Paleohydrologic record of spring deposits in and around Pleistocene pluvial Lake Tecopa, southeastern California

Tufa (spring) deposits in the Tecopa basin, California, reflect the respons e of arid groundwater regimes to wet climate episodes. Two types of tufa ar e represented, informally defined as (1) an easily disaggregated, fine-grai ned mixture of calcite and quartz (friable tufa) in the southwest Tecopa Va lley, and (2) hard, vuggy micrite, laminated carbonate, and carbonate-cemen ted sands and gravels (indurated tufa) along the eastern margin of Lake Tec opa, High delta O-18(VSMOW) (Vienna standard mean ocean water) water values , field relations, and the texture of friable tufa suggest rapid nucleation of calcite as subaqueous, fault-controlled groundwater discharge mixed wit h high-pa, hypersaline lake water. Variations between delta O-18(VSMOW) and delta C-13(PDB) (Peedee belemnite) values relative to other closed basin l akes such as the Great Salt Lake and Lake Lahontan suggest similarities in climatic and hydrologic settings. Indurated tufa, also fault controlled, fo rmed mounds and associated feeder systems as well as stratabound carbonate- cemented ledges, Both deposits represent discharge of deeply circulated, hi gh total dissolved solids, and high pCO(2) regional groundwater with kineti c enrichments of as much as several per mil for delta O-18(VSMOW) values. Field relations show that indurated tufa represents episodic discharge, and U-series ages imply that discharge was correlated with cold, wet climate e pisodes. In response to both the breaching of the Tecopa basin and a modern arid climate, most discharge has changed from fault-controlled locations n ear basin margins to topographic lows of the Amargosa River drainage at ele vations 30-130 m lower, Because of episodic climate change, spring flows ma y have relocated from basin margin to basin center multiple times.