Study On Photodiochemical Dating Of Sediments In Xingkai Lake

Lake plays an important role in the interplay between four spheres (i.e., atmosphere, biosphere, hydrosphere and lithosphere), lake sediments thus could record the past change in cliamte and environment. This kind of sediments have been ultilized by the PAGES projects for paleocliamtic reconstructions for many years. Beach ridges, frequently components of Quaternary coastal plains, are landforms commonly developed on prograded coasts with sea/lake shorelines. The lakeshore landscape can provide the history of the coastal evolution. Robust chronological techniques are needed to build up the age framework.With the development of optical stimulated luminescence (OSL) methods in dating of Quaternary sediments, OSL dating has been successfully applied in the beach sediments.Xingkai lake, situated in the border of China and Russia, is influence by the East Asian Monsoon and polar climatic systems. This lake is sensitive to the global climate change, thus it is proposed as a drilling site by the PAGES for pole-equator-pole research.There are four conspicuous beach redges which can be apparently indentified from the northern margins of Xingkai lake, i.e., Dahugang, Taiyanggang, Erdaogang and Huangang-Nangang. This sandy beach ridges are composed of the sandy sediments which are well-sorted and have a typical Aeolian dune structure, and their formation are likely to be related to the transgression and regression of the lake level. Previous studied showed controversial age constrains on these ridges. Therefore, more chronological work are needed to date these sandy ridges.We collected13samples from two profiles (DHGland DHG2) from the Dahugang for OSL dating. Using the single aliquots regenerative protocol (SAR), the equivalent dose of all samples were measured systemically and the suitability of SAR for coarse quartz grain in Dahugang beach were checked. By analyzing the OSL characteristic curves of all samples, the distribution of equivalent dose and comparing different age models calculation results and independent age results in the same layer as well as the age sequences follow the stratigraphic columns and inter-sratigraphic columns, the thesis indicates that the age is reliable and accurate. The conclusions derive from the thesis as follows: (1) Preheat plateau test and dose recovery test were carried out and indicated that the preheat temperature220℃is suitable for SAR procedure measurement.(2) In the thesis, we analyze the OSL characteristic curves, the distribution of Des, and find that the13OSL samples were bleached well prior to deposition and they are appropriate for OSL dating.(3)The results of Des derived from three age models (Mean age model, Central age model, Minimum age model) are coincident. In addition, the resultant OSL ages are stratigraphic order at each of profiles DHG1and DHG1. Furthermore, the robustness and reliability of our OSL ages are validated by two14C ages of charcoals.(4) The thesis proposes that Dahugang beach from Xingkai lake formed at about1.24-0.5ka.