Charicteristics Of Sedimentary Facies And High-Resolution Sequence Stratigraphy Of Xujiahe Formation, Upper Trias, In The Northeast Sichuan Foreland Basin

On the basis of lots of forerunners' data and my research in this thesis, I put forward that the formation and evolution of the west Sichuan foreland-like basin were controlled asynchronally by thrust action of two tectonic zones ?Longmen mountains and Micang-Daba mountains , and divided the west Sichuan foreland-like basin into three evolutionary phases --early margin foreland basin stage (T3m-T3t), middle foreland-like basin stage (T3x-J3p) and late shrinking and extinct stage (K1桬2). At the same time, I discussed the tectonic-sedimentary configuration, sedimentation and sequence evolutive character of the northeast Sichuan foreland basin in the Xujiahe age , late Trias. In conclution, I drawed the following conclusions. In the early Xujiahe age (T3x2 3), Micang-Daba mountains were still in stable uplift station with low amplitude. On the contrary, the thrust action of Longmen mountains was active. At this age, the northeast Sichuan foreland basin was mainly influenced by remote effect of Longmen mountains' thrust action. In the late Xujiahe age (T3x4-6), Longmen mountains' thrust action intensified further. At the meantime, Micang-Daba mountains began to enter into intensive tectonic uplift before thrust action. At this age, the northeast Sichuan foreland basin was influenced by Micang-Daba mountains' thrust action and remote effect of Longmen mountains' thrust action.Combining drilling data with observation and analysis of six field measured sections, I extracted six sedimentary facies signs from the northeast Sichuan foreland basin, which were rock color, texture, sedimentary structure, paleobiologic fossil, well log and section texture. At the meantime, I devided six sedimentary systems from the research area, which were alluvial fan, braided river, meandering river, fan delta and shallow lake. Each of the sedimentary systems was subdivided into several subfacies and microfacies, which were described and generalized in detail. At last, I concluded that the northeast Sichuan foreland basin mainly developed braided river delta and lake sedimentary systems in early Xujiahe age(T3x2-3), and mainly developed alluvial fan, fan delta, braided river delta and shallow lake sedimentary systems in the late Xujiahe age (T3x4-6). On the basis of the analysis mentioned above, I generalized sedimentary model of the northeast Sichuan foreland basin (i. e. two step fan model) in the Xujiahe age, late Trias.On basis of structure edimentation evolution and distribution of sedimentary facies in the northeast Sichuan foreland basin, adopting the theory ofhigh-resolution sequence stratigraphy and referring classical sequence theory, I devided the strata of Xujiahe Formation in northeast Sichuan foreland basin into one super-long sequence cycle (T3x),two long sequence cycles (corresponding to T3x2-3 and T3x4-6), five middle sequence cycles (corresponding to each number of Xujiahe Formation) and numerous short sequence cycles, and discussed sequence texture style, depositional sequence, stacking pattern and mode of distribution. In the end, I discussed the formation and evolution character of long sequence cycles, which had close relation to asynchronous thrust action of Longmen mountains and Micang-Daba mountains.