Stratigraphy and depositional environments of the Kanawha Formation (Middle Pennsylvanian), southern West Virginia, U.S.A.

Abstract

The Kanawha Formation of southern West Virginia consists of up to 620 m of lithic sandstone and mudrocks with subordinate coal and impure limestone that accumulated in a subsiding foreland basin. The formation contains 26 of the state's 62 minable coal seams. It accounts for about 43% of the coal currently produced in West Virginia. Component sedimentary facies from 46 outcrop localities reflect alluvial, paludal, lacustrine, paralic and shallow marine environments. Internal and architectural facies attributes indicate more evidence for coastal and tidal-estuarine deposition than traditional deltaic models. Evidence for tidal processes includes bipolar paleocurrents, rhythmic textures and structures, and associated biogenic structures. A new, two-part model is presented that relates facies to changing coastal morphology during transgressive-regressive cycles. Eustatic sea level changes played a major role in basin-wide development of major coal zones and marine units. Lowstandss of sea level caused incisement of fluvial channels whereas rising sea level led to expansion of tidal plains and estuaries. Shoreface retreat produced ravinement surfaces and transgressive lags that now separate coastal plain and marginal marine facies from shallow subtidal facies. Coastal progradation began during highstands after estuarine sediment sinks had filled, and may have been intensified during falling sea level.