--> Abstract: Significance of Paleokarst in the Mission Canyon Formation, Southwestern Wyoming Thrust Belt, by J. L. Sieverding and P. M. Harris; #91004 (1991)

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Significance of Paleokarst in the Mission Canyon Formation, Southwestern Wyoming Thrust Belt

SIEVERDING, J. L., Chevron USA, Inc., Houston, TX, and P. M. HARRIS, Chevron Oil Field Research Company, La Habra, CA

Regional studies have shown that widespread karst was developed in Mississippian carbonates of the Madison Group (Mission Canyon equivalent) over most of Wyoming during Meramecian to early Morrowan time. The karst surface was subsequently covered by eastward-transgressive Chesterian to Morrowan siliciclastics of the Amsden Formation and equivalents. These terrigenous clastics filled solution cavities in the carbonate bedrock.

Cores from Whitney Canyon-Carter Creek field in the southwestern Wyoming thrust belt provide an opportunity to examine the Mission Canyon-Amsden contact in an area of limited surface exposures. The cores contain intensely fractured and stylolitic carbonates, but also have textures that are probable solution breccias of karst origin. These breccias consist of dolostone clasts that are commonly rounded and stained to a pinkish hue. The clasts are locally draped by reddish silt and clay coatings and are in a matrix of very fine- to medium-grained, poorly sorted quartz sandstone that sometimes contains laminae, suggestive of current deposition.

The occurrence of carbonate and siliciclastic mixing within brecciated intervals of the uppermost Mission Canyon is significant in a regional sense. Whitney Canyon-Carter Creek field is over 100 mi (160 km) west of the areas most intensively studied by others. These core observations suggest that the Mississippian karst plain and associated paleoshoreline were located considerably further west than the current interpretation, especially when thrust belt structural positions are restored. Palinspastic restoration of a published regional cross section places Whitney Canyon-Carter Creek field paleogeographically 28 mi (45.5 km) west of its present location.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)