AN ABSTRACT OF THE THESIS OF Robert Vincent Visconti for the degree of Master of Science in Geology presented on December 9, 1982 Title: PALEOZOIC STRATIGRAPHY AND STRUCTURE OF THE DRY CREEK AREA, ELKO AND EUREKA COUNTIES, NEVADA. Abstract approved: Redacted for Privacy C) Dr. J.Gljohnson The purpose of this investigation was to test two hypotheses. The first hypothesis interprets allochthonous rocks in the southern Pinyon Range to lie on the Devonian Nevada Group. The second hypothesis interprets allochthonous rocks to lie on the Mississippian Dale Canyon Formation. Evidence presented here supports the second hypothesis. During Late Silurian to Middle Devonian time, deposition in the southern Pinyon Range occurred in a miogeoclinal shallow shelf environment characterized by the Lone Mountain Dolomite and Nevada Group. Deposition of the Pilot Shale in an incipient basin developed within the shelf, beginning no later,than marginifera-Lower velifer Zone time, marked the onset of the Antler orogeny. A westward- dipping subduction zone formed to the west, developing an accretionary wedge which later became the Roberts Mountains allochthon. Incipient subduction of continental crust resulted in obduction of the allochthon onto the continential crust. The Antler foreland basin formed east of the advancing allochthon where deposition of the Dale Canyon Formation unconformably on the Pilot Shale formed a submarine fan complex consisting of siliciclastic sediments shed from the rising allochthon. The Roberts Mountains allochthon in the southern Pinyon Range consists of the Devonian Woodruff Formation forming the base, the Ordovician Vinini Formation thrust over the Woodruff, with slices of the Devonian Roberts Mountains Formation occurring in between at places. The allochthon was emplaced in the southern Pinyon Range, over the Dale Canyon Formation during or after late isosticha-Upper crenulata Zone time. Paleozoic Stratigraphy and Structure of the Dry Creek Area, Elko and Eureka Counties, Nevada by Robert Vincent Visconti A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Completed December 9, 1982 Commencement June 1983 APPROVED: Redacted for Privacy Professor in charge of major Redacted for Privacy Chairman of Department of7blogy Redacted for Privacy Dean of Grad e School d Date thesis is presented December 9, 1982 Typed by Heidi W. Pearson for Robert Vincent Visconti ACKNOWLEDGEMENTS I am grateful to many people for their help in this project. The guidance and encouragement given by Dr. J.G. Johnson was deeply appreciated. I thank Dr. E. Julius Dasch and Dr. Harold Demarest for their critical review of the manuscript. Claudia Regier prepared the conodont samples, which were identified by Dr. Gilbert Klapper of the University of Iowa. A coral was identified by Dr. William Oliver of the U.S. Geological Survey. Graptolites were identified by Dr. W.B.N. Berry of the University of California at Berkeley. Dr. Keith B. Ketner of the U.S. Geological Survey provided an interesting field trip and discussion. Dr. Donald Carlisle and Dr. C.A. Nelson of the University of California at Los Angeles provided a copy of their unpublished map of the Mineral Hill quadrangle and unpublished fossil data. I thank John Whitaker for many helpful discussions and car pooling into town during the field season. I thank my parents for their support and patience. A National Science Foundation grant to Dr. J.G. Johnson provided much of the financial support. TABLE OF CONTENTS Page INTRODUCTION 1 Purpose 1 Location and Accessibility 1 Previous Work 2 Methods and Terminology 5 GEOLOGIC SETTING 7 VININI FORMATION (ALLOCHTHONOUS) 9 ROBERTS MOUNTAINS FORMATION (ALLOCHTHONOUS) 12 WOODRUFF FORMATION (ALLOCHTHONOUS) 13 General Statement 13 Age 13 Lithology 14 Laminated quartz-silty dolomite and bioturbated dolomitic siltstone 14 Chert 14 Partially dolomitized biomicrite 16 Siliceous mudstone 16 Depositional Environment and Regional Significance 16 LONE MOUNTAIN DOLOMITE (AUTOCHTHONOUS) 19 NEVADA GROUP (AUTOCHTHONOUS) 20 Beacon Peak Dolomite 20 Oxyoke Canyon Sandstone 21 Telegraph Canyon Formation 21 Lithology 22 Silicification 23 PILOT SHALE (AUTOCHTHONOUS) 25 General Statement 25 Thickness and Contact Relations 25 Age 26 Lithology 26 Page Lower member 26 Upper member 28 Silicified shale 28 Depositional Environment 32 Regional Significance 32 DALE CANYON FORMATION (AUTOCHTHONOUS) 34 General Statement 34 Age 35 Contact Relations and Thickness 35 Facies Interpretation 36 Basin slope facies 36 Inner fan facies 38 Lithology 38 Chert-arenite 33 Pebbly chert-wacke 41 Fine grained rocks 41 Coarse-grained debris flow deposits 46 Regional Significance 46 INTRUSIVE ROCKS 48 LANDSLIDE DEPOSITS 49 STRUCTURE 50 GEOLOGIC HISTORY 53 SUMMARY 55 REFERENCES CITED 58 APPENDIX 62 LIST OF FIGURES Figure Page 1. Index map of the Pinyon Range. 3 2. Summary Paleozoic stratigraphic section of the mapped area. 4 3. Photomicrograph of bedded chert (Ordovician). 11 4. Photomicrograph of laminated quartz-silty dolomite 15 (Devonian). 5. Photomicrograph of partially dolomitized biomicrite 17 (Devonian). 6. Photomicrograph of jasperoid in the Telegraph Canyon 24 Formation. 7. Photomicrograph of laminated quartz-silty dolomite 27 (Devonian). 8. Photomicrograph of laminated carbonaceous shaly 29 dolomite (Devonian). 9. Silicified Pilot Shale. 30 10. Photomicrograph of silicified shale (Devonian). 31 11. Channel filled with coarse sandstone, basin slope facies 37 of the Dale Canyon Formation. 12. Amalgamated massive sandstone beds (Mississippian). 39 13. Unconformable contact between the Pilot Shale and 40 Dale Canyon Formation. 14. Photomicrograph of chert-arenite (Mississippian). 42 15. Photomicrograph of pebbly chert-wacke (Mississippian). 43 16. Photomicrograph of carbonaceous spicular biomicrite 44 (Mississippian). 17. Photomicrograph of coarse-grained debris flow 45 conglomerate (Mississippian). Figure Page 18. Comparative geologic cross sections along Dry Creek 56 LIST OF PLATES Plate Page I. Geologic map of the Dry Creek Area, Elko and pocket Eureka Counties, Nevada. 2. Geologic cross sections. pocket PALEOZOIC STRATIGRAPHY AND STRUCTURE OF THE DRY CREEK AREA, ELKO AND EUREKA COUNTIES, NEVADA INTRODUCTION Purpose The Paleozoic rocks in the vicinity of Dry Creek, Sulphur Spring and Pinyon Ranges, are in several elongate fault blocks across and subparallel to the toe of the Roberts Mountains thrust. Published and unpublished geologic maps (Smith and Ketner, 1978; Carlisle and Nelson, ms) interpret allochthonous rocks to lie below the Chainman Shale or Chainman-Diamond Peak Formation, undivided. However, Johnson and Pendergast (1981) interpret the same maps to show the allochthon over- lying the Chainman Shale. Remapping of the critical area was done to test the two hypotheses. The Dry Creek area also includes the "Dry Creek fault", recently proposed (Thorman and Ketner, 1979) as an important left-lateral strike- slip fault zone. Johnson (oral commun., 1981) suggests that there is no strike-slip fault zone and that it also is a misinterpretation. These two hypotheses are also tested. Location and Accessibility The area mapped is located approximately 33 miles south of the town 2 of Carlin, lying along the boundary of Elko and Eureka Counties, Nevada. It includes the southwestern edge of the Pinyon Range and the northern tip of the Sulphur Spring Range (Fig. 1). The area mapped occupies roughly 13 square miles (34 square kilometers). Access may be gained from the west on three unimproved dirt roads leading east from Union Summit Road. Previous Work Carlisle and Nelson (ms) mapped the southern one third of the thesis area as part of an unpublishedgeologic map of the MineralHill quadrangle. They mapped the allochthonous units as Ordovician Vinini Group (western facies), Devonian Bruffey Formation (transitionalfacies), and an.unnamed Devonian shale, all thrust over the autochthonous Silurian-Devonian Lone Mountain Dolomite, Devonian Nevada Group, and Devils Gate Limestone. The Mississippian Diamond Peak Formation-Chainman Shale undivided was mapped as overlapping the autochthonous and allochthonous units. Carlisle and Nelson (1955) did not assign an age to the Roberts Mountains thrust. Carlisle and others (1957) described Devonian stratigraphy of the Pinyon and Sulphur Spring Ranges with emphasis on the autochthonous carbonate units. Reconnaissance mapping of Elko County (Granger and others, 1958) included approximately the eastern three fourths of the thesis area. Smith and Ketner (1975, 1977) describe the Paleozoic stratigraphy and interpret the tectonic history of the Pinyon Range. The northern two thirds of the study area was mapped by Smith and Ketner (1978) as part of a U.S. Geological Survey map of the Pinyon Range. Smith and Ketner's mapping shows the same basic stratigraphic sequence as 3 CARLIN 1166 0 40°30' Map Area NEVADA DRY CREEK AREA 0 5 10 15 miles 1 Figure I. Index map of the Pinyon andSulphur Spring Ranges, showing the location of theDry-Creek Area. 4 AGE ROCK UNIT THICKNESS Ordovician Vinini Formation 1500 ft. A A A Roberts Mts. Fm 200 A A A Devonian Woodruff Formation 1200 A A Mississippian Dale Canyon Formation 1000 Pilot Shale . 200 Telegraph Canyon 2065 Formation Devonian Oxyoke Canyon Ss. 400 Beacon Peak Dolomite 675 Lone Mt. Dolomite 1400 Silurian Figure 2. Summary Paleozoic stratigraphic section of themapped area. 5 mapped by Carlisle and Nelson. The allochthonous units were mapped as Ordovician