Integrated astrochronology, isotope and biostratigraphy of the Albian-Cenomanian transition and expression of the OAE 1d in an expanded record of a rapidly subsiding Tethyan synorogenic basin (Core Jásd-42, Transdanubian Range, Hungary)

The OAE 1d is one of the oceanic anoxic events that punctuate the Cretaceous and represent Earth system-wide changes prominently captured by carbon isotope excursions (CIE). Although the positive CIE near the Albian/Cenomanian boundary (ACB) is known from multiple localities, many of these records disagree in the shape of the δ13C curve. Interpretations of OAE 1d and a broader ACB Event (ACBE) remain ambiguous, and their duration is insufficiently constrained. Here we present new analyses on high-resolution samples from Core Jásd-42. The >450 m thick Pénzeskút Marl Fm. provides an expanded record across the ACBE. We generated elemental and stable isotope geochemical data and used these time series for cyclostratigraphic analyses. The derived astrochronologic age model establishes a depositional duration of 4.4–4.83 Myr and is integrated with ammonite and planktonic foraminifera biostratigraphy. This high-resolution chemostratigraphy provides a new, calibrated record of OAE 1d and the ACBE that we correlate with other reference sections, including the GSSP. A minimum estimate of 1.23 Myr and 2.28 Myr is obtained for OAE 1d and the ACBE, respectively. For the latter, a minimum of 602 kyr is assigned to the rising limb, 748 kyr to the culminating interval, and 931 kyr to the falling limb in the δ13Ccarb curve. The δ13C record through OAE 1d appears orbitally controlled, where the positive peaks are paced by long eccentricity. Considering the differences between seasonality extremes, we suggest a model for depositional cyclicity in a synorogenic basin with a high sedimentation rate of 9–15 cm/kyr.