Planktonic foraminiferal biostratigraphy and stable carbon isotope ratios of late middle Eocene sediments from Blake Plateau, West Atlantic Ocean

High-resolution biostratigraphy reveals that the extinctions in the muricate group occurred in a stepwise form. The large acarininids (Acarinina praetopilensis) terminate 10 kyr prior to the extinction of M. spinulosa and small acarininids (Acarinina medizzai and Acarinina echinata) continue into the upper Eocene. High-resolution stable isotope analyses have been conducted on planktonic and benthic foraminifera from the western North Atlantic to reconstruct sea surface temperatures (SSTs) and deep water temperatures and the structure of the water column around this major biotic turnover.

Whilst the extinctions of M. spinulosa and A. praetopilensis occur during a long-term cooling trend, the biotic turnover in the muricate group does not appear to be related to significant climatic change. Sea surface temperatures decrease slowly prior to the extinction events, and there is no evidence for a large-temperature shift associated with the faunal changes. The turnover event was therefore probably related to the increased surface water productivity and the deterioration of photosymbiotic partnerships with algae.