Changes of the paleoenvironments and biological diversity in the Late Eocene impact bolide event

点击翻译按钮获取中文摘要

Ocean Drilling Program Leg 171 drilled the middle to upper Eocene sequences at Sites 1052 and 1053 on the Blake Nose in the western North Atlantic Ocean.(1) We can reevaluate the following biostratigraphic events of planktonic foraminifers using magnetostratigraphy : The last occurrences (LOs) of Acarinina praetopilensis, A. rohri and Morozovella spinulosa (Cron C17n3n), the first occurrences (FOs) of Acarinina medizzai and Porticulasphaera semiinvoluta and the LO of Acarinina collactea (Chron C17n2n), The morozovellids and acarininids extinct in the uppermost of Chron C17n3n and within Chron C17n1n, respectively.(2) The hispid species of morozovellids and acarininids dominates about 20 to 55 % of total assemblages during the Middle Eocene. The major faunal turnover occurred in the upper part of Zone P14 (Chron C17n3n) where those species decreased rapidly to less than 10 %.(3) At Site 1053A, an extinction event of radiolarians has been recorded in Core 8H (the uppermost part of Chron C16n2n, P15 of planktic foraminiferal zones), This bioevent is considered to be related with the Chesapeake Bay bolide impact. However, no remarkable extinction events of planktonic foraminifer species are not yet recognized between the impact horizons.