous financial aid, without which the drain on his private funds would have been unbearably heavy. Dr. T. W. Stanton and, later, Dr. J. B. Reeside, have been very kind in extending the hospitality and technical services of the United States Na­ tional Museum and the United States Geological Survey. Francis E. Dreyer, A. B., assisted in the field in 1929, and Leland H. Dykes, A. B., in 1931. More adequate acknowledgments will be made in the monograph. Ge n e r a l a n d S t r u c t u r a l G eology Mount Jura consists of highly disordered Triassic and Jurassic rocks. These have been severed by faults and piled repeatedly upon one another, producing a very complicated, imbricated structure. This structure, 1 Manuscript received by the Secretary ot the Society, January 30, 1933. (895) Downloaded from gsabulletin.gsapubs.org on November 18, 2014 896 C. H. CKICKMAY----MOUNT JUBA INVESTIGATION which long baffled solution, is made up of a network, or braidwork, of faults, separating imbricated, lance-shaped selvages of various formations. Some of these selvages are overturned. The whole imbricated mass has been hoisted up on the west side, where the oldest rocks in it—the Triassic—are now exposed. In a compensating manner it has been forced down on the east side, where the youngest rocks—the Upper Jurassic— are found. The whole imbricated mass is enclosed by older rocks which have been thrust against it and upon it from both east and west. The overthrust rocks on the east side are of Carboniferous age; those on the west are mostly early Paleozoic. The two thrust faults are opposed to one another in regard to direction of faulting. It may be noted that no other opposed thrusts of this sort seem to have been observed in the structure of the Sierra Nevada, and very few elsewhere. S tratigraphic S u m m a r y Jurassic epigene formations (descending order) : Combe sandstone Trail tuff and conglomerate Lucky S argillite Cooks Canyon agglomerate Forman argillite North Ridge argillite Hinchman arkose Hull agglomerate Moonshine conglomerate Mormon sandstone Thompson tuff Fant volcanics Hardgrave arkose Lilac sandstone As the determination of the Jurassic column is the outstanding result of this work, attention will be confined to the Jurassic epigene deposits in this advance summary. Description of intrusive formations and of de­ posits of other ages must await a later opportunity. The epigene deposits, including on an equal footing both the sedimentary and the volcanic, are here described briefly, beginning with the oldest. L il a c F o r m a t io n Name.— New. Occurrence.— At various separate localities along the west base of ' Mount Jura and elsewhere. Downloaded from gsabulletin.gsapubs.org on November 18, 2014 STRATIGRAPHIC SUMMARY 897 General character.— Calcareous, dark-gray sandstone and argillite. Thickness.— 725 feet. Fauna.— Upper zone : Parapecten praecursor n. sp. Lower zone : Euechioceras exoletum n. sp. Age.— Mid Lower Jurass'c; upper zone, Grammoceratan ; lower zone, Deroceratan, Euechioceras. Relations.— The Lilac formation rests on the Middle Triassic vol- eanics, the oldest rocks in the Mount Jura column. H ardgrave F o r m a t io n Name.— Given by J. S. Diller, 1892. Occurrence.— Most abundant in narrow bands across lower west slope of Mount Jura. General character.— Eed, stratified, marine, volcanic arkose, highly fossiliferous. Thickness.—-150 feet. Fauna.— Cidaris taylorensis Clark C. plumasensis Clark Gervillia gigantea Hyatt 6. linearis Hyatt Pinna expansa Hyatt Entolium meeki Hyatt parapecten acutiplicatus Meek Trigonia sp. "Dumortieria” sp. bispinosa Glyphaea punctata Hyatt Age.—Earliest Middle Jurassic, Ludwigian,----------. F a n t F o r m a t io n Name.— Given by J. S. Diller, 1892. Occurrence.— In broad, prominent bands across west side of Mount Jura and elsewhere. Stands up in cliffs in many places. General character.—Massive, coarsely porphyritic andesite lavas (green) and crystal tuffs (red). Thickness.— 900 feet. Fauna.— None. Age.—Early Middle Jurassic. T h o m p s o n F o r m a t io n Name.— Given by J. S. Diller, 1892. Downloaded from gsabulletin.gsapubs.org on November 18, 2014 89 8 C. H . CRICKMAY----MOUNT JURA INVESTIGATION Occurrence.— In several narrow bands across west slope of Mount Jura, especially about 4200 to 4400 feet elevation on Mill Ravine, near the Knob and near the old Thompson farmhouse. General character.— Mainly a fine, red, stratified marine tuff, with some thick lenses of pale blue-gray limestone. Thickness.— 115 feet. Fauna.— Ptyctothyris n. sp. Nerinea thompsonensis n. sp. Age.—Early Middle Jurassic; Sonninian (?),----------. Mormon F ormation Name.— Given by J. S. Diller, 1892. Occurrence.— In several bands lying across west slope of Mount Jura, one band lying up and down southeast slope. General character.— Mainly fine gray arkose, with red and green con­ glomerate of volcanic debris at the base, and fine, dark gray paper shales at top. Thickness.— 943 feet. Fauna.— Several successive faunas occur. In descending order, num­ bered from the bottom up, these are: (11) Posidonomya sp. (10) Teloceras sp., trephomorph (9) Rhactorhynchia n. sp. Ornithella, n. sp. Scaphogonia n. sp. (8) Scaphogonia n. sp. Haidaia n. sp. Papilliceras juramontanum n. sp. Chondroceras sp. (7) Holcophylloceras falciferum n. sp. Papilliceras blackwelderi n. sp. Otoites reesidei n. sp. Chondroceras russeUi n. sp. “Trigonia" pandicosta Meek Astarte ventricosa Meek (6) Trigonia cf. sculpta Lycett Haidaia sp. Entolium aff. gingense Quenstedt Downloaded from gsabulletin.gsapubs.org on November 18, 2014 STRATIGRAPHIC SUMMARY 899 (5) Kallirhynchia sp. indet. Flabellirhynchia sp. Q-lobirhynchia n. sp. O. ffnathophora Meek Loboidothyris n. sp. PapilUceras stantoni n. sp. (4) Globirhynchia sp. Loboidothyris n. sp. Haidaia n. sp. StiphromorpMtes schucherti 11. sp. (3) KattirhyncMa n. sp. Flabellirhynchia n. sp. Euidothyris n. sp. Entoiium equabile Hyatt Haidaia n. sp. Lima dilleri Hyatt (2) Flabellirhynchia sp. Camptoneotes aff. lens Sowerby (1) Latomeandra orthogrammica n. sp. There are also a number of species of Meek and of Hyatt not allocated to their proper zones: Cidaris califomicus Clark Hemicidaris intwmescens Clark Pseudodiadema emersom Clark Stomechinus hyatti Clark Pinna ouneiformis Hyatt Lima taylorensis Hyatt Mytilus multistriatus Meek Pleuromya depressa Meek Age.—Early Middle Jurassic: Faunas 1 to 3 ..................................................Sonninian, pre-mollis 4 .................................................. “ mollis 5 .................................................. “ Labyrinthoceras 6 ............................................... “ sauzei 7 .................................................. “ alsatica 8 ..................................................Stepheoceratan, Masckeites 9 ...........................................................................................