SAMPLING AND SAMPLE PREPARATION

Sampling was conducted at TAMU ~3 months after the cruise. Samples of ~20 cm³ in volume were taken from Cores 167-1017E-1H through 3H in 3-cm intervals. These samples were immediately placed in k-packs, vacuum sealed, and double packed. Samples for X-ray radiography were taken separately as 20-cm-long thin slabs. The slab samples were taken continuously throughout cores using a plastic case of 20 × 2 × 0.7 cm in size and immediately sealed. These samples were sent to the University of Tokyo and stored in a refrigerator under 10°C. All the samples taken from Core 1H (197 samples) and every other sample from Core 2H (168 samples) were subject to inorganic geochemical analyses.

For X-ray diffraction (XRD), X-ray fluorescence (XRF), and carbon analyses, ~12 g of wet samples were washed and centrifuged twice with double distilled water to completely remove salts. The centrifuged samples were dried at 50°C for 24-48 hr, powdered with an agate mortar, and stored in glass tubes.

For grain-size analysis, the following three steps of chemical treatment, which are modified from the procedure of Rea and Janecek (1981), were applied to the samples to isolate the detrital component. Because the studied samples contain only trace amounts of siliceous bioclasts, an opal removal treatment was not conducted.

Step 1. Sea salt and Fe-Mn oxides removal. A dithionite-citrate system buffered with sodium bicarbonate was used (Mehra and Jackson, 1960). Approximately 0.06 g of sample was placed in a 70-cm³ centrifuge tube and 40 mL of 0.3-M sodium citrate and 5 mL of 1.0-M sodium bicarbonate were added. The tubes were placed in a 80°C water bath, ~1 g of sodium hydrosulfite was added, and it was stirred well. After 8 hr of reaction, dispersed samples were centrifuged until the supernatant became clear and was then siphoned off. Samples were washed with 50 cm³ of 0.3-M sodium citrate and then with 50 cm³ of filtered deionized water (DIFW) and centrifuged.

Step 2. Carbonate removal. Forty cubic centimeters of 20 vol% acetic acid was added to samples and stirred. Dispersed samples were shaken for 8 hr. Then samples were centrifuged until the supernatant became clear and was then siphoned off. Samples were washed with 50 cm³ of DIFW and centrifuged.

Step 3. Organic removal. Approximately 40 mL of 10% H₂O₂ was added to samples, and the centrifuge tubes were placed in a 60°C water bath until the bubbling reaction stopped. The samples were then centrifuged until the supernatant became clear and was then siphoned off. Samples were washed with 50 cm³ of DIFW and centrifuged.

After this chemical leaching procedure, samples were kept wet to prevent aggregation. All the treated samples were introduced into the grain-size analyzer to prevent grain-size segregation during transfer.