Research On Sedimentary Facies Of Yanchang Epoch Of Mesozoic The South Margin Of The Ordos Basin

Southwest Ordos basin is a chief target of increasing resources and production, recently, which have plenty of petroleum resources, so it is crucial for petroleum exploration to understand evolving rules of Sedimentary Characteristics and sand body.The study area in the southern margin of Ordos Basin,which aimed layers is chang8-chang6 oil layer of Yanchang Formation in the Mesozoic.In the paper,uitilized drill core data and logging data, field sections and geochemical data,combined with sedimentology,petrology,logging science,events sedimentology,Identified the symbol of sedimentary facies and the characteristics of sedimentary facies, established the sediment frame, summaried sedimentary facies of the basin.Systemic study in the southern margin of the basin including sedimentary facies, sedimentary facies, sand body morphology and development of Bout points, and analysed the control factors of the oil and gas deposits, The results obtained that the basin mainly have northeast and southwest of the two major deposition system,which composed of the braided river, meandering river,braided river delta,meandering river delta,lacustrine facies and turbidite fan, and its sedimentary characteristics and depositional facies are described in detail.and through several aspects study,such as provenance analysis,basin center migration and the impact of Qinling orogenic,analysised and contrasted the Sedimentary facies in southern margin of the Ordos Basin.Through the flow ancient, heavy minerals,light minerals,REE analysis, suggesting that there are four different sources from the southwest, south, northwest and northeast of the direction in the Yanchang Formation during Late Triassic period, there is no western source, Longxi ancient land in the southwestern part of the Ordos Basin composed of southwest of the source,which provide source of rock for the Middle Proterozoic of the Long Hills and Aurora to the Middle Ordovician Hulu River group. Northwest of provenance from the old land Alxa Alashan Middle Proterozoic base, northeast of the source is mainly from Daqinshan and Yinshan of Jining groups and Wulashan Group in the upper Archean in the back of basin. As the Indo-China movement of Late Triassic in the southern of basin. Qinling Ocean disappeared, the Yangtze and North China block completely flattened, uplift of the Qinling orogenic belt began to constitute the main source area.Through migration of the lake and the Qinling orogenic impact analysis, southern margin of the Ordos Basin, mainly in large-scale orogeny after chang8 stage, Orogeny led to mountain uplift in source area,strongly deformed basement, resulting in uneven settlement, The pattern of basin began to emerge:steep in south and slow in north, and reduce the deposition scope of Yanchang Formation is reduceing,Sham Shui Po area increases rapidly,coarse clastic material bengin to entered the basin.During chang 8 stage,the basin is relatively stable,To the chang 7 stage,Qinling orogenic is the most active period which deposited a series of events,such as frequent earthquakes, volcanic eruptions and source area uplifted, Orogenic front quickly sinking, Lake-level rise, the lake center migrated toward to southwest edge of the basin,which partly affected by the transgression,so the asymmetric basin begin to emerge, The chang 7 stage is a turning point in the basin,so the chang 8 stage is beginning.In this stage, the terrain in the southwest of basin is relatively flat, deposited mainly meandering river delta.To the chang 7 stage,the tectonic movement cause the asymmetry basin formation,Therefore.the pattern which the southwest of basin appears to mainly braided river delta and mainly meandering river delta in northeast bengin to emerge.By comprehensive analysis and comparison of results, find out the Yanchang 8 - Chang 6 oil layer regulation of sedimentary evolution,sedimentary facies distribution characteristics in the plane,sand distribution in the plane, and made sedimentary facies map and sand distribution map in the southern margin of Ordos Basin in the Mesozoic, Analysised sedimentary controlled hydrocarbon accumulation based on sedimentary facies and sand body distribution,which making significance to the next step for the exploration of the southern margin of Ordos Basin.