PALEOHYDROLOGIC AND PALEOCLIMATIC IMPLICATIONS OF LATE PLEISTOCENE SHORELINE DEPOSITS IN THE SOUTHERN BASIN AND RANGE PROVINCE

Paleolake shoreline deposits throughout the southern Basin and Range (SBAR) signify past intervals of steady-state climatic conditions during the Pleistocene-Holocene (P-H) transition. Unfortunately, a lack of knowledge about the age of fossil shoreline deposits—due to ¹⁴C related uncertainties and incomplete dating of shorelines—has left great uncertainty about regional climatic and surface hydrologic conditions during the period of interest. Several studies collectively reveal multiple lake level oscillations during the Last Glacial Maximum (LGM) to terminal Pleistocene interval, with reasonably well dated shoreline deposits existing for only four paleolakes: one in central New Mexico (Estancia), two in southwestern New Mexico (Playas and Cloverdale), and one in southeastern Arizona (Cochise). In summary, there is evidence for LGM high-stands at Estancia and Cloverdale (20-16 Ka), deglacial age (16-13 Ka) high-stands at Playas and Cochise, and latest Pleistocene (13-10 Ka) still stands of as yet undetermined elevation at Playas and Estancia. Subsequent to the latest deglacial high-stands, occurring at Playas and Cochise and ending by ~11.8 and ~11.6 Ka, respectively, high-stands in the SBAR did not occur again until the early Holocene. This strongly suggests that any regional climatic expression of the Younger Dryas—which is detected in the stable isotopic composition of speleothems from Cave-of-the-Bells in southeastern Arizona—was marked primarily by a decrease in mean annual air temperature. Alternatively, if a return to glacial precipitation levels did occur, then it was for an interval so short that sedimentological evidence was not preserved. This presentation will cover the afore mentioned chronologies, as well as the results of preliminary hydrologic modeling efforts directed at constraining the climatic parameters corresponding to chronologically and elevationally constrained lake expansions in the SBAR.