THE PALEOCLIMATIC IMPLICATIONS OF PALEOLAKE FLUCTUATIONS DURING THE PLEISTOCENE AND HOLOCENE EPOCHS IN THE SOUTHERN BASIN AND RANGE PROVINCE, USA

Pleistocene and Holocene climates can be characterized globally as strongly contrasting. Based on paleoenvironmental reconstructions for the Southern Basin and Range province (SBAR), the main characteristics of Pleistocene climate were cooler annual temperatures and the predominate influence of winter precipitation; climate during the Holocene epoch can be characterized as summer precipitation-dominated with significantly greater mean seasonal temperatures. Since the surface area of a lake is primarily a function of the P-E balance (precipitation:evaporation), corresponding differences in past effective precipitation should be evident from the elevations of fossil shorelines in closed basins of the region. However, according to several studies, the elevation of Holocene age shorelines in several basins are nearly equal to that of their late Pleistocene counterparts, signifying that the surface areas of Holocene and Pleistocene paleolakes were nearly equal. Further, we have verified that high lake levels in these systems were not controlled by overflow thresholds. The paleoclimatic implication of these findings is that, during brief intervals throughout the Holocene epoch, the P-E balance nearly equaled those inferred for the LGM and terminal Pleistocene. We present preliminary radiocarbon data from southern Arizona and New Mexico which support this notion and warrant further investigation into the timing and causes of these anomalously moist periods during the Holocene. Finally, our data will serve to assess the degree of synchroneity in the timing of highstand activity within the SBAR and Great Basin, illuminating possible linkages between regional paleoclimates and external/internal climate forcings.