Abstract: Structure and Exploration Significance of the Precambrian Basement of the Southwestern U.S.

KELLER, G. RANDY, and KATE MILLER, Department of Geological Sciences, University of Texas at El Paso, El Paso, Texas

Exploration efforts need to begin with an understanding of the Precambrian basement. Basement structures often exert considerable influence on younger features and late Proterozoic rocks can even be exploration targets themselves. We have much to learn about the basement of the southwestern U. S. because there are few outcrops and penetrations by drilling are shallow and concentrated in a few areas such as the Central Basin platform. Many seismic reflection lines in the area display reflectivity within the basement which can be readily interpreted. Some of the seismically defined layering in the basement is due to volcanic rocks, but some of it is due to Proterozoic sedimentary rocks and good source rocks of this age are known to exist in the Grand Canyon region. When combined with drilling and seismic data, gravity and magnetic data provide a cost-effective way to look at basement structure. For example, gravity data show that the reflective basement beneath the Hardeman basin is most easily interpreted to consist of relatively low density and thus porous rocks. The symmetry of the gravity anomaly crossing this inferred basin, the Wichita uplift and the Anadarko basin suggests the Proterozoic basin is nearly as deep as the 45,000 ft deep Anadarko basin. However, care should be taken to remember that all layered rocks are not sedimentary. For example, a drill hole on the Central Basin platform penetrated 15,000 ft of layered mafic intrusions in the basement. Another area where basement structure is particularly important is along the Ouachita orogenic belt which follows the Paleozoic margin of Paleo North America. Here many subthrust targets are suggested by gravity and deep seismic data because anomalies due to basins along this margin extend far to the south and southeast beneath the known Ouachita thrust front.

AAPG Search and Discovery Article #90936©1998 AAPG Southwest Section Meeting, Wichita Falls, Texas