Grain size analysis of Holocene lacustrine sediments in the Huangqihai Lake of Inner Mongolia and its sedimentological significance

Two sections located at the center and lakeshore respectively in the Huangqihai Lake of Inner Mongolia were investigated. In this study, the grain size analysis result was given, which can be regarded as the complement to the previous magnetic fabric study of the sedimentary environment. The result of grain size analysis shows that the particles become coarser upwards in these two sections, indicating increasing hydrodynamic force. A comparative analysis of the grain size and the magnetic fabric reveals that the grain size and the magnetic fabric show evident comparability in the HQW section which is located at the lake center. The magnetic fabric parameter anisotropy degree (P) shows upward increasing tendency, suggesting strong mineral oriented alignment and relatively high hydrodynamic action. In addition, at the depths of about 20cm, 40cm and 65cm, the grain size and the magnetic fabric all display obvious change, which further indicates abnormal depositional events with strong kinetic energy. In the HQE section which lies near the lakeshore, the fine-sand proportion and medium diameter grains show obvious decreasing although the magnetic fabric analysis fails to display any abnormal depositional events. If all these phenomena were really caused by abnormal depositional events, the deposition process must have been very complex and hence different methods should be employed in studying abnormal depositional events. Because the magnetic fabric is influenced not only by grain size but also by sedimentary structure, it can probably clearly reveal abnormal depositional events at the lake center, where the hydrodynamic energy is low.