Abstract

The mineralogy of the lower Claiborne Group, Eocene, Texas Coastal Plain, is not similar to the mineralogy of updip time-equivalent sandstones at the foothills of the southern Rocky Mountains--the area from which they were most likely eroded, according to traditional views based on paleocurrent information. Numerous studies conclude that the Carrizo Formation and Newby Member of the Reklaw Formation in Texas were derived from three primary source types: 1) low-rank, pelitic metamorphic rocks; 2) high-rank, pelitic metamorphic rocks; and 3) plutonic rocks. Kyanite and staurolite are the most diagnostic heavy minerals found in these Texas sands. As seen in lower Eocene sandstones at the foothills of the southern Rocky Mountains, south-central Colorado, this part of the Laramide range supplied sediments rich in granitic and gneissic debris, with epidote and garnet being the two distinctive, associated heavy minerals. Source areas which could have supplied the metamorphic minerals to the lower Claiborne sandstones in Texas are the southern Rocky Mountains of New Mexico, the Llano Uplift, the Appalachian Mountains, or the Ouachita Uplift. There are difficulties with advancing each of these source areas. In terms of depositional considerations, the Ouachita Mountains are the best choice; however, selecting the Ouachitas as a provenance necessitates proposing an area of higher grade metamorphism than has previously been described.

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