Characteristics of grain sizes and magnetic susceptibility of sediments and sedimentary environment in the Lop Nur Lake Basin, Xinjiang Province

Based on a study of grain sizes and magnetic susceptibility of lake sediments along LB section in western Aqike depression of Lop Nur area, in combination with the sedimentary sequence and lithologic variations, the authors made a preliminary analysis of the sedimentary environment of the Aqike depression since Quaternary. The results show that the grain size component is mainly composed of silt of lake sediments along the LB section, magnetic minerals are composed of a small amount of ferromagnetic minerals, with super-paramagnetic particles being abundant in sediments. The median grain size components, clay (<2μm) and sand (>63μm) are positively correlated to magnetic susceptibility, and fine sand (2~63μm) is negatively correlated to magnetic susceptibility. According to the variation of grain size and magnetic susceptibility, combined with the lithologic characteristics, the authors divide the LB profile into four stages. In the Late Neogene (4.14~3.32m), the climate was warm and dry; in the late Pleistocene (3.32~2.93m), the coarse particles showed an increasing trend after decreasing, and hydrodynamic action tended to become strong, magnetization increased and remained at a high level, and the climate of Lop Nor began to change from warm-dry to warm-wet; in the middle Pleistocene (2.93~1.44m), the climate was humid, the river and the water changed remarkably which resulted in the instability of some amounts of exogenous substances, grain-size and magnetic susceptibility values fluctuated widely, and the climate changes from warm-dry to warm-wet; in the Holocene (1.44~0m), coarse sand was increasing, and magnetic susceptibility values fluctuated and increased, the climate changes towards cold-wet and ultimately dry. Environment and paleoclimate have obviously changed since the Quaternary, suggesting a warm dry and wet climate fluctuation trend and ultimate development towards drought in this area, characterized by moistness in cold periods and drought in warm periods.