DISTRIBUTIVE REGULARITIES OF SEDIMENTARY FACIES DURING CHANGXING PERIOD OF THE LATE PERMIAN IN SU-ZHE-WAN (JIANGSU-ZHEJIANG-ANHUI PROVINCES) ADJACENT AREA

There are marked distributive regularities for the sediments in Chang xing period of the late Permian. Basin facies is found in the area west to Xuan-cheng-Guangde-Yixing-Jiangying. While east-southwardly, in the area of Wuxi-Changxing-Jingxian, basin margin facies is localized. They can be roughly attributed ot Dalong Formation and"Dark Changxing", respectively. East to basin margin facies is platform facial sediments,i.e."White Changxing" distributive area where the sediments of high energized platform margin facies were devloped on the transitive zone between platform facies and basin margin facies. An example is taken——Changxing Formation in Songshan, Wuxi, which is a typical sedimentary assemblage of sponge reef; in contrast, Changxing formation in Mashishan of Xishan belongs to a sediment of chl-orophyceae beach facies with spongeous bioherm interbeded in middle-upper sections.Both reflect a high energized environment of platform margin. Along from Xishan, and Songshan, northwardly to Shazhou and southward to the zone of Nangaoqiao in Wuxing, Changxing Formation becomes thickened compared with the two sides, and the zone is just on the facial change belt between"Dark Changxing" and" White Changxing", showing a trend clearly outlined for the platform margin. Therefore the Changxing Formation in the area is characteristic of regular facies belt distribution in a pattern of basin-basin margin-platform margin-platform. The authors do not think that Jiangying-Yixing palaeo-uplift existed during Changxing period based on the distributive regularities of sedimentary facies. The sediments in Changxing period in the area had been absent due to denudation in early Triassic. The high energy zone of platform margin was distributed on the side of" White Changxing" of the juncture between "Dark Changxing"and" White Changxing". The discovery of sponge-reef biogenic beach in this facies belt provides leads for exploration of hydrocarbons and other related minerals in the area.