Analysis of Lineations in the Eagle Flat Study Area, Hudspeth County, Texas

Abstract

The purpose of this study of the Eagle Flat study area, Hudspeth County, Texas, is to determine the density and orientation of lineaments as part of a characterization study of a proposed site for the Texas low-level radioactive waste repository. Because both the number and total length of lineations per unit area are low at the proposed site (north Paskin Ranch), the results of lineation analyses do not impact repository siting. The lineation study may, however, be a useful adjunct to other ongoing investigations of recharge, Quaternary faulting, geomorphology, and fissures.

The scope of this study is to examine the occurrence of lineations on aerial photographs and lineaments on Landsat imagery as they reflect topography and slopes, drainage, bedrock, soils, and geologic structure, as well as the degree to which analysis of linear elements contributes to understanding of both the geologic history of an arid area and the active geologic processes altering the ground surface. Lineations were identified on black-and-white, 1:22,000-scale, stereographic pairs of aerial photographs and transferred to 7.5-minute quadrangles, digitized, statistically analyzed (number, length, and azimuth) per unit area, and printed on maps that were hand-contoured. The study area was divided into 96 unit areas (4 mi2) for analysis. Thirty rectangular areas were selected to characterize the lineations associated with particular stratigraphic, structural, or geomorphic properties.

Histograms and scattergrams with straight-line curve-fitting of linear and geologic properties were computed to evaluate the characteristics of the lineations in the 30 selected areas. Five separate areas of Cretaceous outcrop have 26, 27, 28, 29, and 32 lineations per square mile; two Precambrian hills have 59 and 58/mi2. For straight-line curve-fitting of lineation lengths to age and type of bedrock, the R values display correlations of 0.918 to 0.982 for three Precambrian outcrop areas, 0.969 for Permian Hueco Limestone outcrop areas, and 0.886 and 0.873 in two Cretaceous outcrop areas. Azimuth R values are: 0.918, 0.950, and 0.988 (Precambrian), 0.823 (Permian), and 0.919 and 0.983 (Cretaceous). The best correlation of the number of lineations per grid and relief is 0.473, but 0.657 is the R factor of all selected slopes.

Lineations were interpreted on seven scenes of Landsat imagery containing the Eagle Flat study area. No lineations pass through or near the proposed site on Paskin Ranch; most lineations parallel structure and drainage.

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