ABSTRACT: Large-Scale Paleoflood Events and Lake Fluctuations Recorded in Sediments from Latest Quaternary Lake Mojave, Silver and Soda Lake Basins, CA

William J. Brown, Y. Enzel, R. Y. Anderson, S. G. Wells

Silver and Soda Lake basins, site of former pluvial Lake Mojave, have been the termini of the Mojave River for ^sim22,000 years B.P. Two major high and persistent lake stands occurred in the Silver Lake basin between about 18 k.a. and 16 k.a. B.P. (Lake Mojave I) and 13.7 k.a. and 11.4 k.a. B.P. (Lake Mojave II). These lake stands were the result of increased frequency of large-scale floods sourced in the upper Mojave River headwaters and probably in seasonal discharge of the Mojave River. Detailed stratigraphic correlation of isotopically dated shoreline features and subsurface lake deposits from 13 drill cores, reveals a complex and well-preserved lacustrine-fluvial history. Thin bands of relatively coarse, nonlaminated sediments occur at irregular intervals within fine grained, laminated to sublaminated clay-size lacustrine sediments, and are interpreted to represent large-scale paleoflood deposits of the Mojave River. Comparison of these paleoflood deposits with recent large-scale Mojave River floods (i.e., 1916, 1938, 1969, and 1983) and their associated deposits indicates similar conditions may have been responsible for both modern events and paleoevents. Drying episodes and lake lowering events were recorded in lake sediments in the characteristic bull's-eye facies evaporite mineral distribution (i.e., calcite, thenardite, and halite) found in closed basin playas. Initial lake lowering deposited CaCO₃ followed by NaSO₄ and NaCl as water levels receded. The temporal and spatial distribution of these deposits served as analogs f r paleolake levels. Ages can be estimated for individual flooding/lake lowering events by calculating basin sedimentation rates from isotopically dated surface and subsurface materials. As water levels receded, CaCO₃ was deposited along the proximal shoreline followed by NaSO₄ and NaCl deposition closer to the basin center.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990