Browsing by Subject "rock magnetism, sediment magnetism, paleoclimate"

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    Contributions of fine‐particle magnetism to reading the global paleoclimate record (invited)
    (Journal of Applied Physics (American Institute of Physics), 1994) Banerjee, Subir
    Paleoclimate changes are recorded by proxy as variations in concentration, composition, and grain size of magnetic minerals, principally magnetite (Fe3O4), in the sediments deposited in lakes,oceans, and continental eolian deposits. Cross‐validated multiple‐parameter magnetic measurements of such sediment cores provide global change data of high temporal resolution, useful for constructing a base‐line record against which anthropogenic modifications may be discerned. Theories of superparamagnetism and magnetic domains are used to explain the physical basis of magnetic proxy recording. Examples of applications to validation of Milankovitch theory of climate change and delineation of the glacial and interglacial stages of the last 1 000 000 years are provided.
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    Rock-magnetic proxies of climate change in the loess-palaeosol sequences of the western Loess Plateau of China
    (Geophysical Journal International (Oxford University Press), 1995) Hunt, Christopher; Banerjee, Subir; Han, J.=M.; Solheid, Peter; Oches, E.A.; Sun, Wei-wei; Liu, T.-S.
    Results of the first detailed study of the climate proxy record in the loess-palaeosol sequence at Xining—one of the few palaeoclimate sites in the currently arid western Loess Plateau of China—illustrate the importance of making many types of rock-magnetic measurements other than susceptibility. A multiparameter approach yielded confirmation that here, as elsewhere in the Loess Plateau, the susceptibility enhancement in palaeosols was caused primarily by ultrafine magnetite and maghaemite. Nevertheless, magnetic enhancement was caused not exclusively by changes in relative grain size, but also by variations in concentration and mineralogy of the magnetic fraction. The effects of concentration variations were removed through normalization of susceptibility and anhysteretic remanence with saturation magnetization and saturation remanence, respectively. The resulting signal was ascribed more confidently to variation in magnetic grain size, which in turn was interpreted as a better proxy of pedogenesis than simple susceptibility. Variations in magnetic mineralogy were also determined to constrain interpretations further. The data were then used to discuss climate history at Xining. Finally, results from Xining were compared with other western sites and contrasted with eastern sites. In summary: (1) data is presented from a new Loess Plateau site which also appears to yield a global climate signal; (2) a demonstration is made of a more rock-magnetically robust way to separate concentration, composition and grain-size controls on susceptibility and other magnetic parameters; and (3) models are provided for inter-regional comparisons of palaeoclimate proxy records.