DAVIS, FITZHUGH D., Utah Geological Survey, Salt Lake City, UT, and CHARLES G. OVIATT, Kansas State University, Manhattan, KS

ABSTRACT: Pliocene-Pleistocene Lake Beds in the Sevier Basin, Utah

Deposits of a large, probably intermittent, Pliocene-Pleistocene lake have been mapped in the Sevier and Black Rock deserts of western Utah. These lacustrine sediments are at the top of a thick (approximately 3350 m) Tertiary fill in the Sevier basin.

The nearshore facies of the Pliocene-Pleistocene lake consist of interbedded light-gray, sandy limestone and calcareous sandstone with local, thin, well-indurated lenses of conglomerate. Exposed thicknesses range to 13 m. The deep-water facies consist of interbedded brown, brownish-red, and light olive-gray calcareous silty clay, silt, and sandy silt in thin beds. Exposures range to about 10 m in thickness. Basalt flows and tephra layers interbedded with the lake strata provide chronometric control. These include the 2.45 Ma Cudahy Mine(?) tephra, basalt flows dated at 2.6 and 1.0 Ma, the 2.02 Ma Huckleberry Ridge ash, and the 0.74 Ma Bishop ash. Unconformities in the section, although likely, have not been identified. Late Pleistocene Lake Bonneville deposits overlie the Pliocene-Ple stocene lacustrine beds in many places. The Pliocene-Pleistocene lacustrine beds overlie Tertiary alluvium exposed at the south edge of the Sevier basin.

A sample of the deep-water facies collected 15 cm below the Bishop ash contained the following ostracode species: Limnocythere staplini, L. platyforma, Candona patzcuaro, C. caudata, C. acuminata(?), Cypridopsis vidua, and Cyprideis beaconensis. This fauna suggests that the lake water was fresh.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.