DECCAN VOLCANISM, CHICXULUB IMPACT AND THE KTB MASS EXTINCTION: COINCIDENCE? CAUSE AND EFFECTS?

Continental flood basalt provinces and major environmental catastrophes are associated with five out of the six largest Phanerozoic mass extinctions. Unique among these is the Cretaceous-Tertiary (Paleogene) boundary (KTB or KPB) mass extinction, which coincides with massive Deccan Trap eruptions and also the Chicxulub impact. Age control for Deccan volcanism, associated climate changes, high-stress conditions and the KTB mass extinction is excellent based on stratigraphy and corroborated by new U-Pb dating providing new evidence for a complex mass extinction scenario. The massive Deccan phase-2 eruptions began in the late Maastrichtian C29r and ended at the KTB depositing 3000 m of stacked lava flows or 80% of the total Deccan eruptions over a period of just 200 ky resulting in rapid global warming on land and sea (4-8°C) and increasingly high-stress environments preceding the mass extinction. Biostratigraphy of cores and outcrops with marine sediments between the longest lava flows near the end of phase-2 in central and eastern India document the rapid mass extinction and ocean acidification ending at or near the KTB. The last Deccan phase-3 erupted in the early Danian C29n depositing ~14% of the total Deccan lava pile and coinciding with high stress conditions and a global warm event (DanC2).

Any KT mass extinction scenario must take into account both Deccan volcanism and the Chicxulub impact. Recently it was suggested that Chicxulub triggered Deccan, which in turn triggered the mass extinction. Given Deccan phase-2 chronology, this scenario requires that Chicxulub predates the KTB. The age of the Chicxulub impact is controversial though generally assumed of KTB age and the sole cause for the mass extinction. This assumption is not corroborated by impact spherule ejecta surrounding the Chicxulub crater: in NE Mexico and Texas impact spherules are in sediments near the base of zone CF1 about 100-150 ky below the KTB, but elsewhere reworked in early Danian sediments (upper P1a) due to a major KTB hiatus linked to intensified Gulf stream circulation. The best age consistent with the data is that Chicxulub crashed into Yucatan about 100-150 ky before the KTB at the time of ongoing Deccan warming and exacerbated warming and environmental stress but had no direct role in the mass extinction.