Low-Temperature Oxidation and Subsequent Downcore Dissolution of Magnetite in Deep-Sea Sediments, ODP Leg 161 (Western Mediterranean)

Abstract

Low-temperature experiments document changes in magnetic mineralogy in Pleistocene hemipelagic sediments at ODP Holes 976D and 977A. The Verwey transition was observed only for samples below ∼1.3 mbsf, which suggests depth-limited appearance of stoichiometric magnetite in the sediment column. Primary magnetite is interpreted to be covered with a maghemite skin as a result of in situ low-temperature oxidation on the sea floor. The oxidized maghemite skin gradually dissolves with depth, and the Verwey transition is observed below ∼1.3 mbsf. This depth matches the iron redox boundary inferred on the basis of a sediment color change from tan to green.