DETRITAL ZIRCON GEOCHRONOLOGY OF PALEOZOIC TO LATE CRETACEOUS SILICICLASTIC STRATA OF THE OZARK DOME, SOUTHERN MISSOURI

Siliciclastic strata exposed in the Ozark Dome provide Late Cambrian to Late Cretaceous snapshots of an evolving paleogeography and regional to far-field tectonic events. U-Pb ages of detrital zircons from the arkosic base of the Upper Cambrian Lamotte Sandstone reflect first cycle derivation from the adjacent ca. 1.31–1.48 Ga Granite-Rhyolite province, with subsidiary input from ca. 1.6–1.7 Ga Mazatzal basement. Feldspathic arenites near the top of the Lamotte Sandstone also contain significant quantities of detrital zircon grains of these ages, with additional peaks centered at ca. 2.7 and ca. 1.1 Ga, signaling the onset of extra-regional detrital input most likely ultimately derived from the Superior Province and the midcontinent rift. Ordovician orthoquartzites of the Roubidoux, St. Peter, and Oil Creek formations feature ca. 2.7 and ca. 1.1 Ga peaks more prominently than the Lamotte Sandstone, suggesting an increasing proportion of northerly-derived, and likely reworked, detritus. A supermature sandstone, originally assigned a Pennsylvanian age, that fills a sinkhole in the Ordovician Gasconade Dolomite is reinterpreted here as Ordovician in age on the basis of petrographic and detrital zircon age similarities between this unit and the St. Peter Sandstone. Detrital zircon age spectra from Devonian (Bushberg Sandstone), Mississippian (Aux Vases Sandstone), and Cretaceous (McNairy Formation) units show a smoothly decreasing proportion of ca. 2.7 Ga grains and an increasing amount of 1.0–1.3 Ga and 500–360 Ma grains with time, marking the arrival of detritus derived from the uplifting Appalachian basement. In aggregate, detrital rocks in the Ozark Dome reflect an evolving depositional environment involving two significant provenance shifts: 1) a Cambrian–Ordovician shift from local basement- to Superior Province-derived detritus, attributed to the rise in base level associated with the Sauk transgression and/or the inversion of Proterozoic basins perched on Superior Province and midcontinent rift basement at the onset of the Taconic orogeny and 2) an Ordovician–Devonian shift to detritus sourced from the emerging Appalachian Mountains to the east. Westward transport of clastic sediment originating from the Appalachian highlands continued sporadically until at least Late Cretaceous time.