THE RELATIVE TIMING OF LATE PLEISTOCENE GLACIER AND PLUVIAL LAKE MAXIMA IN THE NORTHERN GREAT BASIN, NEVADA AND UTAH, U.S.A

During the last Pleistocene glaciation, the northern sector of the Great Basin featured numerous glaciers in the tallest mountain ranges and considerably larger pluvial lakes in neighboring valleys. Examining both glacial and lacustrine records in this setting affords an opportunity to better understand the relative roles of temperature and precipitation changes in driving the expansion and decline of glaciers and lakes. Until recently, knowledge of the relative timing of glacier and lake maxima in the Great Basin has been limited by the small number of numerical age limits on glacial deposits compared to lacustrine deposits. Broad applications of cosmogenic ¹⁰Be exposure dating to terminal moraines in the northern Great Basin combined with recent improvements to models of in situ production of ¹⁰Be in quartz have enabled more accurate comparison of glacial and lacustrine chronologies, the latter being developed chiefly by radiocarbon and other numerical dating methods. A synthesis of a large number of cosmogenic ¹⁰Be exposure ages of moraines in the northern Great Basin reveals two phases of glacier maxima during the last Pleistocene glaciation. The older phase signifies the deposition of terminal moraines at ca. 23-19 ka, corresponding to the later part of the Last Glacial Maximum. The younger phase is represented by the deposition of end moraines indicating glacier lengths within 70-100% of the Late Pleistocene maximum at 18-16 ka, corresponding to the time when Lake Bonneville (the largest pluvial lake) overflowed and to the highstands of several other pluvial lakes in the northern Great Basin. Throughout this region, lakes were below their highstands during the older phase of glaciation, suggesting a cold and dry climate favoring only glacier maxima. Coinciding glacier and lake maxima at 18-16 ka is consistent with models of increased precipitation in the northern Great Basin during the early part of the last deglaciation.