Petrography and correlation of Cenozoic ash layers recovered on Shatsky Rise ODP Leg 198

In this study of volcanic ash retrieved from the Shatsky Rise during Ocean Drilling Program (ODP) Leg 198, the texture and composition of the volcanic components (glass and crystals) were used to fingerprint ash layers for detailed correlation. Correlations among ash layers in holes drilled at the same site as well as between sites, including sites on different parts (highs) of the rise, were tested. Whereas high-to-high correlations failed, intra-high correlations were more successful. My data suggest a significantly different source for some pyroclastic debris, especially at Site 1208, possibly associated with pumice rafts carried northward from the Izu-Bonin Arc by the Kuroshio (Kuro Current). Other ashes are consistent with rhyolitic to dacitic air fall ash from Asian arc volcanoes. It was not possible to texturally distinguish between fallout ash and pumice-raft fallout but suspect that the latter is associated with higher percentages of vesiculated ash components, as shown to occur in more proximal IzuBonin pyroclastic deposits.