Paper No. 2
Presentation Time: 1:20 PM
NEW GEOCHRONOLOGIC CONSTRAINTS ALLOW COMPARISONS BETWEEN LATE TRIASSIC BIOTA AND PALEOENVIRONMENT FROM WESTERN AND EASTERN NORTH AMERICA
Continental-scale comparisons of Late Triassic non-marine sedimentary archives have been hampered by the lack of biostratigraphically-independent age constraints. A major step forward was provided by the Newark Astronomically-calibrated Geomagnetic Polarity Time Scale (Newark APTS) from the predominantly lacustrine Newark Basin of eastern North America, which was further calibrated using high-resolution U-Pb CA-TIMS ages bracketing the Triassic-Jurassic boundary in the same sequence. In contrast, similar age control for non-marine sediments in western North America has been lacking. New U-Pb CA-TIMS ages from the fluvial Chinle Formation of Arizona and New Mexico, along with previously published magnetostratigraphic records, allow age-constrained paleoenvironmental and biotic comparisons across the North American continent for the first time. These data demonstrate that whereas the Newark Supergroup Late Triassic record extends from the Carnian to the end of the Rhaetian, the Chinle Formation is restricted to the Norian-Rhaetian. These age constraints, combined with paleogeographic data, suggest that unlike some tropical paleoequatorial eastern North America records, the western North America deposits were almost wholly between 5-15°N with a semi-arid climate, which may explain the absence of traversodont cynodont synapsids in western North America. Penecontemporaneous Norian vertebrate assemblages from eastern and western North America reveal no unambiguous overlap at the species level, and only a handful of shared taxa at the genus level, supporting previous conclusions of distinct biotic provinciality. More refined comparisons, such the examination of the potential biotic and environmental effects of the mid-Norian Manicouagan bolide impact, require sub-million year resolution. This precision is achievable through integration of the Newark APTS with the dense paleomagnetic and radioisotopic sampling of Chinle Formation strata from the recently recovered Petrified Forest National Park core of the NSF/ICDP-funded Colorado Plateau Coring Project. The resulting chronostratigraphic framework will be integrated with other terrestrial records and directly correlated with marine records in order to scrutinize causality and the spatial extent of paleoenvironmental signals.