Study On The Jurassic Lithofacies And Paleogeography Of Sichuan Basin

Sichuan Basin is the most important concentrated oil and natural gas origin and prospect area in upper Yangtze Plate, it is also other various potential area of sedimentary type ore deposit. For Sichuan basin, predecessors do a large amount of exploration and research work, accumulate substantial results. But most of the study areas are small and concentrated near the oil and gas fields, more than other parts of areas are blank; Although a few results of the study area involved in the whole sichuan basin, but not specializes in sichuan basin, and its research level to stage or more senior, only for the whole Sichuan basin lithofacies paleogeographic phase level- the level of specialized research remains to be perfect.Hope that through the study of the Sichuan basin Jurassic lithofacies paleogeographic, preliminary obtain a basic understanding in Sichuan basin of Jurassic lithofacies paleogeographic characteristics and evolution law, and complete a drawing of the map; Through analyzing the sedimentary facies in the study area and lithofacies palaeogeographic research, explore sedimentary minerals, especially the specific sedimentary environment and facies oil-gas resources constraints.This article combines predecessors' regional geological survey, the fossil record, geochemical and geophysical well logging, remote sensing data, references theory of biostratigraphy, plate tectonics and basin analysis principle and method of sequence stratigraphy thought; under the plate tectonic theoretical guidance of macro, with "structure controlled basin, basin facies" as the research train of thought, on the basis of multiple comparison division in the study area, according to a variety of facies marks for phase analysis and comparison of the typical stratigraphic profile, coupled with some single factor conditions, comprehensively analysis the lithofacies palaeogeographic characteristics in the study area; Finally, explore the sedimentary mineral and its lithofacies palaeogeographic environment.Reference solutions used by the predecessors, they has carried on the multiple comparison from rock stratigraphy, biostratigraphy and chronostratigraphy for Jurassic strata in sichuan basin, and established stratigraphic isochronous framework; Reference sequence stratigraphy theory, according to sedimentology, paleontology, sedimentary geochemistry and geophysics facies marks, on the basic of a typical stratigraphic section profile's sedimentary facies analysis, contrast between sedimentary facies through using the advantage of the main typical profile method, and draw the section between sedimentary compared analysis diagram; On the basis of contrast analysis of sedimentary facies, combining ancient structure, formation thickness, flow and sediment source, comprehensively analyze the lithofacies paleogeographic characteristics in Sichuan basin, and draw early Jurassic lithofacies paleogeographic map of Sichuan basin, Sichuan basin map in middle Jurassic lithofacies paleogeographic, Sichuan basin map in late Jurassic lithofacies paleogeographic; combined with tectonic theory, briefly discusses the Jurassic among the lithofacies paleogeographic development evolution characteristics in sichuan basin,and according to the profile analysis of sedimentary facies and lithofacies palaeogeographic research results, this paper discusses the sedimentary mineral, especially the specific sedimentary environment and facies oil-gas resources constraints.Tectonic framework and its development evolution directly decides the type and properties of sedimentary basin, and the different sedimentary basin produce different sedimentary environments and paleogeographic conditions, so as to develop different sedimentary facies. Early Jurassic, the climate of Sichuan basin overall hot and dry, while the northern warm and humid. Western edge development consists of a series of alluvial fan and fan delta bodies of fan group, develop multiple scale ranging from the eastern edge of the delta of a huge delta facies, shore and shallow lake environment occupy almost the whole of the Sichuan basin, shallow lakes underwater highlands of central and southern development huge dam shell beach. Middle Jurassic, the eastern Sichuan basin lake basin basement uplifted generally, appearing a obvious Lake retreat, so most areas form Lakeside swamp- Shallow Lake Environment. Climate became more and more dry, developing flood- flooding basin environment; north presented by the northern rivers and deltaic alluvial environment, south-central occupied shore and shallow lake environment. Lake basins of late Jurassic, the Sichuan basin tectonic activity was relatively quiet, and the climate was dry, as the strong oxidation depositional environment. Around was composed of alluvial fan, fan delta, river and delta alluvial environment.Central was to shore and shallow lake environment.The sediment filling and fill sequence of different sedimentary facies show differents, indicating the different sedimentary environments. Sedimentary type of mineral resources has its specific metallogenic, in particular sedimentary environment might mineralization and metallogenic.In Jurassic, Sichuan basins' coal mainly occurs in alluvial and diluvial facies while characterized in conventional oil and gas reservoir are mainly developed in delta front subfacies, underwater distributary channel and river mouth bars; Lacustrine shale gas field significantly influenced by shallow lake, half deep lake environment of sedimentary organic matter the spatial distribution of the shale control; Iron ore deposits mainly occur in the limnetic environment.Through this paper, the basic reveals lithofacies palaeogeographic characteristics of the Sichuan basin in the period of Jurassic, contribute to the evolution of continental basin, Sichuan basin development research, and further enrich the Sichuan basin lithofacies palaeogeographic research achievements, also can provide some ideas for the study of other similar sedimentary basin. The main sedimentary mineral source, formation mechanism, the law of occurrence and metallogenic period after save all affected by petrographic characteristics and paleogeographic environment constraints. Studying the lithofacies paleogeographic conditions on the restriction of major sedimentary mineral types of law, to further resources exploration work is very important. For sedimentary mineral analysis of sedimentary facies and lithofacies paleogeographic conditions of discussion, look forward to providing some useful reference work for the Sichuan basin sedimentary mineral resources for the future, especially in the oil and gas exploration and development, providing more basic data, data support in order to looking for sedimentary mineral resources.