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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 13 (1963), Pages 111-117

Simsboro and Adjacent Formations Between Brazos and Trinity Rivers Texas Lithology and Clay Mineralogy(1)

Donald W. Kohls (2)

ABSTRACT

The Simsboro Formation of the Wilcox Group between the Trinity and Brazos Rivers, Texas, is characterized by white, coarse- to fine-grained, cherty, feldspathic, muscovitic sand in a white clay matrix, and minor beds and lenses of white to light-gray, silty clay. The clays and sands are of continental origin. The clay mineral suite consists of kaolinite, illite, and a very small amount of mixed layered illite-montmorillonite, whereas calcium montmorillonite is the most common clay in the overlying Calvert Bluff Formation and underlying Hooper Formation.

The Simsboro is distinct from the light- to dark-gray, carbonaceous, waxy, plastic clays of the Hooper Formation, which also contains lenses of buff, fine-grained sand, ironstone slabs, and ferruginous concretions.

It is also distinct from the Calvert Bluff Formation which is composed of interbedded, thinly laminated, buff to light-gray silt and light-gray clay; fine-grained, cherty sand, light-gray, plastic clay; lignite; and ironstone slabs and ferruginous concretions 0.5 to 5 feet in diameter.

Weathering characteristics are used to distinguish the montmorillonitic Hooper and Calvert Bluff Formations from the predominantly kaolinitic Simsboro Formation.


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