High-Stress Conditions in Early Paleocene Benthic Foraminifera: Evidence from NW Atlantic ODP Site 1050C

Abstract

Benthic foraminifera specimens from deep-sea marine sediments at ODP Site 1050C exhibit morphologic variation, including dwarfing, across the Cretaceous-Tertiary boundary and half a million years after the mass extinction in the Danian stage. This study focuses on two benthic species of the genus Cibicidoides to quantify morphologic responses to stress for bottom-dwelling foraminifera throughout the section. Analysis shows that the average sizes of these two Cibicidoides species vary into the early Danian, with both species decreasing in average size within biozone P1b of the Danian. Relative abundance of the two Cibicidoides species in the benthic population remains relatively constant at around 20% throughout the section. Stable isotope data from previous studies of the site is used to correlate individual planktic and benthic foraminifera species changes in δ\(^{13}\)C and δ\(^{18}\)O alongside morphologic change. The onset of dwarfing quantified in subzone P1b for both species aligns with a negative shift in δ\(^{18}\)O and a gradual negative δ\(^{13}\)C excursion recorded in the bulk rock, suggesting dwarfing on the seafloor occurred during a period of warming and productivity crashes. In the shallow environment of Brazos, Texas, we observe similar benthic dwarfing in the late Maastrichtian and early Danian intervals missing at Site 1050C. The combination of benthic dwarfing, presence of blooms of high-stress planktic species, and previously observed negative excursions of δ\(^{13}\)C and δ\(^{18}\)O in this site and neighboring sites are coeval with the third pulse of Deccan volcanism, a known period of intense volcanic activity thought to be a global stress event.