OCR Text |
Show Mitchell A. Plummer, New Mexico Institute of Mining and Technology, E& ES Dept., Socorro, NM 87801 COMPARISON OF THE TIMING OF MID- TO- LATE PLEISTOCENE GLACIAL ADVANCES AND LACUSTRINE FLUCTUATIONS ACROSS THE GREAT BASIN We have applied cosmogenic 36C1 dating to mid- to- late Pleistocene glacial deposits spanning from the western side of the Great Basin ( the Sierra Nevada) to close to the eastern side ( the Wind River Range). These dates provide a chronology of the major glacial advances in these areas. Lacustrine records describing the fluctuations of large pluvial lakes in adjacent basins are also available for these areas ( Owens/ Searles Lakes and Lake Bonneville). We compare these records and discuss what the similarities and differences in the behavior of the two systems suggests about past climate change across the Great Basin. In general, the similarities of the records in the two regions are more striking than the differences. There are however, some interesting patterns in the differences: ( 1) Both the eastern and western mountain ranges show clear evidence of major glacial advances during isotope stage 6, but evidence of lacustrine highstands is less clear in both areas. ( 2) There is strong evidence of early Wisconsin glacial advances on the western side, but little on the eastern. ( 3) The timing of major ice advance and retreat during the late Wisconsin was the same on both sides of the Great Basin, but the Sierra Nevada shows clear evidence of large oscillations in glacial extent while the Wind River Range does not. In both areas, lacustrine highstands frequently postdate the glacial maxima by approximately 5,000 years. The extent to which these differences are real, or are instead a result of purely local factors, cannot be resolved without investigations in additional localities. |