George I. Smith
James L. Bischoff
George I. Smith
1997
<p>Owens Lake, a now-dry lake in southeastern California immediately east of the southern Sierra Nevada, was the site of a coring project designed to obtain a long paleoclimatic record. During the ensuing study, lacustrine deposits were recovered by the 323 m long core designated “OL-92.” The presence of the Bishop ash (ca. 760 ka) and the Matuyama-Brunhes paleomagnetic reversal (ca. 780 ka) near the base of core OL-92 shows that this core represents about 800 k.y. of deposition in Owens Lake. </p><p>The sediments are dominantly lacustrine clay, silt, and fine sand, although some intervals contain as much as 40 wt % CaCO3. The lowest ~57 m of recovered sediments is mostly silt or clay, but several sand beds are present; the overlying ~60 m of sediment is similar, but its sand content is more dispersed. Together, these two units are composed of ~70 wt % silt and clay and ~30 wt % sand, suggesting deposition in lakes that fluctuated between moderately deep and shallow. Overlying them is ~201 m of sediments that were mostly deposited in deep water; they consist predominantly of silt and clay but include two thin, coarse-sand beds. An oolite bed forms the upper ~4 m of natural deposits, and an anthropogenic salt bed, >2 m thick, forms much of the present surface. In addition to the Bishop ash, several much thinner tephra layers are also present. </p><p>About 70% of the clastic-sediment units are massive, some clearly because of bioturbation; other units display a thin bedding defined by changes in color or grain size. Rhythmic bedding, observed in numerous segments <1 m thick, seems to represent cyclical events ~100 yr long. Thin color bands caused by the chemical alteration of sediments on each side of hairline fractures create irregular subvertical veins. Clastic dikes, as much as ~2 cm wide and ~75 cm long, characterize some zones. Bioturbation structures, sand pods, ice-rafted(?) granules, small faults, minor discontinuities, and possible turbidity-current structures are also present. </p><p>Lithologic variations, in combination with other evidence, indicate that from ca. 810–645 ka, Owens was most commonly a moderately deep fresh-water lake; from ca. 645–450 ka, it was more commonly a shallow—but still fresh-water—lake; from ca. 450–5 ka, it was almost continuously a deep, mostly fresh-water lake; and after ca. 5 ka, it was a shallow, moderately saline lake. Other variations in the sediments and their contents, however, indicate additional cycles of average lake-overflow volumes that are not reflected by sediment-size changes.</p>
application/pdf
10.1130/0-8137-2317-5.9
en
Geological Society of America
Stratigraphy, lithologies, and sedimentary structures of Owens Lake core OL-92
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