TRANSITION FROM SHELF MARGIN TO TRANSCONTINENTAL SEDIMENT DISPERSAL: U-PB DETRITAL-ZIRCON OFPALEOZOIC SANDSTONES IN THE SOUTHERN MIDCONTINENT

The Paleozoic sedimentary record of the southern midcontinent of North America changed from predominantly carbonates of Late Cambrian through Early Mississippian age to a more clastic-rich succession in the Pennsylvanian. In this study, we present the results of U-Pb detrital-zircon geochronology from all of the major Paleozoic sandstones intervals (Ordovician to Pennsylvanian) of the Ozark Region, southern Missouri and northern Arkansas. Results show that the detrital zircon ages from those Paleozoic sandstones include virtually all major basement provenances of the North American craton, with distributions subdivided into six groups: ~350-500, ~900-1350, ~1360-1500, ~1600-1800, ~1800-2300, and > ~2500 Ma. Regional comparison and correlation suggest the southern midcontinent experiences a major provenance shift in the Late Mississippian (Chesterian). Pre-Late Mississippian sediments are typical shelf margin deposits characterized by a single prominent Superior province peak, mainly recycled from the North American craton to the north, while post-Late Mississippian sediments show much broader age distribution with major Paleozoic, Grenville, and Midcontinent Granite and Rhyolite province peaks, mostly derived from the Appalachian orogenic belt to the east and northeast. Additionally, a substantial increase of Yavapai-Mazatzal grains within post-Late Mississippian successions suggests that contributions from Precambrian basement uplifts, potentially related to the Transcontinental Arc and/or Ancestral Rocky Mountains to the west, are needed for the marked enrichment of Late Paleoproterozoic grains. This study provides insightinto the Paleozoic paleogeographic reconstruction of Laurentia, andfurther constrains the transition from a typical continental shelf margin to atranscontinental, sediment dispersal model linking sources from a partly re-emergent Canadian Shield to the north, influx of clastics from an active Appalachian orogenic belt to the east-northeast, and unroofing of the Precambrian basement uplifts to west.