Carboniferous Sequence Lithofacies Palaeogeography Characteristic And Its Evolution In South Guizhou And Middle Guangxi

Recent years China's marine hydrocarbon exploration has achieved some significant breakthrough and discoveries in Sichuan Basin and Tarim Basin. Carboniferous of South Guizhou and Middle Guangxi is one of best developed areas for marine stratum, to figure out whether there is exploration potential or not and the exploration direction, so this thesis focuses on Carboniferous stratum system, depositional system characteristic, sequence stratigraphy, characteristic and evolution of sequence lithofacies paleogeographic and reservoir characteristic within sequence framework in South Guizhou and Middle Guangxi, which can provide some exploration proofs. Several achievements have gained as follow.According to the latest rock stratigraphic and regional geology, the Carboniferous stratum has been regularized in different sedimentary area of different depression, and they has been contrasted.Guided by the theories of sedimentology and the work methods of lithofacies paleogeographic, and based on measurement of main field geological sections, observation of supplementary field geological sections and data of drilling, according to types of rock, combination of rock, section character and sedimentary structure, four depositional systems are distinguished in Carboniferous of study area, they are coastal depositional system, carbonate platform depositional system, platform basin depositional system and shelf depositional system, meanwhile the depositional facies, subfacies and microfacies were divided. Taking one with another, the depositional facies belts was kind of old land-shore-shelf-carbonate platform-platform basin interleaved with platform. The depositional models have also been established. After detailedly study on Carboniferous sequence boundary characteristic and genesis types in South Guizhou and Middle Guangxi, the sequence boundaries, paleocrust of weathering, atmospheric water effect surface, lithology and lithofacies transitional surface and maximum flooding surface, were identified. Based on the sequence boundary identification, Carboniferous can be divided into 2 super sequence and 11 third-order sequence, the system tracts and sequence characteristic of each super sequence and third-order sequence were carefully discussed, and the third-order sequence was contrasted in study area, which are comparable in study area.Based on sequence division and contrasting, taking system tracts of super sequence as compilation unit and using system tracts compression method, five Carboniferous tectonic-sequence lithofacies paleogeographic in South Guizhou and Middle Guangxi were drew, which can show the Carboniferous paleogeographic character of study area. During SS1 lowstand period, Ziyun movement caused the exposure of most parts of study area, shelf and restricted platform developed in south Guizhou, and it showed the sedimentary pattern of platform basin interleaved with platform in Middle Guangxi, then to transgression period, sea level rose quickly, shore developed in South Guizhou, platform basin expanded in Middle Guangxi, during highstand period, the paleogeographic pattern changed little, platform expanded, platform basin shrunk. Then in SS2 stage tectonic movement became weaken, the depositional facies pattern changed a lot. During transgression period, the sedimentary facies mainly were platform and platform basin, platform basin was filling and shrunk continuously, and platform range continued to expand. Finally during SS2 highstand period, due to the Qiangui movement in late of Carboniferous, north and middle Guizhou rose to be land, sea retreated forward south, platform basin shrunk continued, it showed the depositional pattern of basin surrounding by platform.By analysis of pore type and physical property of reservoir, the main reservoir of study area is dolomite and biodetritus limestone in platform of Dabu Formation and Huanglong Formation, which all are reservoir of low porosity and low permeability, the physical property of Dabu Formation is better than the one of Huanglong Formation. Reservoir mainly developed in highstand system tracts, as the fall of sea level, the exposure and erosion of dolomite and biodetritus limestone in platform formed a large number of solution cave.