Exceptional barium-rich clinoptilolite, a heulandite-group zeolite, with Ba contents of up to 1.83 wt.% BaO occurs in Miocene sediments from the Yamato Basin of the Japan Sea (ODP Site 797). 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. The formation of Ba-rich clinoptilolites in a sulfate-depleted environment with elevated pore water Ba concentrations and the concurrent decrease of dissolved Ba in the pore fluids documents the mutual influence of pore water composition and mineral chemistry during diagenetic processes in marine sediments.

Supplement to: Nähr, Thomas H; Bohrmann, Gerhard (1999): Barium-rich authigenic clinoptilolite in sediments from the Japan Sea - a sink for dissolved barium? Chemical Geology, 158(3-4), 227-244