Late Cretaceous-early Eocene mass extinctions in the deep sea

Upper Maastrichtian through lowermost Eocene deep-sea benthic foraminiferal records from Maud Rise (Weddell Sea) demonstrate that there was no mass extinction of these organisms at the end of the Cretaceous. In contrast, there was a global extinction of bathyal to abyssal benthic foraminifera at the end of the Paleocene, occurring in fewer than 25,000 yr at Maud Rise. Many benthic foraminiferal species that had originated during the Cretaceous became extinct, although there was no coeval mass extinction (of comparable importance) of terrestrial organisms and planktonic marine organisms. After this extinction the diversity of benthic faunas on Maud Rise was low for about 260,000 yr, and during the period of low diversity, the assemblages were dominated by species that may indicate the presence of abundant organic carbon, and possibly low concentrations of dissolved oxygen. The dominance suggests that the Paleocene/Eocene deep-sea benthic foraminiferal mass extinction was caused by a decrease in oxygen content of the waters bathing the lower bathyal reaches of the sea floor. Such a change could have been caused by a change in the circulation patterns of deep waters: these waters would become depleted in dissolved oxygen if there were a change from predominant formation of deep waters at high latitudes (cooling and sinking) to initiation of, or a strong increase of, formation at low latitudes (evaporation and sinking). (Auth. mod.)