Stratigraphy of a Playa-Lake Deposit Within the Proposed Alignment of the Amarillo-Area Superconducting Super Collider

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Date

1987

Authors

Caran, S. Christopher

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Abstract

A limited investigation of playa-lake stratigraphy was conducted at a small unnamed playa approximately one mile northeast of Nazareth, Castro County, Texas (figs. 1, 2). This work was done in support of a study of the proposed Amarillo-area site for the Superconducting Super Collider (SSC) and is intended to complement discussion of the areal geology of the Amarillo-area site by Raney and others (1987).

Three shallow boreholes (B6, B6A, and B6B) were drilled in the northeastern quadrant of the playa (fig. 1 inset). Borehole B6 was drilled near the center of the playa basin, B6A approximately half the playa radius to the northeast, and B6B farther northeast, just outside the playa margin. The three boreholes are aligned along a directional azimuth of N68E. Core was collected from each of the boreholes using Shelby tubes. The depth of all three was approximately 70 ft. The playa contained standing water at the time of coring; equipment access was afforded by a narrow levee road constructed across the playa floor. Boreholes B6 and B6A were drilled through the road fill.

Playa deposits are among the most common late Cenozoic stratigraphic units in the Southern High Plains (fig. 2). The number of playas in the Southern and Central High Plains of Texas may exceed 37,000 (Schwiesow, 1965). Several playas are located near the proposed alignment of the Amarillo-area SSC (fig. 2). Despite their large collective areal extent and a long history of scientific interest in playas in general, the age and origin of deposits filling playa basins in this region remain highly controversial (see brief discussion by Raney and others, 1987).

Playas are ephemeral lakes; their deposits typically include a mix of lacustrine and eolian sediments. Lacustrine silty clay and eolian fine sandy silt deposits of varying thickness are found in playas throughout the study area. Although the composition of playa deposits has been reasonably well characterized, the mechanisms by which their associated basins form and are maintained are not fully understood. At many sites, modern playa basins are inset into older lacustrine deposits, indicating possible genetic cyclicity. A variety of mechanisms may be involved in creating and maintaining playas as a group, and many individual playas may be polygenetic.

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