DELAYED FAUNAL RECOVERY IN THE AFTERMATH OF THE END-CRETACEOUS MASS EXTINCTION: LINKS TO DECCAN VOLCANISM AND DAN-C2 WARMING?

Persistent high stress environmental conditions and over 1 Myr delayed recovery in planktic foraminiferal communities in the aftermath of the end-Cretaceous mass extinction have been linked to continued Deccan volcanism activity in India. In addition, the Dan-C2 hyperthermal event in the early Danian (planktic foraminiferal zone P1b) has been associated to the last pulse of Deccan volcanism. We test these potential cause-and-effect relationships at ODP Site 1049 in the western North Atlantic based on high-resolution quantitative planktonic foraminiferal biostratigraphy, oxygen and carbon stable isotopes, bulk-rock mineralogy, major element geochemistry, and mercury anomalies as proxy for volcanism.

Results show that a double spike in mercury concentrations is recorded in zone P1b, C29n, coeval with increased relative abundance of opportunist species, a 2 ºC warming, and decreased productivity, marking climate instability and biotic stress directly linked to the last phase of Deccan volcanism, thus supporting previous findings of volcanically-induced high stress conditions during this time. The onset of planktic foraminiferal recovery is recorded in zone P1c(1) after the last phase of Deccan volcanism ended also supporting previous claims that the delayed recovery was due to Deccan volcanism. But results also show that the Dan-C2 event occurred in zone P1c(1), well after the last phase of Deccan volcanism ended, and caused no faunal changes in planktic foraminiferal assemblages. This climate event appears to be the result of increased shallow water input (commonly observed in continental slope locations in the North Atlantic) rather than a hyperthermal event related to Deccan volcanism. Other isotopic anomalies observed in the South Atlantic, Italy and Ukraine, initially interpreted as the Dan-C2 event and claimed as evidence of its global extent, actually occurred during the early Danian C29r (zone P1a) phase of Deccan volcanism. High-resolution studies are still needed to determine the precise timing of these isotopic excursions and their links, if any, to Deccan volcanism.