CONTINUING INVESTIGATION OF A HIGH-RESOLUTION DATE-CONSTRAINED RECORD OF THE VALANGINIAN CARBON ISOTOPE EXCURSION OR "WEISSERT EVENT" IN TERRESTRIAL SEDIMENTS OF THE YELLOW CAT MEMBER IN UTAH, USA

There is general agreement that the earliest Cretaceous record of a major perturbation of the global carbon cycle is in the Upper Valanginian, and that it was linked to the activation of the Gondwanan Paraná-Etendeka large igneous province (PELIP) at ~135–132 Ma. Optimally, this perturbation appears in published (predominantly marine) chemostratigraphic profiles as a distinctive double-peak positive δ¹³C excursion, which is frequently referred to as the “Weissert Event” (WE). We have identified the WE in two nearby SOM δ¹³C chemostratigraphic profiles (values ranging between approx.−30‰ and −23.5‰ VPDB) through the Yellow Cat Member (YCM), a “time-rich” mudstone-dominated and pedogenically altered part of the Cedar Mountain Formation, in the Poison Strip of Utah. We have also produced two high-resolution CA-ID-TIMS U-Pb ages from each of two paleosol cryptotephras in the same well-constrained stratigraphic interval. These high-resolution ages constrain the falling limbs of the lower and upper organic δ¹³C peaks of the WE (Joeckel et al., 2023; https://doi.org/10.3390/geosciences13020032); furthermore, they correspond to the timing of eruptions in the PELIP. We observe that δ¹³C values in the YCM attributable to the WE clearly exhibit greater magnitudes than multiple correlative marine records of the WE, but this kind of relationship, as well as a generally greater magnitude of δ13C excursions themselves, is readily apparent in comparisons of the terrestrial and marine records of other Cretaceous examples (e.g., OAE-1a, -1b, and C15) and in the Paleocene–Eocene Thermal Maximum. The reasons for this difference in magnitude between marine and correlative terrestrial δ¹³C excursions are arguable. A viable interpretation, however, is that the terrestrial records more accurately record the magnitude of concurrent paleoatmospheric changes in carbon isotopes. We have produced a composite chemostratigraphic section from our two nearby stratigraphic sections using a common stratigraphic datum. In doing so, we show an even more complete view of the intricate structure of the WE that emerges from the terrestrial chemostratigraphic record of the YCM.