Increasing seasonality at the Early Danian Dan-C2 hyperthermal: A case study from the Boltysh impact crater, Ukraine

Past negative carbon isotope excursions (CIEs) are understood to have caused major environmental and ecological disturbances, including rapid increases in global mean temperature, mass extinction, and ocean acidification. Additionally, various marginal marine and terrestrial sites from the Paleocene-Eocene Thermal Maximum, Eocene Thermal Maximum 2, and Toarcian Oceanic Anoxic Event indicate an amplification in seasonality and storm activity.

Here, we present borehole data from the K/Pg Boltysh meteorite impact crater, Ukraine, which contain ~400 m of Early Danian lacustrine sedimentary rocks. Carbon isotope data suggest that this succession was deposited prior and across the Dan-C2 hyperthermal. In this study, we examine the sedimentological rock record to assess climate change and potential changes in seasonality during Early Danian warming.

Facies analysis of the Boltysh borehole indicates a more pronounced variability in sediment supply, lake facies, stratification and water chemistry prior to and across the onset of the CIE. This is supported by regular moisture availability oscillations inferred from palynological examinations. The data present suggest that the Dan-C2 hyperthermal was associated with phases of increased seasonality, supporting the current understanding of the impact hyperthermals have had on climate. However, more detailed research on micro-scale sedimentation is required to better constrain the timing and scope of seasonality changes.