The Research Of Depositional System And Sequence Stratigraphy Of Xujiahe Formation Of Upper Triassic In Guangyuan Area

This artiele uses sedimentology, sequenee stratigraphy, petrology, logging, seismie and combination of mult-disciplinary to reseach sedimentary features and analyze the deposition types of the Xujiahe formation of the Upper Triassic Series in Guangyuan area. It reserches the sequence stratigraphy of outcropping profile, then establishing sequence stratigraphic framework and further based on depositional sequence analyzes sequence-based lithofacies palaeogeographic features of Guangyuan to Yuanba area, concrete steps and results are as follows:Firstly, On the basis of lots of forerunners'data and my research in this thesis, Combining drilling data with observation and analysis of the well core, Xujiahe formation can be divided into six kinds of sedimentary systems such as alluvial fan, river, lake delta, lake, marine delta and beach-barrier by using sedimentary facies signs which is rock feature, sedimentary structure, well log and section texture, Each of the sedimentary systems was subdivided into several subfacies and microfacies, which were described and generalized in detail. By generalizing, I conclude that two relevant sedimentation model of Guangyuan area to Yuanba area. The first sedimentation model is transitional facies- marine facies in Xujiahe formation one-two section, which is made up of marine delta, bay, beach-barrier and epeiric sea. The second sedimentation model is alluvial fan-river-delta or fan delta-lake in Xujiahe formation three-five section, which is changed along with the time and space alter of basin. Further, it can be subdivided into two sedimentation model. The one: alluvial fan-river(alluvial plain)-braid river delta-lake. The second: alluvial fan-fan delta-lake.On the basis of analysis on seismic sequence, defining the stratic interface by the surface of unconformity, this paper divids the Xujiahe Formation of outcropping cut plane in Guangyuan Gongnong town into three tectonic sequence and five sedimentary sequence, and also deeply investigates the characteristics of all levels sequence. It establishes sequence stratigraphic framework of the Xujiahe Formation of the Upper Triassic in Guangyuan Gongnong town to Yuanba area.The sequence-based lithofacies-paleogeographic maps of the Xujiahe Formation of the Upper Triassic in study area are compiled by choosing sedimentary sequence as the isochronous mapping unit. This paper demonstrats in details the characteristics of lithofacies aleogeography and their evolution during different sedimentary sequence developing period.