SDSU - Department of Geological Sciences - Thesis Defense - Fall 2008

ABSTRACT

The Eocene-Oligocene Transition (EOT) is marked by a double-stepped ~1.3‰ positive excursion in d18O over an ~300 kyr interval (i.e., Oi-1; Miller et al., 1991; Zachos et al., 1996; Coxall et al., 2005) and a deepening of the calcium compensation depth (CCD) interpreted to represent marked Antarctic glaciation and global ocean-atmosphere cooling. A ~0.5 m (~55-70 kyr) resolution ostracode faunal study of the Massicore, drilled adjacent to and up-section from the Italian Massignano quarry stratotype section that contains the Eocene-Oligocene GSSP (i.e., base of the Priabonian stage), revealed two transient increases in Krithe and decreases in faunal evenness, enthalpy, eH, and Simpson’s Index that lag two surface water cooling pulses based on a dinocyst-based sea surface temperature (DSST) proxy (van Mourik et al., in prep). These transient ostracode faunal changes may reflect changing physico-chemical water properties, increased sedimentation rates, variable food availability in the benthos, and/or intensifying thermohaline circulation from the Indian or Atlantic Ocean through the paleotethyan seaway. Ordination and cluster analyses also show minor faunal differences during times of relatively cold and warm surface waters based on the DSST proxy. Comparisons made between these Massicore ostracode data and re-analyzed Massignano Quarry ostracode data from Dall’Antonia et al. (2003) revealed major similarites (i.e., similar relative abundances among common taxa where both studies overlap) making it practical for us to combine both records in order to provide a more complete Tethyan ostracode record through the broader EOT and spanning Oi-1 at the stratotype locality.