Data report: consolidation characteristics of sediments from Sites C0002, C0006, and C0007, IODP Expeditions 315 and 316, NanTroSEIZE Stage 1

Abstract

Eighteen constant-rate-of-strain consolidation tests were performed on whole-round core samples from Integrated Ocean Drilling Program Sites C0002, C0006, and C0007. These sites are located along the Kumano transect of the Nankai Trough offshore south-central Japan; Site C0002 is in the forearc basin and the other two are in the frontal thrust zone. Sample depths range from ~35 to 920 m core depth below seafloor. The objectives of the laboratory tests were to obtain the compression characteristics of the sediments, to estimate the maximum pretest consolidation stress (P′c), and to determine values of hydraulic conductivity (K), intrinsic permeability (k), and compression index (Cc). Values of Cc at Site C0002 range from 0.391 to 0.780 (average = 0.584); comparable values are 0.236 to 0.418 (average = 0.302) in the trench-wedge facies at Sites C0006 and C0007. Values of in situ intrinsic permeability (ki) at Site C0002 show no trend with depth, ranging from 2.67 × 10–17 m2 to 2.56 × 10–18 m2. Estimates of ki at Sites C0006 and C0007 decrease with depth and range from 1.85 × 10–16 m2 to 6.08 × 10–18 m2. Test-derived values of P′c are consistently greater than the estimates of in situ hydrostatic vertical effective stress at equivalent sample depths, which means the specimens are overconsolidated. Environmental scanning electron microscopy was used to assess the degree of preferred particle orientation of the microfabric. The index of orientation averages 0.33 at Sites C0006 and C0007 and 0.38 at Site C0002. Most vertical sections show indexes of orientation greater than those for horizontal sections; exceptions to this pattern include several samples from Sites C0006 and C0007 where bedding dips >40°. Samples from deeper intervals of the forearc basin (Site C0002) and from the accreted upper Shikoku Basin facies at Site C0007 yielded the highest values of orientation index (>0.40), indicating better alignment of platy grains.