澄湖SC7孔沉积物粘土矿物特征及其古地理意义

Clay Mineral Characteristics of SC7 Core Sediments from Chenghu Lake (Suzhou) and Their Paleogeographic Significance

苏州澄湖湖底残留有一条NNW—SSE延伸且已被淤平的古河道。通过对湖心区古河道段SC7孔沉积物的粘土矿物XRD分析及与湖底硬粘土(Q3)、湖岸区沉积(Q4)和长江口滩地现代沉积的比较,表明古河道充填沉积中的粘土矿物主要为伊利石,其次为高岭石、绿泥石、蛭石,还有少量蒙皂石及蛭石/绿泥石混层矿物;其中的伊利石和绿泥石含量均明显偏高,高岭石含量则偏低,伊利石结晶度也较高。粘土矿物组合兼具太湖流域地带性粘土矿物和长江口沉积物的特点,表明古河道充填沉积既有来自本流域表层物质和澄湖扩大过程中的湖岸崩积,也受到长江物源的影响。这一沉积过程也说明古河道在最大海侵时涨潮流和洪水引起海水和江水的频繁倒灌,直至淤塞和淹废。

Chenghu,a medium-size and shallow lake,is situated in the central Taihu Plain of Lower Changjiang River,China.In its north-central part,a temporal water pumped area from 2003~2007,there have developed a NNW-SSE paleo-channel filled up with deposits on the flat bottom.Sediment core（SC7） from this paleo-channel near the central part of the lake was taken and the clay minerals were studied through X-ray diffraction.Studies show that the main clay minerals,calculated by comparing major peak heights,are illite（70.0%~72.4%）,kaolinite（10.0%~11.6%）,1.4 nm minerals（12.8%~14.6%）,and small amounts of smectite（5%）.Compared with the bottom material（hard clay＇） and lakeshore sediments,the sediments are characterized by higher content of illite,chlorite and better illite crystallinity,but lower content of kaolinite.These characteristics of clay minerals indicate that the sediments may come from both the lake catchment and the Changjiang River,and that the paleo-channel（the ancient Dongjiang River） must have experienced frequent tidal upstream flow or Changjiang River＇s floods after entering the Mid-Holocene.As the Dongjiang River was filled up,the coastal development stage of Chenghu area ended.