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Houston Geological Society Bulletin


Houston Geological Society Bulletin, Volume 51, No. 09, May, 2009. Pages 37 and 39.

Abstract: Mid-Tertiary Volcanism in the Gulf of Mexico Coastal Plains: Origin of the Catahoula Tuffs Reconsidered

John J. Morony

The Oligocene Catahoula Formation is currently believed to be a product of exclusively exogenic processes principally fluvial in nature. All volcaniclastics of the Catahoula, of whatever age (Eocene to Miocene), size (fine ash to boulders), chemistry (basalt to rhyolite), variety (accretionary lapilli to mud flow tuffs), location (Mexico to Alabama) or magnitude of deposition (up to 1,000 feet thick), are assumed to be derived exclusively from a distant volcanic provenance: the Trans-Pecos or the Sierra Madre Occidental or both.

However, Thomas L. Bailey’s long-forgotten 1924 hypothesis— that the Catahoula Formation is a consequence of local volcanism, and thus constitutes a volcanic terrain rather than a sedimentar y formation, needs to be revisited. In 1977, a massive igneous intrusion was identified subjacent to Catahoula volcaniclastics in Live Oak and McMullen Counties, Texas where surface remains of tuff rings have recently been identified. These discoveries provide conclusive evidence of past endogenic forces in the region. Likewise,

Pyroclastic surge deposit, Catahoula tuff, along US 281, 7.5 miles N of Three Rivers, Texas. Previously identified as an ash-fall originating from the Trans-Pecos and/or the Sierra Madre Occidental.

Chalk bluffs, McMullen County, Texas. These exposures are identified as the fragmented remains of ramparts of tuff rings; a consequence of hydrovolcanism. The prevailing opinion is that they are simply accumulation of reworked air-fall deposits that originated in the Sierra Madre Occidental.

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the igneous intrusion may be the heat source for the adjacent Wilcox geothermal corridor. Subsequent circulation of hydrothermal fluids accompanying hydrovolcanism provides a plausible explanation for the origins of the uranium deposits currently believed to have been ash-expressed from the Sierra Madre Occidental a thousand kilometers distant. The breeching of the basement rock is suggested to have been along the hinge line of the thick and thin transitional crusts in close proximity to the Stuart City Trend and coeval with and possible tectonically related to plate movements to the west and northwest.

Rejection of a valid scientific hypothesis, as presented by Bailey, coupled with non-recognition of the rules of Previous HitparsimonyTop (Occam’s razor), customarily employed in scientific expositions, has obscured an understanding of the geology of the Gulf Coastal Plain. If the Catahoula volcaniclastics are other than local in origin one must ask—what is the geological evidence?

Walls of the Sickenious uranium quarry, Karnes County, Texas. Pyroclastic surge deposits in a marine environment surmounted by a bed of lignite subsequently subject to liquefaction. Subsidence was followed by additional marine deposits.

Ramparts of a tuff ring in the wall of the Stoelje uranium quarry, Karnes County, Texas. The lower bed is tuffaceous clay, interspersed with accretionary lapili that was wet at the time the next pyroclastic surge was deposited on top resulting in soft sediment deformation of both. “Hydroplastic slickenslide” can be found on the upper surface of the clay in response to gravitational instability resulting from syndepositional sliding or shifting of the upper bed. The high heat of the latter surge deposit served to bake the upper portion of the underlying tuffaceous clay.

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