MAGNETIC MEASUREMENTS USED TO IDENTIFY PALEOXIDATION FRONTS IN DEEP-SEA SEDIMENTS FROM THE MADEIRA ABYSSAL-PLAIN

We describe the results of rock-magnetic measurements of a sediment co re from the Madeira Abyssal Plain which contains multiple turbidites. Previous studies of trace element (e.g. U) concentration and observati ons of sediment color changes have shown that turbidite emplacement ha s resulted in reductive diagenesis and the formation of paleoxidation fronts. We show that variations in sediment lithology and postdepositi onal sedimentary processes can be characterized very sensitively using magnetic measurements. Low concentrations of magnetic minerals occur in turbidites with a high organic content, reflecting the destruction of magnetic material via the process of reductive diagenesis. In addit ion, fossil redox fronts are readily identified by rock-magnetic prope rties.