Superparamagnetism and reduction diagenesis in pelagic sediments: enhancement or depletion?

Superparamagnetic grains, ultra-fine (d < 0.05µm) particles unable to retain a remanence at room temperature, have come under increased scrutiny as indicators of the diagenetic and authigenic history of sedimentary 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, low-temperature, and geochemical studies of pelagic sediments from the western equatorial Pacific Ocean, it is proposed that reduction processes increase rather than deplete the ultra-fine magnetic grain population. At the modern Fe-redox boundary enhanced superparamagnetism coincides with a coarsening of remanence-carrying grains. Superparamagnetism also tracks proposed temporal changes in magnetite reduction caused by climatically-driven fluctuations in organic carbon (Corg) supply. Together with hysteresis characteristics, changes in superparamagnetism may help the identification of paleointensity artifacts resulting from non steady-state magnetic mineral reduction.

[1]  P. Flanders.  Collection, measurement, and analysis of airborne magnetic particulates from pollution in the environment (invited) , 1994 .

[2]  J. Tarduno.  Temporal trends of magnetic dissolution in the pelagic realm: gauging paleoproductivity? , 1994 .

[3]  R. Frankel,et al.  Rock magnetic criteria for the detection of biogenic magnetite , 1993 .

[4]  L. Meynadier,et al.  Geomagnetic field intensity and reversals during the past four million years , 1993, Nature.

[5]  D. Burdige.  The biogeochemistry of manganese and iron reduction in marine sediments , 1993 .

[6]  D. Dunlop,et al.  The effect of oxidation on the Verwey transition in magnetite , 1993 .

[7]  Subir K. Banerjee,et al.  Separation of local signals from the regional paleomonsoon record of the Chinese Loess Plateau: A rock‐magnetic approach , 1993 .

[8]  J. Tarduno,et al.  32. PALEOMAGNETIC ANALYSES OF SHORT NORMAL POLARITY MAGNETIC ANOMALIES IN THE MATUYAMA CHRON1 , 1993 .

[9]  F. Heller,et al.  Magnetic susceptibility of loess in China , 1991 .

[10]  M. Delaney.  Inorganic Geochemistry Summary , 1991 .

[11]  Lisa Tauxe,et al.  Normalized remanence in sediments of the western equatorial Pacific: Relative paleointensity of the geomagnetic field? , 1990 .

[12]  J. Mattei,et al.  Magnetic transition at 30-34 Kelvin in pyrrhotite: insight into a widespread occurrence of this mineral in rocks , 1990 .

[13]  R. Karlin,et al.  Authigenic magnetite formation in suboxic marine sediments , 1987, Nature.

[14]  D. Dunlop.  Hysteresis properties of magnetite and their dependence on particle size: A test of pseudo‐single‐domain remanence models , 1986 .

[15]  Hojatollah Vali,et al.  Fossil bacterial magnetite in deep-sea sediments from the South Atlantic Ocean , 1986, Nature.

[16]  R. Karlin,et al.  Geochemical and sedimentological control of the magnetic properties of hemipelagic sediments , 1985 .