Calcium carbonate in sediments at DSDP Leg 92

The carbonate contents of sediments recovered at Leg 92 Sites 597, 598, and 601 were determined at 5-cm intervals. The long-term record of carbonate variation at Sites 597 and 598 shows the effect of decreasing dilution by hydrothermal phases as the sites moved away from the ridge crest at which they formed. Superimposed on this trend are high-amplitude variations in carbonate content. In the lower portions of Sites 597 and 598 the high-amplitude variations have a duration of a few hundred thousand years. The upper portion of the sediment column at both sites was deposited below the lysocline, and high-amplitude variations in this interval represent 1 to 2 m.y. The data suggest that only very intense carbonate dissolution events can be identified reliably at sites with low accumulation rates. At sites like Site 598, where the sedimentation rate is higher, the details of carbonate variation can be correlated with the carbonate lithostratigraphies developed for sites in the equatorial and North Pacific oceans.