Sedimentary Characteristics And Environmental Evolution In The North Of Liaodong Bay Since Medium-term Of Late Pleistocene

Liaodong Bay lies in the north of Bohai Sea and the bay extends to NNE. Its south borderline is from the estuary of Daqinghe River in Hebei province to the Laotieshan in the south of Liaodong peninsula. In geologic tectonics, it lies in the Liaohe River to Bohai Sea subsidence of the second giant subsiding belt. The Tan-Lu fault zone and some smaller faults across the area, which form the base into the configuration of Chinese word "duo". Because the base have been kept on subsiding continuously since late Pleistocene, the sediment is thick here. This provide us the good condition in study the stratigraphical structures and the environmental evolution of Liaodong Bay.The study of sedimentary characteristics and environmental evolution in the north of Liaodong Bay since medium-term of late Pleistocene is based on the analysis of the sediments in surface layer, core of the borehole and interpretation of high-resolution seismic profiles. We can find that the distributions of the sediments in surface layer are controlled by the condition of hydrodynamic and the content of sand in water, which is mainly composed of sand, silty sand, sandy silt, silt, clayey silt, silty clay and clay etc. The granularities of the sediments in the east are coarser than those in the west. The core that 120.4m long is divided into 16 strata, which are belonged to three marine beds and three continental beds respectively. As a whole, the sediments of continental facies other than lagoon and swamp faces are coarser than those of marine facies. Six seismic units are defined from the seismic profile, in which units A, C and E belong to sea faces formed when the sea level was high, but units B, D and F belong to continental facies formed when the sea level was deep. However, the ancient river ways and stackeddunes interpreted in the seismic profile indicate that the riverine actions had been much more developed and this area had ever been deserted during the glacial stages.The deposit environment in the north of Liaodong Bay since the medium-term of late Pleistocene is rebuilt by the analyses of the core and the seismic profile. Since the medium-term of late Pleistocene, the climate in the study area varied frequently and the annals was divided into six stages which are Weichsel I, earlier sub-interglacial, Weichsel II, later sub-interglacial, Weichsel III and postglacial. The sea level changed with the climate variation, and three transgressions, Shuiyuan transgression, Xianfeng transgression and Panshan transgression happened successively, which are corresponding to the Bohai Sea transgression, Xianxian transgression and Huanghua transgression each other.