(Table 1) Chemical composition of green clays in sandstone from different depths at ODP Site 126-793B

Microbial green marine clays in deep-sea sediments were recovered from the Izu-Bonin fore-arc basin at Leg 126 of the Ocean Drilling Program (ODP) along the Bonin-Mariana trench. Green spherical materials and remnants of dead microbial cells of filamentous bacteria are abundant in the green marine clays. Organic carbon and graphite were found in the volcanic sandstone. Transmission electron microscope observations clearly show processes of graphite mineralization from low-crystallinity to well-crystallized graphite. However, X-ray photoelectron spectrochemical analyses (micro-ESCA) indicate that the green marine clays contain high C (1s) of microbial origin carbon, and COO, C---O, C---C and graphite structures. Fourier transform infrared spectra (FT-IR spectra) of the green spherules show peaks between glauconite and celadonite. X-ray powder diffraction data show the presence of smectite and 1.03-1.22-nm mica-clay minerals with abundant zeolites, which are hydrothermal alteration products. The results suggest that fossil remnants of graphite mineralized organisms, in particular filamentous bacteria, might play an important role in the formation of green marine clays.