Sedimentary, Sequence Filling Process And Its Accumulation Effect Of Late Triassic To Middle Jurassic In Ordos Basin

Ordos basin is the most complete preservation of a large Mesozoic inlandpetroliferous basins, which is very rich in energy mineral resources.The YanchangFormation of Triassic is the first obtain onshore oil and gas formation of the basin. Inthe Mesozoic, late Triassic Yanchang Formation-middle Jurassic Yanan Formationhas for years been the main objectiive of clastic rock petroleum exploration, andobtained the huge economic benefits.The paper based on the late Triassic-middleJurassic sequence stratigraphy, provenance, sedimentary system characteristics,sequence lithofacies palaeogeography, depositional model and accumulationcharacteristics in many aspects have made comparatively systematic analysis andresearch, has obtained certain achievement.By using various research methods of provenance analysis, in view of lateTriassic Yanchang Formation and middle Jurassic Yanan Formation sedimentaryperiod of the whole basin in Mesozoic has carried on the systematic analysis of thesource situation, has been clear about the distribution of the source, laid thefoundation for the research of sedimentary system.The results show that the tectonicsetting of the provenance of the Mesozoic late Triassic Yanchang Formation is givenpriority to recycled orogenic belt (southwest) and the stable continental craton (east),mainly developed three major provenance of the northeast, southwest and west, and inbasis of these development have multiple secondary source.Early and middle Jurassicalso has multiple provenance, in the west and northwest of the basin is the most mainprovenance for the whole Jurassic. In different periods palaeocurrent direction, waterdistribution and channel direction has obvious inheritance. Provenance has thecharacteristics of stable inheritance.According to the facies indicators features of depositional fabric, rockassociation, sectional structure phase signal feature, proposed the comprehensiveclassification scheme of sedimentary system of the basin in the late Triassic-Jurassic,and studied the development features of sedimentary facies. From the TriassicYanchang Formation-Jurassic Yanan Formation, sedimentary systems divided intoalluvial fan, river, lake delta, lake and turbidity deposits, and established thecorresponding depositional model.Thinking that in southwestern and southern basinYanchang Formation developed typical turbidite rock, and set up the turbiditeformation development mode during the period.On the basis of systematic formation cleaning and comparison, using outcrops,well logging, seismic the research methodsof high-resolution sequence stratigraphy. Inthe late Triassic-Jurassic in the basin, the characteristics of sequence boundary andthe genetic type of the interface were studied intensively and summarized. The basin clastic sequence interface identified four genetic types, seven kinds of sequenceboundary material manifestation.Based on the identification of sequence boundary, established the Triassic-Jurassic high resolution sequence stratigraphy framework in ordos basin for the firsttime, and researched the developmental characteristics of the sequence.The Mesozoicordos basin system is divided into six super long-term cycles and20long-term cycles.Triassic contained three super long-term cycles, Jurassic developed three superlong-term cycles, and the development characteristics of medium-term base-levelcycle is studied. For the characteristics of sequence filling structure of different faciesbelt in ordos basin, divided into five types of sequence structure, carried out analysisof the different sedimentary system of sedimentary sequence filling dynamics process,established sequence filling structure model of large inland depression basin.Worked out the sequence lithofacies paleogeographic map of each major periodof late Triassic Yanchang Formation-middle Jurassic Yanan Formation in the wholeOrdos basin for the first time, revealed the lithofacies paleogeographic evolutioncharacteristics and law of the basin in the late Triassic-middle Jurassic, providedimportant basic geological maps for oil and gas exploration in the basin, andestablished the palaeogeographic evolution model of the late Triassic-middle Jurassicin the basin.Evolution of sedimentary basin was separated. Different sedimentary evolutionstage was studied for the difference control function of sedimentary system andsequence distribution, and further discussed the coupling relationship between innerand outer dynamic process and sediment, the sequence filling in the basin.Ordos basin was discussed the accumulation effect of the process of sedimentarysequence filling evolution. Mesozoic clastic rock series in the basin are mainlylithologic reservoir, think that the basin sedimentary and the sequence fillingevolution controlled the time and space distribution of reservoir and caprock. Underthe influence of datum plane lifting and episodic tectonic movements, commoncontrolled source-reservoir-cap assemblages and their distribution. Depositionalsystem types and lithofacies characteristics controlled the distribution of favorablereservoir development, different lithofacies palaeogeographic units controlled thedifferences of regional reservoir geological conditions.