Big Nine Lake Basin Since Late Pleistocene In The Palaeoclimate Reconstruction

The East Asia, which is the world’s most typical monsoon region, is an important area of global change research. Shennongjia, located in the transition zone of humid areas and sub-humid subtropical areas, is sensitive to climate change, so it is an ideal study area for Quaternary climate change. The continuous core, which length is4357cm, from Dajiuhu basin in sub-alpine Shennongjia, recorded climatic change information since MIS8stage. We have analysed the core column characteristic, dated the age and done the environmental parameters data analysis. And we tried to reconstruct the process of the ancient climate environment evolution since the late Middle Pleistocene.We observed the lithology of the section and measured the grain size with the distance of2to3cm. The section experienced lakes and swamps, sometimes developed proluvial fan and bottomland. The sedimentary facies character reflected that the basin experienced the climate changes.We chose13samples which contained more organic matter and dated the age with the method of amino acid racemization. Combined with previous7AMS14C age data, we confirm the age of the bottom lithology is275.8kaB.P..Based on the data of elements、grain size、pollen and the curve of SPECMAP, we divide the stages of climate changes and adjust the age point of start-stop stage.Based on the pollen record and the age data, we divided8pollen zones.This result corresponded to marine isotope stage8-1respectively.①43.57-37.20m (275.8～245.OkaB.P):during this stage, there were cold temperate coniferous forest, and then became swamp.②37.20-30.70m(245.0～188.0kaB.P):during this stage, the basin developed subtropics evergreen broad-leaved forest and subtropical evergreen and deciduous broad-leaved mixed forest.③30.70-15.0m(188.0～129.OkaB.P):during this stage, cold temperate coniferous forest transited to swampmeadow.④15.0-10.34m(129.0～71.8kaB.P.):during this stage, swampmeadow transited to evergreen broad-leaved forest.⑤10.34-8.98m(71.8～60kaB.P.):during this stage, this area were cold temperate coniferous forest.⑥8.98-3.93m (60～26kaB.P.):during this stage, cold temperate coniferous forest transited to swampmeadow. There also grew subtropics evergreen broad-leaved forest and subtropical evergreen and deciduous broad-leaved mixed forest.⑦3.93-1.92m (26～11kaB.P.):during this stage, there were mainly cold temperate coniferous forests. In the second place, there were subtropical evergreen and deciduous broad-leaved mixed forest.⑧1.92-0.3m (1～11kaB.P.), in this stage, subtropical evergreen and deciduous broad-leaved mixed forest transited to subtropics evergreen broad-leaved forest.The climate revolution of Dajiuhu basin have a high coincidence with the curve of SPECMAP and the record of Shanbao cave oxygen isotope since late Middle Pleistocene, especially the last glacial and interglacial period.This responds the global environment change, particularly the change of East Asian Monsoon. It also reflects the character of subalpine wet land.