Biotic response of Tethyan bathyal ostracodes through the Eocene–Oligocene Transition: The composite faunal record from the Massicore and Massignano Global Stratotype Section and Point (east central Italy)

•Provides first complete Tethyan ostracode record across Eocene-Oligocene Transition.•Transient faunal event (TFE) coined Krithe Pulse (KP) identified.•TFE correlative to Oi-1 and is interpreted to reflect cooling.•TFE defined as a relative increase in Krithe and decrease in diversity.

The Eocene–Oligocene Transition (EOT) is marked by a double-stepped positive δ18O excursion of ~ 1.3‰ and a deepening of the calcium compensation depth (CCD) interpreted to represent marked Antarctic glaciation and global ocean–atmosphere cooling (i.e., Oi-1 event). A ~ 0.5-m (~ 55–70 kyr) resolution ostracode faunal study of the Massicore, drilled up-section from the Italian Massignano Quarry containing the Eocene–Oligocene Global Stratotype Section and Point (GSSP), revealed a relative increase in Krithe and decreases in faunal evenness and Shannon Index correlative to the Oi-1 event. These transient faunal changes may reflect local water column changes (e.g., export production) or intensified thermohaline flow of cooler deep waters through the paleotethyan seaway. Comparison of these Massicore ostracode faunal data to previously-published Massignano Quarry ostracode faunal data reveals similar relative abundances among common taxa where the study intervals overlap, and thereby provide a more complete Tethyan ostracode record spanning all of C13n and the broader EOT at the GSSP locality.