Small-scale imagery: a useful tool for mapping geological features in the Texas Gulf Coastal Plain.
Imagery taken from altitudes of 150 to 500 km with high-resolution cameras offers the exploration geologists a reconnaissance tool at a new scale and very reasonable costs. Most of the United States and portions of the rest of the world have been imaged recently by NASA spacecraft. In addition, large portions of the United States have been photographed by NASA aircraft from altitudes of 15 to 18 km. A sample of this imagery includes photographs and multispectral scanner imagery from the Apollo, LANDSAT, and Skylab spacecraft over an area west of Houston, Texas. Large circular features and lineaments can readily be mapped. One of the circular features identified by drainage, vegetation, and soil-tone anomalies, occurs in Fort Bend County, Texas, and covers an area about 25 miles in diameters. Another circular feature lies to the north, immediately west of Houston, and is about 15 miles in diameter. These features may represent the surface expression of deeply-buried positive structures. A photolinear expressed in drainage and vegetation patterns extends from Matagorda on the Gulf Coast toward the north along the Colorado, Brazos, and Navasota Rivers. This lineament and others possibly mark surface traces of old, deep-seated fractures that would extend approximately at right angles to the coastline and to mapped growth faults. The geologic causes, if any, for the very large photo anomalies have not been determined, but similar, smaller photo anomalies can be identified as the surface traces of geological structures. Photolinears are readily mapped on small-scale, color-infrared, aerial photographs in the Houston area. Some of these linears coincide with surface traces of previously-known, active faults. Others coincide with faults mapped during this investigation.