SEDIMENTARY FACIES OF CARBONIFEROUS SYSTEM IN THE LOWER YANGTZE BASIN

The Lower Yangtze Basin in Late Paleozoic time covers most part of Jiangsu, Anhui and Zhejiang provinces in southeast China, with an area more than 100,000 km2. Carboniferous sediments, consisting mainly of clasolite in lower and carbonate rock in upper, are widely spread in the basin. According the sedimentary characteristics and differences of biota, the basin in Early Carboniferous may be divided into four sedimentary facies regions, they are. 1, Binhai-Hongze region; 2. Dafeng Chaohu region; 3. Yixing-Xuancheng region, 4. Qiantang region, and two swelling regions. Tongling Peninsula and Jiangnan oldland.The sedimentary environments in the Lower Yangtze area (Jiangsu-Anhui) were shown as shore plain, gulf and delta. The Qiantang area between Jiangnan oldland and Wuyi oldland is characterized by strong tectonic activity, larger subsidence, obvious stream cutting and the development of alluvial fans and braided rivers. In the late stage of Early Carboniferous, the braided river evoluted into meandering river,a set of sandy mudstones containing coal seams appeared. The regional distribution of sedimentary facies in Late Carboniferous were controlled obviously by regional paleostructure.The Lower Yangtze Basin were separated by Wujin-Mazhen rift into two diferent sedimentary area-Lower Yangtze area and Qiantang area. The thickness of Carboniferous sedimentary rocks reaches about 1000m in Qiantang area, indicating a larger subsidence range, it is an active part in the platform relatively. The area of Lower Yangtze Basin is very vast with an area about 140,000km2. Neither sediments of platform margin facies such as biohe-rm, carbonate buildup, nor sediments of shelf slope facies, such as talus breccias and sediments of basin facies had been found in this ca- rbonate platform. There are only three kinds of subfacies such as edge tidal flat facies, open platform and shoal facies, which suggest that it is a carbonate platform of ramp type. The sedimentary features of Qiantang area are similar to those of the Lower Yangtze region, but different in microfacies and fossils. So Qiantang area is a carbonate platform with a large subsidence range within the basin.