DECCAN VOLCANISM AT K-PG TIME

The last major mass extinctions in Earth history (e.g., end-Guadalupian, end-Permian, end-Triassic, and end-Cretaceous) are all correlated closely in time with the main-phase eruptions of major flood basalt provinces (Emeishan, Siberian, CAMP, and Deccan Traps, respectively). The causal relationship between flood volcanism and mass extinction is not clear, but likely involves the climate effects of outgassed volatile species such as CO₂, SO₂, Cl, F, etc., from some combination of magma and country rocks. In a surprising “coincidence”, the end-Cretaceous (K-Pg boundary) micro-faunal extinction also corresponds precisely in time to what may have been the largest meteor impact of the past billion years of Earth history, the Chicxulub crater at 66.05 Ma. The Deccan Traps eruptions were underway well before K-Pg/Chicxulub time, and are most likely the result of the mantle plume “head” that initiated the presently-active Reunion hotspot track – thus the Deccan Traps were clearly not generated, fundamentally, by the impact. However, recent high-precision ⁴⁰Ar/³⁹Ar geochronology indicates that conspicuous changes in basalt geochemistry, lava flow morphology, emplacement mode, and a possible 50% increase in eruption rate at the Lonavala/Wai subgroup transition in the Deccan Traps lava group corresponded, within radioisotopic age precision, to the K-Pg boundary and the Chicxulub impact. This has led to the testable hypothesis that the Mw~11 seismic disturbance of the Chicxulub impact may have affected the Deccan eruptions. Here we review a broad landscape of evidence regarding Deccan volcanism and its relation to the K-Pg boundary including the recent high-precision⁴⁰Ar/³⁹Ar and U/Pb geochronology results, volcanological and paleo-proxy based estimates of eruption characteristics, and evolving ideas regarding the Deccan crustal magmatic system. Based on these, we discuss our views of the most important questions than can and should be answered by further research to better understand both the onshore and largely unknown offshore components of Deccan-related volcanism, and what their climate and environmental impacts at K-Pg time may have been.