Abstract

Two contiguous Landsat TM images cover the Devil’s River and Marathon Uplifts and adjacent areas in the Val Verde Basin of Southwest Texas. Flat-lying Cretaceous carbonates at the surface mask the underlying geology over most of the area. Yet the subtle lineaments and anomalies seen on the Cretaceous surface in the images reflect the structure of the underlying Paleozoic rocks: both basement block faults and Ouachita thrusts.

Straight lineaments, which may be intermittent and subtle, persist over tens of miles and appear to track high-angle basement fractures and associated structures in the lowermost Paleozoic section.

Curved lineaments, interpreted mainly from anomalous drainage, are more continuous and appear to be the surface manifestations of Ouachita thrusts, which cut the upper Paleozoic section. The Ouachita Thrust Front, rather than being one continuous front, appears to be a series of overlapping lobes formed by imbricate thrusts.

Regional Bouguer gravity and magnetic trends support these interpretations in some areas. In others area, the correlation between features on the Cretaceous rocks at the surface and structures at depth is not obvious. In general, magnetic anomalies appear to more closely follow basement structures. Gravity values show the best correlation with the thick Permian section south of Fort Stockton and with the basement high in the western part of the Devil’s River Uplift.