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Preliminary Analysis of the Physical Stratigraphy, Depositional Environment, and Paleoecology of the Miocene Non-Marine Deposits

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Preliminary Analysis of the Physical Stratigraphy, Depositional Environment, and Paleoecology of the Miocene Non-Marine Deposits 7 Preliminary Analysis of the Physical Stratigraphy, Depositional Environment, and Paleoecology of the Miocene Non-Marine Deposits, Stewart Valley, Nevada A thesis submitted in partial fulfillment of the requirement for a Master of Science in Geology by Thomas P. Lugaski, Ph.D. Ul JULY 1986 1 MINES bIBRARY i The thesis of Thomas Peter Lugaski is approved: T J t e 3 1 0 8 sis Advisor ACKNOWLEDGMENT S I wish to express my sincerest appreciation to my committee members: Dr. James Firby, Dr. Joseph Lintz and Dr. James Hulse for their efforts on my behalf. I also wish thank Drs. Don Savage and Harvey Scudder for their help in the field. A special thanks is due Dr. James Firby, Dr. Jack Kepper and Howard Schorn for their help in the field and discussions on the origin and formation of the Stewart Valley beds. This study was funded in part by a grant from the Bureau of Land Management. A very special thanks and appreciation is due my wife, Lhly and daughter, Kate for their support and understanding throughout the study. ABSTRACT The Late Tertiary lake beds of Stewart Valley, Mineral County, Nevada were examined. The lake sediments represent the remnants of Miocene Lake Savage, a chemically stratified, meromictic lake. Deep-water, fine-grained, laminated, silicified and non-silicified paper shales accumulated in the anoxic hypolimnion of the lake. Within the laminae are preserved complete leaves, insects, articulated fish skeletons and other fauna. Early in its depositional history, Lake Savage was a net siliciclastic depositional system, later Lake Savage became a net carbonate depositional system. X-ray diffraction analysis of the shales reveals they are made up of cristobalite. Shallow-water bedded diatomaceous clays and mudstones, gypsiferous mudstones, elastics, marlstones, ostracodal limestones, stromatolites, tufa domes, and oolites were also formed. Molluscs, ostracodes, and pertified logs are abundant. Fluvial portions of the sediments consist of numerous cut-and-fill structures, and point bar deposits. Trace fossils are locally abundant. Pyroclastic (volcanic mudflows, surge deposits and air-fall ashes) units are interbedded with the sediments. These sediments preserve an excellent and unique record of changes in depositional rates, lake level fluctuation, lake chemistry, flora and fauna through time. TABLE OF CONTENTS PAGE ACKNOWLEDGMENTS.................................. ^ ABSTRACT........................................ i±i TABLE OF CONTENTS................................ v LIST OF FIGURES................................. vii LIST OF TABLES.................................. viii LIST OF PLATES.................................. ix INTRODUCTION..................................... 1 Present Topography, Climate and Environment. 5 Objective and Scope of Work.................. 10 Present and Future Status of the Fossil Beds 11 Previous Work................................. 12 General Mesozoic Geologic History............ 16 General Cenozoic Geologic History............ 18 RESEARCH METHODS AND RESULTS................... 26 X-ray Diffraction Analysis.................. 96 Sedimentary Structures........................ 97 DISCUSSION........................................ 106 Ancient and Modern Comparisons............... 113 Green River Formation......................... 113 Miocene Wassuk Group 129 Oligocene Florissant Lake, Colorado........ 132 Eocene Freshwater Deposits of British Columbia.............................. Pleistocene Rita Blanca Lake Deposits, Texas 136 Deep Springs Lake, California............... 140 Fayetteville Green Lake, New York.......... 142 Pluvial Pleistocene Lake Lahontan........... 144 Lake Classification......................... 149 Siliceous Beds............................... 155 Sedimentary Pyrite Formation................ 166 Lacustrine Carbonates....................... 171 Carbonate Sediments-Ooids................... 182 Varves and Varving Mechanisms............... 184 Trace Fossils or Lebensspuren............... 190 CONCLUSIONS..................................... 194 LITERATURE CITED................................ 201 vi i LIST OF FIGURES FIGURE PAGE 1 Location map of the Stewart Valley study site, Mineral County, Nevada.... 2 2 Landsat 5 Thematic Mapper false color image (bands 4, 3, 2 RGB) of west- central Nevada......................... 3 3 Landsat 5 Thematic Mapper false color image (bands 4, 3, 2 RGB) of Stewart Valley, Mineral County, Nevada............ 4 4 Landsat 5 Thematic Mapper false color image (band ratios 5/7, 5/6, 4/2 RGB) of Stewart Valley, Mineral County, Nevada................................... 7 5 Landsat 5 Thematic Mapper false color image (band ratios 3/6, 5/6, 4/2 RGB) of Stewart Valley, Mineral County, Nevada................................... 24 6 Lineation map made from Landsat 5 Thematic Mapper image (Figure 5), showing the major structural blocks in Stewart Valley......................... 25 vi i i 7 Photograph of Pacific Union Canyon where Stewart Valley Stratigraphic Section 27 was measured........................ 93 8 This illustration graphically displays the variation in lithology and bed thickness in Stewart Valley Stratigraphic Section 27 from Pacific Union Canyon............................. 94 9 The common x-ray diffraction pattern found during the analysis of shales from Stewart Valley, Nevada............. 98 LIST OF TABLES TABLE PAGE 1 Results of the x-ray diffraction analysis on selected rocks from Stewart Valley, Nevada.......................... 100 2 A listing of the sedimentary structures found in the Stewart Valley beds by stratigraphic section................... 102 IX LIST OF PLATES PLATE 1 Stewart Valley, Mineral County, Nevada Stratigraphic and geologic cross section locations 2 Stewart Valley Section III. 3 Stewart Valley Sections IV and V. 4 Stewart Valley Sections VI, VII, and VIII. 5 Stewart Valley Sections XI and XII. 6 Stewart Valley Section XXVII. 7 Stewart Valley Generalized Composite Stratigraphic Section. 8 Stewart Valley Cross Sections. 1 INTRODUCTION Stewart Valley is located in the northeastern portion of Mineral County, Nevada. It is a northwest trending valley located between the Pilot Mountains and the Gabbs Valley Range, on the southwest, and the Cedar Mountains, on the northeast ( Tonopah 1:250,000; Ross, 1961 Plate 1, Figure 1 and 2). Stewart Valley is accessible via Nevada State Route 23 (the Gabbs to Luning, Nevada highway) which crosses the valley on its nothwestern end and via a county road from Mina to the Simon mine in the southern end of the valley. Secondary county roads from the north also intersect the Stewart Valley road. The area of interest in Stewart Valley lies some 12 miles (19.3 km) southeast of the Stewart Valley-State Route 23 intersection, at a point starting at the Rawhide ranch (Granny Goose Well Quadrangle 1.24,000 map, Plate 1, Figure 1 and 2) and continuing down the valley for some 10 miles (16 km) to just below the junction of the Stewart Springs road with the Stewart Valley road (Stewart Springs Quadrangle 1:24,000 map, Plate 1) . This study was undertaken, in part, to provide a detailed description of the physical stratigraphy and NEVADA Figure 1. Location map of the Stewart Valley study site, Mineral County, Nevada. Figure 2. Landsat 5 Thematic Mapper false color image (bands 4, 3, 2 RGB) of west central Nevada. The arrow is at the junction of Fingerrock Wash and Omco Wash. ? i ixM 4 Figure 3. Landsat 5 Thematic Mapper false color image (bands 4, 3, 2 RGB) of the Stewart Valley, Mineral County, Nevada area. The arrow is at the junction of Fingerrock Wash and Omco Wash. The light colored beds in the center of the image are the "Esmeralda" beds of Stewart Valley. The Cedar Mountains are to the right and Gabbs Valley Range to the left. 5 depositional environments of the Miocene non-marine deposits in the areas for the Carson City District of the Bureau of Land Management as part of their project to set aside this area as an area of critical environmental concern (ACEC) in order to protect the paleontological resources found in these beds. While other Miocene and Pliocene non-marine beds in the area were examined, those reported here are only those units found in Stewart Valley proper from below the Rawhide ranch to just below Stewart Spring, which contain the paleontological resources to be preserved. Future reports by the author will include detailed examination of the rest of the Miocene and Pliocene non-marine beds in southern Stewart Valley and lone Valley to the east. Present Topography, Climate and Environment Stewart Valley has an average elevation of 5,500 feet (1676.4 m) and is flanked by the Pilot Mountains, Gabbs Valley Range, and Cedar Mountains which average 7,000 feet (2133.6 m) in elevation with some areas exceeding 8,000 feet (2438.4 m) in elevation. Stewart Valley drains northwestward via Fingerrock Wash (In this report the term Fingerrock Wash will be used as a single word, which is the 6 traditional usage as opposed to the usage of Finger rock Wash on U.S.G.S. topographic maps.) to the Gabbs Valley playa, some 35 miles (56.33 km) northwest. This playa is the local base level of erosion and is some 1,550-2,000 feet (472.4-609.6 m) lower than Stewart Valley. A series of older (Pleistocene?) erosional surfaces and pediments can be seen in the valley, especially along the eastern front of the Pilot Mountains and Gabbs Valley Range. This series of older surfaces are covered in many areas with desert pavement has been incised with numerous gullies and stream beds that have exposed
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