BARITE FRONTS IN CONTINENTAL-MARGIN SEDIMENTS - A NEW LOOK AT BARIUM REMOBILIZATION IN THE ZONE OF SULFATE REDUCTION AND FORMATION OF HEAVYBARITES IN DIAGENETIC FRONTS

Micro-crystalline barites recovered by deep-sea drilling from Site 684 on the Peru margin and Site 799 in the Japan Sea are highly enriched in the heavy sulfur isotope relative to seawater (delta(34)S up to +84 parts per thousand). This isotopic composition is consistent with rem obilization of biogenic barite triggered by sulfate reduction, and sub sequent reprecipitation as a diagenetic barite front. The high levels of barium sulfate in these deposits (10-50%) cannot be explained by a diffusive transport model in sediments experiencing a constant rate of sedimentation. When sedimentation rates change radically, the barite front will remain at a given depth interval leading to large accumulat ions of barium sulfate. Such conditions may have generated the barite deposits at Site 799. At Site 684, on the other hand, there is evidenc e that the barite deposits are a result of the tectonically-driven adv ection of sulfate-bearing fluids through the sediment column.