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Diagenesis of carbonates in deep-sea sediments - evidence from Sr/Ca ratios and interstitial dissolved Sr (super 2+) data ()

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Laboratory determinations of the distribution coefficient of strontium in calcite (k Sr ) have confirmed the earlier results of Katz et al. (1972). In addition, we observed that at higher concentrations of strontium, values of k Sr were somewhat lowered. Chemical analyses of several deep-sea carbonate sediment sections and their associated porewaters (DSDP Sites 288, 289, 315, 317, and 357) as well as previously published data of other workers (DSDP Sites 116 and 305) have been used to demonstrate that these k Sr values are appropriate for use in diagenetic studies. We have successfully modeled the distribution of strontium in the pore waters and sediments. As a result, we conclude that recrystallization of these carbonates (and many other limestones as well) is essentially isochemical, the cement being derived from within the formation. Advective fluid flow through the rock is unnecessary to explain its lithification. Recrystallization of the bulk of the calcite in deep-sea sections is largely complete within the upper few hundred meters, but cementation is generally a later process. These results have important implications for the study of oxygen isotopic compositions of foraminifers and coccoliths in many sediments older than about 20 m.y. B.P. From correlations between changes in Sr/Ca and Mg/Ca ratios of recrystallized carbonates of DSDP Site 305 a distribution coefficient of magnesium in calcite sediments of 8.1 x 10- 4 ( nearly equal 5 degrees C) has been estimated. This value is many times smaller than previously published values.


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