Magnetic Fabric Study of Late Holocene Sediments in Huangqihai Lake, Inner Mongolia and its Sedimentary Significance

The detailed magnetic susceptibility anisotropy study on the sediments of two sections, which are located in the lake-center and the lakeshore of the Huangqihai Lake, Inner Mongolia, revealed their hydrodynamics and sedimentary environment changes in the recent 2000 years. The results show that the sediments of two sections both display normal depositional magnetic fabrics, of which the minimum susceptibility axes (K3) are oriented perpendicular to the bedding plane and the maximum magnetic susceptibility axes (K1) lie parallel with the bedding plane. In addition, the lakeshore presents higher magnetic anisotropy degree (P), magnetic foliation (F) and current factor (Fs) than the lake-center, showing that the lakeshore has higher flow velocity. For the west Huangqihai Lake (HQW) section in the lake-center, the magnetic matrix grain degree (Q) and the inclination of the minimum susceptibility axes sharply increased and decreased, respectively, at a depth of about 10 cm, 24 cm, 45 cm and 74 cm, which indicate abnormal depositional events with strong kinetic energy. Through comparative analysis, the HQW section can be divided into three stages from top to bottom. The upper stage was a stable depositional environment with strong hydrodynamic energy and low water level, which shows relatively higher Fs value and the Q value varies similarly with P and F. The middle stage was a stable depositional environment with high water level and low hydrodynamic energy, intermitted with high-energy abnormal events, which shows relatively lower Fs and the Q value was negatively correlated with P and F. The lower stage was an unstable depositional environment with low hydrodynamic energy and high water level, which shows relatively lower P, F, and Fs value.