[MIS11-P08] Variation of pore water geochemistry across the mass transport deposits off Cape Erimo, Hokkaido, Japan
Keywords:Chikyu SCORE, Mass transport deposit, 129I, Iodine geochronology, Pore water
Pore waters were collected from sedimentary sequences intercalated with MTDs down to ~100 mbsf off Cape Erimo, Hokkaido, Japan during the Chikyu Shallow Core Program (SCORE) by D/V Chikyu in 2017. The pore water geochemistry shallower than sulfate-methane interface (SMI) rapidly changes due to anaerobic methane oxidation, decomposition of organic matter, methane production from organic matter, precipitation of carbonates etc. On the other hand, below the SMI, the pore water composition was changed mainly by the mineral alterations in high temperature environments and the diffusion of components which released into or removed from the pore water due to decomposition of biogenic sedimentary rocks and organic matter. In particular, the concentration gradients of iodine and magnesium become smaller around the upper boundary of the MTD, unlike the gradual changes in concentration through the entire drilling depth. In addition, barium and lithium showed a curve-like concentration change with minimum values at the upper boundary of the MTD. The radioisotopic analysis of iodine showed significantly high value in the MTD, reflecting seawater component dominates in the interval. These changes were caused by trapping, migrating, and accumulating shallow pore water in the deeper sediments, pore water geochemistry can be modified along with the development of the MTD.