Title: Pennsylvanian deposystems and paleoclimates of the Appalachians
Abstract: Central Appalachian basin rocks indicate major changes in source areas, base level, and climate for Late Mississipian through Late Pennsylvanian time. Through time, dominant source areas change from craton and northeastern orogen to southeastern orogenic mountains. The Mississipian—Pennsylvanian uncomformity correlates with a worldwide eustatic event. Early Pennsylvanian rocks contrast markedly with underlying Mississippian Mauch Chunk redbeds in composition and texture yet the source areas and alluvial plain setting were similar. Seas transgressed northeastward during Middle and earliest Late Pennsylvanian time along axes of the Pocahontas and Dunkard basins while fluvial-dominant deltas prograded northwestward. This progradation (1) progressively extended the coastal plain, (2) provided coastal swamp environments for peat accumulation, and (3) eventually cut off the narrow seaway of Dunkard basin from the Central Interior by Late Pennsylvanian and transformed it into a large shallow freshwater lake. Redbeds, calcium carbonate concretions and gilgai paleosol structures of Late Mississippian and Late Pennsylvanian rocks suggest seasonally dry tropical climate whereas the lithologies of the earlier Pennsylvanian rocks are indications of everwet tropical climates with their quartz-rich fluvial sandstones, high quality coals, and aluminum-rich clay deposits. Streams change from predominantly bedload to suspended load generally from Early to Late Pennsylvanian, in response to changes in paleoslope gradient, distance from source area, unvegetated highland, and change from everwet to intermittently dry tropical climate. Greater dryness is suggested for increased alkaline conditions observed in paleosols, carbonates, and coal beds of Late Pennsylvanian time, but sufficiently wet to prevent evaporite deposition.
Publication Year: 1985
Publication Date: 1985-06-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 60
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