SEDIMENTARY DISPERSAL SYSTEMS AND DEVELOPMENT OF THE EARLY ALLEGHENIAN FORELAND BASIN: A DETRITAL ZIRCON APPROACH

The wedgetop and foredeep depozones of the Appalachian foreland basin preserve the dynamic history of orogenesis and sediment dispersal during the Alleghenian orogeny. Four samples of lower Mississippian to middle Pennsylvanian sandstone were collected from the hanging wall (n = 3) and footwall (n = 1) of the Pine Mountain thrust sheet at Pound Gap, Kentucky, the end-Alleghenian wedgetop-foredeep boundary. New paleocurrent and U-Pb detrital zircon age data were analyzed to interpret the relative influence of wedgetop and foredeep drainage systems during the transition into the Alleghenian orogeny. Lower Mississippian to lower Pennsylvanian samples are characterized by a broad age distribution dominated by Paleozoic and Grenville peaks with Pan-African/Brasiliano-, Central Plains-, Mid-Continent-, Trans-Amazonian/Eburnean-, and Superior-aged zircons. These signatures suggest primary influence of transverse drainage systems stemming from the developing hinterland, including the newly accreted Carolina terrane, and significant contribution from cratonic sediment dispersal systems. An increase in 1300-1900 Ma and 2600-2800 Ma grains in lower Mississippian to lower Pennsylvanian samples records uplift of western provinces during cratonward forebulge migration driven by hinterward crustal loading, supporting recent hypotheses of a middle Mississippian onset of the Alleghenian orogeny. Absence of 1600 Ma and older grains by middle Pennsylvanian time suggests principal sediment derivation from advancing thrust sheets carrying Grenville, Paleozoic and Pan-African/Brasiliano detritus, with further influence from uplifted Granite-Rhyolite province of the proximal forebulge. Collectively, U-Pb age peaks suggest sediment provenance shifted from equal cratonic and hinterland sources to primarily hinterland sources in the Alleghenian foreland basin system during early-middle Pennsylvanian time.