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Bulletin of South Texas Geological Society


South Texas Geological Society Bulletin
Vol. 38 (1997), No. 4. (December), Pages 9-21

Evidence of Midtertiary Hydrovolcanism in the Texas Gulf Coastal Plain

John J. Morony, Stephen Hoog, Garry Morrison


Remnants of a maar (a volcano with the crater below ground level) are identified in Live Oak County associated with the Catahoula tuffs. The outcrops are characterized by extensive exposure of volcanic ramparts exhibiting pyroclastic surge deposits with associated hydroclastics. This surge formation caps a series of bedded tephra of vesiculated tuff interbedded with friable tuffaceous clay.

Bailey in the early 1920’s was the first geologist to attribute local volcanism for the mass of volcaniclastics comprising the Catahoula tuffs. However, as no source volcano was ever located, it was later assumed that the volcaniclastics were from a distant source, such as the Trans-Pecos volcanic province of west Texas and/or the Sierra Madre Occidental of western Mexico.

Had there been volcanism in the Gulf Coastal Plain hydrovolcanism (volcanism resulting from contact of external water and magma and may be a steam eruption [phreatic] or magmatic + water-[phreatomagmatic] would be the expected mode due to the extensive network of deep subsurface aquifers in the region. Hydrovolcanism readily explains features associated with the Catahoula tuff that are otherwise unexplainable.

The volcaniclastic material in the Catahoula tuff can be assumed to have been produced by local volcanism. Past hydrovolcanism may also explain the presence of the Wilcox geothermal corridor and origin of uranium deposits that are coextensive with the Catahoula Formation.

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