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doi:10.2204/iodp.proc.320321.212.2013

Introduction

Development of Cenozoic benthic foraminiferal assemblages after the prominent extinction during the Paleocene/Eocene Thermal Maximum (PETM; ~56 Ma) has been correlated to periods of global cooling and associated changes in oceanic environments (Kennett and Stott, 1991; Thomas, 2007). Before development of Antarctic ice sheets during the major global cooling at the end of the Eocene, however, several smaller hyperthermals occurred following the PETM, culminating in the early Eocene climatic optimum (EECO, ~52 Ma). These smaller hyperthermals resemble the PETM in geochemical and biotic features (Lourens et al., 2005; Agnini et al., 2009; Zachos et al., 2010; Stap et al., 2010).

Deep-sea benthic foraminifers thus experienced severe climatic fluctuations during latest Paleocene to middle Eocene times. The cause of the benthic extinction during the PETM is still not fully understood, but one convincing explanation could be the change in adaptive strategy of the benthic foraminifers to changes of bentho-pelagic coupling as recognized in the modern ocean (Gooday, 2003; Thomas, 2007), possibly due to changes in temperature and thus metabolic rates, which could have led to the expansion of the trophic resource continuum (D’haenens et al., 2012), which also related to the global change in ocean ventilation, oxygenation, and productivity (Winguth et al., 2012). Changes in climatic-related oceanic productivity and export productivity thus could have strongly influenced benthic foraminiferal assemblages, and investigating the mode and tempo of the development of early to middle Eocene benthic assemblages may significantly add to our understanding of the mechanisms of paleoceanographic and biotic co-evolution.

Integrated Ocean Drilling Program (IODP) Expedition 320 and Ocean Drilling Program (ODP) Leg 199 (Pacific Equatorial Age Transect [PEAT]) provided unique paleoceanographic information that will be useful for the further development of an orbitally tuned geological timescale because the sites were well placed to obtain information along gradients in paleolatitude, paleodepth, and paleoproductivity. Eocene carbonate-rich sediments were recovered and used to recognize and define carbonate accumulation events (CAE) (Lyle et al., 2005; Pälike et al., 2009). These sites also allowed reconstruction of changes in the carbonate compensation depth (CCD) over time (Pälike et al., 2009), allowing us to test whether there were correlations between biotic evolution and the oceanic carbonate cycle (Griffith et al., 2010).

This report continues our description of lower Eocene benthic foraminifers from ODP Leg 199 Sites 1215, 1220, and 1221 (Nomura and Takata, 2005). The benthic assemblages at IODP Sites U1331 and U1333 at abyssal paleodepths are comparable to those at ODP Sites 1215, 1220, and 1221, also in the abyssal zone (~3000 m paleodepth). These results are very significant to adding to further information from the deeper ocean (Fig. F1).

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