Accumulation rate, carbon geochemistry and clay mineralogy of ODP Site 181-1123 sediments, southwest Pacific

Site 1123 is located on the northeastern flank of the Chatham Rise. Sedimentological and clay mineralogical analyses indicate a very fine grained carbonate-rich sediment. Smectite and illite are the main constituents of the clay mineral assemblage. High smectite values in the Eocene decrease in younger sediment sequences. Illite and chlorite concentrations increase in younger sediments with significant steps at 13.5, 9, and 6.4 Ma. The kaolinite content is near the detection limit and not significant. We observed only small fluctuations of the clay mineral composition, which indicates a uniform sedimentation process, probably driven by long-term processes. Good correspondence is shown between increasing illite and chlorite values and the tectonic uplift history of the Southern Alps.

Sulphur geochemistry of interstitial waters and squeeze cake samples of ODP Leg 181 sites

Seventy-nine interstitial water samples from six sites (Ocean Drilling Program Sites 1119-1124) from the southwestern Pacific Ocean have been analyzed for stable isotopes of dissolved sulfate (34S), along with major and minor ions. Sulfate from the interstitial fluids (34S values between +20.7 and +57.5 vs. the Vienna-Canyon Diablo troilite standard) was enriched in 34S with respect to modern seawater (34S +20.6), indicating that differing amounts of microbial sulfate reduction took place at all investigated sites. Microbial sulfate reduction was found at all sites, the intensity depending on the availability of organic matter, which is controlled by paleosedimentation conditions (e.g., sedimentation rate and presence of turbidites). In addition, total reduced inorganic sulfur (essentially pyrite) as a product of microbial sulfate reduction was quantified in selected sediments from Site 1119.