TIMING AND PALEOENVIRONMENTAL IMPLICATIONS OF DECCAN VOLCANISM RELATIVE TO THE KPG EXTINCTION

Several studies evaluated the relationship between mercury anomalies in sediments and LIP activity across mass extinction horizons. The bulk (80%) of Deccan Trap eruptions occurred over a relatively short time interval in magnetic polarity C29r. U-Pb zircon geochronology reveals the onset of this main eruption phase 250 ky before the Cretaceous-Tertiary (KT) mass extinction and continued into the early Danian suggesting a cause-and-effect relationship. We investigate the Hg contents of sections in France (Bidart), Spain (Zumaya), Denmark (Nye Klov), Austria (Gams), Italy (Gubbio), Croatia (Hvar and Brac islands),Tunisia (Elles, El Kef), Egypt (Wadi Nukhul, Sinai, Duwi, Eastern Desert), Israel (Negev), India (Megalaya), Texas USA (Brazos River) and NE Mexico (El Penon, La Parida). In all sections, results show Hg concentrations are more than 2 orders of magnitude greater during the last 100ky of the Maastrichtian up to the early Danian P1a zone (first 380 Ky of the Paleocene). These Hg anomalies are correlative with the main Deccan eruption phase. Hg anomalies generally show no correlation with clay or total organic carbon contents, suggesting that the mercury enrichments resulted from higher input of atmospheric Hg species into the marine realm, rather than organic matter scavenging and/or increased run-off. At Gams, Bidart and Elles, Hg anomalies correlate with high shell fragmentation and dissolution effects in planktic foraminifera indicating that paleoenvironmental and paleoclimate changes drastically affected marine biodiversity. In all sections, an increase in Hg content is observed in the upper part of zone CF2 as well as in zone CF1. The striking Hg increase present in the uppermost CF1 is observed in both proximal (Elles) and distal sections (Caravaca, Gubbio). Hg content from Elles are clearly more elevated than in the deepest section of Gubbio. However, in both sections, the uppermost CF1 interval is marked by a sharp increase in Hg content (3-5X background levels), which corresponds to the paroxysmal eruptions that ended with the end-Cretaceous mass extinction at the KPB. The KPB clay layer is marked by the highest Hg anomaly at Elles, Caravaca, Agost and Gubbio, but not at Mishor Rotem and Zumaia, where the KPB is truncated by a hiatus. These observations provide further support that Deccan volcanism played a key role in increasing atmospheric CO₂ and SO₂ levels that resulted in global warming and acidified oceans, increasing biotic stress that predisposed faunas to eventual extinction at the KPg