A GEOPHYSICAL STUDY OF THE SUBSURFACE STRUCTURE OF THE MARFA BASIN, TRANS-PECOS TEXAS

Basin and Range/Rio Grande Rift, and to a lesser extent Laramide structures, control the topography of the Trans-Pecos region, although the area has experienced repeated deformation since the Precambrian. The basins in Trans-Pecos Texas are one key to understanding these tectonic events and are also important sources of groundwater. We are studying the hydrogeology and subsurface structure of this area utilizing gravity, magnetics, remote sensing, GIS technology, and drill hole information. Thus, we are compiling a large database of geological, geophysical, and other geospatial data. The Marfa basin initially formed in the late Paleozoic as a result of the Ouachita orogeny. However, the same general area was also a basin that collected volcanics and sediments during the Cenozoic. The area is bounded by a series of large normal faults along the Sierra Vieja to the west. Abundant fault scarps and the Valentine earthquake in 1931 attest to the continuing tectonic activity. Gravity data suggest that the Cenozoic fill thickness increases toward the north, producing a feature we call the Valentine basin that is an asymmetric graben. These data also suggest some structural continuity with the Salt Flat graben near Van Horn.