Contents of B and other elements in Leg 192 sediments are given in Table T1. Boron content and H intensity of the sediments are plotted vs. depth in Figure F1.
Boron contents of the chert samples (17-62 ppm) are distinctly higher than those of the carbonates (2-15 ppm). Our B values are in the same range as reported values for marine sediments (Vengosh et al., 1991; Ishikawa and Nakamura, 1993). The high B contents in the chert samples are probably caused by the uptake of boron from seawater into tetrahedral silicon sites (Ishikawa and Nakamura, 1993).
Figure F1 shows that Unit I (ooze to chalk) has higher B contents than the lower units, Unit II and IIIA (limestone), at Site 1183. Positive correlation between B content and H intensity is also observed. The correlation could be explained by loss of B and H2O during fluid expulsion from the sediments as a result of compaction and shortening (e.g., You et al., 1995a). Average B content is 9.1 ppm for the chalk and 5.2 ppm for the limestone.
Most carbonates in Subunit IIIB have high B contents (up to 91 ppm), probably derived from clay minerals (predominantly illite), because clay minerals are high in B (>100 ppm) (Ishikawa and Nakamura, 1993).