| Abstract: | The concentrations and isotopic compositions of strontium in interstitial waters from several DSDP sites, where sediments consist chiefly of carbonate oozes and chalks, are used as indicators of carbonate diagenesis by reference to a recently-produced curve showing detailed variations in the87Sr/86Sr ratio of seawater with time. Carbonate sediments of the Walvis Ridge show increases in interstitial Sr2+ concentrations in the upper carbonate-ooze sections with the highest concentrations near the ooze-chalk boundary where maximum rates of carbonate recrystallization occur. Below this, in situ production of Sr2+ diminishes and there is a diffusive flux of Sr to an underlying sink, presumably volcanogenic sediments or basalts, leading to Sr isotopic disequilibrium between carbonates and interstitial waters. In some other sites, however, there is no apparent Sr sink at depth and isotopic equilibrium is retained. Overall, diffusive smoothing of profiles exerts an important control on the87Sr/86Sr ratios, although lower ratios than contemporaneous seawater values in the carbonate oozes often correlate with zones of Mg2+ loss and reflect a combination of a flux of Sr2+ from the zone of maximum recrystallization rates together with a contribution from the in situ alteration of volcanic matter. |
