DETRITAL ZIRCON GEOCHRONOLOGY OF CHESTERIAN SANDSTONES IN THE ILLINOIS BASIN, USA

Chesterian (late Mississippian) strata mark the first appearance of significant Appalachian-derived siliciclastic sediment deposited in the Illinois Basin. Four Chesterian sandstones (n=962) were analyzed using detrital zircon geochronology. These are the Aux Vases (n=241), Cypress (n=187), Tar Springs (n=267) and Hardensburg (n=267) sandstones. K-S analysis indicates that the age spectra are statistically the same. About half of the detrital zircon age spectrum is Grenville (1000-1300 Ma) in age, with a peak age of 1042 Ma. Other easterly source areas with a strong Appalachian signature include Pan-African (620-530 Ma), Taconic (490-440 Ma), Acadian (420-350 Ma) ages. Smaller populations of zircon ages include the Midcontinent Granite-Rhyolite Province (1.5-1.3 Ga), the Yavapai and Mazatzal Provinces (1.8-1.6 Ga), Penokean and Trans-Hudson Orogens (1.9-1.8 Ga) and the Superior Province (>2.5 Ga) ages. The Archean fraction contains three zircons older than 3.6 Ga. These Chesterian sandstone are interpreted to have been deposited in marginal marine and marine environments. As the North American craton became more emergent as the Kaskaskia seas waned and tectonic activity in the Appalachian orogenic belt peaked, predominant first-cycle sediment was transported by fluvial systems more than 1000 km from the Appalachian Mountains to the Illinois Basin. This indicates that potential barriers like the Cincinnati Arch were bypassed by the sediment transport systems. The underlying Dutch Creek Sandstone has a detrital zircon age spectrum that indicates that it was derived from early Paleozoic cratonic sandstones. Overlying Pennsylvanian sandstones have similar detrital zircon age spectra to the Chesterian sandstones analyzed as part of this study.