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doi:10.2204/iodp.proc.311.210.2009

Summary

This data report presents new stable isotope results of authigenic carbonates from the Cascadia margin, IODP Expedition 311. There is a general trend both for calcite and dolomite of decreasing δ18O values and increasing δ13C values with depth. At Sites U1328 and U1329, there is a sharp gradient of δ13C values of dolomite crossing the BGHSZ that corresponds to the transition from negative δ13C values above the BGHSZ to positive δ13C values below the BGHSZ; a similar δ13C gradient is evidenced at Site U1327 for calcite. However, this transition occurs ~110 m above the BGHSZ at Site U1326 and it is absent at Site U1325.

The strong lateral heterogeneity between adjacent boreholes noticed in the preliminary conclusions of Expedition 311 is therefore also evidenced in the distribution of the stable isotope compositions of authigenic carbonates.