MAGNETIC PROPERTIES OF THE LAKESHORE SEDIMENTS OF THE BOSTEN LAKE, XINJIANG, CHINA AND THEIR ENVIRONMENTAL IMPLICATIONS

The lakeshore sediment and its magnetic characteristics may suggest hydrodynamic conditions, sedimentary environment and paleoclimate. In this paper, we choose the samples of different lithology from the cores obtained at the Bosten lakeside for magnetic studies. Combined with the data of X-ray diffraction, grain size and TOC content, the depositional process was inferred. The magnetic minerals of the samples are dominated by ferrimagnetic minerals with low coercivity and rather coarse particle size. Magnetite is the main magnetic mineral in the sediment. In the samples of different lithology, magnetic susceptibility values show distinct differences. In the upper part of the core,the values are relatively high, while in the middle part of the core consisting of dark silty mud, the values are apparent high and vary vertically. However, the magnetism of the peat soil with high TOC matter is quite weak. In the lower part, the samples show low values of magnetic susceptibility. To the bottom, the color of the sediment turns to black and the susceptibility values increase. XRD analysis reveals that the sediment mainly consists of sands and silts of quartz and feldspar showing a coarsening upwards sequence in general with some opposite fluctuations. Organic matter of the middle part varies apparently, suggesting the shifting of the sedimentary environment. With the changes in magnetic properties in the samples of different lithology, and based on the response of grain size, organic matter and sediments color to sedimentary dynamics, we can tentatively infer that the lake has experienced a complicated history of sediment dynamic changes, reflected by alternating lakeshore facies, limnic facies and shallow lake facies.