Table T3 shows the percentage of sand-, silt-, and clay-sized particles by weight (equivalent setting diameter) for the four sites studied. Where measured, the percentage of organic matter by weight is also shown. Typical total losses through digestion by H2O2 were ~2% by weight, although this amount also includes any small losses during the sieving process. In cases in which the loss through digestion was not measured, the nonsand portion of the sediment is assumed to be 100% minus the percent by weight of sand. Table T3 also shows the percentage of counts per cubic centimeter <4 µm, as measured by the LPC, as well as the mean particle size and standard deviation of distribution calculated from the LPC results. Figures F2, F3, and F4 show the variations of grain-size classes with depth for Sites 1173, 1174, and 1177, respectively.
Figures F2, F3, and F4 also show the percentage of clay by weight as determined by the empirical correlation of LPC measurements to pipette analysis and mean grain size and sorting. We correlated each of these parameters to moisture and density properties for each site, and representative plots of these regressions may be seen in Figure F6. Because of the low weight percentages of sand and organic matter, the percentage of silt is approximately equal to 100% minus the percentage of clay and is therefore not displayed in the illustrations.
Grain-size data were collected from the upper and lower Shikoku Basin facies at this site, with a single datum for the volcaniclastic facies. As expected for hemipelagic sediments, the proportion of sand is low, averaging 2% by weight in the upper Shikoku Basin facies and <1% in the lower Shikoku Basin facies. Mudstones from the lower Shikoku Basin facies contain more clay-sized particles than mud from the upper Shikoku Basin facies, ranging from 30% to 80% by weight. Except for two very low values, the average percentage of clay by weight for the upper Shikoku Basin facies is 41%, and for the lower Shikoku Basin facies it is 64%. This increase in the abundance of clay-sized particles coincides with an increase in total clay minerals at the boundary between the upper and lower Shikoku Basin facies (Shipboard Scientific Party, 2001b).
The average mean particle size as calculated from LPC for samples from the upper Shikoku Basin facies is 2.6 µm and 2.2 µm for samples from the lower Shikoku Basin facies. The average standard deviation of particle size for samples from the upper Shikoku Basin facies is 2.2 µm and 1.8 µm for the lower Shikoku Basin facies.
Grain-size data were collected from the hemipelagic sediments of the trench-wedge, upper, and lower Shikoku Basin facies at Site 1174. The relative proportion of sand is low. The trench-wedge samples have an average of 1% of sand by weight, the upper Shikoku Basin facies shows an average of 2%, and the lower Shikoku Basin facies contains an average of 1%. The increase of clay-sized particles with depth is more subtle at Site 1174 than at Site 1173 but nonetheless present. Clay increases from ~50% at the top of the trench-wedge facies to ~65%-70% at 850 mbsf. Below this depth, the percent clay remains at ~60% to the base of the unit. This increase in clay-sized particles coincides with an increase of total clay minerals (Shipboard Scientific Party, 2001c). The average percent clay by weight for the trench-wedge facies is 44%, for the upper Shikoku Basin facies it is 56%, and for the lower Shikoku Basin facies it is 65%.
The average mean particle size is 2.4 µm for the trench-wedge facies, 2.3 µm for the upper Shikoku Basin facies, and 2.2 µm for the lower Shikoku Basin facies. The average standard deviation is equal to 2.1 µm for samples from the trench wedge, 2.0 µm for samples from the upper Shikoku Basin facies, and 1.7 µm for samples from the lower Shikoku Basin facies.
The four samples of sediment from Site 1175 are generally richer in sand than those from the other sites, ranging from 2% to 8%. Silt ranges from 32% to 55%, and clay ranges from 38% to 64%. The mean size of the <63-µm fraction is 2.3 µm, and the average standard deviation for these samples is 2.0 µm.
We collected grain-size data from the hemipelagic sediments of all units at this site. The upper Shikoku Basin facies has average proportions of <1%, 42%, and 57% for sand, silt, and clay-sized particles by weight, respectively. The lower Shikoku Basin hemipelagic facies contains averages of 1% sand-, 39% silt-, and 59% clay-sized particles, although only four samples from this unit were analyzed. Mud from the lower Shikoku Basin turbidite facies contains an average of 1% sand, 34% silt, and 63% clay, exclusive of one anomalously sandy sample that came from a turbidite. The volcaniclastic-rich facies contains averages of 2% sand-, 47% silt-, and 51% clay-sized particles, although the data are scattered with the percent clay ranging from 10% to 75%.
The average mean grain size for the upper Shikoku Basin facies is 2.3 µm, 2.2 µm for the lower Shikoku Basin hemipelagic facies, 2.1 µm for the lower Shikoku Basin turbidite facies, and 2.3 µm for the volcaniclastic-rich facies. The average standard deviations are 1.9 µm for the upper Shikoku Basin facies, 2.0 µm for the lower Shikoku Basin hemipelagic facies, 1.8 µm for the lower Shikoku Basin turbidite facies, and 2.0 µm for the volcaniclastic-rich facies.
As may be seen in Figure F6, bulk density seems to increase with weight percent clay. Porosity, void ratio, and water content decrease with weight percent clay. Nearly identical trends are also seen with mean grain size and standard deviation. The correlations between physical properties and grain-size distribution are stronger for samples from Sites 1173 and 1174 than for those from Site 1177. For Site 1173, correlation coefficients between weight percent clay, mean grain size, or standard deviation and porosity, bulk density, void ratio, or water content range from 0.53 to 0.58. For Site 1174, correlation coefficients range from 0.48 to 0.58. For Site 1177, correlation coefficients range from 0.15 to 0.36.
Results from analyses of variance demonstrate that all correlations between all three grain-size measures and properties for Sites 1173 and 1174 are statistically significant above the 95% confidence interval. For Site 1177, only correlations between average grain size and standard deviation with the properties of bulk density and water content, as well as percent clay with bulk density, were significant at the 95% confidence interval.