Chemical analysis of clinoptilites from ODP Hole 127797B

The clinoptilolites with highest Ba-concentrations occur directly below the base of the sulfate reduction zone, where pore water Ba concentrations are high due to the dissolution of biogenic barite. Downcore variations of the Ba content in clinoptilolites and pore water show that the formation of Ba-rich crystals at 299 m depth coincides with a decrease of the pore water Ba concentration.

Thus, formation of Ba-rich zeolites seems to provide a sink for dissolved Ba, although the occurrence of authigenic barite near the base of sulfate reduction might also contribute to the depletion of pore water Ba. These findings show that the intrachannel cation content of authigenic clinoptilolite is not directly controlled by a mineralogical precursor, but seems to reflect the geochemical conditions of the surrounding pore fluids.