Lithofacies Paleogeography And Evolution Of Niutitang And Mingxinsi Formations In North Guizhou And Its Adjacent Areas

The Middle-Upper Yangtze Craton which is based on the crystal and fold basement driven by Jingning tectonic movement formed in Greenville. From Nanhua Period on, the Yangtze Block had started the evolution into Craton Basin because of the plate movement mechanism and during the Cambrian the Middle-Upper Yangtze Craton is under the extensional tectonic background. This study is based on the theory of “Geologic Structure Controls Basin and the Basin Controls Sedimentary Facies”, and focuses on filling sequences and sedimentary evolution of Niutitang and Mingxinsi Formations in North Guizhou and its adjacent region(the study area). Moreover, we estimate hydrocarbon potential of Niutitang black shlale and get the following achievements:1. We divided Niutitang Formation into two parts(i.e. organic shale and upper part) on the basis of TOC(0.5 wt. %). In addition, we establish sequence stratigraphy framework of Mingxinsi Formation on the basis of predecessors’ work. CS+EHST is considered the lower part of Mingxinsi Formation and LHST is Upper part of Mingxinsi Formation.2. In study area, the lithology of Niutitang and Mingxinsi consists of oolitic limestone, bioclast limestone member, micrite, shale, silty shale, organic shale, siliceous shale, silty mudstone, argillaceous siltstone, quartz sandstone, shingly quartzarenite and the mainly facie consists of shoreside facies and shelf facies.3. Throung the research on Dingtai Profile in Zunyi area, we accomplished the detailed description of the shoreside facies of Mingxinsi Foramation for the first time. Moreover, we investigate the range of distribution of Mingxinsi sandstone, and suggest that the sandstone covered the most area of North Guizhou and its adjacent region.4. We draw four lithofacies paleogeographic map with the method of dominant facies, such as Niutitang organic shale lithofacies paleogeographic map, upper part of Niutitang lithofacies paleogeographic map, lower part of Mingxinsi lithofacies paleogeographic map, upper part of Mingxinsi lithofacies paleogeographic map. In addition, we acquire the sedimentary evolution of Niutitang and Mingxinsi Formations.5. The organic matter type of Niutitang black shale is type I. The TOC value is between 0.1-20.57 wt. %(mainly between 0.4-4.5 wt. %) and TOC values in most area are greater than 3 wt. %, partial area greater than 8.02 wt. %. Maturity of organic matter(Ro) which is between 1.74-4.48 wt. % indicate that maturity of organic matter is mainly in early evolutionary stages, and partly in late evolutionary stages. By analyzing the shale gas geology characteristics including organic matter type, TOC value, and maturity of organic matter and by estimatying the hydrocarbon potential, we success to direct the shale gas exploration.