Depth-Transect Across the Cretaceous/Paleogene Boundary in the SE Atlantic Ocean: New Insights From the Benthic Foraminiferal Record.

Friday, 19 December 2014
Laia Alegret, Universidad de Zaragoza, Department of Earth Sciences, Zaragoza, Spain and Ellen Thomas, Yale University, New Haven, CT, United States; Wesleyan University, Middletown, CT, United States
The response of benthic foraminifera to the Cretaceous/Paleogene (K/Pg) impact event is key to reconstruct paleoenvironmental changes and the specific mechanisms triggering faunal turnover in the marine realm, especially because this group did not suffer significant extinction (thus shows a continuous record across the boundary), and because its faunal turnover shows paleobiogeographic differences that remain to be explained.

The K/Pg transition was cored along a depth transect on ODP Leg 208 (Walvis Ridge, eastern South Atlantic Ocean), where the K/Pg boundary is marked by a sharp transition from Maastrichtian clay-bearing nannofossil ooze to Danian dark reddish to brown, clay-rich nannofossil-ooze and clay. We analysed the benthic foraminiferal turnover at Sites 1262 (upper abyssal paleodepth; present depth 4755 m) and 1267 (lower bathyal; present depth 4355 m). The record at 1267 appears to be more complete than at 1262, especially the interval just at the K/Pg boundary (Westerhold et al. 2008).

The percentage of infaunal taxa (living buried within the sediment) was slightly lower at Site 1262 than at Site 1267, as expected for a deeper, more oligotrophic setting where the scarce food available is preferentially taken up by epifaunal morphogroups. The dominance of calcareous taxa suggests that both sites were located above the CCD throughout the K/Pg transition. Benthic assemblages from both sites are similar, but the species Tappanina eouvigeriniformis is common at Site 1267, as at lower bathyal Southern Ocean Site 690, but is absent at Site 1262.

Extinction rates across the K/Pg boundary were very low at both sites. Morphogroup composition did not significantly change across the boundary at Site 1262, but the increase in % infaunal morphogroups and benthic foraminiferal accumulation rates at Site 1267 point to an enhanced food supply immediately after the impact. These results suggest that a short interval is missing from the lowermost Danian at Site 1262.