Sedimentary Evolution And Paleoclimate Research Since MIS 2 In Chaohu Lake

The Chaohu Lake Basin is a typical area of paleoclimate reconstruction and environment changes in the middle of the lower reaches of the Yangze River,controlled by the East Asian summer Monsoon（EASM）,but the time series of previous studies are mostly limited to the period since Holocene.In this paper,based on AMS¹⁴C dating,the upper dating frame was determined,and the bottom dating is inferred according to the deposition rate and the comparison of other deposition.Through the collection and analysis of the core CZK,conbined grain size,TOC,magnetic susceptibility,the change of sedimentary environment in the Chaohu lake area is analyzed.This paper analyzes the change of sedimentary environment in Chaohu lake Basin,discusses the reasons for the evolution of Chaohu lake,rebuilds the climate change since MIS2,and compares it with other climate records in east Asian monsoon area and discusses the mechanism of climate change in Chaohu lake area.The results are as follows:1.The core CZK mainly consists of two parts.The buried depth of 15-0m is dominated by lacustrine deposit,while the buried depth of 50-15m is dominated by fluvial deposit.Most of the 50-15m are fluvial deposits,and the 37.2-36m is a swampy deposits.The 15-13m of core is a fluvial and lacustrine deposit.The 13-10.7m is a lacustrine deposit.The 10.7-8.5m is a lakeside facies deposit.The 8.5-4.7m is a deep lacustrine deposit.The 4.7-2.9m is fluvial and lacustrine deposit with underwater deltas;The 2.9-1m of core is a shallow lacustrine deposit.2.When the magnetic susceptibility is deposited in the lake,the high value represented warm and wet,and the low value represented cold and dry.In the river,magnetic susceptibility is influenced by grain size,material source and climate.There is a strong correlation between TOC and TN in the lake.The high value represents the warm and wet,while the low value represents cold and dry.The grain size of the lake reflects the climate change.When the grain size is fine,the water level of the lake is high and the climate is wet,while when the grain size is coarse,the climate is relatively dry.Moreover,the grain size has a good response to the cold events.3.Since～24.6 cal ka BP several subtages of climate change in Chaohu lake are divided.They are cold and dry substages of 24.6-18.1 cal ka BP,warming up and wet substage of 18.1-15.1 cal ka BP.The sedimentary environment is stable and the fluctuation is not obvious from 15.1-12.2.The lake is in the shrinking stage of 12.2-9.9cal ka BP,the overall climate fluctuated significantly,and it is in the transitional stage.The Holocene is generally warm and wet.From 9.9-6.1 cal ka BP this stage is a relatively suitable climate period.During this period of 6.1-4.8 cal ka BP,Chaohu Lake as a whole is in the relatively dry and cold period.From 4.8-0 cal ka BP,the climate was relatively humid and warm.In the last 1,000 years,it has been greatly influenced by human activities.