Successive extinctions of muricate planktonic foraminifera (Morozovelloides and Acarinina) as a candidate for marking the base Priabonian

The formal placement of the Global Stratotype Section 25 and Point (GSSP) for the base of the Priabonian (Upper Eocene) is currently under discussion. We suggest that two closely spaced extinctions of planktonic foraminifera at ~38 Ma offer excellent potential for long-distance correlation in marine strata and is the most suitable level to place the GSSP. The double extinction, which occurred within 11 kyr, involved the loss of the distinctive ‘muricate’ taxa Morozovelloides and the large acarininids. We present detailed biostratigraphic analyses from the Adriatic Sea and re-evaluate the magnetobiochronology of the extinction of these muricate taxa from previous studies from Ocean Drilling Program Site 1052 (western North Atlantic) and the Alano di Piave Section (NE Italy). We show these bioevents are robust, synchronous across the Atlantic Ocean and among the best calibrated and most easily recognised foraminiferal biohorizons for the entire Cenozoic. The two separate but very closely spaced bioevents provide a means for testing for completeness in the proposed stratotype and other sections that contain these fossils. The muricate extinctions coincide with a large turnover in radiolarians, within the short Subchron C17n.3n, providing distinct correlation horizons in siliceous and terrestrial sediments. We propose that the lithological level at 57.62 m in the Alano Section associated with the HO of Morozovelloides crassatus define the base of the Priabonian and the Middle/Upper Eocene boundary.