Mauch Chunk alluvial plain and mud-flat sediments in northern West Virginia

Regional subsurface analysis of red beds of the Mauch Chunk Group (Upper Mississippian) in northern West Virginia, using oil and gas well logs and cuttings, suggests that deposition was in alluvial-plain environments grading basinward into mud flats. Thickest net sandstone in the Mauch Chunk Group is in Barbour, Tucker, and Preston Counties in a belt 10 to 15 mi (16 to 20 km) wide striking north-northeast parallel with and just west of major fold axes of the Appalachian Plateau. This belt comprises numerous dip-oriented (west to northwest), vertically stacked, anastomosing subbelts and dendroids. Belt position reflects a gradient change from what were higher elevations on the east onto more level and tectonically stable areas of northwestern West Virginia. Lithofacies interpreted for the area include (1) channel fill-levee deposits as gray-green sandstone, siltstone, or non-red shale, and (2) flood-basin (overbank-levee) sediments as red and green shale. Streams carried a large suspended load and very fine to fine-grained sand. To the northwest, sandstone percentage decreases, and alluvial-plain fades interfinger with mud flats. Distal mud fades include laterally persistent limestone beds, and tidalchannel units with massive sandstone fill. The overall genetic aspect of Mauch Chunk stratigraphy is a general regressive facies shift to the northwest. The boundary between Mauch Chunk red beds and coarse clastic alluvial sediments of the overlying Pottsville Group reflects changes in gradient, supply, and source area relief.