LATE PALEOZOIC SEDIMENT DISPERSAL ACROSS LAURENTIA THROUGH DETRITAL ZIRCON U-PB GEOCHRONOLOGY (Invited Presentation)

Sediment dispersal across Laurentia triggered by the Alleghanian-Ouachita-Marathon Orogeny during the late Paleozoic was influenced by spatially and temporally complex landscapes developed by episodic flooding of the continent. Bill Thomas was known for addressing these issues through detailed stratigraphic field studies, data integration and synthesis, big-picture thinking, and adopting cutting edge approaches. Early on, large-scale systems of drainage and sediment dispersal were proposed for the late Paleozoic on the basis of regional stratigraphy and sedimentary petrology. With the dawn of detrital zircon U-Pb geochronology, Bill and his students were some of the first to resolve the detailed provenance of Pennsylvanian-Permian strata in the Appalachian clastic wedge. After detrital zircon data from Paleozoic strata exposed in the Grand Canyon identified potential transcontinental sediment transport from the Appalachian margin, Bill recognized the importance of critical analysis of dispersal systems across the continent to link together sediment dispersal among the intracratonic basins between the Appalachians and the southwestern United States. He along with many others spent the next decade developing and synthesizing datasets in order to test the transcontinental transport hypothesis and elucidate the nuances of this large-scale, long-lived sediment dispersal system. In the eastern mid-continent, the detrital-zircon age distributions of Mississippian–Pennsylvanian sandstones in the Michigan, Illinois, and Forest City basins match well with the signature of late Paleozoic sandstones in the Appalachian basin, suggesting a provenance in the Alleghanian orogen and cratonward dispersal of sediment. A more unique source from Gondwanan terranes in the northern Appalachians may have supplied sediment to the northern fringes of both the Illinois and Forest City basins, but that system did not enter the Michigan basin. Sediment transport may not have extended beyond the Michigan basin to any of the other intracratonic basins; drainage systems in the Forest City basin often appear to have ended in deltaic facies within the basin although some may have continued southwest at lowstand; whereas drainage systems in the Illinois basin sometimes extended through the basin and out to the southwest.