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doi:10.2204/iodp.proc.348.202.2016

Results

Table T2 shows all of the peak-area XRD values (total counts) for common minerals in the clay-size fraction. We also list the calculated values of mineral abundance (wt%) using SVD normalization factors and percentages using the Biscaye (1965) peak-area weighting factors. Relative abundances vary considerably, in accordance with the diverse lithologies recorded in visual core descriptions (Fig. F3). Values for clay-size smectite range from 11.4 to 98.2 wt%, with a mean (µ) of 39.5 wt% and a standard deviation (s) of 17.9. Values for illite range from 1.6 to 46.7 wt% (µ = 32.4; s = 8.5). Percentages of kaolinite + chlorite range from 0.1 to 37.0 wt% (µ = 25.1; s = 7.8); in all cases, chlorite is the dominant mineral over kaolinite. Percentages of clay-size quartz range from 0.1 to 13.9 wt% (µ = 3.0; s = 4.1). In comparison, mineral abundances in cuttings from the same depth intervals of Hole C0002P are more uniform, and values are close to the averages from core samples (see Underwood, submitted).

Figure F3 shows the exact position of each sample interval on core-scale graphical depictions of lithology. Plotted next to each position are the calculated relative abundances of smectite, illite, and kaolinite + chlorite within the bulk mudstone. Those bulk smectite values range from 4.4 to 71.6 wt% (µ = 23.8; s = 13.2). Most percentages of smectite are significantly lower than what Underwood and Guo (2013) documented for coeval Miocene strata (9.56–10.73 Ma) at IODP Sites C0011 and C0012 in the Shikoku Basin (i.e., subduction inputs). Illite in the bulk sediment ranges from 1.2 to 27.6 wt% (µ = 18.7; s = 4.9), and kaolinite + chlorite ranges from 0.1 to 21.7 wt% (µ = 15.0; s = 5.0).

Indicators of clay diagenesis are tabulated in Table T3. Illite crystallinity (Kübler) indexes range from 0.71 to 0.40Δ°2θ, with an average value of 0.52Δ°2θ. As a frame of reference, the upper limit for diagenesis is 0.52Δ°2θ, and the upper limit for anchizone metamorphism (incipient greenschist facies) is 0.32Δ°2θ (Warr and Mählmann, 2015). The expandability of illite/smectite mixed-layer clays ranges from 90% to 62%, with an average value of 70%. The proportion of illite in illite/smectite mixed-layer clays ranges from 13% to 54%, with an average value of 41%.

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