SEDIMENTARY CHARACTERISTICS OF THE WUXUE FORMATION IN THE SUSONG-FANCHANG REGION,ANHUI

The Wuxue Formation,a lenticular stratigraphic body distributed along the Yangtze River between Susong and Fanchang in Anhui and in the Pengze district,Jiangxi,consists of algal limestone,fusulinid limestone,sponge limestone,echinoderm limestone,oncolite dolostone and dolostone.According to the radios of elast to matrix in four sections,three sequences called basic units are easily recognized.These sequences are dominated by the normal fining-upward sequences from the base upwards.The inversely graded fine-coarse-fine sequence almost composed of the echinoderm limestone,algal limestone and sponge limestone cemented by sparite,however,is also found,which indicates a rapidly deposition-al process and a barrier environment.The sponge bindstone exhibiting mega-and coarse-crystallized grain textures observed at the base and on the top of these units represents the products in the extremely shallow-water environments where the rates of organic upbuild-ing were temporarily greater than those of sea-level,rise,This kind of depositional units is usually called organic buildups.It is inferred from tectonic settings and sedimentary char-acteristics that this kind of isolated geological bodies may come into existence in Guangji, Daye,Jingshan,Nanzhang and other places in Hubei.