Research Of Sedimentary Facies And Paleogeography Of Middle And Later Permian In The Northern Margin Of Middle And Upper Yangtze Region

By field reconnaissance, grain size and composition statistic on thin sections, carbonate microfacies, isotope geochemistry, loss of ignition, geochemistry of calstic rocks on middle and later Permian sections in the northern margin of middle and upper Yangtze region, followed results has been educed:Middle and late Permian rock styles in studied area can be divided into four categories, with carbonate rocks being the major component, clastic rocks and siliceous rocks being subordinate, and coal being the least. Carbonate rocks include limestones and dolostones, with former being the main composition. Limestones include grainstone, packstone, wackstone, mudstone, reef limestone, calcirudite. By characteristics of microfacies, carbonate rocks could further be compartmentalized as followed categories: bioclastic mudstone, bioclastic wackstone, bioclastic packstone, bioclastic grainstone, peloid grainstone, oncoid grainstone, oolitic grainstone, detritus-bioclastic sparite, reef limestone, micrite calcisiltite. Dolostones include mud-silt-sized crystalline dolostone and fine-medium-sized crystalline dolostone. Clastic rocks includes sandstone, siltstone, mudstone and shale. Siliceous rocks include thin-bedded siliceous rocks, stratoid siliceous rocks and lenticular, nodular siliceous rocks.By assigning weights to mean grain size, winnowing ratio and grain/matrix in quantitative analysis of carbonate rocks, we obtain the index of hydrodynamatic force which could reflect the hydrodynamatic condition of limestone during its deposition time. Combining former research and correlation between winnowing ratio and the index, the conditions could be divided into five categories, with I,II<4.90 being no or poor winnowing, 4.90