Mineralogy and oxygen isotope ratios of <0.1 mu m authigenic clay minerals were determined for the nine volcanic ash layers in the sediment column from 580 to 1255 meters below sea floor at ODP Site 808 in the Nankai Trough. Seven of 9 samples comprise of monomineralic smectite, and 2 samples from 922.2 and 998.6 mbsf comprise of R=1 illite-smectite mixed-layered clay minerals. Assuming that oxygen isotope compositions of the clay minerals are equilibrated with those of the coexisting porewater, of which composition is the same as that of sea water, formation temperature of the clay minerals was estimated to be ca 50 degrees C regardless of burial depth. It means that the smectite was formed most actively when the temperature of sediments rose at ca 50 degrees C during burial, and no distinctive change of oxygen isotope composition occurred after its formation. Three samples from 775.6, 812.3 and 1253.8 mbsf gave the high formation temperature of ca 75 degrees C, probably due to the simultaneous formation of clinoptilolite and/or analcime. R=1 illite-smectite mixed-layered clay minerals may be formed at the same temperature as smectite but under different condition(s) of water/rock ratio and/or porewater chemistry.

West: 134.5634 East: 134.5646 North: 32.2111 South: 32.2105

Expedition: 131

Site: 131-808

Expedition: 196

Site: 196-808

Provider: SEDIS Publication Catalogue

Data set link: http://sedis.iodp.org/pub-catalogue/index.php?id=2011-015653 (c.f. for more detailed metadata)

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