Planktonic and benthic foraminiferal extinction events during the last 100 m.y.

Abstract

Five major planktonic and benthic foraminiferal extinction events occurred during the past 100 m.y.: at the Cenomanian/Turonian ( C T) boundary, at the Cretaceous/Tertiary ( K T) boundary, in the latest Paleocene, in the late Eocene, and in the early middle Miocene. To clarify the character of the five events, I estimated (1) paleo-waterdepths and paleoenvironments where foraminifera were affected, (2) the duration of each extinction event, and (3) evaluated possible causes for each extinction event, on the basis of recent literature. These extinction events can be classified into three fundamentally different types: (1) the mass extinction event at the K T boundary was abrupt and concentrated among surface dwelling species, (2) extinctions at the C T boundary and during the latest Paleocene were abrupt and mainly affected intermediate- and deep-water taxa over short periods, (3) the late Eocene and early middle Miocene events affected surface- and deep-water species, and involved stepwise or gradual extinctions over a long period (∼ 4 m.y.). I attributed the extinction events to: (1) a bolide impact for the K T event, (2) a decrease in dissolved oxygen in intermediate- and deep-waters due to climatic warming for the C T and latest Paleocene events, and (3) long-term global cooling for the late Eocene and early middle Miocene events. The following relationships exist between the causes and types of extinction events: (1) large extraterrestrial impacts strongly affected surface-dwelling organisms in short-term extinction events, (2) intermediate- and deep-water low oxygen conditions induced by climatic warming have severely affected intermediate- and deep-water organisms over medium- and short-terms (< 1 m.y., < 0.1 m.y.), and (3) long-term global coolings have induced faunal changes among surface- and deep-water organisms over long periods (1 m.y.).