AUTHIGENIC MANGANESE DEPOSITS SURROUNDING THE MISSISSIPPI CANYON 118 GAS HYDRATE AND COLD-SEEP FIELD: THEIR DOCUMENTATION, INTERPRETATION, AND UTILITY FOR EVALUATING REDOX STATE AND STABILITY OF SEDIMENTATION
Evaluation of the Mn-layers using reductive dissolution and acidification procedures indicates they are primarily Mn carbonate, suggesting dysoxic deposition associated with a “Mn-pump”. Spatially, the individual Mn-layers vary in concentration and frequency with respect to the position of seafloor gas hydrates and cold seeps, occurring more frequently and with lower concentrations of Mn at core sites positioned adjacent to MC118 field. This study investigates this key observation and a possible connection to dynamic sedimentation, which is in turn linked to the geomorphology of the field itself (related to salt diapirism), and importantly, variable redox conditions through changes in the duration and frequency of steady state versus non-steady state conditions. These highly-resolved Mn-deposits may provide important insight into the consistency of sedimentation at MC118, and by inference, related interactions between seafloor gas hydrates, cold seeps and associated salt diapirism at the site during the late Pleistocene and Holocene.