Sequence Lithofacies Palaeogeography Characteristic And Its Evolution From Permian To Middle Triassic In South Guizhou And Middle Guangxi

South Guizhou and middle Guangxi located in south edge of Upper Yangtzee platform, influenced by the evolution of Paleo-Tethys ocean, from Permian to middle Triassic, within the unique tectonic-sedimentary evolution, there developed marine stratum with good exploration prospects. Based on the predecessors'research achievements, guided by the theory of tectonic geology, sedimentology, sequence stratigraphy, taking the main line of basin evolution, sediment evolution and sequence evolution, according to the study on drilling and outcrop, with the method of macro-observation and indoor analysis on microfacies, this thesis have comprehensively studied on depositional system, sequence stratigraphy, sequence lithofacies paleogeographic and basin evolution.Through comprehensive analysis on outcrop, drilling core and logging data, it is believed that there developed 4 depositional systems from Permian to middle Triassic in south Guizhou and middle Guangxi, which are shore, carbonate platform, platform basin and mixed shelf. The characteristic of each depositional system have been studies in detail, the depositional model of shore, carbonate platform and shelf were established.After regularizing the division and comparison plan of Permian to middle Triassic in south Guizhou and middle Guangxi, sequence boundary identification and sequence stratigraphy analysis are studied on section of outcrop and drilling. It can be divided into 2 super sequence and 19 third-order sequence of Permian to middle Triassic in study area, there are 12 third-order sequence in Permian and 7 third-order sequence in lower to middle Triassic. Each sequence and its characteristic of system tracts were discussed in detail, and the sequence framework has been established.Based on research of depositional system and sequence stratigraphy, taking super sequence system tracts as compilation unit, seven tectonic-sequence lithofacies paleogeographic were drew, which show the depositional facies distribution pattern of different stage from Permian to middle Triassic. Overall, the SS1 and early highstand period of SS2, the open and restricted platform developed in south Guizhou, and the pattern of platform interleaved with basin developed in middle Guangxi, the clastic rocks developed in late highstand period of SS2.Combined with evolution dynamics setting and eustasy, it is analyzed the filling process of three evolution stage from Permian to middle Triassic in study area, which are stage of rift valley basin of passive margin, stage of rift valley basin of back-arc, stage of foreland basin. In the stage of rift valley basin of passive margin, controlled by synsedimentary faulting of NW and NE in late Permian, which formed the typical fractured craton edge, and influenced by the fall of sea level, most of study area exposed to denude, the SS1 lowstand system tracts only filled in graben. In early middle Permian, with the rose of sea level , open platform and restricted platform developed in south Guizhou, and the pattern of platform interleaved with basin developed in middle Guangxi, which formed the SS1 regression system tracts. Then in late middle Permian, regression expanded further, it was the maximum flooding period of late Paleozoic, and due to the rim of platform, the pattern of platform interleaved with basin was more obvious , which formed the highstand system tracts of SS1. In stage of rift valley basin of back-arc, during early late Permian, Dongwu movement reached the climax, crust rose strongly, sea level fell, most of study area rose to expose, the SS2 lowstand system tracts only developed in southwest deep water platform basin, from middle to late of late Permian, with rose of sea level, upheaval zone submerged by water again, the pattern of platform interleaved with basin appeared again. During early Triassic, the depositional pattern didn't changed much, sea level rose continuously and reached highest at Olenekian stage, which formed the early highstand system tracts of SS2 super sequence. In stage of foreland basin stage, influenced by Indosinian movement, sea level fell, a set of thick epicontinental clastic turbidite deposited in study area, which formed highstand system tracts of SS2 super sequence.