Geochemistry and source of ash layers in Bering Sea sediment at IODP site 323-U1341

Abstract

IODP Expedition 323 to the Bering Sea drilled seven sites (U1339–U1345) with the aim of collecting high-resolution ocean and climate data for the last five million years. The Bering Sea has extremely high surface productivity allowing recovery of sediment with abundant microfossils and other paleoceanographic proxies. Sites were located along the slope edge of the Alaskan continental margin in the region of the Arctic gateway and Umnak Plateau, and on Bowers Ridge, a submarine high, formed by an extinct and submerged volcanic arc. Sediment cores recovered during IODP Expedition 323 contained numerous volcanic ash layers. This study concentrates on ash layers in Hole U1341B on the Bowers Ridge. This hole was about 600 m deep corresponding to an age at the bottom of the hole of approximately 3.9 Ma. Ash from U1341B was analysed for major and trace elements and the results compared with ash from surrounding volcanic sources and ash layers intersected in other drill holes in the region. The ash at Site U1341 varies in composition from felsic to mafic with a silica range from 40.35% to 79.90%. The high silica ashes cannot be matched with sources in Alaska or the Aleutians. While most siliceous ash from Japan has lower TiO₂, there are some ash layers that do overlap with the U1341B compositions, for example the Ah ash from Kikai caldera south of Kyushu. Basaltic and andesitic ash layers from U1341 are compared with volcanic ash analyses from the Aleutians, Alaska, Kamchatka and Japan. Some analyses overlap with analyses from Unimak Island in the Aleutians. Most analyses of Bering Sea ash have slightly higher TiO₂, FeO, and lower MgO compared to ash from nearby arc volcanoes.1 page(s