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Devonian Stratigraphy and Depositional Environments of the Northern Antelope Range, Eureka County, Nevada

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Devonian Stratigraphy and Depositional Environments of the Northern Antelope Range, Eureka County, Nevada AN ABSTRACT OF THE THESIS OF William R. Trojan for the degree of Master of Science in Geology presented onNovember 17, 1978 Title: DEVONIAN STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE NORTHERN ANTELOPE RANGE, EUREKA COUNTX, NEVADA' Abstract approved: Redacted for Privacy DrC J. G. Johnson Lochkovian to Frasnian carbonate rocks in the northern Antelope Range reflect an eastward shift of the gradational facies boundary between the eastern assemblage of shallow-shelf dolomites, lime- stones, and quartz arenites and the transitional assemblage of basin and basin-slope limestones and fine-grained clastics in the Cordilleran Miogeocline. The Lochkovian upper part of the Lone Mountain Dolomite represents primary dolomite formed under peritidal condi- tions on the shelf.Early Pragian transgression caused onlap and deposition of the Kobeh Member of the McColley Canyon Formation over the Lone Mountain platform complex followed by subtidally deposited fossiliferous limestones of the Kobeh and Bartine Members. A continued deepening of depositional enviornments is inferred from the laminated lime mudstones and restricted fauna of the lower Coils Creek Member. Late Dalejan to early Couvinian offlap caused a brief period of shallow water sedimentation before deposition of the basinal lime mudstones with interbedded allodapic debris flows and turbidites of the Denay Limestone. Early Givetian shallowing along the inner shelf margin is indicated by the abundant easterly derived allcdapic beds present in the middle unit of the Denay. An interlude of quiet- water, suspension deposition separated the middle unit from easterly derived allodapic beds containing the Tecnocyrtina Fauna in the middle portion of the upper unit.Allodapic sediments of Tecnocyrtina Fauna age were deposited in a previously unrecognized intrashelf basin situ- ated west of the shoal-water Devils Gate platform complex and east of the incipient Antler orogenic highland.Silty shales present in the upper portion of the upper unit represent, in part, westerly derived clastic detritus.Allochthonous quartzose packstones and grainstones of the Devonian sandstone (informal unit) represent sediment gravity- flow deposits shed eastward of the incipient Antler orogenic highland into the intrashelf Pilot Shale basin during middle and late Frasnian time. Devonian Stratigraphy and Depositional Environments of the Northern Antelope Range, Eureka County, Nevada by William R. Trojan A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Completed November 1978 Commencement June 1979 APPROVED: Redacted for Privacy P ofes or of Get log in charge of major Redcted for Privacy Chairman of Department of ,ology Redacted for Privacy Dean of Graduate School Date thesis is presented November 17, 1978 Typed by Opal Grossnicklaus for William R. Trojan TABLE OF CONTENTS INTRODUCTION 1 Acknowledgements 7 GEOLOGIC SETTING 8 TERMINOLOGY 10 LONE MOUNTAIN DOLOMITE 11 Introduction 11 Lithology 12 Contacts 15 Depositional Environments 16 McCOLLEY CANYON FORMATION 18 Introduction 18 Kobeh Member 20 General 20 Biostratigraphy 23 Depositional Environment 24 Bartine Member 25 General 25 Biostratigraphy 28 Depositional Environment 29 Coils Creek Member 31 General 31 Biostratigraphy 34 Depositional Environment 36 DENAY LIMESTONE 40 Introduction 40 Lower Unit 42 Genera/ 42 Diagenesis 58 Biostratigraphy 61 Middle Unit 63 General 63 Dolomite 74 Biostratigraphy 77 Upper Unit 79 Lower Portion 80 Middle Portion 82 Upper Portion 86 Biostratigraphy 92 DEVONIAN SANDSTONE 94 DENAY LIMESTONE - DEPOSITIONAL ENVIRONMENT 99 Basinal Criteria 99 Depositional Mechanism for Allochthonous Beds 102 Lower Unit 104 Upper kirki Zone and S. cf. coriacea Fauna 107 Middle Unit 110 Dolomite 113 Upper Unit 116 Lower Part 116 Middle Part 117 Upper Part 121 DEVONIAN SANDSTONE 123 UNDIFFERENTIATED MISSISSIPPIAN AND OLDER PALEOZOIC THRUST ROCKS 126 REFERENCES CITED 129 LIST OF FIGURES Figure Page 1. Index map of central Nevada 2 2. Summary faunal sequence 4 3. Biostratigraphic correlation chart 6 4. Photomicrograph of silty sandy Upper Coils Creek 35 5. Polished section of crinoidal packstone 44 6. Outcrop of breccia bed in lower Denay 46 7. Outcrop of soft sediment slump 46 8. Polished section of kirki coquina 54 9. Crinoidal packstone containing S. of coriacea 56 10. Correlation chart of middle and upper units of Denay 65 11. Outcrop of conglomerates and breccia 68 12. Outcrop of graded conglomerate 68 13. Outcrop of graded pebbly calcarenite 72 14. Flame structures 72 15. Graded bed in lime dolomite 73 16. Photomicrograph of pressure solution contact 73 17. Graded bed 83 18. Graded bed 83 19. Polished section of graded bed 84 20. Graded bed 89 Figure E21.9_ 21. Graded bed in Devonian sandstone 89 22. Graded beds in Devonian sandstone 98 23. Photomicrograph of Devonian 98 24. Graded chert- pebble- conglomerate 127 LIST OF PLATES Plate 1 Geologic map of the northern Antelope Range in pocket 2 Measured section II in pocket 3 Measured section III in pocket 4 Measured section IV in pocket 5 Measured section V in pocket 6 Measured section VI in pocket 7 Measured section VII in pocket 8 Measured section VIII in pocket 9 Measured section IX in pocket 10 Measured section Va in pocket 11 Explanation of measured sections in pocket PRELUDE Although the rocks may confuse us The desert remains in all its beauty Sunrise from the northern Antelope Range looking north towards Lone Mountain with the Roberts Mountains in the distance. DEVONIAN STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE NORTHERN ANTELOPE RANGE, EUREKA COUNTY, NEVADA INTRODUCTION This study synthesizes biostratigraphic and petrographic investi- gations of Devonian carbonate rocks in the northern Antelope Range, southern Eureka County, Nevada (Fig. 1). The objectives of this paper are fourfold:(1) to describe the geology and stratigraphy of Devonian strata, (2) to place the rock units in a time-stratigraphic framework, (3) to evaluate the depositional environments of these rocks, and (4) to propose correlations between these units and various rock units in central Nevada. The faunal sequence that was collected during the course of this study represents one of the most complete biostratigraphic sections for the Devonian in western and arctic North America (J. G. Johnson, 1978, pers. comm.).This faunal sequence is summarized on Figures 2 and 3. The Lone Mountain Dolomite, the Mc Colley Canyon Formation, and the lower and middle units, and the lower portion of the upper unit of the Denay Limestone correlate well, both lithologically and faunally, with previously described rock- stratigraphic units present elsewhere in central Nevada. The middle and upper parts of the upper unit of the Denay and the Devonian sandstone (informal unit) are 2 I 9 Miles 0 0 20 PINYON RANGE 0 10 20 30 4 Kilometers .1 CORTEZ IT N. SIMPSON 14) MTS. PARK RANGE 11\RUBY ( MTS. p SULPHUR SPRING COAL RANGE CANYON if ROBERTS MTS. 7 DEVILS y GATE LONE DIAMOND RANGE MAHOGANY ALHAMBRA HILLS ....--- HILLS 144 ANTELOPE RGE. RABBIT HILL I _ _ _"_ _ _ MONITOR RANGE .#1'- RANGE DOBBIN BLACKROCK SUMMIT HOT CREEK CANYON N RANGE CL EAR CREEK d44, 1 A A Figure 1.Index map of central Nevada with Devonian outcrops shown in black.Inset in upper right shows area covered. 3 Figure 2. Summary faunal sequence in the northern Antelope Range showing brachiopod faunas and zones with corresponding conodont zone. Numbers 1-30 are brachiopod intervals of Johnson (1977). 4 BRACHIOPOD CONODONT INT. STAGE ZONE FAUNAS & ZONES L. PAL. TRIANGULAR /S UPPERMOST GIGAS U. G/GA 5 L. G/GAS FRASNIAN ANCY. TRIANGULAR /S U. ASYMMETR/CUS M. ASYMMETR/CUS 30 L. ASYMMETR/CUS 29 ALLANEL LA F. LOWERMOST 28 TECNOCYRT/NA ASYMMETR/CUS FAUNA PAL. 0/SPAR/US F 27 BELOW 26 A5Y MME T R/C US 25 H /PPOCASTANEA Z. HERMANN/ U. 24 U. STR/NGO F CR/STATUS L. 23 GIVETIAN U. VARCUS 22 5FR /NGOCEPHALUS M. VARCUS 2 I FAUNA L. VARCUS 20 CASTANE A ZONE EA/SENS/S 19 18 COR/ACEA F KOCKEL/ ANUS U. U KIRK/ F I 7 C/ RCULA COUVINIAN AUSTRAL/5 16 ZONE COS. COSTATUS 15 PE/VTAMERELL A F. PATULUS WARRENELL,4 F. 14 SEROT /NUS DALEJAN IN VERSUS 13 GRONBERG/ 12 I I ZLICHOVIAN 10 ELONGATA F. DEH /SCENS 9 KOBEHANA 8 ZONE r. SULCATUS 7 COST/SF'/R/FER F. PRAGIAN n. subsp. 6 SULCATUS 5 PESAV/S 4 O. n. sp. D 3 LOCHKOVIAN EUREKAENSIS 2 HESPER/US I 5 Figure 3.Biostratigraphic correlation chart for the northern Antelope Range. Roman numerals at top refer to measured sections aligned in relative east (right) to west (left) positions. Numbers in vertical columns below section numbers refer to footages in measured sections where faunal samples were collected.Num- bers 1-30 are brachiopod intervals of Johnson (1977). Conodont zonation after Klapper (1977, Johnson (1979), and Ziegler (1971).Dots beside footages indicate zonal assignment based on brachiopods (upper dot) or based or conodonts (lower dot).Refer to Plate 1 for location of measured sections.Brachiopod identifica- tions by J. G. Johnson.Conodont identifications by G. Klapper. 6 CONODONT I NT. 322 la al VIE II VII Va V DI ZONE L. PAL. TR /ANGULAR /S UPPERMOST G/GAS 255. U. G/GAS L. G/GAS ANCY. TR/ANGULAR/S U. ASYMMETR/CUS 1530 M. ASYMMETRICUS 30 63. L. ASYMMETRICUS 29 40.-50. 380. LOWERMOST 28 8' -20 369: 1450' ASYMMETR/CUS 1320:-1425: PAL. 0/SPAR/L/S F. 27 153-160: 335. A: -B' BELOW 26 ASYMMETR/CUS 2 5 1245. Y. HERMANN/ U. 24 258. D. CR/STATUS L. 23 U. VARCUS 22 C. 1240. M. VARCUS 2 1 1235. 1120 L. VARCUS 20 50. 1575: 235-265' 1035: 995-1020 ENSENS/S 19 10'-33 65:-72 1545 182'-190' 18 1480:-1490. 5-10 810. KOCKELIANUS 1400: 720' 1120'-1328: 485. 1110. 440 AUSTRAL/S 16 760. 153: -190 665: 119.-120'95:-109: 15 COS.
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