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A Mushwad of Floyd Shale in the Appalachian Thrust Belt in Alabama, Combining the Structure of the Conasauga Gas Play with the Stratigraphy of the Floyd Gas Play

William A. Thomas
Department of Earth and Environmental Sciences, University of Kentucky, Lexington, KY

In the southern Appalachian thrust belt in Alabama, tectonically thickened, ductilely deformed duplexes (mushwads) of the Middle Cambrian shale-dominated Conasauga Formation recently have become an important shale gas objective. Meanwhile, the Upper Mississippian Floyd Shale (an approximate lithologic and temporal equivalent of the Barnett Shale) is a shale gas prospect in the Black Warrior foreland basin in northeastern Mississippi and northwestern Alabama. Within the several hundred feet of Floyd Shale (a lithostratigraphic formation dominated by dark-colored shale) in the Black Warrior basin, one interval approximately 100 feet thick is lithologically a “black shale” (informally, the Previous HitNealNext Hit shale).

The stratigraphic strike of the Previous HitNealNext Hit black shale is northwest-southeast, parallel with structural strike in the down-to-southwest Black Warrior basin in the Ouachita foreland. The northwest-striking Black Warrior basin is structurally truncated by the younger, northeast-striking Appalachian thrust belt, which imbricated the Ouachita foreland. The southeast-trending Previous HitNealNext Hit shale is imbricated at approximately right angles by Appalachian thrust faults. The projection of the trend of the Previous HitNealNext Hit shale from the Black Warrior basin into the Appalachian thrust belt is aligned with the Vandiver upper-level mushwad within the Coosa synclinorium. The Vandiver mushwad consists of a tectonically thickened, ductilely deformed, shale-dominated succession of Mississippian Floyd Shale (black and dark-gray shale) and Parkwood Formation (shale and sandstone interbeds). If the black shale (Previous HitNealTop) component of the Floyd Shale absorbed a significant proportion of the tectonic shortening and thickening in the Vandiver mushwad, then the favorable structure of the Conasauga mushwads is combined with the favorable stratigraphy of the Floyd Shale.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas