Department of Geology, Marshall University, Huntington, West Virginia, U.S.A.
The Glenshaw Formation consists predominantly of sandstones and mud-rocks with thin limestones and coals, which are thought to have accumulated in alluvial, deltaic, and shallow-marine environments. Analysis of 87 Glenshaw outcrops from southern Ohio, eastern Kentucky, and southern West Virginia has revealed widespread, well-developed paleosols. These paleosols are used, along with marine units and erosional disconformities, to develop a high-resolution sequence-statigraphic framework. The tops of the paleosols constitute boundaries for nine allocycles, which are interpreted as fifth-order depositional sequences. Allocycles in this framework correlate with similar allocycles described from the northern Appalachian basin.
A sequence-stratigraphic model is proposed that provides a framework for interpreting facies architecture in terms of base-level dynamics linked to relative sea level changes. Lowered base level caused valley incision along drainage lines and sediment bypassing of interfluves, which led to development of well-drained paleosols. Rising base level produced valley filling by fluvioestuarine systems (lowstand systems tract/transgressive systems tract), whereas pedogenesis continued on interfluves. As drainage systems aggraded, the coastal plain water table rose, and interfluvial paleosols were onlapped by paludal and lacustrine deposits. Histosols succeeded and partially overprinted paleosols with vertic and calcic features. High-stand systems tract (HST) facies in the coastal plain consist of widely separated, high-sinuosity fluvial channel and estuarine channel sandstones encased in over-bank mudstones, whereas within marine units, HST facies with coarsening-upward regressive deltaic and interdeltaic facies are developed.
The sequence-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 central Appalachian basin. The paleoenviron-mental and sequence-stratigraphic context of channel and valley fills may benefit future petroleum exploration in the Appalachian basin and other analogous settings.