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Late Cretaceous–early Eocene mass extinctions in the deep sea

By
Ellen Thomas
Ellen Thomas
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Published:
January 01, 1990

Upper Maastrichtian through lowermost Eocene deep-sea benthic foraminiferal records from Maud Rise (Weddell Sea, Antarctica) demonstrate that there was no mass extinction of these organisms at the end of the Cretaceous. There is no significant drop in diversity across the Cretaceous/Tertiary boundary, but just above this boundary there is a peak in relative abundance of species that may indicate low-nutrient conditions, probably reflecting the decrease in food supply to the ocean floor resulting from the large-scale extinction of surface-dwelling primary producers. 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 was 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). Thus, one of the largest Phanerozoic extinctions at the Earth's surface is not reflected by the deep-water foraminifera, and the largest Cenozoic extinction event in the bathyal-abyssal realm of the oceans is of little importance to surface biota: even some of the largest extinction events that we know do not reach all environments of the Earth.

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GSA Special Papers

Global Catastrophes in Earth History; An Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality

Virgil L. Sharpton
Virgil L. Sharpton
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Peter D. Ward
Peter D. Ward
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Geological Society of America
Volume
247
ISBN print:
9780813722474
Publication date:
January 01, 1990

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