ediments and porewaters were subsampled from two box cores collected at ~ 135 m depth on the landward slope of the largest basin of the Saguenay Fjord (Quebec, Canada). The Saguenay Fjord sediments are composed mostly of eroded glaciomarine clays surrounding the fjord area. The sediments contain relatively large concentrations of organic carbon and are sulfidic a few millimeters below the sediment-water interface. They are characterized by anomalously high Hg concentrations and acid volatile sulfide (AVS):pyrite ratios. The vertical distribution of total Hg concentrations in the sediments can be correlated to the organic matter content and an anthropogenic source. The high AVS:pyrite ratios reflect conditions conducive to preservation of Fe monosulfides.
In 1971, a catastrophic landslide resulted in the displacement and transport of 6.9 × 106m3 of post-Wisconsinian marine clay into the Saguenay Fjord. The landslide material was deficient in organic carbon and anthropogenic Hg relative to the indigenous sediment. Subsequent to burial, the landslide deposit influenced the migration and deposition patterns of mobilizable elements, acting alternatively as a sink and a source of reduced Fe and Mn as the redox boundary migrated through it. Nonsteady-state sulfate reduction rates were established due to the nonuniform distribution of organic carbon with depth. Iron sulfide peaks reflect this distribution and the position of the relict redox boundary. Manganese remobilization was apparently unaffected by the deposition of the landslide layer, and reduced Mn migrated freely to the redox boundary. A schematic representation of the sequence of diagenetic events which led to the postdepositional remobilization of Fe and Mn and the migration of the oxidation front following the deposition of the landslide material is proposed.