Oxidation fronts in pelagic sediments: diagenetic formation of metal-rich layers.

The periodic deposition of distal turbidites at a site on the Madeira Abyssal Plain causes the development of a nonsteady-state diagenetic system in which an oxidation front migrates downward into the sediment. Data presented here show that iron, manganese, and particulate organic carbon are oxidized at this front by oxidants (molecular oxygen and nitrate) diffusing from above. A numerical model of systems of this type predicts the formation of iron-rich layers under certain nonsteady-state conditions. The layers predicted by the model are closely comparable in thickness and general morphology to iron-rich layers found in certain ocean sediments, the origin of which has been until now unexplained.