PROVENANCE ANALYSIS OF PENNSYLVANIAN SANDSTONES IN THE ILLINOIS BASIN USING DETRITAL ZIRCON GEOCHRONOLOGY

U-Pb detrital zircon (DZ) ages from Atokan and Desmoinesian sandstones (Caseyville, Bernadotte, Vermilionville, and Copperas Creek) from the Illinois Basin indicate an evolution in provenance. Three distinct DZ age populations are present in each sample. Along with these three distinct age populations a “tail” of mixed craton DZ between 1400-3000 Ma is seen on the samples probability density plots. The three distinct peaks occur at approximately 450, 600 1100 Ma. The ~1100 Ma zircons are interpreted to be derived from the Grenville basement to the east; the ~450 Ma zircons are interpreted to be Acadian-Taconic; and the 600 Ma peak is believed to be derived from a granitic pluton in the Gander Terrane. Paleogeographic reconstructions show that all three sources have fluvial pathways to the Illinois Basin during the Pennsylvanian. The lowermost Caseyville and Bernadotte sandstones have all three eastern DZ age populations along with a mixed cratonic Proterozoic-Archean DZ age population. The mixed Proterozoic-Archean population is interpreted either as recycled local early Paleozoic sandstones or from distal early Paleozoic sandstones eroded during the unroofing of the Appalachian Mountains. The Vermilionville and Copperas Creek sandstones have the same three easterly age populations as the older sandstones, but lack the mixed cratonic source. The Vermillionville and Copperas Creek Sandstones are interpreted to be derived from completely from distal Appalachian sources.