Minimum Duration of Valanginian “Weissert Event”—The First Major Perturbation of the Cretaceous Global Carbon Cycle—Constrained by New High-Precision U–Pb Dates from Terrestrial Sediments in Utah, USA

The Early Cretaceous (Valangian) double-peak positive δ13C excursion known as the “Weissert Event” (WE) appears to have been a consequence of the release of excess CO2 during voluminous flood basalt eruptions from the Gondwanan Paraná–Etendeka large igneous province (~135–132 Ma). This major global carbon-cycle perturbation likely spurred oceanic eutrophication, the deposition of marine organic matter, biotic changes, and possible enhanced silicate weathering on land. The accurate identification and in-situ dating of the WE are vital in attaining a more refined understanding of global change during the Cretaceous.

Joeckel et al (2023; https://doi.org/10.3390/geosciences13020032) produced organic δ13C chemostratigraphic profiles through the paleosol-bearing Yellow Cat Member (YCM) of the Cedar Mountain Formation near Moab, Utah. These profiles clearly manifest the characteristic double-peak excursion of the WE in comparison with multiple correlative marine records. The terrestrial δ13C shifts from the YCM exhibit higher magnitudes than multiple correlative marine records of the WE, but this kind of relationship is readily apparent in comparisons of the terrestrial and marine records of multiple Cretaceous and Paleogene CIEs.

We provide new in-situ CA-ID-TIMS ages of two paleosol cryptotephras from the same sections for which we have produced chemostratigraphic profiles in the YCM. These ages indicate that the minimum duration of the WE was ~3 m.y., effectively coeval with the Gondwanan flood basalts. The stratigraphic positions of the two paleosol cryptotephras from which we have acquired high-precision U–Pb ages correspond to the falling limbs of the lower and upper organic-carbon δ13C peaks in our composite chemostratigraphic profile.