--> Abstract: Authigenic Calcite and Barite in Sediments from the Derugin Basin, Sea of Okhotsk, by A. N. Derkachev, G. Bohrmann, and J. Greinert; #90920 (1999).

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DERKACHEV, ALEXANDER N., Pacific Oceanological Institute, Vladivostok; GERHARD BOHRMANN, and JENS GREINERT; GEOMAR Research Center, Kiel

Abstract: Authigenic Calcite and Barite in Sediments from the Derugin Basin, Sea of Okhotsk

Authigenic minerals were recovered in the Derugin Basin in 1981, 1986, and 1993 consisting of various morphological types of barite-carbonate-associations from Holocene to Pleistocene sediments. The precipitates appear as tubular bodies 2-15 mm in diameter and 20-100 mm in length and often have dendritic forms. The bodies consist of monomineralic barite or Mg-calcite cementing the sediment, or show a concentric precipitation of Mgcalcite followed by small needle-shaped barites growing in a formerly open pore space. They represent a diagentic cementation of open worm tubes. Apart from these bodies, soft calcite concretions with smooth edges (15-20 mm) and dense, flat and irregular calcite concretions (20-60 mm) were also found in distinct horizons.

Isotope analyses of the carbonates are d18O = 3.8 to 4.9 ‰ PDB and d13C = -37.6 and -42.3 ‰ PDB, clearly implicating methane as the major C-source. In different horizons both values show variations with a maxima in d13C and d18O which correlate with the Holocene/Pleistocene boundary. This may possibly be induced by intensity changes of methane oxidation and different bottom water temperatures during glacial-interglacial times. Typically for vent sites, the oxidation of methane occurs via bacterial sulfate reduction causing an increase of d 34S values in the residual sulfate which could be recognized in the d 34S values for barite (<64.5 ‰ CDT). For the Ba-source we suppose remobilisized biogenic Ba from below the sulfate reduction zone which ascends with methane to the sediment surface and causes the calcite-barite precipitation

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California