太湖16000年来沉积环境的演变

EVOLUTION OF SEDIMENTARY ENVIRONMENTIN TAIHU LAKE DURING THE LAST 16 000 YEARS

通过对太湖钻孔岩芯岩性、结构、构造的剖析及粒度、磁化率的测试，发现冰后期东太湖形成于距今６５００年前。在距今６５００—５８００年，为一水深约２—３ｍ的、经常受到流水作用影响的浅水湖泊。距今约５８００—５７００年，东太湖曾一度干枯或接近于干枯。距今５７００年以来湖泊变浅，平均水深只有１ｍ左右。由于湖泊变浅，湖底经常遭受波浪的扰动，形成波状层理或透镜状层理。西太湖局部洼地集水成湖的时间比东太湖早，并且水深比东太湖大。在５０００ａＢ．Ｐ，东、西太湖并未连通。东、西太湖的连通及太湖统一水体的形成开始于４０００—３５００ａＢ．Ｐ．。东太湖的成湖及东、西太湖的连通，湖面的扩大与水深的变浅，与冰期后海面上升引起的河谷与洼地沉积充填、淤塞有关。

Sediment data on lithofaces,sedimentary structures,grain-size analysis,magnetic susceptibility,and 14C dating of two Taihu Lake cores were analyzed to understand the evolution of sedimentary environments during the last 16 000 years in Taihu Lake.The sedimentdata showed that prior to 12 000 a B.P.the East Taihu Lake area was dry land composedprimarily of loess deposit.East Taihu Lake was formed about 6 500 aB. P.in the postglacial period.Based on the data on sediment texture and sediment depositional pattern,weestimate that between 6 500 and 5 800 aB. P. East Taihu Lake was about 2-3 metersdeep lthe lake sediment shows a pattern attributable to current effect. The East Taihu Lakewas dry or nearly dry,with a water depth lower than 0.5 meters between 5 800 and 5 700aB.P.Lfrom 5 700 a B.P.to present,this lake has maintained a water depth of between0'5-1.sin.In contrast,West Taihu.lake was formed earlier than East Taihu Lake,and has a water depth of 3-4 meters prior to 5 000 aB. P and of 2-3 meters after that. The data showthat East Taihu Lake and West Taihu Lake were not connected prior to 5 000 aB.P.andthey became one lake between 4 000 and 3 000 aB.P.as a result of rising sea level.The rising sea level led to increased siltation in the lake outlets,which in turn blocked thedrainage of lake water,resulting in a lake with expanded surface.At the same time,manyold river channels, holes,and deep pits in the lake were gradually filled by sediment.Thelake became a large shallow dish-shaped'aquatic environment.