TECTONIC ORIGIN OF THE MISSISSIPPI RIVER USING EVIDENCE FROM THE CRETACEOUS MCNAIRY SAND

U-Pb geochronology of detrital zircons from the McNairy Sand characterizes when the Ancestral Mississippi River changed its flow direction from westward in the Early Cretaceous, progressing to southerly in the Late Cretaceous. The sediment accumulated during the reactivation of the Late Proterozoic to Early Paleozoic Reelfoot rift system at the end of the Mesozoic Era. The zircons used for this study are from southern Illinois, western Kentucky, western Tennessee, and northern Mississippi colorless, translucent, tabular to prismatic, euhedral to subhedral, subrounded to subangular, have orange and yellow iridescence and low sphericity. U-Pb ages and Th/U ratios of zircons records evidence of sedimentation driven by the tectonic activity of the Reelfoot rift system, which resulted in the topographic low for the drainage system of the Mississippi River. U-Pb ages were dominantly ~1350 - 900 Ma U-Pb ages (Grenville; 80%), and smaller populations of ~1500 - 1350 Ma (Mid Continent Granite-Rhyolite; ~8%); ~490 - 450 Ma (Taconic - Acadian; ~6%), ~900 - 500 Ma (Gondwanan Terranes; ~4%), 1800 - 1600 Ma (Yavapai Mazatzal; ~2.4%), and >2500 Ma (Wyoming-Superior provinces; ~0.002%) suggesting an Appalachian region provenance. The results support characterizing the provenance and age of deposition, clarifying the drainage patterns of the Late Cretaceous and orientation of the Ancestral Mississippi River and its tributaries. The U-Pb age signatures coupled with the Th/U ratio zircon grain results suggest two source regions that routed sediments to the Mississippi Embayment, 1. Appalachian Foreland Basin and 2. the Appalachian Piedmont region.