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

Now showing 1 - 4 of 4
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    Magnetic stratigraphy of Chinese loess as a record of natural fires
    (Geophysical Research letters (American Geophysical Union), 1995) Kletetschka, Gunther; Banerjee, Subir
    Magnetic susceptibility records of paleosols and loess show high correlation with oxygen-isotope stratigraphy of ocean sediments [Kukla, 1987], providing a global paleoclimatic record. Different models have been put forth to explain the nature and cause of susceptibility variations, but consensus has not yet been achieved. Our low-temperature studies reveal a secondary magnetite component in paleosols that is characterized by a higher Verwey transition (115K) than that for the magnetite (100 K) in unaltered loess. The same shift in the Verwey transition can be achieved by heating and cooling loess samples. This is consistent with a new hypothesis that the magnetic signal from paleosols may be produced by natural fires in the past. Natural fire intensity is sensitive to the amount of annual precipitation, so that increased fire-induced susceptibilities should reflect an increase in the humidity of regional climate.
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    Millennial-scale climatic change during the last interglacial period: Superparamagnetic sediment proxy from paleosol S1, western Chinese Loess Plateau.
    (Geophysical Research Letters (American Geophysical Union), 1999) Fang, Xiaomin; Li, J.-J.; Banerjee, Subir; Jackson, Mike; Oches, E.A.; Van der Voo, Rob
    Detailed magnetic analyses of samples from the Jiuzhoutai well section on the western Chinese Loess Plateau reveal high-resolution signals of summer monsoon change. The last interglacial period is represented here by the 8-meter thick S1 paleosol complex. We have used low-temperature remanence studies to analyze variations in the concentration of Superparamagnetic (SP) grains, which previous studies have shown to be largely of pedogenic origin. The SP concentration, interpreted as a proxy for the extent of pedogenesis, shows millennial scale variations within S1. We conclude that the last interglacial period in Asia was characterized by rapid climate fluctuations, with at least one brief return to near-glacial conditions in the middle of oxygen-isotope substage 5e.
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    Sediment reveals Early Holocene climate change in China
    (EOS (American Geophysical Union), 1996) Banerjee, Subir
    A major question regarding paleorecords is whether the easy-to-acquire oceanic record can be validated by continental proxy records that are available only from the Arctic and Antarctic ice cores. The ice core records may not provide a complete record of the changes that have occurred in the temperate and tropical regions of the continents. Thick (100–300 m) deposits of wind-borne dust in China are providing new insight into paleoclimate. These deposits vie with the ice cores in providing a record of continuous accumulation over the last 2.6 m.y., but they are poorer in temporal resolution than the ice cores.
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    Soil magnetism, an approach for examining archeological landscapes
    (Geophysical Research Letters (American Geophysical Union), 1996) Dalan, Rinita
    To investigate archaeological landscapes and the extent to which humans have influenced them, we have developed an innovative approach that employs complementary geophysical methods drawn from the fields of exploration geophysics and soil magnetism. Integrating soil magnetic techniques with exploration surveys and more standard archaeological procedures (i.e., topographic mapping, excavation, coring, and soil-chemical studies) at the Cahokia Mounds site has helped us to better understand the formation of this premier North American mound center and has also demonstrated a scientific methodology of great potential for subsurface investigations of archaeological terrains.