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Show Tim K. Lowenstein, Department of Geological Sciences and Environmental Studies, State University of New York at Binghamton, Binghamton, NY 13902. DEATH VALLEY SALT CORE: 200,000 YEAR PALEOCLIMATE RECORD FROM SEDIMENTARY STRUCTURES, SALINE MINERALOGY, FLUID INCLUSIONS IN HALITE, AND OSTRACODES Core DV- 93 is a 186 m long core composed of interbedded salt and mud from Badwater Basin, Death Valley. A 200,000 year record of closed basin environments and paleoclimates ( lake levels, aridity, and temperatures) has been constructed from sedimentary structures, ostracodes, saline mineralogy, and fluid inclusions in halite ( Figure 1). Evaporite minerals from 12 stratigraphic intervals were dated using the uranium- series isochron method. Given age errors are one standard deviation derived from counting statistics and from the fitting of isochrons. Dates not directly obtained via the U- series isochron method were calculated by interpolation, assuming constant accumulation rates for stratigraphic intervals with similar sediment types and depositional environments. Death Valley has been a mudflat and saline pan over the past 10 ka ( 0- 7.7 m: disrupted muds overlain by a 0.25 m thick halite crust). Climate was arid with the water table normally below the surface. A perennial saline lake existed in Death Valley for a 25 ka period, from 10- 35 ka ( 7.7- 18 m: interlayered mud with rare ostracodes and halite cumulates, chevrons, pisoids, and bottom growth textures). Periods of mud deposition represent the deepest lake phases, whereas salts were deposited in shallower saline lakes. Saline pan sediments, from 35- 60 ka ( 18- 60 m: halite with dissolution pipes and saline pan textures) indicate that Death Valley was commonly desiccated at that time, but received enough inflow water to supply the solutes required to accumulate thick salts relatively rapidly. Five thin halite intervals between 43 and 52 meters ( approximately 50 to 54 ka) indicate that, during this time, shallow saline lakes occurred in Death Valley. From 60 to 120 ka ( 60- 109 m), mudflat environments with subordinate saline pans dominated Death Valley, a time when Death Valley was mostly desiccated and similar in aridity to the modern ( silty muds with sand patch textures, mudcracks and diagenetic saline minerals formed from groundwater brines). A halite interval, interpreted to have been deposited in shallow saline lake/ saline pan environments occurs at depths of 74- 87 m. U- series dates from the top and bottom of the interval are 98.6 ka and 97.1 ka, which suggests rapid evaporite accumulation. Black lacustrine muds ( 127- 161 m) overlain by saline lake halites and layered muds ( 109- 127 m) form a remarkable succession of perennial lake deposits that lasted more than 60 ka, between 120 and 186 ka. The perennial lake mud section contains halite layers at 152 m ( 170 ka) and 137.5 to 139.5 m ( 146 ka), indicating saline lake conditions and probable shallowing of lake waters during deposition of these thin intervals. The upper 18 meters of the perennial lake succession consists of interlayered halite and mud which record the shallowing of the perennial lake between 120 and 128 ka, and its eventual desiccation at 120 ka. Finally, the bottom 25 meters of the core, 186 to 192 ka ( 161 to 186 meters) contains interlayered halites and muds, formed in saline pan/ shallow saline lake settings. Ostracodes from core DV- 93 provide information on the lower limits of water salinities of the long- lived perennial lakes in Death Valley during the last glacial, 10- 35 ka, and the penultimate glacial, 120- 186 ka ( marine oxygen isotope stages 2 and 6). Perennial lake muds contain ostracode species Limnocythere staplini, Limnocythere sappaensis, Limnocythere Ceriotuberosa |
