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

Key words: 
• Chenghu Lake

Abstract: 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.