Depositional and diagenetic processes in the formation of the Eocene Jackson Group bentonites, Gonzales County, Texas


Depositional and diagenetic processes in the formation of the Eocene Jackson Group bentonites, Gonzales County, Texas

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dc.contributor.advisor Kyle, J. Richard
dc.creator Michaelides, Michael Nicholas 2012-02-17T18:51:18Z 2012-02-17T18:51:18Z 2011-12 2012-02-17 December 2011
dc.description.abstract Bentonite clays are exposed in Paleogene strata stretching over 650 km parallel to the Texas coastline. This study focuses on a white and blue and a yellow and brown commercial Ca-montmorillonite bentonite near the city of Gonzales, Gonzales county, Texas. The deposits have stratigraphic ages of Late Eocene (~36.7 - 32.7 Ma). The bentonites in these deposits have varying colors, purities and brightness affording them diverse industrial uses. The distribution and geologic character of the high purity white and blue bentonite suggests that the deposit represents an accumulation of volcanic ash in a secondary tidal channel during the ash-fall event. A low rate of terrigenous clastic sedimentation and rapid accumulation of fresh ash were critical to the formation of high purity clay. The lower purity yellow and brown bentonites appear to have a fluvial origin marked by higher rates of detrital sedimentation and episodic accumulation of clay and ash. The bentonite and associated strata were studied using optical microscopy, SEM, XRD and REE analyses to constrain their textural, mineralogic, and chemical character. vii Eocene pyroclastic volcanism is well documented from sources in southwestern North America, specifically in the Sierra Madre Occidental (Mexico), Trans-Pecos (Texas) and Mogollan-Datil (New Mexico) volcanic fields. Projected Eocene wind patterns support this region as a potential source for the Gonzales bentonites. A comparison of the trace and REE fingerprints of the white and blue bentonites and the yellow and brown bentonites with data available for Late Eocene volcanics in the North American Volcanic Database provides a couple of potential matches. The strongest potential match for the Late Eocene bentonite protolith is described as a sample of silicic tuff with an age range of 32.2 – 30.6 Ma, located in the southern Mexican state of Oaxaca. While the trace and REE match is strong, the tuff is somewhat young compared to the Jackson Group sediments. In addition, the sample location is due almost directly south of the Gonzales deposits, rather than the western location expected for a Gonzales bentonite source. The other potential matches are located in New Mexico, and the Mexican state of Chihuahua. These potential matches only have 6 REE available for comparison, and require further investigation. Many Paleogene volcanic units in southern North America are undocumented with regard to REE data or precise absolute ages. As additional geochemical analyses become available for a more extensive suite of Paleogene volcanic units, stronger matches with Gulf of Mexico Basin bentonites are expected to emerge.
dc.format.mimetype application/pdf
dc.language.iso eng
dc.subject Bentonite clay
dc.subject Alteration
dc.subject Rare Earth Elements
dc.subject REE
dc.subject Gulf Coast
dc.subject Texas
dc.subject Gonzales County
dc.subject Tephrachronology
dc.subject Trace elements
dc.subject Fractionation
dc.subject Depositional
dc.subject Diagenetic
dc.subject Eocene
dc.subject Oaxaca
dc.subject Ca-montmorillonite
dc.subject Jackson Group
dc.title Depositional and diagenetic processes in the formation of the Eocene Jackson Group bentonites, Gonzales County, Texas 2012-02-17T18:51:49Z
dc.identifier.slug 2152/ETD-UT-2011-12-4790
dc.contributor.committeeMember Gardner, James
dc.contributor.committeeMember Heister, Lara
dc.contributor.committeeMember Serenko, Thomas
dc.description.department Geological Sciences
dc.type.genre thesis
dc.type.material text Geological Sciences Geological Sciences University of Texas at Austin Masters Master of Science in Geological Sciences

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