SUPERPARAMAGNETISM AND REDUCTION DIAGENESIS IN PELAGIC SEDIMENTS - ENHANCEMENT OR DEPLETION

Superparamagnetic grains, ultra-fine (d < 0.05 mu m) particles unable to retain a remanence at room temperature, have come under increased s crutiny as indicators of the diagenetic and authigenic history of sedi mentary rocks. In marine sediments, fine-grained magnetite with large surface area to volume is thought to be preferentially removed during magnetic mineral reduction. On the basis of new magnetic hysteresis, l ow-temperature, and geochemical studies of pelagic sediments from the western equatorial Pacific Ocean, it is proposed that reduction proces ses increase rather than deplete the ultra-fine magnetic grain populat ion. At the modern Fe-redox boundary enhanced superparamagnetism coinc ides with a coarsening of remanence-carrying grains. Superparamagnetis m also tracks proposed temporal changes in magnetite reduction caused by climatically-driven fluctuations in organic carbon (C-org) supply. Together with hysteresis characteristics, changes in superparamagnetis m may help the identification of paleointensity artifacts resulting fr om non steady-state magnetic mineral reduction.