Signature of Non-steady-state Diagenesis in Continental Shelf Sediments

The phenomenon of non-steady-state diagenesis is well recognized in open ocean sediments and occurs either due to the deposition of turbidites on pelagic sediments or to changes in ocean productivity. However, the occurrence of oxidized sediment below reducing sediments in many near-shore and continental shelves indicates that non-steady-state diagenesis takes place even in shallow-water regimes. This paper shows that oxic conditions on the continental shelf result from low sedimentation rates induced by the rapid rise in sea level during the early Holocene to the beginning of late Holocene time, whereas a comparatively high rate of sedimentation (with increased burial of organic matter, generating reducing conditions) due to a relatively stable sea level during the late Holocene, is responsible for the initiation of non-steady-state diagenesis. The lower oxidized sediments have not yet experienced a sufficient flux of reductants to mobilize base metals. In contrast, base metals in the upper reducing sediments have undergone mobilization and diffused out of the sedimentary column to the overlying water.