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 core from the Madeira Abyssal Plain which contains multiple turbidites. Previous studies of trace element (e.g. U) concentration and observations of sediment color changes have shown that turbidite emplacement has resulted in reductive diagenesis and the formation of paleoxidation fronts. We show that variations in sediment lithology and postdepositional 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 addition, fossil redox fronts are readily identified by rock-magnetic properties.