A study of the effect of matrix properties on post-depositional remanent magnetization ( pDRM) acquisition in sediments

Laboratory deposition of either synthetic or natural sediments shows that clay minerals greatly affect the properties of magnetic remanence. Both remanent intensity and inclination shallowing can be linearly related to clay content. The experimental determination of water retention indicates the importance of sediment pore spaces in the remanence acquisition process. More pore spaces correspond to larger intensities and less inclination shallowing. Scanning electron microscope photographs identify a major difference in sedimentary textures between synthetic and natural samples. Synthetic samples have a dense book-like texture, whereas natural samples have a spacious card-house texture. The photographs also suggest that the difference in particle shape is responsible for the various textures. Therefore, stronger remanent intensity and less inclination shallowing are found in clay-rich natural samples since high clay content favors the formation of a card-house texture. The opposite is true for synthetic samples because of the absence of pore spaces in high clay content sediments.;Magnetic study of ocean sediments from Site 808 Ocean Drilling Program found two extremely low NRM intensity zones at great depths. The concentrations of light-weight hydrocarbon gases and calcite are relatively high in these two zones. Detailed study suggests that the low intensity zones are caused by diagenesis at depth, in which magnetite grains are dissolved by catagenetic decomposition of organic matter due to high temperatures. As a result, magnetite content drastically decreases, producing the weak NRM intensities. Magnetic grain size determination shows finer grains in these zones. It also suggests that for sediments with weak NRM intensity, the ratio of anhysteresis remanent magnetization (ARM) to saturation remanent magnetization (J...