Paleoclimatic implications of magnetic susceptibility in Late Pliocene-Quaternary sediments from deep drilling core SG-1 in the western Qaidam Basin (NE Tibetan Plateau)

Lake sediments are important archives of paleoclimate change and erosion history. A 938.5 m long core (SG-1) of lacustrine sediments, dated at 2.77 Ma to 0.1 Ma, was obtained from the western Qaidam Basin in the northeastern Tibetan Plateau, consisting of dark grayish mudstone and grayish siltstone, intercalated with salts and fine sandstones in the upper part. Magnetic susceptibility data, combined with detailed rock magnetic properties, were analyzed for revealing the significance of ferro(i)magnetic concentration for past changes of climate and erosion. Mass-specific susceptibility (chi) shows a striking cyclic and long-term variation. Samples with high chi values are dominated by magnetite and maghemite with pseudo-single-domain properties. In contrast, samples with low chi values contain maghemite from single-domain to multidomain and, additionally, a significant fraction of hematite. The driving mechanism of chi variation can be explained by three alternative models: (1) different source regions with alternations of wind and cryoclastic erosion in a wider hinterland (dry-cold climate) and surface runoff erosion from a narrower area (more humid climate) and (2 and 3) low-temperature oxidation, occurring either in the lake sediments (dry climate) or in the catchment area during weathering (more humid climate). Trends of chi match with changes in sedimention rates and are roughly synchronous with the deep-sea delta O-18 record on a glacial-interglacial timescale. Therefore, the concentration of magnetic minerals in the western Qaidam Basin sediments is likely controlled by both tectonic influence and paleoenvironmental changes but can be best interpreted by alternations and trends of dry-cold and more humid periods due to Asian drying and global cooling.