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Detrital magnetizations from redeposition experiments of different natural sediments

Abstract : We carried out several experiments with carbonate-rich and clay-rich sediments that were redeposited in plastic cubes or in 1-meter-long cylindrical tubes with the aim of investigating the sensitivity of the depositional remanent magnetization (DRM) to various environmental and physical parameters. In contrast to previous studies, we did not observe any difference in the DRM acquired with or without saline water for either kind of sediment. Taking advantage of a gelatin that fixes the position of particles in suspension, we were able to measure the magnetization of suspended sediments within water-filled columns and thus to test the degree of alignment of magnetic grains. The magnetization of clay-rich sediments was not far from saturation but the magnetization was considerably reduced after deflocculation because the large flocs that favored alignment of magnetic grains were destroyed by the deflocculant. Similarly, the large flocs found at the bottom of the deposition tubes also reveal an efficient magnetic alignment. In contrast, the weak magnetization of the carbonate-rich sediments with small flocs yielded accurate and well-grouped magnetization directions that were not sensitive to deflocculation. Only a fraction of magnetic grains was mechanically oriented by the field in this case because of the weak net magnetic moments of the grains embedded within small flocs. The DRM was constrained by redeposition in plastic cubes performed without gelatin and with different field intensities. The DRM intensity of the carbonate-rich sediments is linearly related to field strength, which attests to their suitability for studies of relative paleointensity. Tests performed with mud from several stratigraphic levels in different marine sediment cores failed to reveal a significant influence of carbonate content on DRM, which suggests a relatively minor role of lithological changes on records of relative paleointensity.
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Submitted on : Monday, February 21, 2022 - 3:33:28 PM
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Simo Spassov, Jean-Pierre Valet. Detrital magnetizations from redeposition experiments of different natural sediments. EARTH AND PLANETARY SCIENCE LETTERS, 2012, 351, pp.147-157. ⟨10.1016/j.epsl.2012.07.016⟩. ⟨insu-03583019⟩

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