Figure 31. Plot of dissolved Ca, Mg, and SiO2 at northern Woodlark Rise sites. The shapes of the Ca and Mg profiles reflect the effects of carbonate diagenesis and a variable extent of alteration of volcanic matter in the upper portion of the sedimentary column of each site. Deeper downhole, alteration of volcanics exerts a more dominant control on pore-water profiles. Large increases in dissolved Ca result primarily from alteration of plagioclase whereas depletion of Mg reflects its uptake during authigenic smectite formation. The dissolved SiO2 profiles depict a downhole progression including dissolution of volcanic ash in the upper sedimentary column, and WST reactions deeper downhole. Particularly elevated SiO2 concentrations deep in Site 1118 are attributable to an abundance of fresh to slightly altered volcanic matter in higher porosity sediments.
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