The Study Of Sequence-based Lithofacies-paleogeography Between Early To Middle Triassic In The Southeast Of Sichuan Basin

Commercial gas streams were obtained from the Well Ba3 after 1963, researchers took great effects to get more achievements, and then Puguang gas field was discovered. The research shows that the development of gas reservoir of the Feixianguan formation in northern Sichuan Basin mainly controlled by the Kaijiang-Liangping inter-platform basin, and distributed around the Kaijiang - Liangping inter-platform basin. The geotectonic background of the studying area was similar to the Puguang gas field, did it have the same depositional environment? And how far did the Kaijiang - Liangping inter-platform basin extend to the south? These are what I interest.The studying area is located in the southeast of Sichuan basin. In the line with the research actuality and arguing focus on this area, combined with the principle of sedimentology, tectonic geology, sequence stratigraphy and sedimentary basin analysis etc., the following several principal issues between early to middle Triassic have been studied:1) The stratigraphic classification and characteristics. Five sedimentary system has been recognized , that is shore depositional system (T)2b) , shelf depositional system (T₁f), carbonate platform depositional system(T₁f～T₂l), carbonate slope depositional system(T₁f) and inter-platform basin depositional system(T₁f); then this article tell about the characteristics and the distribution of time and areas of the sedimentary systems;2) sequence boundary was typeâ…¡, and then, five sequences identified and divided. The features of every sequence are discussed in detail and meanwhile, sequence stratigraphic framework has been built which was built on the regional tectonic background.3) Ten sequence- based lithofacies and paleography maps of the early to middle Triassic in the studying area has been drawn up by way of condensation with mapping units of sedimentary systems tracts. In the light of sequence- based lithofacies and paleogeography maps, the characteristics and evolution of sequence-based lithofacies and paleogeography have also been discussed in detail. Inter-platform basin developed in the north of the studying area from TSQ1HST to TSQ2EHST and shelf depositional system is the mainly depositional setting which occurs in TSQ1TST. Carbonate platform depositional system is the mainly depositional setting from TSQ1HST to TSQ5 and shore depositional system mainly developed in the TSQ5 of Shizhu area. Ooid beach developed commonly in the studying area, but it developed largest in TSQ2EHST.4) From the early to middle Triassic, the development of the studying area located in the Upper Yangtze craton, and the variety of the sea lever is the main factor control the development.