Pleistocene Lake Lomax: A Mystery On the Texas High Plains.

Pleistocene Lake Lomax, first named by Frye and Leonard (1964), is a low-relief depression in the Texas High Plains. Since the Tertiary Period, the western escarpment of this 140,000-ha basin has been backwearing and the eroded material aggrading as coalescing fans along its western edge.  A structurally- controlled, intermittent stream flows through the basin.  Researchers have consistently proposed many origins for similar High Plains basins.  To better understand this basin’s geologic history and its past and present climatic conditions, both clastic depositional sequences and profile characteristics of surface and buried soils were examined, sampled, and analyzed from 4 deep cores drilled to a Triassic datum and from 2 surface transects sampled within the basin. A fifth deep core was drilled on the escarpment representing a nearly complete Cenozoic rock-stratigraphic section of the High Plains stratigraphy. The presence of stacked buried soils in exposures and cores, many containing petrocalcic horizons, indicates periods of episodic landscape stability and soil formation rather than continual rates of deposition in the low-relief area. The near-surface petrocalcic horizons are likely relict and in places appear to be degrading under current climatic conditions. Basin surface sediments include colluvium from eroded Ogallala, Cretaceous, and Tertiary clastic sediments as well as down-valley redeposition of eolian and alluvial sediments. Few buried A horizons are preserved in the paleosols and many paleosols are welded. At depth, an abrupt sedimentary and geochemical boundary is marked by the loss of carbonates and rests unconformably on a clayey, red 2.5YR truncated Triassic paleosol. This paleosol contains numerous root casts and insect burrows, representing preservation of indicators from a level of biotic activity in this weathered shale paleosol greater than found in any of the overlying soil sequences.

Frye and Leonard, 1964. Texas Bureau of Economic Geology Report No.51