U-PB DETRITAL ZIRCON SIGNATURE OF THE CARBONIFEROUS DEEP-WATER CLASTIC DEPOSITS IN THE OUACHITA MOUNTAINS AND ITS IMPLICATIONS

The southern margin of the North American continent transformed from a passive margin to an active margin during the Ouachita orogeny. Thick and near–continuous Paleozoic successions in the Ouachita Mountains provide a unique opportunity to document changes in both sedimentation and tectonics. In this study, a total of six outcrop samples (n=617) from the Mississippian Stanley Group and Lower-Middle Pennsylvanian Jackfork and Johns Valley Groups were collected and processed for U-Pb detrital zircon geochronology, aiming to depict sediment sources and dispersal patterns during the Ouachita orogeny.

Compilation and comparison of coeval strata show that the Carboniferous deep-water clastic deposits share great similarities in age distributions and were mainly recycled from the Appalachian orogenic belt and associated foreland strata to the east and northeast with minor contributions from local sources to the south and northwest. Enrichment of Neoproterozoic age populations (~550-800 Ma) within the Mississippian Stanley Group (up to 35%) are interpreted as a local contribution originating from the peri-Gondwana terrane to the south. This southerly derived sediment source was short-lived and likely blocked by the formation of the Ouachita Mountains acting as a topographic barrier. The Pennsylvanian Jackfork and Johns Valley Groups show a marked enrichment of a Paleozoic age population (up to 25%), most likely associated with Appalachian sources to the northeast. Similarities between Lower-Pennsylvanian conglomerates within the Appalachian foreland and the Lower-Pennsylvanian strata from this study possibly suggest sediment was transported from the central and southern Appalachian forelands to the Ouachita Mountains. From the Mississippian Stanley Group to the Pennsylvanian Jackfork and Johns Valley Groups, the marked increase of Yavapai-Mazatzal population (up to ~12%) suggest basement cored uplifts within Laurentian craton were another potential source. Overall, despite its proximal location, these Carboniferous deep-water clastic deposits in the Ouachita Mountains received limited contribution from the Ouachita orogenic belt itself.