• Chapter contents
• Abstract
• Introduction
• Methods
• Sample preparation
• X-ray diffraction
• Calculations of mineral abundance
• Results
• Site C0011
• Site C0012
• Acknowledgments
• References
• Figures
• F1. Shikoku Basin study area.
• F2. Seismic in-line section.
• F3. Representative X-ray diffractograms.
• F4. Calculated relative abundances, Site C0011.
• F5. Total clay minerals, Site C0011.
• F6. Calculated relative abundances, Site C0012.
• F7. Total clay minerals, Site C0012.
• Tables
• T1. Normalization factor matrix.
• T2. XRD analyses results, Site C0011.
• T3. XRD analyses results, Site C0012.
• PDF file

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doi:10.2204/iodp.proc.333.205.2017

Introduction

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) comprises several sampling expeditions that crossed the subduction system offshore southwest Japan (Ashi et al., 2009; Screaton et al., 2009; Tobin et al., 2009, 2015; Underwood et al., 2010; Strasser et al., 2014; see the “Expedition 333 summary” chapter [Expedition 333 Scientists, 2012a]). Integrated Ocean Drilling Program (IODP) Expeditions 322 and 333 concentrated on coring the inputs of sediment to the subduction zone (see Underwood et al., 2010; also see the “Expedition 333 summary” chapter [Expedition 333 Scientists, 2012a]). IODP Sites C0011 and C0012 are located in the Shikoku Basin (Fig. F1), on the northwest flank and at the summit of a basement high known as Kashinosaki Knoll (Ike et al., 2008). The stratigraphic column for those sites is divided into five major facies units (Fig. F2). The section above the basement high is condensed, but all of the facies units can be correlated between sites.

The dominant lithology within Unit I of the Shikoku Basin (hemipelagic/pyroclastic facies) is clayey silt (hemipelagic mud to mudstone) with abundant interbeds of silt- to sand-size volcanic ash. At Site C0011, the depositional age of Unit I ranges from Quaternary to late Miocene (~7.6 Ma), based on integration of calcareous nannofossil events, paleomagnetic datums, and tephrachronology (see the “Site C0011” chapter [Expedition 333 Scientists, 2012b]). The base of Unit I at Site C0012 is approximately 7.8 Ma in age using a similar integrated age-depth model (see the “Site C0012” chapter [Expedition 333 Scientists, 2012c]).

Because of time limitations during Expedition 322, coring at Site C0011 started 340 meters below seafloor (mbsf) rather than at the mudline. The lithologic characterization of Unit I was based initially on logging-while-drilling results (see Underwood et al., 2010); those results were not verified by coring until Expedition 333 (see the “Expedition 333 summary” chapter [Expedition 333 Scientists, 2012a]). Coring of the upper intervals at Site C0012 was likewise deferred until Expedition 333. Previous studies in the Nankai-Shikoku region showed that hemipelagic mud(stones) change in composition largely as function of depositional age (e.g., Chamley, 1980; Chamley et al., 1986; Underwood et al., 1993a, 1993b; Steurer and Underwood, 2003; Underwood and Steurer, 2003; Guo and Underwood, 2012; Underwood and Guo, 2013). Hemipelagic sedimentation during the Miocene was dominated by expandable clay minerals (smectite group), whereas the proportions of detrital illite and chlorite increased steadily through the Pliocene and Quaternary. It is important to demonstrate whether or not sediments at Sites C0011 and C0012 conform to that temporal trend because the diagenetic and hydration states of subducting Shikoku Basin strata influence fluid production and hydrogeological properties within and beneath the Nankai accretionary prism (e.g., Saffer et al., 2008). This report documents the results of X-ray diffraction (XRD) analyses of 211 samples recovered during Expedition 333. Underwood and Guo (2013) presented complementary XRD data from the deeper Expedition 322 samples.

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