2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 7
Presentation Time: 3:00 PM


JAIN, Sreepat, Paleobiology, MRC-121, Smithsonian Institution, Washington, DC 20560, HUBER, Brian T., Department of Paleobiology, Smithsonian Institution, 10th and Constitution Ave, Washington, DC 20013-7012 and MACLEOD, Kenneth G., Department of Geological Sciences, University of Missouri-Columbia, 101 Geological Sciences Bldg, Columbia, MO 65211, jains@si.edu

The extinction of inoceramid bivalves during the middle Maastrichtian has been linked to changes in the bottom water environment, but the nature of those changes are poorly resolved. Benthic foraminifera provide a perspective to address this shortcoming, thus enabling a better understanding of Maastrichtian deep ocean dynamics. At a deep-sea site on Blake Nose (western subtropical North Atlantic), benthic foraminiferal data indicate low productivity and well-oxygenated environment between 72-69.4 Ma marked by high % of Eouvigerina spp., Nuttallides spp. and Gavelinella spp., low magnetic susceptibility (MS), high benthic δ13C and lightness (L*) values. High productivity and low oxygen conditions are noted between 69.4-68.1 Ma with low % of Eouvigerina spp., Nuttallides spp. and Gavelinella spp., high % of Praebulimina spp. and Bulimina kugleri, high MS, low benthic δ13C and L* values. Previous studies have noted that Eouvigerina spp., Nuttallides spp. and Gavelinella spp. prefer well-oxygenated low organic flux environments whereas species of Praebulimina and Bulimina are adapted to modern high productivity low oxygen conditions. Negative and significant correlations between Eouvigerina spp. and Praebulimina spp. and Bulimina kugleri also indicate differing habitat preferences between the former and the latter two species. Eouvigerina spp. correlates significantly and negatively with MS and positively with L*, corroborating the preference of this species for low productivity conditions. In summary, at Site 1052E, during the interval of the inoceramid decline and eventual extinction at ~68.5 Ma, high productivity and low oxygen conditions prevailed. This contrasts with the previous hypothesis that suggested increased oxygenation as the probable cause for the final demise of this important bivalve group. However, it is also plausible that regional dynamics (the availability of nutrients, changes in the intensity of upwelling, etc.) might have played a far greater and varying role than previously thought leading to the extinction of inoceramids.