High-resolution mercury (Hg) records across the K/Pg boundary: Assessing Deccan volcanism as a global climatic driver

The Cretaceous/Paleogene (K/Pg) boundary (~66 Ma), at which the mass extinction induced by the Chicxulub impact occurred, is preceded by the onset of Deccan Traps volcanism. According to high-precision radiometric dating, the emplacement of this large igneous province occurred from ~300 kyr prior to ~400 kyr after the boundary, potentially affecting Earth’s global climate before, during, and after the extinction event. Nonetheless, despite refined studies published over the last decade, uncertainties persist regarding the rates of volcanic eruption and outgassing, and whether volcanism played a role in the main climatic events across this interval.

In this study, we generated new high-resolution mercury (Hg) concentration data from the internationally recognized K-Pg sites of Zumaia and Caravaca (Spain) and Walvis Ridge Site 1267 (South Atlantic). Our goal is to establish reliable stratigraphic correlations and develop robust, independent age models to infer the temporal relationship between Deccan volcanism and the paleoclimatic changes recorded in the sedimentary record. We calculate Hg mass accumulation rates (MARs) to investigate the nature of the observed Hg anomalies over time. Measured Hg values and calculated Hg MARs display considerable variability between sections; in some cases, higher Hg anomalies were recorded well before the main phase of Deccan volcanism began. This finding raises questions about the utility of Hg as a standalone proxy. Consequently, we argue that for Hg to be considered a reliable geochemical marker for tracking Deccan volcanism, anomalies must be temporally consistent across distant localities and align strictly with the known eruptive history. Our results point out that the greater fit for the Hg anomalies between the studied sections occurred between ~230 kyr prior and 50 kyr after the boundary. These high Hg values are temporally compatible with the emplacement of the bigger eruptive pulses, i.e. the oldest eruptive pulse which includes Kalsubai-Lonavala subgroups formations, and the Poladpur and Ambenali formations respectively, while not showing any clear track of the fourth eruptive pulse related to Mahabaleshwar formation.

According to the extensive climatic proxies generated over the past decades, the only recognizable global climatic event beyond the K/Pg boundary during this interval is the Late Maastrichtian Warming Event (LMWE). Our Hg and MARs anomalies suggest that during the LMWE, Deccan volcanism was involved to some extent. However, the LMWE onset can be dated to ~60 kyr prior to the onset of the temporally consistent Hg and MARs anomalies, suggesting that Deccan volcanism was not the sole trigger of the LMWE. The temperature increase of the LMWE appears to track the last long eccentricity maximum of the Maastrichtian, as originally proposed by Gilabert et al. (2022), reinforcing the hypothesis that orbital forcing played a significant role in the development of this hyperthermal event.  Further studies and age refinement of sedimentary proxies are still required for a better understanding of this episode of Earth’s climatic history.

 

Gilabert, V., Batenburg, S.J., Arenillas, I., Arz, J.A., 2022. Contribution of orbital forcing and Deccan volcanism to global climatic and biotic changes across the KPB at Zumaia, Spain. Geology 50, 21–25. https://doi.org/10.1130/G49214.1