RARE-EARTH ELEMENT DEPOSITION IN PELAGIC SEDIMENT AT THE CENOMANIAN-TURONIAN BOUNDARY, EXMOUTH PLATEAU

ODP Site 762 (eastern Indian Ocean) includes a section of sediment tha t spans the Cenomanian-Turonian Boundary (CTB) and was deposited along a continental margin during a period of widespread oceanic O-2 defici ency. The rare earth element (REE) content of pre- and post-boundary s ediment is similar to that of present-day continental slope material d eposited in well-oxygenated seawater, whereas the CTB section is chara cterized by significantly depleted REE abundances, a bulk Ce anomaly t hat increases to maximum of 1.0, and a REE pattern that resembles that of present-day fluvial material. We suggest the change in REE pattern s reflects release of scavenged REEs upon reductive dissolution of aut higenic Fe-Mn oxyhydroxides, such that sediment deposited during the C TB is dominated by the lithogenous REE fraction. These results are con sistent with recent models concerning pervasive fractionation of Mn an d Fe and redirection of Mn in pelagic CTB waters.