The 372 samples were selected from the recovered sedimentary sequence at Site 997 with about one sample per 2-m section. A portion of the selected sediment was dried at 50°C, after being desalinized with deionized water twice. The dried sediment sample was powdered for further analyses.
The powdered sample was heated until dry at 50°C in an oven for more than 12 hr to get rid of moisture from humidity, then it was heated at 110°C over 6 hr to determine the loss of H2O(-) and was heated further at 1100°C in a muffle furnace for 2 hr to obtain the result of loss on ignition (LOI).
The heated powder sample of 0.4000 ± 0.0004 g was mixed with 4.000 ± 0.0040 g anhydrous lithium borate and fused at 1150°C for 7 min to make a glass bead, by which the contents of SiO2, Al2O3, TiO2, Fe2O3, MnO, CaO, MgO, Na2O, K2O, and P2O5 were determined using a Rigaku 3270 X-ray fluorescence spectrometer with Rh tube at the Ocean Research Institute, University of Tokyo. The analytical conditions are 50 kV of acceleration voltage and 50 mA of electric current.
For ensuring accuracy, the standard sample was run once for each batch of 11 samples. The precision was tested by repeating measurements of three samples, and the obtained standard deviation is listed in Table 1, which shows excellent reproducibility.