THE WEST FALLS FORMATION, IMPLICATIONS OF PAST TECTONIC INHERITANCE

The Appalachian Foreland Basin has undergone multiple periods of orogeny and subsequent sediment deposition contains characteristics indicative of underlying basement structures. The West Falls Formation in West Virginia contains many correlative units that coincide with structures created during the Ordovician. Past research has suggested that the Rome Trough provided the necessary sediment sink to deposit the organic-rich shales and was reactivated during the Acadian Orogeny. However, there is a closer relationship between the Central West Virginia Arch blocks, than the Rome Trough.

The Angola Member is characterized as an organic-poor, silty facies that ranges in thickness from 50 to 200 feet. The Angola is restricted by the Pipe Creek shale above in the western part of West Virginia and the first Alexander Sandstone above in the eastern part of the state. The Rhinestreet Shale Member contains many highly correlative and continuous organic-rich shale facies. Mappable subsurface gamma-ray log signatures signify a changing depositional thickening and is shown within the internal stratigraphy including: 3 to 5 foot sporadic organic-rich units interbedded with siltstone/organic-poor facies at the top of the member; a continuous 40 to 60-foot thick sequence in the middle of the member that occurs across the entire western geographic region of West Virginia; and intermittent organic-rich beds coupled with intertonguing organic-poor units and/or siltstone in the lower part of the member and increases in thickness towards the paleo-geographic foredeep. Furthermore, the Rhinestreet Shale Member in the western part of the state is in contact with a major subaerial unconformity. Towards the east, a pronounced deltaic subenvironment interfingers with the organic-rich facies.

The depositional history of West Falls Formations can aid in our understanding of changing depositional patterns that may be related to tectonics or associated large- and small-scale sea-level change. Most importantly, the study of the West Falls Formation builds upon previous research focused on understanding the kinematic history of the Acadian and earlier orogenies.