CHARACTERISTIC FEATURES OF THE SEDIMENTARY SAMPLES FROM THE BOREHOLE M₁ IN JIANGHAN PLAIN AND RECONSTRUCTION OF PALAEOENVIRONMENT

By an analysis of the lithology,grain size,spore and pollen of the lake sediments from borehole M₁ in Jianghan Plain as well as ¹⁴C dating the palaeoclimate and palaeoenvironment since Late Glacial have been reconstructed as follows.There was a lake expansion at the close of the Late Great Ice Age when the climate was temperate and wet and the lacustrine sediments were deposited.The climate was temperate and turned dry at the end of Late Ice Age,when the boring site was controlled by fluvial environment.In early Holocene(10-8.9kaBP),the climate turned temperate and wet.It was warm and wet generally in Holocene Megathermal(8.9-3.5kaBP),in which the period of 6.8-4.9kaBP was the optimum,and there were 2 cool events occurring at 4.9-4.8kaBP and 4.4-4.2kaBP.Lakes began to form at 4.8kaBP,and the fossil Yunmengze lake was at its climax of development at 3.9-3.5kaBP.The temperature decreased in late Holocene(3.5-1.7kaBP) compared with that in Megathermal,in which it was temperate-cool and wet in 3.5-2.5kaBP,temperate and wet in 2.5kaBP with a stable lake environment.The Yunmengze lake shrank since 1.7kaBP,leading to exposition of the boring site.