Graduate Thesis Or Dissertation
 

Reconstruction of late Pleistocene paleoclimatic characteristics in the Great Basin and adjacent areas

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pk02cd510

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  • 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.
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