江汉平原沔城M1孔的沉积特征与古环境重建

CHARACTERISTIC FEATURES OF THE SEDIMENTARY SAMPLES FROM THE BOREHOLE M1 IN JIANGHAN PLAIN AND RECONSTRUCTION OF PALAEOENVIRONMENT

通过对江汉平原沔城Ｍ１孔湖泊沉积物进行沉积特征、粒度、１４Ｃ年代、孢粉分析，重建了晚冰期以来该地区古环境、古气候演化的过程和序列：晚冰期后期有一扩张期，气候温湿并出现湖泊相沉积；晚冰期末期气候温凉偏干、河流环境；全新世初期（１０—８．９ｋａＢＰ），气候转向温湿；全新世大暖期（８．９—３．５ｋａＢＰ），总体上气候温暖湿润，其中６．８—４．９ｋａＢＰ是最宜期，４．９—４．８ｋａＢＰ和４．４—４．２ｋａＢＰ为两次降温事件，４．８ｋａＢＰ积水湖盆开始形成，３．９—３．５ｋａＢＰ为云梦泽鼎盛期；全新世晚期（３．５—１．７ｋａＢＰ），气温较大暖期有所下降，其中３．５—２．５ｋａＢＰ温凉偏湿，２．５—１．７ｋａＢＰ较为温湿，湖泊较为稳定，１．７ｋａＢＰ开始，云梦泽萎缩。

,By an analysis of the lithology,grain size,spore and pollen of the lake sediments from borehole M1 in Jianghan Plain as well as 14C 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.