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doi:10.2204/iodp.proc.331.105.2011

Petrology

Only two cores were taken at Site C0015 (Cores 331-C0015B-1H and 331-C0015C-1H), to a depth of 9.5 mbsf. Holes C0015B and C0015C were drilled 2 m apart and therefore can be considered a single drilled section for petrological interpretation. These cores lack hydrothermal alteration of the type seen at Sites C0013, C0015, and C0016. Except for the interval from 3.2 to 5.6 mbsf in Hole C0015B discussed below, the fine-grained sediment, sand, and pumiceous gravel we recovered show weak oxidation, expressed as yellow to brown coloration for the fine sediment and development of orange to brown iron oxide staining on some pumice fragments. Orange to brown botryoidal aggregates of Fe-Si oxyhydroxides 1–2 mm in size were also noted in Section 331-C0013C-1H-3. Scanning electron microscope (SEM) imaging of this material (Fig. F6) showed a filamentous structure typical of oxyhydroxides associated with seafloor hydrothermal systems (e.g., Scott and Binns, 1995). No sulfide mineralization is associated with the oxidized material at Site C0015.

The interval from 3.2 to 5.07 mbsf in Hole C0015B comprises reduced olive-green mud with abundant biogenic fragments. This interval shows no evidence of oxidation. As expected, very fine grained framboidal pyrite, likely to have been formed by microbial processes, is found in trace quantities within this interval.

X-ray diffraction analysis of samples from Site C0015 (Table T5) identified a suite of minerals that are consistent with the lack of hydrothermal alteration at the site.

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