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doi:10.2204/iodp.proc.342.204.2016

Introduction

Because of the relatively stable and monotonous deep-sea environment, the stratigraphic range of benthic foraminiferal species is relatively long, and their usefulness for biostratigraphy is less advantageous compared to planktonic foraminifers (e.g., Boltovskoy, 1980; van Morkhoven et al., 1986; Thomas, 2007). On the other hand, benthic foraminiferal species provide useful indicators of environmental change, and significant changes in benthic foraminiferal assemblage composition usually imply severe climatic and/or paleoceanographic perturbations (e.g., in global ocean circulation). One of the most severe perturbations occurred across the Paleocene/Eocene boundary accompanied by a major redistribution of benthic foraminiferal faunas (e.g., Kennett and Stott, 1991; Thomas and Shackleton, 1996).

Following this major turnover across the Paleocene/Eocene boundary, three benthic foraminiferal faunas can be recognized: (1) Paleogene-like fauna during the Eocene, (2) transitional fauna in the late Oligocene to early Miocene, and (3) near-modern-like faunas that developed from the late Miocene onwards (Thomas, 1992, 2007). These three different faunas are separated by faunal turnovers associated with the global cooling event at the Eocene/Oligocene boundary and the middle Miocene climatic optimum.

Although morphotypes of benthic foraminifers do not exclusively represent ecology and/or habitat of a given species, it has been reported that changes in morphotype composition and/or the reaction of specific morphotypes are related to environmental perturbations (e.g., Rosoff and Corliss, 1992). One example for this pattern is the significant decrease of elongated morphotypes, such as pleurostomellids and stilostomellids, across the Eocene/Oligocene boundary and during the middle Miocene turnover (e.g., Thomas, 2007). This pattern suggests the response of a specific morphotype, and therefore a specific habitat, to climate perturbations. Relative changes in the abundances of benthic foraminiferal morphotypes may therefore represent faunal turnover and/or climate variation.

Integrated Ocean Drilling Program (IODP) Expedition 342 recovered semicontinuous sequences from the Lower Cretaceous to middle Miocene. Especially for the lower Eocene through lower Miocene interval, many continuous cores containing well-preserved microfossils were drilled at multiple sites (see the “Expedition 342 summary” chapter [Norris et al., 2014a]).

Among those sites, coring at Site U1406 recovered carbonate-rich sediments of late Paleocene through early Miocene age, including the Eocene/Oligocene and Oligocene/Miocene boundaries (see the “Site U1406” chapter [Norris et al., 2014c]).

In this data report, we present changes of benthic foraminiferal morphotype distribution across these cooling events at Site U1406.

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