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doi:10.2204/iodp.proc.320321.204.2012

Introduction

The Eocene/Oligocene (E/O) boundary marks a major transition in climate, oceanography, and ocean circulation, and it takes place over a rather brief span of geologic time. For radiolarians it is associated with a comparatively large turnover of fauna (Funakawa et al., 2006). Unfortunately, the record of this transition in Pacific sediments is usually marked by poor carbonate preservation in the uppermost Eocene, hiatuses in the recovered sections, and immixed reworked older siliceous microfossils. In this report we present a detailed sampling of the only three sites from the equatorial Pacific that are believed to contain a complete stratigraphic record of the E/O boundary: Ocean Drilling Program (ODP) Site 1218 and Integrated Ocean Drilling Program (IODP) Sites U1333 and U1334 (Fig. F1, Table T1). In the data tables (Tables T2–T7) we give the abundance of 76 radiolarian species, species groups, and transitional forms in samples that span the time period of ~40 to 30 Ma. References to species descriptions and remarks concerning our observations and the nature of the transitional forms are given in a taxonomic list (see “Taxonomic notes”). Illustrations of most of the species and forms used are given in Plates P1–P10.

Also given in the data tables are the counts of older, reworked radiolarian microfossils in each sample, as well as the ratio of diatom fragments to radiolarian shells (see “Methods and materials”). Based on our evaluation of this reworking, we give our best estimate of the first and last in situ occurrences of the species and forms whose range overlap or are included within the sampled interval at each site. We have used the corrected and adjusted sample depths at each site generated by Westerhold et al. (2012) and their correlation of these depths to similarly adjusted depths at Site 1218. In this way we hope to obtain the best possible constraints on individual biostratigraphic datum levels (Table T8).

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