Tectonic-sequence-based Lithofacies And Paleogeography Of Permian In South Of China

There is remarkable marine petroleum resource in Permian in south of China which has been one of the most important petroleum exploration target, but the finding of petroleum is still poor compared with its big sedimentary area. How to choose more favorable block and enlarge finding of petroleum in other regions in south of China had been the main problem. So this paper regards systems analysis of the depositional evolvement as a goal of Periman in south of China, applying theories of sequence statigraphy, paleogeography and geology of petroleum, The tectonic-sequence-based lithofacies and paleogeography of Permian in south of China are studied based on lots of outcrop section data and analysis of regional tectonic background and sequence statigraphy by ways of tectonic controlling basin and basin controlling lithofaciese. Through above study, the basin deposition filling evolution and the distribution laws of source and reservoir rock under isotime sequence statigraphy trellis are revealed in Permian which provided geology basis for later exploration of marine oil-gas in south of China. At the same time the research methods and expressing skills of tectonic- sequence-based lithofacies and paleogeography are proposed in this paper, and could be used for reference of the same type research.The main conclusions and innovations are as follows:①Two super sequences and twelve third order sequences are divided in Permian in south of China through analysis and contrast of six backbone sections and twenty-two adjective sections and parts of well-sections by the way of classical sequence statigraphy theories proposed by Vail. Third order sequences mainly belong to type II, but type I sequences mainly developed in the top and bottom of Permian and between Middle Permian and Upper Permian.②Pulling setting presents in southern China in Permian forming rift basins, which extends and develops from the edge to the inside of continent. Under the influence of Dongwu movement, two second order cycles forming by up and down of sea level happened in Yangtze and Huaxia craton. Rift basins in continental margin are primary sedimentary location of LST. But craton areas are the main deposition area of TST and HST. Weathering on land and river sediment or only thin coaly clasolite of marsh facies present mainly in LST deposition.③Regarding the sytem territory of super sequence as a unit, and depending on more than two handred data points, the space-time distribution of lithofacies and paleogeography in six key periods of Permian and the filling characters of prototype basins are reveal. Deposition period of Middle Permian belongs to deposition type of slow expanding, and single carbonate platform system with gentle slope presents in Middle Permian. Delta systems of HST only develop in late period of Permian in southeast shore areas. Deposition type of Late Permian belongs to gradual shrinking deposition, in which sedimentary systems of land- carbonate or mixed platform are formed on two sides of Xianggui rift basin.④According to the space distribution characters of tectonic-sequence-based lithofacies and paleogeography, it is showed that three types of hydrocarbon source-rock including carbonate rock, clay and coal in Permian mainly are developed in transgression and maximal sea flooding of two order sequences, and they deposite respectively on platforms with gentle slope in craton, in rift basins and around old lands.⑤According to the conditions of reservoir facies, it is showed that many kinds of reservoirs such as carst develop on sequence boundary. Reef-flat at the edge of platforms, dolostone and clastic of river, delta and littoral facies develop at the middle and up of Yangtze craton, and reservoirs such as carbonate gravity fluid in slope, turbitite fan in basin bottom and carbonate on isolated platforms develop in Youjiang and Xianggui rift basins. These reservoirs may form upside and underside of source rock, or lateral contact with source rock in space.