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doi:10.2204/iodp.proc.314315316.222.2015

Summary

The sediments recovered during Expedition 316 obtained flattened fabrics at their initial stage of deposition and partly overprinted when they were affected by later mechanical deformation. The shape parameter showed a scattered plot in the section of the megasplay fault (Site C0004) and mass wasting deposits (Sites C0004 and C0007). In contrast, the mass transport complex at Site C0008 has an enhanced compaction fabric. Despite many thrusts, the sediments of Sites C0006 and C0007 reveal a trend associated with compaction, with a drastic change in the orientation of magnetic fabric at the bottom of the holes.

Our results reflect the acquisition of compaction fabric in sedimentary materials during burial. However, anomalies in this general (and expected) trend provide information about the sediment deformation or diagenesis. In the lower part of the prism toe, at Sites C0006 and C0007, AMS fabrics occasionally rotate almost 90°, interpreted by Kitamura et al. (2010) as indication of horizontal compression. Later discussions raised the question of whether this horizontal compression is apparent, and this issue is under examination. The sedimentary character of the mass transport complex at Site C0008 was compared against another mass transport complex from neighboring Site C0018 in a previous paper (Kitamura et al., 2014). Results from Site C0004 showed complex magnetic fabrics across the megasplay fault. Thorough comparison between lithology, deformation, physical properties and magnetic fabric is necessary to document the magnetic fabric change associated with large-scale thrusting, which contributes to understand surface process of subduction zone and to provide better view of the evolution of accretionary prism.

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