Paleogeographic Evolution And The Source-reservoir-cap Assemblage’s Distribution Regularity Of Marine Stratigraphy, South Guizhou-Central Guangxi Depression

South Guizhou-Central Guangxi depression is a residual basin formed in active belt of intraplate, and it is also the typical representative of marine residual basin in the Yangtze region, developed Paleozoic marine strata mainly. South Guizhou depression retained the more comprehensive Paleozoic strata, with thickness of 6000-10000m; Central Guangxi depression mainly developed upper Paleozoic strata, with thickness of 6000-8000m approximately. Because of the unique formation environment of hydrocarbon generation layer, reservoir layer and cap rock layer in the basin, and the hydrocarbon generation, reservoir formation and the preservation condition in the later period are complicated, the ways and the key elements of petroleum exploration are different to the stable marine basin. In order to study the formation and distributional characteristics of material that for hydrocarbon producing, reserving and sealing in sequence framework, and their difference to the stable basin, and make clear the configuration rule of source, reservoir and cap in South Guizhou-central Guangxi depression, this article based on the field outcrop section, drilling and logging data, seismic data interpretation, and samples analyzed and tested data. It comprehensively researches the Sequence stratigraphy, the sedimentary system and the sequence-based lithofacies-paleogeography of Sinian-middle Triassic series marine strata in south Guizhou-central Guangxi region. It also analyzes the evolution of Paleogeography in Sinian system-Triassic period, shows the source-reservoir-cap assemblage character and allocation relation in sequence framework, predicts the favorable exploration zones, and quests the petroleum exploration ideas of marine residual basin in active belt of intraplate.Firstly, we redefine the project of Sinian-middle Triassic stratigraphy division in south Guizhou-central Guangxi region. Using the classic sequence stratigraphy theory, we divide the Sinian-middle Triassic strata into 13 super sequences(i.e. tectonic sequence) and 92 third-order sequences, and build the sequence stratigraphic framework. Then, we analyze the sedimentary system of sequence framework, and recognize five sedimentary system, they are the fluvial, shore, carbonate platform, platform basin and continental shelf. From that, we focus on the type and characteristics of the reefs, and construct the sedimentary model.Based on the tectonic-sequence lithofacies-paleogeography map that uses tectonic sequence system tract as mapping unit, and the constitution of a successive vertical evolution map, it shows that the sedimentary framework in south Guizhou-central Guangxi region is controlled by a deep fault in the plane. South Guizhou mainly deposits shore-platform sedimentary, while central Guangxi displays the platform-basin palaeogeographic framework. The characteristic of platform-basin sedimentary system tract display that low stand system tract shows the basin-upwarping framework, transgressive system tract shows the construction period of platform-basin framework, highstand system tract shows the stereotype period of platform-basin framework. Combined with regional tectonic setting, the depositional filling response characteristics show the basin evolution process in south Guizhou-central Guangxi region. In the Sinian-early Ordovician, south Guizhou-central Guangxi region is a marginal basin of middle-upper Yangtze continent. In the middle Ordovician-Silurian, it converted to foreland basin. In the Hercynian-early Indosinian, it is a rift basin that in the development period. In the middle Triassic, it evolved to foreland basin again.Sedimentary evolution of the basin controls the favorable developmental situation of source-reservoir-cap assemblage. The favorable source-reservoir-cap assemblage in south Guizhou depression developed in passive margin basin in early Paleozoic, while central Guangxi depression developed in the rift basin in late Paleozoic. The south Guizhou depression develops five marine source-reservoir-cap assemblage, primary exploration target is lower Paleozoic strata, neritic facies sandstone in Wengsan Member of lower Silurian is the key to exploration. The central Guangxi depression develops two marine source-reservoir-cap assemblage, the focal point of exploration is dolostone or dolomitized reef flat in Devonian.Using a pool-forming pattern called "generate in the basin and assemble in the platform" as the guiding thought, we consider that the favorable source-reservoir-cap assemblage in central Guangxi depression developed in upper Paleozoic mainly, the favorable target is isolated platform margin reef&bank facies in middle Devonian-lower Carboniferous. Hongdu shallow depression and the south of Liujiang low uplift, Huanjiang shallow depression is a favorable exploration zone. Compare to it, the favorable source-reservoir-cap assemblage in south Guizhou depression is Niutitang Formation-Honghuayuan Formation and wengxiang Formation. The favorable target is Ordovician weathering crust and Member 3 of Wengxiang Formation. And the favorable exploration zone is Changshun depression in the north of Luodian fault sag and Huangping shallow depression.