Midde Trias sic Molluscan Fossils of iostratigraphic Significance from the Humboldt Range, Northwestern Nevada Middle Triassic Molluscan Fossils of Biostratigraphic Significance from the Humboldt Range, Northwestern Nevada By N. J. SILBERLING and K. M. NICHOLS GEOLOGICAL SURVEY PROFESSIONAL PAPER 1207 Taxonomic and superpositional documentation of an unusually complete faunal succession UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1982 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES G. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging in Publication Data Silberling, Norman John, 1928- Middle Triassic molluscan fossils of biostratigraphic significance from the Humboldt Range, northwestern Nevada. (Geological Survey Professional Paper 1207) Bibliography: p. 71 Supt. of Docs. No.: I 19.16: 1207 1. Mollusks, Fossil. 2. Paleontology Triassic 3. Geology, Stratigraphic Triassic. 4. Geology Nevada Humboldt Range. I. Nichols, Kathryn Marion, 1946- joint author. II. Title. III. Series: United States. Geological Survey. Professional Paper 1207. QE801.S64 564 80-607925 For sale by the Distribution Branch, U.S. Geological Survey 604 South Pickett Street, Alexandria, VA 22304 CONTENTS Page Page Abstract ---------------------------------------- 1 Paleontology Continued Introduction ------------------------------------ 1 Systematic descriptions Continued History ------------------------------------- 1 Class Cephalapoda Continued Description of study and acknowledgments 3 Subclass Ammonoidea Continued Stratigraphic occurrence and composition of faunas 3 Genus Japonites -------------- 39 General statement --------------------------- 3 Genus Gymnites -------------- 39 Lower Anisian ------------------------------ 4 Genus Epigymnites ------------ 41 Middle Anisian ----------------------------- 5 Genus Sturia ----------------- 41 Upper Anisian ------------------------------ 5 Genus Discoptychites ---------- 41 Lower Ladinian ----------------------------- 7 Genus Isculites ---------------- 42 Upper Ladinian ----------------------------- 10 Genus Czekanowskites --------- 43 Age and correlation ------------------------------ 11 Genus Pseudodanubites -------- 44 Genus Unionvillites ------------ 45 Genus Lenotropites ------------ 46 Genus Intorrdtes -------------- 48 Paleontology ---------------------------- 11 Genus Longobardites ---------- 50 Procedures and conventions ---------- 11 Genus Metadinarites ---------- 52 Systematic descriptions -------------- 14 Genus Aplococeras ------------ 52 Class Cephalopoda -------------- 14 Genus Tropigastrites ---------- 54 Subclass Ammonoidea ------- 14 Genus Tozerites --------------- 55 Genus Sageceras -------- 14 Genus Thanamites ------------ 56 Genus Koipatoceras ----- 18 Genus Proarcestes ------------- 57 Genus Alanites ---------- 19 Genus Protrachyceras ---------- 58 Genus Ismidites --------- 20 Genus Sirenites --------------- 59 Genus Amphipopanoceras 20 Genus Ussurites --------------- 60 Genus Humboldtites ----- 21 Genus Monophyllites ---------- 60 Genus Paracrochordiceras 21 Subclass Nautiloidea -------------- 61 Genus Cuccoceras ------- 23 Genus Aulametacoceras -------- 61 Genus Nicomedites ------ 24 Genus Germanonautilus ------- 62 Genus Hollandites ------- 24 Genus Grypoceras ------------- 62 Genus Anagymnotoceras - 25 Genus Paranautilus ----------- 62 Genus Gymnotoceras ---- 25 Genus Michelinoceras --------- 63 Genus Parafrechites ----- 27 Subclass Coleoidea ---------------- 63 Genus Frechites --------- 29 Genus Atractites -------------- 63 Genus Paraceratites ----- 31 Class Bivalvia ------------------------ 66 Genus Eutomoceras ----- 34 Genus Pteria---------------------- 66 Genus Nevadites -------- 36 Genus Daonella ------------------- 66 Genus Hungarites ------- 38 References cited ------------------------------- 69 Genus Tropigymnites ---- 39 Index ---------------------------------------- 73 ILLUSTRATIONS [Plates 1-3 in pocket, 4-38 follow "Index"] PLATE 1. Geologic map of part of the Humboldt Range, Nev., showing collecting-sites A, B, and C. 2. Locality map of collecting-site A on the south side of Fossil Hill, Humboldt Range, showing fossil localities. 3. Locality map of collecting-site C on the south spur of Saurian Hill, Humboldt Range, showing fossil localities. 4. Sageceras, Koipatoceras, and Acrochordiceras. 5. Acrochordiceras and Sageceras. 6. Hollandites, ^Anagymnotoceras, Nicomedites, Thanamites?, Amphipopanoceras, and Unionvillites. 7. Gymnotoceras. 8. Gymnotoceras. 9. Gymnotoceras and Frechites. 10. Frechites. 11. Frechites and Parafrechites. m IV CONTENTS 12. Parafrechites. 13. Parafrechites. 14. Frechites. 15. Frechites and Paraceratites. 16. Paraceratites. 17. Paraceratites. 18. Eutomoceras. 19. Eutomoceras, Pseudodanubites, and Czekanowskites. 20. Cuccoceras, Hungarites, and Intornites. 21. Intornites, Longobarbites, Metadinarites, and Aplococeras. 22. 'Aplococeras and Nevadites. 23. Nevadites. 24. Nevadites and Protrachyceras. 25. Protrachyceras and Sirenites. 26. Tropigymnites and Tropigastrites. 27. Tozerites and Proarcestes. 28. Proarcestes, Humboldtites, Isculites, Ismidites, and Alanites. 29. Paracrochordiceras, Isculites, Lenotropites, and Alanites. 30. Isculites, Gymnites, and Sturia. 31. Gymnites, Aulametacocerasf and Epigymnites. 32. Monophyllites, Ussurites, Germanonautilus, Paranautilus, and Grypoceras. 33. Michelinoceras? and Airaciites. 34. Atractites. 35. Daonella. 36. Daonella. 37. Daonella. 38. Daonella and Pteriaf Page FIGURE 1. Index map showing the Humboldt Range ----------------------------------------------------------------------- 2 2. Photograph showing view south across South American Canyon towards Fossil Hill -------------------------------- 2 3. Photograph showing view northwest towards collecting-site A on the south side of Fossil Hill ----------------------- 6 4. Photograph showing view southeast across collecting-site C on the south spur of Saurian Hill ----------------------- 6 5. Correlation chart showing the stage and substage assignments of Middle Triassic biostratigraphic units-------------- 12 6. Frequency distributions of morphologically different variants within single species of ammonites -------------------- 14 7-18. Drawings of suture lines of: 7. Koipatoceras discoideus ------------------------------------------------------------------------------ 18 8. Alanites mulleri -------------------------------------------------------------------------------------- 19 9. Alanites obesus -------------------------------------------------------------------------------------- 20 10. Ismidites aff. /. marmarensis -------------------------------------------------------------------------- 20 11. Amphipopanoceras cf. A. selwyni ---------------------------------------------------------------------- 21 12. Humboldtites septentrionalis -------------------------------------------------------------------------- 21 13. Acrochordiceras hyatti -------------------------------------------------------------------------------- 23 14. Acrochordiceras cf. A. carolinae ----------------------------------------------------------------------- 23 15. Cuccoceras bonaevistae ------------------------------------------------------------------------------- 24 16. Nicomedites sp. -------------------------------------------------------------------------------------- 24 17. Hollandses aff. #. uoiiz ------------------------------------------------------------------------------ 25 18. Frechites johnstoni ----------------------------------------------------------------------------------- 31 19. Scatter diagram comparing width between ventral spines to whorl height in population samples of Nevadites ------- 37 20-23. Drawings of suture lines of: 20. Gymnites tregorum ----------------------------------------------------------------------------------- 40 21. Gymnites perplanus ---------------------------------------------------------------------------------- 40 22. Gymnites cf. G. humboldti --------------------------------------------------------------------------- 40 23. Discoptychites sp.------------------------------------------------------------------------------------ 42 24. Diagrammatic cross section of Discoptychites sp.--------------------------------------------------------------- 42 25-26. Drawings of suture lines of: 25. Isculites meeki --------------------------------------------------------------------------------------- 43 26. Isculites tozeri --------------------------------------------------------------------------------------- 43 27. Scatter diagram comparing Isculites tozeri with /. meeki -------------------------------------------------------- 44 28-43. Drawings of suture lines of: 28. Pseudodanubites halli -------------------------------------------------------------------------------- 45 29. Unionvillites asseretoi -------------------------------------------------------------------------------- 46 30. Lenotropites caurus ---------------------------------------------------------------------------------- 46 31. Intornites mctaggarti --------------------------------------------------------------------------------- 48 32. Intornites nevadanus --------------------------------------------------------------------------------- 49 33. Longobardites parvus --------------------------------------------------------------------------------- 50 CONTENTS Page 34. Longobardites zsigmondyi ----------------------------------------------------------------------------- 51 35. tMetadinarites desertorus -----------------------------------------------------------------------------