ASSESSING THE DECCAN TRAPS ERUPTION RECORD FROM GEOCHRONOLOGY AND EVALUATING THE RELATIONSHIP TO THE K-PG BOUNDARY

The Deccan Traps and the Chicxulub bolide impact have been argued to contribute to the end-Cretaceous mass extinction. Recent attempts to establish the eruption record of the Deccan Traps have used both U-Pb (Schoene et al., Science, 2019) and Ar-Ar (Sprain et al., Science, 2019) geochronology. Both datasets agree that the main phase of eruptions began near the C30n-C29r magnetic reversal and waned shortly after the C29r-C29n reversal, totaling ~600-700 ka. The U-Pb dataset reveals four major eruptive pulses ~100 ka long, each separated by relative lulls in volcanism – with one pulse beginning within tens of ka of the Chicxulub impact. The Ar-Ar dataset, in contrast, has been used to argue for an increase in eruption rates coincident with the Chicxulub impact, supporting a model in which impact induced seismicity rejiggered the magmatic system and increased eruption rates.

We revisit both datasets and apply similar statistical techniques to each in order to generate comparable age models for the Deccan Traps, evaluate eruption rates, and calculate the probability distribution of the position of Chicxulub within the Deccan stratigraphy. From the Ar-Ar dataset, it is possible that the impact occurred at the base of the Poladpur formation, as concluded by Sprain et al. (2019), but it is more probable that it lies above or below. An equivalent analysis of the U-Pb dataset yields a very high probability that the impact occurred near the top of the rapidly erupted Poladpur formation. It is not likely that the Ar-Ar and U-Pb datasets agree as to the position of the impact within the Deccan stratigraphy, but it is definitive that neither dataset supports an increase in eruption rate as a result of the Chicxulub impact. The Ar-Ar dataset results in broadly constant eruption rates through the duration of the Deccan Traps, though large uncertainties cannot verify or disprove the pulses identified by the U-Pb data. Further evaluation of the Deccan eruption record should include targeting distal portions of the Traps, and continued efforts to calculate volume models for the basalt pile. Such efforts will continue to refine our understanding of volcanism and associated volatile release before and after the Chicxulub impact and the mass extinction.