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doi:10.2204/iodp.proc.333.201.2014

Results

All nomenclature is provided in Table T1. Consolidation, grain size, and specific surface data are summarized in Table T2. MICP data are summarized in Table T3. Complete experiment data for consolidation (333_CONSOL), grain size (333_GRAIN_SIZE), and MICP (333_MICP) are provided in “Supplementary material.”

Porosity values determined in the laboratory are shown in Figure F5 along with shipboard MAD results. The laboratory values agree well with the MAD values. However, neither the laboratory nor the MAD porosity values were corrected for smectite content. Smectite contains significant volumes of interlayer water, and uncorrected porosity may overestimate the volume of intergranular porosity available for fluid flow. Gamage et al. (2011) showed that smectite corrections in Nankai sediments can decrease porosity by roughly half. Deeper samples from Sites C0011 and C0012 have smectite contents of 31–55 wt% (Underwood and Guo, 2013), which correspond to interlayer water mass fractions of roughly 6–11 wt% assuming clay interlayer spacing of 1.5 nm (Gamage et al., 2011). Detailed clay mineralogy information on the samples we measured would make this correction possible. The results we present here, as well as the shipboard MAD values, therefore represent an upper limit of the true intergranular porosity.

Laboratory measurements are plotted against depth in Figures F6, F7, and F8. The depth reference is meters core depth below seafloor (CSF-B), which corrects the core depth for expansion in cases where core recovery exceeds 100% (see IODP Depth Scales Terminology v.2 at www.iodp.org/program-policies/procedures/guidelines/). Permeabilities (k₀) interpreted from CRS consolidation experiments for Sites C0011, C0012, and C0018 range from 2.3 × 10^–14 m² to 5.9 × 10^–19 m² and generally decrease with increasing depth (Table T2; Figs. F6A, F7A, F8A). Compression indexes (C_c) range from 0.26 to 2.7 and decrease with increasing depth, except at Site C0011, where the highest values are encountered between 90 and 200 m CSF-B (Table T2; Figs. F6B, F7B, F8B). The general decrease in C_c with depth is consistent with established trends of decreasing C_c with decreasing porosity (e.g., Long et al., 2011). This trend is reversed, however, in lithologic Subunit IA at Sites C0011 and C0012, and the depth interval of this reverse trend corresponds with the depth interval of anomalously high porosity at these sites (see the “Site C0011” and “Site C0012” and “Expedition 333 summary” chapters [Expedition 333 Scientists, 2012a, 2012b, 2012c]). OCRs range from 0.20 to 4.1 and generally decrease with depth, with a few exceptions at Sites C0011 and C0018 (Table T2; Figs. F6C, F7C, F8C). The three samples from Mass Transport Deposit (MTD) 6 at Site C0018 show an increase in OCR toward the base of the MTD, which is consistent with observations of shearing-induced consolidation in MTDs (e.g., Dugan, 2012). The CRS consolidation tests performed on Sample 333-C0012E-3X-4, 31.5–37.5 cm, perpendicular to the borehole axis (i.e., horizontal) yielded permeability 56 times higher than the vertical permeability and a similar value of C_c (Table T2).

Specific surface (S_a) values range from 25.7 to 77.7 m²/g (Table T2; Figs. F6D, F7D, F8D). S_a generally increases with depth within Subunit IA at all sites. Median grain size (D₅₀) ranges from 1.10 to 15.4 ?m, and samples are dominated by silt- and clay-sized particles, with silt-sized particles comprising 32.3% to 67.1% of all samples by mass (Table T2; Figs. F6E, F7E, F8E). Clay-sized particles account for 22.5% to 67.7% of all samples by mass (Table T2; Figs. F6F, F7F, F8F). The only sample with >10% sand-sized particles by mass is located at 222.28 m CSF-B in Hole C0018A. For spherical grains, S_a is inversely proportional to grain size (Santamarina et al., 2002). Our S_a values show little correlation with grain size (Fig. F9), except for one sample from Site C0018 which has low S_a and relatively high D₅₀. This overall lack of apparent trend may be due to the narrow range of D₅₀ present in these data.

Median pore radii (r₅₀) interpreted from MICP measurements range from 0.087 to 0.36 ?m, and air-water capillary entry pressures (P_c) range from 64 to 770 kPa (Table T3; Figs. F10A, F10B, F11A, F11B, F12A, F12B). Although consolidation would be expected to reduce pore sizes and increase capillary entry pressure (e.g., Dewhurst et al., 1999), neither r₅₀ nor P_c exhibit any consistent trends with depth across the three sites. The samples from MTD 6 at Site C0018 exhibit a general decrease in r₅₀ and increase in P_c with increasing depth within the MTD (Fig. F12A, F12B). Hydraulic radius theories of permeability predict a power-law relationship between permeability and pore size (Dullien, 1992), and from Equation 9 there should be a corresponding power-law relationship between permeability and P_c. The data from Site C0011 show such trends (Fig. F10A, F10B), but the relationships at Sites C0012 and C0018 are more complicated (Figs. F11A, F11B, F12A, F12B).

Our results were determined at laboratory conditions and are therefore subject to sample disturbance during coring and during experimental preparation in the laboratory. Visual inspection of samples prior to trimming the CRS consolidation tests did not reveal any flaws in the samples, which was consistent with the shipboard sampling procedure of selecting intervals free of cracks or voids based on CT images. However, several samples were computed to have an OCR <1, suggesting underconsolidation. Underconsolidation may be associated with in situ fluid pressure in excess of hydrostatic pressure (e.g., Long et al., 2008), and this may be the cause of the low OCR for Sample 333-C0018A-16H-2, 40–45 cm, which experienced expansion in the core barrel (see the “Site C0018” and “Expedition 333 summary” chapters [Expedition 333 Scientists, 2012d, 2012a]) and was difficult to remove from the liner in the laboratory. However, the other OCR values <1 are associated with extended punch coring system (EPCS) and extended shoe coring system (ESCS) cores, which were noted to return poorer quality cores than the hydraulic piston coring system (HPCS) (see the “Site C0018” chapter [Expedition 333 Scientists, 2012d]). Coring disturbance erases some of the original stress history from samples and causes yield to virgin consolidation at lower effective stresses (La Rochelle et al., 1981) and therefore results in low OCR values. This probably affected some of the deeper samples from Sites C0011 and C0018.

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