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Regional Clay Petrology of Permian Shale in Southwestern Oklahoma: Abstract
Permian strata cover an area in excess of 50,000 square miles in the western half of Oklahoma, northern Texas, and southern Kansas. These strata are about 4,000 feet thick, are essentially flat lying, and consist dominantly of shale, mudstones, siltstones, and sandstones. In addition to these terrigenous redbeds, the Blaine and Cloud Chief Formations contain on the outcrop two major evaporite units.
This study and the resulting preliminary report are directed toward the genetic relationships of this redbed-evaporite sequence. Funds for the study are from a two-year National Science Foundation Grant No. G19186 entitled, Mineralogy and Chemistry of Permian Shales in Western Oklahoma.
Samples for this preliminary report were obtained from four-inch cores supplied by the U. S. Army, Corps of Engineers. Information from the unpublished master of science thesis of Mr. A. Gordon Everett was used to supplement the core-hole data.
The framework clay mineralogy of the Wichita, Hennessey, Flowerpot, Blaine, Dog Creek, and Marlow Formations is a mixture of illite and chlorite. The intensity and width of the first-order (001) reflections suggest variations in the degree of crystallinity of the illite and chlorite.
A 7-angstrom clay mineral in the overlying Rush Springs Formation marks a significant change in the clay mineralogy. Part and perhaps all of this 7-angstrom material is a trioctahedral analogue of kaolinite. This may be related to the 7-angstrom chamosites, but a detailed study has yet to be completed.
The overlying Cloud Chief Formation contains montmorillonite as the major clay mineral. This well-crystalline montmorillonite has a widespread distribution and defines a significant change from the mineralogy of the preceding units.
The mineralogy of the Doxey Member of the Quartermaster Group is similar to that of the lower units, except the 14-angstrom material may be a vermiculite.
A source for all the clay minerals cannot as yet be accurately defined. However, the abundance of illite and chlorite in the lower Paleozoic rocks of the Ouachita Mountains area suggests a source for the illite and chlorite of the Permian strata. The polytypism (2 M) of the illite in the Permian rocks is the same as the polytypism of the illite in the Ouachita Mountains. This fact lends support to the above hypothesis. The abundance of montmorillonite in the Cloud Chief Formation suggests a source area of basic igneous rocks, possibly volcanic.
Acknowledgments and Associated Footnotes
1 Univ. of Okla., Norman
2 Univ. of Okla., Norman
3 Univ. of Okla., Norman
Copyright © 2006 by the Tulsa Geological Society