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Integrated Ocean Drilling Program (IODP) Expedition 320/321 recovered sediment cores from eight sites in the eastern equatorial Pacific (see the “Expedition 320/321 summary” chapter [Pälike et al., 2010]). Sediment in a transition interval from late Eocene to early Oligocene was recovered at four sites, U1331–U1334, that commonly show an abrupt change in lithology from siliceous microfossil-rich Eocene sediment (typically radiolarian ooze) to calcareous microfossil-rich Oligocene sediment (typically nannofossil ooze).

In this study we report volcanic glass shards separated from a sediment interval across the Eocene–Oligocene transition at Site U1333. We also measured major element compositions of volcanic glass shards by an element microprobe analyzer (EPMA). Based on morphological and chemical data, together with paleogeographical information, we discuss the potential source(s) of these glass shards.