DETRITAL ZIRCON U-PB DATA FOR PENNSYLVANIAN SANDSTONES FROM THE EASTERN SHELF OF THE PERMIAN BASIN - INSIGHTS INTO SYN-COLLISIONAL OUACHITA SEDIMENT PROVENANCE AND SEDIMENT ROUTING SYSTEMS

The Fort Worth and Permian Basins of central and southwest Texas are part of the Ouachita flexural foreland basin that developed along the southern margin of Laurentia in late Paleozoic times. Significant uncertainty surrounds sediment provenance of Pennsylvanian syn-orogenic strata, paleo-drainage evolution, and sediment routing system during progressive Ouachita collision. In particular, the existence of an Alleghanian axial drainage system versus a transverse sediment delivery system from the Ouachita orogenic belt and Gondwana hinterland remains debated. This study presents new zircon U-Pb data from sandstone samples from the Eastern Shelf of the Permian Basin, spanning Atokan Smithwick, Desmoinesian Strawn, and Virgilian Lower Cisco sandstones exposed along the NW margin of the Precambrian Llano Uplift. The data exhibit consistent detrital zircon U-Pb spectra dominated by Grenville and late Neoproterozoic, and minor Carboniferous, Ordovician, Cambrian, Meso- and Paleoproterozoic, and Archean age components. The observed DZ U-Pb signatures are in stark contrast to typical Alleghanian spectra, dominated by >1 Ga and Ordovician zircon ages, strongly arguing against major input via a regional axial sediment routing system. In particular, the presence of 320-350 Ma zircons, likely sourced from the pre-collisional magmatic arc, prominent Neoproterozoic, and 930 Ma age peaks imply sourcing from the Ouachita hinterland and tapping into Gondwana and Oaxaquian source terranes and therefore a transverse syn-collisional sediment routing system. Interestingly, the age-equivalent Pennsylvanian Haymond Fm. in the Marathon area shows identical DZ U-Pb signatures, suggesting a possible axial connection to the Eastern Shelf or tapping into similar orogenic hinterland source terranes. Up-section in the Lower Cisco Group exhibits more Cambrian DZ ages pointing to possible a linkage to northern source in the S Oklahoma aulacogen. In summary, the consistent and cosmopolitan detrital zircon U-Pb age signatures of Pennsylvanian syn-orogenic strata in central Texas argue for a persistent and dominant sediment delivery system to the southeastern Permian Basin via the Eastern Shelf directly from the Gondwanan orogenic hinterland as well as a possible axial linkage the incipient Marathon foreland basin.

Key Words: Detrital zircon, geochronology, Pennsylvanian, Eastern Shelf, Permian Basin