Depositional Pattern and Historical Evolution of DongPing Lake

The Dongping Lake is a large shallow water body located in Taian, Shandong Province, China. The lake is on the lower reach of the Yellow Valley, and its form and evolution is influenced by Yellow River and human activities. In order to understand the sediment deposition pattern and human activities, sedimentary cores were collected from the lake in 2008. Pb-210,Cs-137, and C-14 were analyzed to study chronology of Dongping Lake during Holocene. Environmental indices such as grain size and loss-on-ignition are also analyzed to study the deposition pattern and historical evolution of Dongping Lake. Studies show that the 156-cm-long sediments of Dongping Lake has reflected about the past 6000 years' environmental evolutionary history. About 5500 years ago, this area was mainly in rivers development stage, lithologic characters were mainly composed of silt and the grain size was in the most coarse period of the whole section; the section relying mainly on grayish yellow clay 5500 years later belongs to the Dayeze Lake Depositional stage, before and after about 3000, due to changes in the course of the Yellow River as well as sedimentation and shrinkage of the Dayeze Lake, which caused depositional hiatus; from Five Dynasties to Song Dynasty, the floods occurred in the Yellow River poured into Dongping Lake area, forming Liangshanpo Lake which took Liangshan as the centre and the pale yellow clay deposition; governmental taming of the Yellow River in the Ming Dynasty made the Liangshanpo Lake lose water supply of the Yellow River, then the lake shrank and retreated into Anshan Lake and other small lakes, thus the sedimentary environment changed greatly; in 1855, floods occurred in the Yellow River were held up at low-lying areas of Dongping Lake because the Yellow River burst and changed its course at Tongwaxiang, Lanka, which formed Dongping Lake in the mordern sence of the word and deposited a set of sediment relying mainly on pale yellow clay.