We analyzed 38 carbonate samples collected from Sites 1183 and 1186 (Table T1). The sedimentary sequences of these two sites are divided into three lithologic units based mainly on the presence or absence of chert (Mahoney, Fitton, Wallace, et al., 2001). Unit I consists of ooze to chalk, and Units II and III mainly consist of chalk to limestone. Although the sedimentary units of these sites are dominated by carbonates, Unit II is characterized by intercalation of chert blocks and the lowermost part of Unit III includes dark calcareous volcaniclastic sandstone.
Boron, Ca, Na, and Gd concentrations and H intensity (measured in counts per second per gram) were determined by prompt gamma neutron activation analysis (PGNA) at the thermal and cold neutron beam guide of the JRR-3M reactor, Japan Atomic Energy Research Institute (Yonezawa et al., 1999). Samples were washed in an ultrasonic bath containing distilled water and then dried for >12 hr in an oven at 110°C. The cleaned samples were ground to a fine powder in a tungsten carbide mill. The sample powder (0.5-0.6 g) was cold-pressed into disks (12 mm in diameter and 2-3 mm in thickness). These disks were heat-sealed in 25-micron-thick fluorinated ethylenepropylene resin film smaller than 14 mm x 14 mm. A compton suppression prompt gamma activation spectrum was accumulated for 1,200-12,000 s. Geological Survey of Japan standards JLs-1 and JB-2 were used to calibrate the B, Ca, Na, and Gd contents. Details of the analytical procedures have been described in Sano et al. (1999). Replicate analyses of JB-2 indicate overall precision and accuracy on the order of 3% for B, Na, and Ca and 6% for Gd.