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

¹ Department of Geology, S389 ESC, Brigham Young University, Provo, Utah 84602, USA
² Department of Geosciences, Box 1053, Texas Tech University, Lubbock, Texas 79409, USA
³ U.S. Geological Survey, Box 25046, M.S. 963, Denver Federal Center, Denver, Colorado 80225, USA
⁴ Department of Geology, Brigham Young University, Provo, Utah 84602, USA
⁵ Los Alamos National Laboratory, 1261 Town Center Drive, Las Vegas, Nevada 89134, USA

Tufa (spring) deposits in the Tecopa basin, California, reflect the response of arid groundwater regimes to wet climate episodes. Two types of tufa are represented, informally defined as (1) an easily disaggregated, fine-grained mixture of calcite and quartz (friable tufa) in the southwest Tecopa Valley, and (2) hard, vuggy micrite, laminated carbonate, and carbonate-cemented sands and gravels (indurated tufa) along the eastern margin of Lake Tecopa. High ¹⁸O_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 with high-pH, hypersaline lake water. Variations between ¹⁸O_VSMOW and ¹³C_PDB (Peedee belemnite) values relative to other closed basin lakes such as the Great Salt Lake and Lake Lahontan suggest similarities in climatic and hydrologic settings. Indurated tufa, also fault controlled, formed mounds and associated feeder systems as well as stratabound carbonate-cemented ledges. Both deposits represent discharge of deeply circulated, high total dissolved solids, and high pCO₂ regional groundwater with kinetic enrichments of as much as several per mil for ¹⁸O_VSMOW values.

Field relations show that indurated tufa represents episodic discharge, and U-series ages imply that discharge was correlated with cold, wet climate episodes. In response to both the breaching of the Tecopa basin and a modern arid climate, most discharge has changed from fault-controlled locations near basin margins to topographic lows of the Amargosa River drainage at elevations 30–130 m lower. Because of episodic climate change, spring flows may have relocated from basin margin to basin center multiple times.

Key Words: hydrology • isotope geochemistry • nuclear waste • paleoclimate • paleohydrology

This article has been cited by other articles:

				D. Larsen Revisiting silicate authigenesis in the Pliocene-Pleistocene Lake Tecopa beds, southeastern California: Depositional and hydrological controls Geosphere, June 1, 2008; 4(3): 612 - 639. [Abstract] [Full Text] [PDF]

				C. M. Menges Multistage late Cenozoic evolution of the Amargosa River drainage, southwestern Nevada and eastern California Geological Society of America Special Papers, January 1, 2008; 439(0): 39 - 90. [Abstract] [Full Text] [PDF]