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doi:10.2204/iodp.proc.322.211.2015

Introduction

The primary objective of Integrated Ocean Drilling Program (IODP) Expedition 322 was to document the characteristics of incoming sedimentary strata and uppermost igneous basement prior to their arrival at the subduction front of the Nankai Trough (see the “Expedition 322 summary” chapter [Underwood et al., 2010]). IODP Site C0011 is located seaward of the trench on the northwest flank of Kashinosaki Knoll in the Shikoku Basin (Fig. F1), whereas Site C0012 is located near the crest of the knoll. IODP Expedition 333 returned to both sites to core previously unsampled intervals, measure temperature, and collect additional basement material (see the “Expedition 333 summary” chapter [Expedition 333 Scientists, 2012a]).

Values of intrinsic permeability (k) and hydraulic conductivity (K) for natural clay–rich sediment and shale (e.g., Neuzil, 1994; Gamage et al., 2011) typically span several orders of magnitude. This is because hydrogeological properties of fine-grained sediments and sedimentary rocks depend on many factors, some of which are inherited from the time of deposition. Grain size and shape, sorting, particle orientation, surface charges on clay particles, and fabric are important, as are the superimposed effects of burial diagenesis (e.g., Moon and Hurst, 1984; Bennett et al., 1989). Microfabric and permeability can be highly anisotropic, especially as the depth of burial increases and alignment of platy minerals becomes more uniform with respect to the orientation of maximum principal effective stress (e.g., Clennell et al., 1999; Kim et al., 1999; Bolton et al., 2000; Aplin et al., 2006). The anisotropy of permeability should follow changes in grain fabric as burial increases because pore fluids flow more easily along, rather than across, the long-axis direction of grain alignment. To quantify the hydrogeologic anisotropy of Shikoku Basin sediments, we compared horizontal (cross-core) permeability (k_h) and vertical (along-core) permeability (k_v) at the same sampling depths. These tests add to an extensive set of transect-wide hydrogeological data as part of the Nankai Trough Seismogenic Zone Experiment (e.g., Dugan and Daigle, 2011; Ekinci et al., 2011; Rowe et al., 2012; Yue et al., 2012; Dugan and Zhao, 2013; Screaton et al., 2013).

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