ABSTRACT

A region in central east Texas outlined by a thickened Mesozoic section is described as a new feature, 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. It 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, located just north of the Cretaceous shelf edge.

Compared to the East Texas basin and Houston embayment, the Brazos basin represents a relatively under-explored region, completely lacking Jurassic production. However, thermal and subsidence histories indicate the potential for significant hydrocarbon generation and entrapments. The Brazos basin originated as a faulted 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 indices 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 subsided, 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 several types of traps that have no relationship to the basin's present structure.