(Table 1) Stable carbon and oxygen isotope ratios of interstitial-water samples of ODP Leg 133

The chemical compositions of the interstitial pore-water samples measured on board the JOIDES Resolution are compared with shore-based analyses of the samplesÆ strontium, oxygen, and carbon isotopic compositions. These analyses support conclusions of large-scale water movement through the sediment overlying the Queensland Plateau at Sites 811, 812, 813, and 814, possibly leading to massive platform dolomitization.
At the Queensland continental margin sites, complete sulfate reduction and abundant methanogenesis occurs, yet little evidence of these processes is seen in the d13C of the pore waters. The failure to observe these signatures is a consequence of large-scale recrystallization of carbonate sediments masking the isotopic signatures of these processes. Although abundant igneous material is present at these sites, we do not think that significant alteration of these minerals is taking place in situ. Decreases in the Mg2+ and Ca2+ concentration result from the formation of dolomite and calcite; decreases in K+ are a consequence of absorption onto clays; and decreases in the d18O are caused by carbonate recrystallization, with perhaps some minor influence from the alteration of volcanic glass.
At several sites there is evidence of diffusion of saline fluids from an underlying source, presumably evaporitic in nature, but this cannot be confirmed using either Sr or O isotopic data.