REE Geochemistry of Sedimentary Rocks Middle Ordivician in Central Hunan Province

There is a suit fine grain black rocks,Middle Ordivician,in central Hunan province, including black shale,banded silt一shale,mudstone and siliceous shale (sillcalite) and so on. They were formed at slope一 basin facies zone,and they high characters of REE geochemistry such as:high abundance of REE (FREE 271. 7ppm ),high ratio of ELREE/EHREE, La/Yb, (La/Yb)_n,δCe value, and low bEu value. The REE patterns are comparcd to sediments of passive contnental margin region. Because of affecting sub-sedimentary environment,the sediments of background passive continental margin in the studied area are not only bigger δCe value,but also higher abundance of REE. Other sedimentary data demonstrated that they are products of anoxic environment at studied area. but they aren't appeared bigger δCe negative anomaly on the model curve of REE distribution. So δCe value cannot be take as indicator of anoxic environment. This paper discusses the tectonic background,the relationship bCe value between anoxic event and manganese origin,mudstone REE abundance and so on. It is made intelligible characteristics and distribution of REE anoxic down一warping basin of passive continental margin region.