Controls of Alluvial Stratigraphy in the Upper Pennsylvanian-Lower Permian Dunkard Basin

DOMINIC, DAVID F., Wright State University, Dayton, OH

The Casselman, Pittsburgh, and Waynesburg formations exposed in northern West Virginia were deposited within a foreland basin adjacent to the Alleghenian fold and thrust belt. Sandstones were deposited in fluvial channels on an aggrading and prograding coastal plain. However, unlike mid-continental cyclothems, these channels were isolated from eustatic changes because previous delta progradation had blocked circulation between the local depositional basin and the larger mid-continental sea. Thus, eustatic changes had no direct or strong influence on Dunkard basin deposition, a conclusion supported by interbasinal correlation. Also, climate was largely stable during this interval. The evolution of channel properties, therefore, most likely reflects the influence of intrabasinal control and possibly tectonism.

Detailed correlation indicates that coeval channel belts were separated by about 50 km with an intervening area of slower subsidence and deposition. Quantitative reconstruction of bankfull hydraulics and geometry indicates that channels were of moderate sinuosity, were not braided, and were of two distinct sizes (average widths, 80 and 250 m, respectively). An overall decrease in discharge in the smaller channels throughout the studied interval may be attributed to a slowing of subsidence rates as the locus of sedimentation prograded beyond the northwestern margin of the Rome Trough or to thrustward migration of a forebulge following episodic thrusting. The increase in size and discharge of channels in the uppermost Waynesburg Formation is attributed to progradation of the upper fluvi l-deltaic plain over the lower fluvial-deltaic plain, a progradation that may likewise have been promoted by thrusting.

AAPG Search and Discovery Article #91005 © 1991 Eastern Section Meeting, Pittsburgh, Pennsylvania, September 8-10, 1991 (2009)