In this study, we analyzed 96 samples from Cores 167-1020B-1H through 8H that were taken on the drill ship at intervals of ~70 cm. The sediments consist of alternating pelagic and nannofossil clay. Wet samples of 10 cm3 were vacuum packed after sampling and stored in a refrigerator at 4°C. After freeze drying for 24 hr, samples were ground to powder in an aluminum mortar.
Biogenic opal contents of bulk samples were measured according to a method modified from the one described in Mortlock and Froelich (1989; Fig. 2A). Both total carbon (TC) and total organic carbon (TOC) contents were measured by using a LECO WR-112 carbon analyzer. Total inorganic carbon (TIC) content was calculated by subtracting TOC from TC content. TIC content represents biogenic carbonate carbon content because TIC content distinctly correlates with the peak intensities of calcite as determined by powder X-ray diffractometry (Fig. 2B). No dolomite was detected in any X-ray diffractograms, and terrigenous calcite was rare in the sediments, according to smear-slide observation. Biogenic calcium carbonate contents were therefore calculated by using the formula
Bulk mineralogies were also analyzed by powder X-ray diffractometry using a MacScience MXP3HF X-ray diffractometer to estimate the ratios between terrigenous and biogenic components. Major minerals in the samples are quartz, feldspar, calcite, and clay minerals. Quartz correlates negatively with calcite and positively with feldspar and clay minerals. Accordingly, the peak intensities of quartz were used as indices of terrigenous input. Total terrigenous material content were further calculated using the formula
An age model for Hole 1020B was constructed by using the oxygen isotope stratigraphy of Mix et al. (1995) during the past 340 k.y., the last appearance datum of Pseudoemiliania lacunosa, and the Brunhes/Matuyama magnetic boundary described by the Leg 167 shipboard scientific party (Lyle, Koizumi, Richter, et al., 1997) from 340 to 800 k.y. The age at the bottom of Core 167-1020B-8H is calculated to be ~800 ka.