The Devonian West Falls Formation, implications of sedimentation controlled by preexisting structures, West Virginia

Abstract

The Devonian (Frasnian) aged West Falls Formation in West Virginia contains gamma-ray signatures that have been interpreted to indicate sedimentation within a foreland (foredeep) basin. The West Falls Formation includes the Angola Member, and the underlying Rhinestreet Member. The Angola Member is an organic-poor, silty facies that ranges in thickness from 15 to 60 meters. The Rhinestreet Member gamma-ray signatures are indicative of an organic-rich shale facies and are easily recognized throughout the basin in West Virginia. One- to three- meter(s) thick organic-rich units interbedded with organic-poor siltstone facies characterize the top of the member. A continuous 12 to 18-meter thick sequence in the middle of the member occurs across the entire western geographic region of West Virginia. Organic-rich beds coupled with intertonguing organic-poor units and/or siltstone occur in the lower part of the member and increase in thickness towards the paleo-geographic foredeep and Central West Virginia Arch. Multiple orogenic periods have shaped the Appalachian Foreland Basin, and the successive depositional patterns of Devonian strata are related to underlying basement structures formed during earlier orogenies. The Rhinestreet Member of the West Falls Formation in West Virginia contains gamma signatures that spatially coincide with the Central West Virginia Arch blocks created during the Ordovician, and later reactivated in the Acadian Orogeny. Past research has suggested that the Rome Trough provided the necessary accommodation space for Devonian organic-rich shales. However, this study shows that there is closer spatial relationship between organic-rich shales and the Central West Virginia Arch blocks, as opposed to the Rome Trough.