A 100 ka record of water tables and paleoclimates from salt cores, Death Valley, California

Abstract

Sedimentary and petrographic features of evaporites and associated sediments from a 185 m deep core taken in Death Valley, CA, together with uranium-series dating have been used to reconstruct the history of water table fluctuations and climate changes in Death Valley for the past 100 ka. Death Valley has been arid during the Holocene (0–10 ka), with predominantly mudflat and saline pan subenvironments. A perennial lake, 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 fluctuations 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 core 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. These sediments record repeated flooding by dilute waters, dissolution of subaerially exposed surface salt crusts, deposition of mud from suspension, precipitation of halite during the saline lake phase, and cementation by diagenetic halite. Mudflat sediments consist of clayey silt, with sand patches and mud cracks, which document long periods of desiccation and the formation of efflorescent salt crusts from the evaporation of groundwater brines. Saline pan and mudflat deposits formed during periods when Death Valley was relatively arid, similar to the modern climate. Lacustrine deposits consist of mudhalite cycles, accumulated during the early lake stage, bedded thenardite (Na2SO4) and mud above, and a cap of massive halite formed during the latest lake stage, all of which record fluctuating salinities and lake levels in a perennial system. Such deposits document a relatively wet climate with a high ratio of water inflow to evaporation. Ostracodes in mud layers represent the least saline, deepest lake phases. Halite layers are made of fine grained cumulates and clear, vertically-oriented crystals precipitated during shallower, perennial lake stages. Of significance is the nearly complete absence of syndepositional dissolution of saline minerals in the lacustrine interval, indicating that accumulated salts were permanently protected from dissolution by saline lake waters. Such evidence strongly suggests that lakes existed continually, without desiccating, for 25 ka between 10 and 35 ka B.P.