New investigations of Pleistocene glacial and pluvial records in northeastern Nevada

The Great Basin of the western United States offers tremendous potential for exploring the response of mountain glaciers and lowland lakes to climate changes during the Last Glacial Maximum (LGM, MIS-2, ca. 22–18 ka B.P.) and subsequent glacial-interglacial transition. The combination of well-distributed alpine moraine records and pluvial lake deposits offers an unparalleled opportunity to develop a more precise understanding of temperature and precipitation changes during the latest Pleistocene and into the Holocene. This fi eld trip provides an overview of recent and ongoing work illuminating aspects of the glacial and pluvial history of northeastern Nevada from the LGM to the present. The route of this trip involves three full days of stops separated by two nights in Elko, Nevada. The fi rst day focuses on glacial deposits at the type locality for the LGM Angel Lake Glaciation on the eastern side of the East Humboldt Range. The second day explores the geomorphic record of pluvial Lakes Franklin and Clover on the east side of the Ruby–East Humboldt Mountains and describes recent efforts to develop a chronology for the late Pleistocene regression of these lakes. The fi nal day again focuses on glacial geology, starting with the type locality of the pre-LGM Lamoille Glaciation on the west side of the Ruby Mountains, and ending with several stops along the scenic drive up Lamoille Canyon. Munroe, J.S. , and Laabs, B.J.C. , 2011, New investigations of Pleistocene glacial and pluvial records in northeastern Nevada, in Evans, J.P., and Lee, J., eds., Geologic Field Trips to the Basin and Range, Rocky Mountains, Snake River Plain, and Terranes of the U.S. Cordillera: Geological Society of America Field Guide 21, p. 1–XX, doi: 10.1130/2011.0021(01). For permission to copy, contact editing@geosociety.org. ©2011 The Geological Society of America. All rights reserved. INTRODUCTION The Great Basin of the western United States offers tremendous potential for exploring the response of mountain glaciers and lakes to climate changes during the Last Glacial Maximum (LGM) and subsequent glacial-interglacial transition (GIT). Despite the modern arid climate and hot summer temperatures, numerous mountain ranges in the region contain evidence of former glaciers (Blackwelder, 1931; Sharp, 1938; Osborn and Bevis, 2001; Blackwelder, 1934). For instance, the Sierra Nevada, which form the western border of the Great Basin, were extensively glaciated and were one of the fi rst locations in which cosmogenic surface-exposure dating was employed to develop a moraine chronology (Phillips et al., 1996). At the eastern border of the Great Basin, a detailed chronology of latest Pleistocene glaciation has been developed for the Wasatch Mountains (Madsen and Currey, 1979; Lips et al., 2005; Laabs et al., 2007) and glacial records there have been used in numerical modeling exercises 2 Munroe and Laabs fl d021-01 1st pgs page 2 to yield paleoclimatic inferences (Plummer and Phillips, 2003; Laabs et al., 2006). Yet in contrast to these wellstudied ranges at the margins, little is known about the timing of late Pleistocene glacier fl uctuations in the interior ranges of the Great Basin, an area covering more than 500,000 km. The largest glaciers between the Wasatch and Sierra Nevada were located in the East Humboldt and Ruby Mountains of northeastern Nevada where moraines document the LGM and multiple glacial stillstands during the last GIT (Laabs and Munroe, 2008). Indeed, the last glaciation in the Great Basin was designated the “Angel Lake Glaciation” after well-preserved glacial deposits in the East Humboldt Range (Sharp, 1938). Three pluvial lakes were also present near the East Humboldt and Ruby Mountains during the Angel Lake Glaciation: Lakes Franklin, Clover, and Waring. Although these lakes were small compared with the better-known Lakes Lahontan and Bonneville, their deposits are easily recognized and mapped, allowing their former extents to be delineated (Reheis, 1999). The combination of welldistributed alpine moraine records and pluvial lake deposits offers an unparalleled opportunity to develop a more precise understanding of temperature and precipitation changes during the latest Pleistocene and into the Holocene.