(Table 1) Carbon, oxygen and strontium isotopic composition of the rhodochrosite nodules from DSDP Sites 503A and 503B

Calcic rhodochrosite occurs as nodules around burrows in late Neogene-early Pleistocene pelagic sediments of the Galapagos Ridge in the Guatemala Basin, eastern equatorial Pacific (DSDP Leg 68; Site 503). Growth was accomplished in the suboxic zone (d13C = -4.3 per mil to -1.3 per mil) at an estimated depth between ~30 and 70 cm beneath the seafloor. The rhodochrosites have 87Sr/86Sr ratios (0.708945–0.709073) that largely record the small-scale changes in seawater Sr-isotopic composition. The anomalous enrichment of the rhodochrosite in 18O isotopes (d18OPDB up to +6.4 per mil is attributed to the dissociation of gas hydrates.