Coal-accumulating Patterns Of High Resolution Sequence Stratigraphy Of The Middle Jurassic In Yuqia, Qinghai

On the base of many previous studies，Systemly collecting previous information、thefield profiles、 Logging data and comprehensive indoor study, with the guidance ofsedimentary geology, high resolution sequence stratigraphy etc. theories and methods, Yuqiaarea middle Jurassic stratas were systemly divided, in Qinghai Province, and the sedimentarysystem, the high resolution sequence stratigraphy, sequence lithofacies palaeogeography, coalaccumulation and its controlling factors were studied. The low accommodation (fan), theaccommodation space in (River-delta) and high accommodation space (lakes) of the coalaccumulation models were respectively established, the coal accumulation was presented indetail.First of all, through the study of the field profile observation, comprehensive analysis ofwell logging, seismic and regional data, based on analyzation of the rock type, sedimentarystructure, section structure,1sedimentary system group,5sedimentary facies, as well asmany subfacies and microfacies types in the study area in the Jurassic were identified, andcharacteristics of phase of deposition was discussed in detail. Based on the above,coal-forming environment of alluvial fan, braided river, braided river delta, meandering riverdelta and lake and other types of sedimentary facies were studied in detail.Secondly, according to the study of the regional unconformity surface, converting corefacies, erosion surfaces and ancient soil layer interface，5long sequence interface in theMiddle Jurassic coal-bearing strata were identified. According to the evolution of thesedimentary environment, lithological sequence characteristics and features of sequenceboundary, the Middle Jurassic was divided into4long sequence. On this basis, according tothe different sedimentary facies types of coal-bearing formation were unified developed，withthe sequence stratigraphy theories and methods. Short-term, medium-term, long-term3levelsof base-level cycle were identified，and every cyclic sequence characteristics was furtherlyanalyzed. High resolution sequence stratigraphy of every district has been established，and coal seam distribution in the high resolution sequence stratigraphic framework was discussedin detail. The results show that the thickness of coal seam is usually located in the lake earlyinvasion， and the thin coal were usually developed in the later period of sequencestratigraphic frameworkFinally, on the basis of the coal accumulating environment, coal accumulation model andbasic research on high resolution sequence stratigraphy，reference to previous researchresults，the coal accumulation law of coal-bearing strata in high resolution sequencestratigraphy has been systemly summarized，in middle Jurassic of Qinghai Yuqia area.