Reconstruction of Late Pleistocene Paleoclimatic Characteristics in the Great Basin and Adjacent Areas
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AN ABSTRACT OF THE THESIS OF Kenneth A. Bevis for the degree of Doctor of Philosophy in Geology presented on March 3. 1995. Title: Reconstruction of Late Pleistocene Paleoclimatic Characteristics in the Great Basin and Adjacent Areas Signature redacted for privacy. Abstract approved:. Peter U. Clark A sequence of glaciation based on relative dating parameters was established in each of nine mountain ranges located along a northwest to southeast transect through the northern Great Basin. Each sequence consists of two or three drift units. Degree of weathering suggests that the younger drift unit in a two-fold sequence and the intermediate drift unit in a three-fold sequence represents deposition during the late Pleistocene. The late Pleistocene equilibrium-line altitude (ELA) in each range was determined by reconstructing the maximum ice extent associated with these drift units and using the accumulation area ratio technique. Paleo-ELAs increase from about 2100 m in northeastern Oregon to approximately 3200 m in central Utah. Paleoclimatic conditions along the study transect were estimated by comparing modern climatic conditions at the reconstructed late Pleistocene ELAs with climatic conditions occurring at the ELAs of modem mid-latitude glaciers. Assuming no change in winter accumulation or in the seasonal distribution of precipitation from the present, a mean summer temperature depression ranging from about 9.0 °C at the northern end of the transect to about 4.0 °C at the southern end would have been necessary to sustain glaciers in these ranges during the late Pleistocene. To simulate possible changes in late Pleistocene precipitation patterns, a change in winter accumulation between 0.5 and 2.0 times the modem value resulted in a respective increase or decrease in temperature depression by approximately 2.0 °C. These results suggest that increases in precipitation during the late Pleistocene alone could not have sustained glaciers in the mountain ranges of the study transect, except possibly at its southern end, in the central Great Basin. An increase in precipitation in this area during the late Pleistocene agrees with the interpretation of other paleoclimatic records and paleoclimatic model simulations for the Great Basin. Reconstruction of Late Pleistocene Paleoclimatic Characteristics in the Great Basin and Adjacent Areas by Kenneth A. Bevis A THESIS submitted to Oregon State University in partial fufflilment of the requirements for the degree of Doctor of Philosophy Completed March 3, 1995 Commencement June 1995 ACKNOWLEDGMENT I would especially like to thank my major professor Dr. Peter Clark for his assistance through every stage of this project. I would also like to thank the rest of my committee for putting up with me, particularly Dr. Raymond Burke for setting me on this path, and Dr. William Scott for his timely editing. Much appreciation goes to my father for the good times in the field and to my mother for all the support over the last few years. TABLE OF CONTENTS Page INTRODUCTION 1 1.1 Objectives 2 1.2 Geographic and Geologic Setting 3 1.2.1 Siskiyou Mountains 5 1.2.2 The Aspen Butte Area, Southern Oregon Cascades 9 1.2.3 Elkhorn Mountains 11 1.2.4 Strawberry Mountains 13 1.2.5 Steens Mountain 15 1.2.6 Pine Forest Range 17 1.2.7 Ruby Mountains 19 1.2.8 Deep Creek Mountains 21 1.2.9 Tushar Mountains 23 1.3 Modern and Late Pleistocene Climatic Conditions 25 1.3.1 Modern Regional Climate 25 1.3.2 Regional Late Pleistocene Paleoclimatic Interpretations 30 PALEOCLIMATIC INTERPRETATIONS FROM LATE 35 QUATERNARY PALYNOLOGICAL RECORDS IN THE GREAT BASIN AND ADJACENT AREAS 2.1 Present-day Vegetation Patterns 35 2.2 Vegetation History 37 2.2.1 Late Pleistocene Vegetation 38 2.2.2 Holocene Vegetation 43 2.3 Vegetation Dynamics and Paleoclimatic Interpretations 50 LATE QUATERNARY PLUVIAL LAKES iN THE GREAT BASIN 58 AND THEIR PALEOCLIMATIC SIGNIFICANCE 3.1 Lake-level Fluctuations 58 3.1.1 Factors Affecting Lake-level Fluctuations 60 3.1.2 Late Quaternary Lake-level Fluctuations 62 3.2 Paleoclimatic Implications of Lake-level Chronologies 74 3.3 Regional Climatic Patterns and Lake-level Fluctuations 78 3.4 Montane Glaciers and Lake-level Fluctuations 81 3.5 Summary 84 LATE QUATERNARY PERIGLACIAL FEATURES AND THEIR 86 PALEOCLIMATIC IMPLICATIONS 4.1 Introduction 86 4.2 Evidence for Late Pleistocene Periglacial Conditions in the 86 Western United States 4.3 Summary 89 Dll-FERENTIATION AND CORRELATION OF DR[FT UNITS 91 5.1 Methodology for Establishing a Glacial Chronology 91 5.2 The Results of Analyses for each Study Area 95 5.2.1 Siskiyou Mountains 95 5.2.2 Aspen Butte Area 98 5.2.3 Elkhorn Mountains 102 5.2.4 Strawberry Mountains 105 5.2.5 Steens Mountain 109 5.2.6 Pine Forest Range 112 5.2.7 Ruby Mountains 115 5.2.8 Deep Creek Mountains 118 5.2.9 Tushar Mountains 121 5.3 Drift Unit Ages 125 5.3.1 Methodology 125 5.3.2 Drift Unit Ages in each Mountain Range 137 5.4 Correlation of Drift Units among Mountain Ranges 142 5.5 Influence of Lithology and Climate On RD Parameter 145 Development and Correlation of Drift Units 5.5.1 Methodology 145 5.5.2 Lithologic Controls 154 5.5.3 Climatic Controls 157 5.6 Summary 160 ESTIMATION OF LATE PLEISTOCENE PALEOCLIMATIC 162 CHARACTERISTICS FROM RECONSTRUCTED EQUILIBRIUM- LINE ALTITUDES 6.1 Estimation of Late Pleistocene ELAs 162 6.1.1 Reconstruction of Former Ice Limits 162 6.1.2 Basal Shear Stress Calculations 163 6.1.3 Equilibrium-line Altitudes 166 6.2 Climatic Characteristics of Modern Glaciers 176 6.3 Modern Climatic Characteristics at Paleo-ELAs 178 6.4 Estimation of Late Pleistocene Temperature Depression 180 6.5 Estimation of Changes in Winter Accumulation 183 6.6 Possible Sources of Error 187 6.7 Discussion of Results 189 6.8 Comparison of Estimated Paleoclimatic Conditions between 194 this Investigation and Interpretations made from Glaciological, Paleobotanical, Pluvial, and Periglacial Data 6.9 Summary 199 7. CONCLUSIONS 204 BIBLIOGRAPHY 211 APPENDICES 227 Appendix 1 228 Appendix 2 245 Appendix 3 259 Appendix 4 269 LIST OF FIGURES Figure Page 1.1The Great Basin and adjacent areas of the Western United States. 4 The hachured line indicates the approximate areal extent of the Great Basin. 1.2 The extent of late Pleistocene glaciers in the western United States 6 (modified from Porter et al., 1983). The hachured line indicates the approximate areal extent of the Great Basin. Glaciated mountain ranges proposed for study in this investigation are labeled: (AB) Aspen Butte, (DC) Deep Creek Mtns., (EH) Elkhorn Mtns., (PF) Pine Forest Range, (RM) Ruby Mtns., (SB) Strawbeny Mtns., (SI) Siskiyou Mtns., (SM) Steens Mtn., and (TM) Tushar Mtns. 1.3Topographic map showing the upper portion of the Clear Creek 8 watershed in the Siskiyou Mountains. 1.4Topographic map of the Aspen Butte area in the southern Oregon 10 Cascades. 1.5Topographic map showing several glaciated watersheds in the 12 Elkhorn Mountains. 1.6 Topographic map showing several glaciated watersheds in the 14 Strawbeny Mountains. 1.7Topographic map showing the glaciated watersheds of Steens 16 Mountain. 1.8Topographic map showing the glaciated watersheds of the Pine 18 Forest Range. 1.9Topographic maps of selected watersheds in the Ruby Mountains. 20 1.10 Topographic map of several glaciated watersheds in the Deep 22 Creek Mountains. 1.11 Topographic map of several glaciated watersheds in the Tushar 24 Mountains. 1.12 Precipitation gradients in the Great Basin (after Houghton, 1969). 27 1.13 Winter air-mass distribution pattern for the western United States 28 (modified from Mitchell, 1976). Region I is dominated by a Pacific component, region II by a continental component, and region ifi by a Gulf component. The wavy pattern indicates mountainous barriers to air flow. 1.14 The late Pleistocene ELA trend surface for the western United States 31 based on lowest cirque-floor altitudes (adapted from Porter et aL, 1983). 1.15 North American paleoclimatic model simulations for 18,000 years 34 B .P. and the present, based on the interpretation of atmospheric, biological, and geological data from the last glacial to interglacial transition (COHMAP Members, 1988). 2.1Site locations of pollen records of late Quaternary age discussed in the 39 text. The hachured line indicates the approximate areal extent of the Great Basin. Key to sites by state: Washington; 1) Big Meadow, 2) Bonaparte Meadows and Mud Lake, 3) Waits Lake, 4) Creston Fen, 5) Carp Lake, 6) Battle Ground Lake. Idaho; 7) Murphey's Rock Shelter, 8) Rattlesnake Cave, 9) Swan Lake, 10) Grays Lake. Wyoming; 11) Yellowstone area. Utah; 12) Confusion Range, 13) Danger Cave, 14) Deep Creek Range, 15) Hogup Cave, 16) Snowbird Bog, 17) Wah Wah Range. Oregon; 18) Chewaucan Marsh, 19) Diamond Pond, 20) Kiamath Lake, 21) Steens Mountain, 22) Warner Lake. California; 23) Bodie Canyon, 24) Eureka Valley, 25) Death Valley, 26) Westgaard Pass Cave, 27) Balsam and Exchequer Meadows, 28) Osgood Swamp. Nevada; 29) Calm's Cave, 30) Eleana Range, 31) Esmeralda Rockshelter, 32) Fishbone Cave, 33) Gatecliff Rockshelter, 34) Guano Cave, 35) Hidden Cave, 36) Leonard Rockshelter, 37) Meadow Valley Wash, 38) Mission Cross Bog, 39) Ruby Marshes, 40) Schell Creek Range, 41) Snake Range, 42) Toquima Range, 43) Winnemucca Lake basin. 2.2 The late Pleistocene/Holocene vegetation transition in the Great Basin. 52 The hachured line indicates the approximate areal extent of the Great Basin. Dashed lines separate the Great Basin and adjacent areas into a northward time-transgressive zonation that indicates approximately when modern vegetation was reestablished in this region. 3.1Pluvial lakes in the Great Basin and adjacent areas of the western 59 United States (adapted from Benson and Thompson, 1987a).