SEDIMENTARY ENVIRONMENT OF EARLY CAMBRIAN PHOSPHORITES IN THE JINNING ANNING REGION,YUNNAN
Luo Huilin,Hu Shixue(Yunnan Institue of Geological Science, China) Zhang Shishan, Tao Yonghe(Kunyang Phosphorite Mine, Yunnan)
The Jinning Anning area is the most famous phosphorite producing area in China. Many large and medium phosphorite mines are located here. Yuhucun Formation and Qiongzhusi Formation are the main phosphatic strata from Late Sinian to Early Cambrian. The former can be ascendingly divided into five members: the Jiucheng Member, Baiyanshao Member, Xiaowaitoushan Member, Zhongyicun Member and Dahai Member; the latter may be divided into Shiyantou Member and Yuanshan Member. The Xiaowaitoushan Member is predominantly dolomite with siliceous stripes, indicating relatively upwelling second order platform deposits on carbonate and phosphate platform, while the Yulu Member is dominantly composed of silicalite with argillaceous dolomite, representing a relatively syneclise deposits comparing to the Xiaowaitoushan Member. So they can be treated as contemporanenous and heteropic deposits. Controlled by the east west oriented Xiangtiaochong ancient uplift, a distiinct sedimentary environment exists between the two flanks of the uplift in early Cambrian Zhongyicun Member within the Jinning Anning region. Sedimentary features are indicative of a shoal phosphate facies on the south side while they show a tidal phosphate facies on the north side on the Lower phosphorite layer of Zhongyicun Member. The Upper phosphorite layer is divided into a shoal phosphate facies and a lagoon tidal phosphate facies.