Paper No. 327-2
Presentation Time: 1:15 PM
THE ROLE OF AN INTRACRATONIC BASIN IN TRANSCONTINENTAL SEDIMENT DISPERSAL AND RECYCLING SYSTEMS
No comprehensive geochronologic assessment of provenance in the Illinois Basin of North America currently exists. We present 1842 detrital zircon U-Pb ages from Cambrian – Cretaceous strata that suggest a reorganization of continental-scale sedimentary distribution systems throughout the Phanerozoic history of midcontinent North America. The lowermost Paleozoic strata yield predominantly ~2700 Ma U-Pb ages, indicative of a mostly Superior (northern) source. We also sampled an Upper Ordovician sandstone deposited coevally with the Taconic Orogeny, which yielded few Superior ages and an increased Grenville (950 – 1300 Ma) component. Similarly, Mississippian – Pennsylvanian strata lack Superior ages but also contain ages between ~1350 – 1800 Ma and ~350 – 500 Ma, which we interpret as originating from midcontinent basement sources (very proximal) and Appalachian (eastern) plutons, respectively. Two Cretaceous samples yield Appalachian and Grenville ages with few midcontinent basement ages. The youngest Cretaceous sample yielded less of an Appalachian signature than the older, suggesting a late Mesozoic rejuvenation of the Appalachians. We question if observed disparities in U-Pb ages among Illinois Basin strata reflect source terrane occlusion, dilution of older source terranes by the increased contribution of younger sources, multiple recycling episodes, or if paleogeography baffled transcontinental sedimentary transport. In either case, our data clearly show a fundamental change in sedimentary transport regimes of cratonic North America from Cambrian – Cretaceous time. This suggests that intracontinental sags like the Illinois Basin are potentially more dynamic than previously considered, and they played a crucial role in the Phanerozoic transcontinental sedimentary distribution systems of North America.