Detrital zircon evidence for the unroofing of the northern Appalachians in early-middle Pennsylvanain sandstones of North America

We analyzed detrital zircons in Lower-Middle Pennsylvanian strata collected from seven sandstones in the Forest City Basin and seven sandstones in the Illinois Basin. In these basins, Lower-Middle Pennsylvanian strata unconformably overlie Mississippian and Devonian strata and reflect a renewed influx of detritus after a significant depositional hiatus. In the total combined dataset (n=3,106), U-Pb ages of approximately 66% of zircons match ages interpreted to be derived from the Appalachian region, including Grenville (1.3-1.0 Ga), Pan-African (530-620 Ma and 750 Ma), Taconic (440-490 Ma), Acadian (350-420 Ma), and Alleghenian (330-270 Ma) ages. Subordinate populations of grains consist of Granite-Rhyolite (1300 -1500 Ma), Yavapai and Mazatzal Terrane (1600- 1800 Ma), Penokean and Trans-Hudson orogens (1800-1900 Ma), and Superior Province (>2.0 Ga) ages. Proportions of grains matching Appalachian sources increased in the Illinois Basin from ~46% to ~79% between our stratigraphically lowest and highest samples, respectively. The Forest City Basin exhibited a similar upsection increase in Appalachian derived grains, which increased from ~52% in our stratigraphically lowest sample to ~70% in our stratigraphically highest sample. Proportions of grains from northern sources (the Canadian Shield and Penokean Province) diminished upsection as these source areas and recycled sediments containing associated grains become covered with Appalachian-derived sediments. Overall, these shifts are interpreted to reflect an increased flux of Alleghenian erosional detritus across the Laurentian craton as a result of the overfilling of the Appalachian foreland region. These results supplement our understanding of the stratigraphic and provenance records left by fluvially dominated large-scale sedimentation events that occur during the formation of supercontinents.