SEQUENCE STRATIGRAPHY OF THE GLENSHAW FORMATION (LATE PENNSYLVANIAN) IN THE SOUTHERN DUNKARD BASIN

The Glenshaw Formation consists predominantly of sandstones and mudrocks with thin limestones and coals which are thought to have accumulated in alluvial, deltaic, and shallow marine environments. Analysis of 87 outcrops from southern Ohio, eastern Kentucky, and southern West Virginia has revealed the presence of widespread well-developed paleosols. These widespread paleosols are used along with marine units and erosional disconformities to develop a high resolution sequence statigraphic framework. The tops of these paleosols constitute boundaries for nine allocycles which are interpreted as fifth order depositional sequences. Allocycles within this framework can be correlated with similar allocycles described from northern Dunkard Basin. A sequence stratigraphic model is proposed that provides a framework for interpreting the facies architecture in terms of base level dynamics linked to relative sea level changes. Lowered base level associated with relative sea level lowstands, valley incision took place along drainage lines while sediment bypassing of interfluves led to development of well-drained paleosols. Rising base level produced valley-filling by fluvio-estuarine systems (LST/TST), while pedogenesis continued on interfluves. As drainage systems aggraded, the coastal plain water table rose interfluvial paleosols were onlapped by paludal and lacustrine deposits. Histosols succeeded and partially overprinted paleosols with vertic and calcic features. HST facies within the coastal plain consist of widely separated, high sinuosity fluvial channel and estuarine channel sandstones encased in overbank mudstones, while within marine units coarsening upward regressive deltaic and interdeltaic facies are developed. The improved stratigraphic framework provides the basis for a better understanding of the depositional systems, base level dynamics, and climatic changes that influenced the infilling of the Dunkard Basin. The paleoenvironmental and sequence stratigraphic context of channel and valley-fills may be of benefit in future exploration in the Dunkard Basin and other analogous settings.