Rock magnetic studies are extensively used to check the reliability of the geomagnetic record in sediment successions. For the interpretation of the paleomagnetic results it is important to identify the degree of preservation of the magnetic carriers and to recognize post-sedimentary alteration. To improve our knowledge about the controls on the magnetic assemblage we carried out a comparative study based on several sediment cores recovered from Lake Huguang Maar (21° N, 110° E). We focused on the determination of the magnetic fraction and the analysis of the remanence acquisition process. The main magnetic carrier in the sediment samples from Lake Huguang Maar is magnetite with a small amount of titanium. The preservation/dissolution of the magnetite and other Fe-bearing minerals in the sediment was mainly controlled by the limnological conditions in the lake. In parts of the sediment corresponding to a partly oxygenated lake bottom magnetic properties are dominated by the well preserved primer magnetic mineralogy. When anoxic conditions developed in the sediment due to a stratification of the water body magnetite particles have been largely affected by reductive dissolution. In principle the dissolution of magnetite under anoxic conditions has preceded that of the antiferromagnetic minerals like hematite or goethite. Indeed in Huguang Maar the relative abundance of haematite (S-ratio) turns out to be an indicator of the lake bottom conditions in terms of oxygen availability. Based on the rock magnetic as well as geochemical parameters we subdivided the samples in magnetic clusters with a corresponding sedimentary environment. Additionally, climatic controls appear to modulate the sedimentary magnetic signal when certain limnological conditions in the lake are true.
Partner: Liu J.