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doi:10.2204/iodp.proc.314315316.207.2011

Introduction

The systematic investigation of particle size distribution of clastic sediments dates back to benchmark studies by, for example, Udden (1914), Wentworth (1922), Spencer (1963), and Folk (1966). More recently, grain size analysis of large populations of sediment samples obtained with modern and fast instruments has found an important application in the study of sedimentary processes and their environmental significance (Stow and Wetzel, 1990; Weedon and McCave, 1991; Jones et al., 1992; Lucchi and Camerlenghi, 1993; Rothwell et al., 1994; Sutherland and Lee, 1994).

The Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) complex drilling project defines as one of its foremost objectives to shed light on the changes in physical properties and stress state of the Nankai Trough plate boundary thrust as well as prominent out-of-sequence thrusts (OOSTs) splaying off this detachment surface (Tobin and Kinoshita, 2006). On board the D/V Chikyu, no apparatus for grain size measurements exists. As a consequence, the systematic study of particle size distributions along the NanTroSEIZE transect of drill sites off the Kii Peninsula (Fig. F1) is hampered. On the other hand, such a study, when combined with X-ray diffraction (XRD) analysis, seems crucial to unraveling how particle size and mineralogical composition influence the onset of faulting at the toe of the accretionary prism and within the incoming sedimentary sequence and further downdip along the plate boundary thrust (see similar work in western Nankai [Brown et al., 2003], central Nankai [Kopf and Brown, 2003; Underwood et al., 2003], Barbados [Deng and Underwood, 2001], and Costa Rica [Spinelli and Underwood, 2004]). In this short manuscript we show results from particle size analyses of a large number (>600) of sediment samples from all NanTroSEIZE Stage 1 drill sites where coring took place (see Tobin et al., 2009a). These data hopefully will become an important component in future manuscripts concerning sediment-tectonic stratigraphy and processes, but also the physical properties and mechanical response of fault zone materials and surrounding hanging wall and footwall sediments.

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