STRUCTURAL FEATURES WITHIN SLIDES AND DEBRIS FLOWS OF THE MORGANTOWN SANDSTONE, EASTERN MARGIN OF THE APPALACHIAN PLATEAU, WESTERN PENNSYLVANIA

The Morgantown Sandstone of the Casselman Formation (Conemaugh Group) of western Pennsylvania has traditionally been classified as a fluvial channel deposit. Recently recognized distinctive structures at multiple outcrops suggest that lithified and semi-lithified sandstone bodies moved as gravity driven slides and debris flows.

An outcrop of Morgantown Sandstone along US-22 W and US-119 N near Blairsville, PA in Indiana County, which lies at the western margin of the northeast trending Chestnut Ridge, within the Appalachian Plateau records features similar to those documented in the Greater Pittsburgh Region. It is the easternmost known exposure of the distinctive style of deformation that marks the base of the Morgantown Sandstone. The approximately 300-meter exposure has been mapped by Coughenour and Hawk (2016) who interpreted the outcrop as recording a complex of fluvial deposits, which they interpret as representing strong periodic fluxes of sediment that may be a function of proximity to sediment sources, tectonic forcing or dry climate (or some combination thereof).

Mapping reveals a matrix supported conglomerate near the base of the outcrop with sandstone clasts in a sandy matrix and discontinuous beds of sandstone that record strong planar fabric with locally developed tight to isoclinal folds. Lenses of medium-gray fine-sandstone to mudstone that record chaotic layering and tan sandstone beds commonly cross-bedded are also present. These units are overlain by medium-bedded sandstone and yet higher boulder conglomerate, which is matrix-supported and locally contains clasts of platy fine-grained sandstone in a sandy matrix.

Based on structures documented at outcrops of the Morgantown Sandstone, we suggest deposition of sand into a foreland basin by slides, sand and debris flows accompanied by fluvial processes. This work will contribute to the geologic understanding of the depositional processes during uplift of mountain belts.