Sequence Stratigraphy of Upper Mississippian Strata in the Central Appalachians: A Record of Glacioeustasy and Tectonoeustasy in a Foreland Basin Setting

The Upper Mississippian Hinton, Princeton, and Bluestone formations of southern West Virginia constitute a westwardly thinning wedge of strata that filled the central Appalachian basin over a ~7 million year time interval. Up to 17 unconformity bounded, transgressiveregressive sequences comprise the study interval in the basin depocenter. Five sequence types are recognized based upon the degree of basal incision, the overall thickness, and the character of the dominant facies. These are: 1) major incised valley-fill to coastal plain, 2) major incised valley-fill to deltaic, 3) minor incised valley-fill, 4) coastal plain, and 5) marine-dominated sequences. Sequence development is ascribed to fourth-order (~400 k.y.) glacioeustatic cycles that reflect climatic change associated with variations in orbital eccentricity during the early stages of the Permo-Carboniferous Gondwanan glaciation. The cyclic character of the Upper Mississippian stratigraphic record is comparable to Pennsylvanian cyclothems in the Appalachian and Interior basins. The fourth-order sequences stack into two third-order (2-4 million year) composite sequences that are bounded by regional unconformities. Each composite sequence consists of: 1) a basal retrogradational interval comprised of a major paleovalley-fill sequence overlain by a thick aggradational sequence set of fluvial/ coastal plain sequences that together constitute the transgressive systems tract; 2) a marine interval that demarcates maximum flooding; and 3)(where preserved) a progradational sequence set consisting of minor incised valley-fill sequences that comprise the highstand systems tract. The third-order sequences document longterm changes in accommodation that are ascribed to tectonically driven eustasy.