Revised Classification and Nomenclature of the Jackson Group (Eocene), South-Central Texas: GEOLOGICAL NOTES

Abstract

Recent study of exposures in deep open pits in the Karnes uranium district, and detailed mapping and exploration by boring, have shown the need for updating my earlier nomenclature of the Eocene Jackson Group in south-central Texas. The proposed changes are: 1. Recognizing the Tordilla Sandstone Member of the Whitsett Formation, an important ore-bearing unit that differs in lithologic character from, but is correlative with, the Calliham Sandstone Member southwest of the Karnes district. As the Tordilla was formerly considered a bed in the Dubose Member, the Dubose now is restricted to beds between the Tordilla and the underlying Deweesville. 2. Replacing the name Stones Switch, designating a sandstone member of the Whitsett Formation, with the name Deweesville, a change necessitated by miscorrelation of the Stones Switch with the Dilworth Sandstone Member in the early mapping of the region. 3. Lowering the base of the Whitsett Formation to the base of the Dilworth Sandstone Member, which, with the overlying Conquista Clay Member, I had previously placed in the underlying McElroy Formation. 4. Raising to formational rank the Manning Clay, formerly the basal member of the McElroy Formation, but long considered a formation in East Texas; abandoning McElroy as a stratigraphic name. End_Page 561------------------------------