Journal of Geophysical Research (American Geophysical Union)
Our previous study of deep sea sediments from site 808, leg 131 of the Ocean Drilling Program has demonstrated that the two anomalously low-intensity zones of natural remanent magnetization (NRM), 675 to 925 and 1080 to 1243 m below seafloor, were caused by unusually low magnetite content in the sediment sections and that this was not related to the variations in sediment sources, calcite dilution, or magnetite destruction occurring in the top sediment layer during early diagenesis. For an explanation, we now suggest that these low INRM intensity zones were produced by catagenesis at great depth by organic matter decomposition in sediments, which in turn causes magnetite dissolution and hence a lower magnetite content. A similar process also applies to manganese ions; as a consequence, iron and manganese concentration, grain size and content of magnetite, and NRM intensity all decrease, whereas sulfur content increases in these sediments. Our interpretation is also supported by other studies of organic geochemistry and sedimentology of these same sediments. We suggest, therefore, that detailed rock magnetic and geochemical tests should be carried out before geomagnetic field variations are studied using ocean sediments from such great depth. Additionally, we suspect that catagenesis may have been retarded and magnetic degradation was prevented near a décollement due to cold water percolation.
Lu, R., and S. K. Banerjee (1994), Magnetite dissolution in deep sediments and its hydrologic implication: A detailed study of sediments from site 808, leg 131, J. Geophys. Res., 99(B5), 9051–9059, doi:10.1029/93JB03204.
This work is supported by National Science Foundation grant EAR-9005776 and Texas A&M Research Foundation grant P020475 to S.K. Banerjee and
R. Lu. This paper is contribution 9207 from the Institute for Rock Magnetism, established by the Keck Foundation, the National Science Foundation, and the University of Minnesota.
Lu, Ran; Banerjee, Subir.
Magnetite dissolution in deep sediments and its hydrologic implication: a detailed study of sediments from site 808, leg 131.
Journal of Geophysical Research (American Geophysical Union).
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