REFINED TEMPORAL CONSTRAINTS FOR THE TRACE CREEK SHALE MEMBER, ATOKA FORMATION, WITH IMPLICATIONS FOR REGIONAL AND GLOBAL STRATIGRAPHIC CORRELATIONS OF CARBONIFEROUS CYCLICITY

Icehouse climates comprise an abbreviated portion of Earth history, ca. 25% over the last billion years, but have a profound impact on biogeochemical cycling, sea water chemistry, the distribution and occurrence of mineral resources, and the evolution of continental crust and biota. The Carboniferous period was the apex of Earth’s penultimate icehouse, the late Paleozoic ice age (LPIA). High-frequency base-level shifts are well documented across the late Paleozoic Laurentian continent, which characterize the far-field response to a dynamic high-latitude glaciation. Current temporal constraints for this period are limited to eastern European and Eurasian basins in present day Ukraine and Russia. Very limited high-resolution U-Pb zircon age control exists for the Carboniferous and Permian age North American record and correlations using biostratigraphic approaches are inconclusive and untested. Here we report new U-Pb zircon and Hf-isotope data from a volcaniclastic deposit hosted within Trace Creek Shale of the Atoka Fm, which was identified from a newly drilled core in the Arkoma Basin of Arkansas. Preliminary LA-ICP-MS zircon analysis confirms a volcaniclastic origin, with a distinct Bashkirian-Moscovian age peak and an evolved Hf isotopic composition with a Grenvillian age crustal source. The volcaniclastic unit is hosted within a thick (~20 m) regionally correlative black shale interval deposited above a flooding surface. Importantly, we observe multiple high frequency base-level changes throughout the 138-m-thick cored interval across the Atokan-Morrowan stage boundary, which we interpret as glacioeustatically forced. The new U-Pb age data for the Trace Creek Shale Member also provide an upper age constraint to the onset of middle Atokan growth faulting within the Arkoma Basin. High-resolution U-Pb CA-TIMS analysis and ⁴⁰Ar/³⁹Ar geochronology of the ash deposit are ongoing to test the possible correlation between this newly discovered volcaniclastic unit with the Fire Clay tonstein of the Appalachian Basin.