Ancient Vegetation And Paleoclimate Since The Late Miocene In The XH-2 Hole Of The Subei Basin

Chinese environmental pattern is founded in the background of the global climate change,especially developed during the Quaternary period.The uplift of the Tibetan Plateau,along with the formation and the development of the Asian monsoon are the most important Geological events during the Cenozoic period.The Northern Jiangsu Basin is controled largely by the east Asian monsoon,having undergone long times of depression since Cenozoic.Because of its continuous deposition and high resolution,it contains a great amount of geological infonnation,so it plays a more and more important role in the study of the evolution of East Asia monsoon and regional environmental change.Take the continuous core of XH-2 at the Northern Jiangsu Basin for the study,we set up chronostratigraphic sequence based on paleomagnetic method and sedimentary rate.The XH-2 spans the period of 6.65Ma since the late Miocene to present.In this paper,we analyze the pollen data of XH-2 and establish the evolution of the climate and vegetation transition since the the late Miocene.According to the characteristic of pollen data,we devide the biostratigraphi c of XH-2 into 17 pollen assemblage zones.Based on pollen data of XH-2,co mbined with grain size measurement,natural gamma logging and magnetic susce ptibility,seven stages of environmental evolution were established since 6.65Ma for the XH-2 of the Northern Jiangsu Basin.(1)6.65-5.29Ma:warm-humid period with dry-wet fluctuations.(2)5.29?3.70Ma:change from dry period into humid period.(3)3.7?2.78Ma:cold-dry dominated period with warm-cold fluctuations.(4)2.78?1.86Ma:a relative dry period,puctuated by dry-wet fluctuations.(5)1.86?0.94Ma:a relative dry period,with warm-humid phase frequently.(6)0.94?0.39Ma:a relative warm-humid period with dry-humid fluctuations.(7)0.39Ma?0:tends to be warm and humid.Compare to the record of continental sedimentary environment in other regions since the late Miocene,we found that the evolution of climate in the Northern Jiangsu basin is analogous to other areas since the late Miocene.However,due to various different geographical areas,there are some differences in the evolution of the internal environment of the leaf area.Environmental evolution of the Northern Jiangsu Basin is largely effected by the uplift of Tibetan and the change of global climate.In addition,the sedimentary environment,water adjustment and other factors have a major impact on the climate evolution of the Northern Jiangsu Basin since the late Miocene.