东太湖全新世水下河道沉积特征及环境演变

在详细研究东太湖Ｅ２孔全新世沉积基础上，总结和归纳了水下河道的沉积特征和相组合规律。识别出高湖面型和低湖南型两种沉积层序，划分了东太湖晚更新世末以来环境演变阶段：１）１５８８５－６５７５ａＢ．Ｐ．冲积黄土基础上发育而成的古河道；２）６５７５－５８００ａＢ．Ｐ．高湖面时期水下河道沉积环境；３）５８００ａＢ．Ｐ．后，演化为低湖面型水下河道，并逐渐淤积形成开敞湖缘环境。结合西太湖Ｗ１孔沉积特征和层位对比

EVOLUTION OF SEDIMENTARY ENVIRONMENT OFA HOLOCENE RIVER CHANNEL IN EAST TAIHU LAKE

The E,core from East Taihu Lake is a 2.3 meter long sediment core collected from aHolocene river channel site.This core covers the last 16 000 yrs and provides critical information for the study of the character and development of the Holocene river channel andEast Taihu Lake.The data on lithofaces,sediment structures,grain-size distribution andsediment sequences of this Holocene river bed exhibit unique features which differ from either normal lacustrine delta channel or lakeshore environments.They show that the channel-filling depositions were controlled by complex environmental conditions possibly associated with sea-level fluctuation and regional climate changes.In the comparison of the core from East Taihu Lake to the W,core from West TaihuLake,using depositional sequences we showed that the development of the river channel inEast Taihu Lake can be divided into three stages corresponding to sea level fluctuations.(1)There were river channels about 1.8 m in average depth extending from west to east inthe Taihu Lake basin between 16 000 and 6 600 aB.P.(2)Sea level rose between 6 600and 5 800 aB.P.1 the water level was comparatively high during this period and non-migration sediment features were developed in the river channels.These features occur in70-140 years cycles and appear to reflect wet and dry climate changes. (3)The riverchannel has evolved under low water level conditions since 5 800 aB.P.and has graduallyfilled up with sediment,transforming it into a nearshore environment.The thin layer offerromanganese deposited during from 5 800-5 700 aB. P.is an indication that the areawas dry at that time.