Abstract

Understanding the magnetic properties of natural sediments, which include magnetic concentration, composition and grain size, is fundamental in paleomagnetic and paleoenvironmental studies. Systematic magnetic measurements and non-magnetic methods (e.g., transmission electron microscopy, TEM) provide detailed information of magnetic minerals. In this paper, we established a high efficient magnetic extraction method to separate magnetic minerals from surface sediments of Miyun lake in Beijing. We analyzed the bulk samples, magnetic extracts and residues. Saturation magnetization (M-s), volume magnetic susceptibility (kappa) and saturation isothermal remanent magnetization (SIRM) of the magnetic extracts is about 85%, 75% and 70% of the bulk samples, respectively. Multiple-parameter rock magnetic measurements indicated that the major magnetic minerals in sediments are multi-domain (MD) and single domain (SD) magnetite. TEM analyses revealed detrital MD titano-magnetite, biogenic SD magnetite (magnetofossils) and authigenic superparamagnetic (SP) magnetite. We propose that the combination of rock magnetism and TEM observations is useful to accurately identify the magnetic minerals in sediments.

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