A 100 KA RECORD OF WATER TABLES AND PALEOCLIMATES FROM SALT CORES, DEATH-VALLEY, CALIFORNIA

Sedimentary and petrographic features of evaporites and associated sed iments from a 185 m deep core taken in Death Valley, CA, together with uranium-series dating have been used to reconstruct the history of wa ter table fluctuations and climate changes in Death Valley for the pas t 100 ka. Death Valley has been arid during the Holocene (0-10 ka), wi th predominantly mudflat and saline pan subenvironments. A perennial l ake, up to 90 m deep, existed in Death Valley from 10 to 35 ka. Saline pan and mudflat subenvironments dominated Death Valley from 35 to 100 ka. The chronology of changing subenvironments and water table fluctu ations in Death Valley generally correlates with other climate records in the western US (Owens Lake and Searles Lake, CA, Browns Room cave calcite, NV), the marine oxygen isotope record, and the Vostok ice cor e record. Core intervals through saline pan sediments are composed of interbedded halite, chaotic muddy halite, and mud. The halite contains abundant vertical dissolution pipes, cemented with clear halite. Thes e sediments record repeated flooding by dilute waters, dissolution of subaerially exposed surface salt crusts, deposition of mud from suspen sion, precipitation of halite during the saline lake phase, and cement ation by diagenetic halite. Mudflat sediments consist of clayey silt, with sand patches and mud cracks, which document long periods of desic cation and the formation of efflorescent salt crusts from the evaporat ion of groundwater brines. Saline pan and mudflat deposits formed duri ng periods when Death Valley was relatively arid, similar to the moder n climate. Lacustrine deposits consist of mud-halite cycles, accumulat ed during the early lake stage, bedded ethnarchies (Na2SO4) and mud ab ove, and a cap of massive halite formed during the latest lake stage, all of which record fluctuating salinities and lake levels in a perenn ial system. Such deposits document a relatively wet climate with a hig h ratio of water inflow to evaporation. Ostracodes in mud layers repre sent the least saline, deepest lake phases. Halite layers are made of fine grained cumulates and clear, vertically-oriented crystals precipi tated during shallower, perennial lake stages. Of significance is the nearly complete absence of syndepositional dissolution of saline miner als in the lacustrine interval, indicating that accumulated salts were permanently protected from dissolution by saline lake waters. Such ev idence strongly suggests that lakes existed continually, without desic cating, for 25 ka between 10 and 35 ka B.P.