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When and why sediments fail to record the geomagnetic field during polarity reversals ArchiMer
Valet, Jean-pierre; Meynadier, Laure; Simon, Quentin; Thouveny, Nicolas.
We present four new records of the Matuyama–Brunhes (M–B) reversal from sediments of the Equatorial Indian Ocean, West Equatorial Pacific and North Atlantic Oceans with deposition rates between 2 cm/kyr and 4.5 cm/kyr. The magnetic measurements were performed using 8 cc cubic samples and provided well-defined reverse and normal polarity directions prior and after the last reversal. In three records stepwise demagnetization of the transitional samples revealed a succession of scattered directions instead of a well-defined characteristic component of magnetization. There is no relationship with changes in magnetic mineralogy, magnetic concentration and magnetic grain sizes. This behavior could be caused by weakly magnetized sediment. However the transitional...
Tipo: Text Palavras-chave: Geomagnetic reversals; Magnetization acquisition; Rock magnetism; Sediment; Demagnetization.
Ano: 2016 URL: https://archimer.ifremer.fr/doc/00347/45868/45561.pdf
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Acquisition of detrital magnetization in four turbidites ArchiMer
Tanty, Cyrielle; Valet, Jean-pierre; Carlut, Julie; Bassinot, Franck; Zaragosi, Sebastien.
Turbiditic events are mostly avoided in paleomagnetic studies and therefore their remanence and magnetic properties are poorly described. Turbidites are exempt of bioturbation and potentially provide pertinent information about depositional remanence. We studied four quaternary turbidites of different origins in marine sediment cores. Upward fining of both magnetic and sedimentary fractions indicates that coarser grains reached the bottom first. We observe a progressive shallowing of the magnetic inclinations between the upper and bottom layers of the turbidites that increases with the size of the events and obeys a simple linear scaling law. Measurements of magnetic anisotropy suggest that hydrodynamic conditions prevailing during deposition seem to be...
Tipo: Text Palavras-chave: Detrital remanence; Turbidite; Sediment; Rock magnetism; Magnetization.
Ano: 2016 URL: https://archimer.ifremer.fr/doc/00421/53226/54792.pdf
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