Evidence for a Deep Mesozoic Basin in Central East Texas: Implications for Petroleum Exploration

DAVIDOFF, ANDREW J., Texas A&M University, College Station, TX

A region of thickened Mesozoic sediments in central east Texas occupies a distinct basin, called the Brazos basin. The basin is approximately 120 mi (190 km) long and 50 mi (80 km) wide, extending from Houston and Trinity counties in the northeast to Austin and Fayette counties in the southwest. The Brazos basin is separated from the East Texas basin by the Houston arch, a northeast-southwest-trending positive feature located just southeast of the Elkhart-Mt. Enterprise fault zone. The southeast margin of the basin is formed by the Angelina-Grimes terrace (also known as the Angelina-Caldwell flexure), located just north of the Cretaceous shelf edge.

Compared to the East Texas basin and Houston embayment, the area occupied by the Brazos basin represents a relatively underdrilled region completely lacking Jurassic production. However, thermal and subsidence histories indicate the potential for significant hydrocarbon generation and entrapment. The Brazos basin originated as a fault half-graben in association with the rifting that opened the Gulf of Mexico. Maximum subsidence within the Brazos basin occurred during the Jurassic, and gradually diminished through the Cretaceous. Time-temperature indexes indicate that potential source rocks reached maturity during the Early Cretaceous. During this time, hydrocarbon migration over much of the basin was to the south. Starting in the Paleocene, the southern limb of the Brazos basin subsid d, causing a reversal of the northward dip of strata along the Angelina-Grimes terrace. Diagenetic seals could have prevented further migration when the region tilted south during the Tertiary, thus forming a variety of traps that have no relationship to the basin's present structure.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)