CORRELATION OF PLUVIAL MUD LAKE, NEVADA SHORELINE CHANGES WITH PLEISTOCENE TEMPERATURE FLUCTUATIONS

Distinctive linear ridges capped by beach gravel lag deposits surround the Mud Lake playa in the Ralston Valley, Nevada. As many as eight concentric ridges ranging in elevation from 1,587 m to 1,609 m surround the playa. Each gravel-capped ridge exists at a unique elevation around the playa and records a different lake stand for pluvial Mud Lake. Several beach deposits contain fossil stromatolites similar to the modern stromatolites existing on the active shoreline of Walker Lake. Recent C-14 age data from these fossils indicate a complex history of pluvial lake expansion and contraction from 23,560 yrs to 37,080 yrs Before Present (BP) as lake levels oscillated between 1,587 m, 1,589 m, 1,592 m, and 1,594 m above sea level. These lake level changes correspond to Pleistocene temperature fluctuations as recorded by delta O18 values in GISP2 ice core data from Greenland. At 37,080 yrs BP pluvial Mud Lake was at a high stand of 1,594 m during a period of relatively warm temperatures from 38,000 and 37,000 yrs BP. Lake level fell to 1,592 m by 36,320 yrs BP as temperatures declined to a minimum at 35,500 yrs BP. By 30,860 yrs BP lake level was at 1,589 m, which corresponds to another period of relative cold temperatures. A modest lake level advance to 1,592 m at 29,820 yrs BP corresponds to a small positive spike in temperature. The rise in lake level from 1,587 m to 1,592 m that occurred at 28,490 yrs BP corresponds to a sharp temperature increase between 28,800 and 28,600 yrs BP. A slow decline in lake levels from 1,592 m at 26,970 yrs BP to 1,589 m at 24,950 yrs BP parallels a general decline in temperatures for the same period. The final lake advance to 1,592 m at 23,560 yrs BP corresponds to another sharp increase in temperature. Pluvial lake advances consistently correlate with warmer temperatures and retreats with colder temperatures, implying that precipitation trends followed temperature trends in the western Great Basin during the Late Pleistocene.