Insights Into the Stratigraphic Evolution of the Early Pennsylvanian Pocahontas Basin, Virginia

• Main Author: Grimm, Ryan P.
• Other Authors: Geosciences, Eriksson, Kenneth A., Kowalewski, Michal, Greb, Stephen F., Read, James Fredrick, Henika, William S.
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: Virginia Tech 2010
• Subjects: Sequence Stratigraphy; Seal Evaluation; Appalachian Basin; Facies Analysis; Pennsylvanian; Alleghanian Orogeny; Ice Sheet
• Online Access: http://hdl.handle.net/10919/40424; http://scholar.lib.vt.edu/theses/available/etd-12152010-225246/

Early Pennsylvanian, coal-bearing, siliciclastic strata of the Breathitt Group within the Pocahontas Basin, southwestern Virginia, define a southeasterly thickening clastic wedge deposited in continental to marginal marine environments influenced by recurring, high-magnitude relative sea-level fluctuations and low-frequency changes in tectonic loading. A robust dataset of >1200 well logs, cores and numerous outcrops allowed a unique review of the Central Appalachian lithologic record during both the Late Paleozoic Ice Age and onset of the Alleghanian Orogeny. The tropical depositional landscape produced stacked deposits of braided-fluvial channels, broad alluvial plains, tidally-influenced estuaries and small deltas. Trends in facies associations allowed development of a high-resolution sequence stratigraphic architecture based on regional flooding surfaces and bounding discontinuities. Analysis of vertical stacking patterns of lithofacies on regional cross-sections identified 15 widespread, unconformity-bounded depositional sequences with an average duration of ~80 kyr based on available geochronology. Glacioeustatic control on stratigraphic architecture is supported by corresponding sequence duration within the short-eccentricity periodicity of the Milankovitch band, as well as the magnitude and extent of rapid facies shifts, suggesting that far-a-field variations in overall Gondwanan ice-sheet size and volume impacted base-level changes in the tropical basin. The progressive increase in magnitude of transgressions, as indicated by brackish-marine ichnofacies and other faunal indicators within regional high-frequency transgressive system tracts, indicate extrabasinal trends in ice-volume and eustasy. High-frequency eustatic sequences are nested within four asymmetric composite-sequences, attributed to low-frequency variations in tectonic accommodation. Evidence for tectonic forcing on foreland-basin accommodation is based on abrupt facies shifts, angular stratal terminations and wedge-shaped ...