Insights into the origin of ferromanganese-rich deposits associated with South China Sea contourite depositional systems

Contourites are globally-distributed features along continental margins where deep-water masses come across the seafloor; however, the genesis and metal-sources of marine mineral deposits associated with contourite deposits remain largely unknown. Abundant Fe-rich nodules were recovered along the continental margin of the South China Sea, where extensive cold-seep systems were also discovered. We measured synthetically geochemical elements, δ13C, Sr and Nd isotopic data and organic proxies in Fe-oxy-hydroxide deposits from the upper and lower slope. Fe-rich nodules recovered from the upper slope represent the effect of an integrated diagenetic-hydrogenetic formation environment, in which fluid venting from deep-seated hydrocarbon reservoirs and deep-water erosion and chemistry could play an important role. In contrast, another kind of ferromanganese nodule forming along the lower slope and predominantly hydrogenetic is connected to a distinct deep-water flow from the North Pacific. These results give us a new insight into the mineralization processes associated with Fe oxidation-reduction processes on continental margins affected by contourite systems with abundant hydrocarbon seep, bottom water, and terrigenous inputs.