A comprehensive study of marine sediments of NanTroSEIZE Project, offshore Japan: clay mineralogy, consolidation, and microfabric
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] This dissertation investigates the clay mineral assemblages, consolidation state, and microfabric of sedimentary strata along the Kumano transect of Nankai Trough, offshore southeast Japan. The marine samples were retrieved during IODP Expeditions 315, 316, 322, and 333. The approaches include X-ray diffraction, 1-D consolidation test, and imaging with Environmental Scanning Electron Microscope. The clay mineral assemblages show that detrital supplies shifted gradually from a smectite-rich assemblage during the early through late Miocene to a more illite- and chlorite-rich assemblage during the Pliocene and Pleistocene. A model of smectite-to-illite reaction model indicates release of bound water after Shikoku Basin strata are buried more than 3460 m beneath the prism. The seaward edge of the Kumano Basin (forearc) is leaking because turbidite beds crop out along a fault-controlled bathymetric depression. Overpressure is possible in the turbidite beds top-sealed by onlaps farther landward in the basin. The main cause of apparent overconsolidation of the upper Shikoku Basin mudstones is the amorphous silica-rich cementation. Authigenic growth of smectite lithifies the lower Shikoku Basin strata. Removal of overburden by slumping caused true overconsolidation of sediments near the crest of Kashinosaki Knoll. Enhanced drainage from the landward underthrust section may occur along the permeable lower Shikoku Basin turbidites.
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