Sequence Stratigraphy And Sedimentary Facies Of The Longwangmiao Formation In The Eastern Margin Of The Sichuan Basin

In this study,the eastern margin of the Sichuan Basin refers to the vast majority of the upper-middle Yangtze in the east of the Sichuan Basin,east to Sichuan Moxi,west to Hubei Yichang,north to Chongqing Wushan,south to Guizhou Jinsha.The target stratum in the study was the Longwangmiao Formation(Qingxudong formation or Shilongdong formation).Based on the previous study,the authors take a study of the sedimentary facies of the Longwangmiao Formation in the eastern margin of the Sichuan Basin combined with their personally field geological work experience.The 4 across profiles,Hunan Cili Nanshanping section,Guizhou Jinsha Yankong and Xishui Tuhe section,Hubei Xuanen Gaoluo section had been measured.The 2 across profiles Guizhou Songlin Zhongnan and Pengshui Taiyuan section had been observed.The 1 drilling profile Hubei Yichang M well had been observed,too.The auther proposed a concept “stacking of the tidal flat and particle beach” to realized the change of the sea level easily.With the Characteristics of the Sequence Boundary,it had been proved that the formation was divided into three sequences(Sq1,Sq2 and Sq3).Among them,Sq1 and Sq2 were generally developed over the basin and show a trend of declining sea level as a whole.Sq3 was only finned in Hunan Cili,Guizhou Jinsha and other parts of the basin.On the basis of this,5 kinds of sedimentary subfacies were identified and 13 species were deposited.The area had 2 kinds of Sedimentary environment from the east to the west.In the west of Jinsha-Wulong-Shizhu,there were dolomitic tidal flat in the limited platform.The lagoon deposition was located in the area of Luzhou – Jiangjin,while there were particle beaches locating in the area of Moxi.There were also many particle beaches developed along the area of Jinsha-Wulong – Shizhu,but was replaced by the ash gray tide deposition in the open platform to the east.The Longwangmiao Formation in the eastern margin of the Sichuan Basin had been proved a carbonate platform deposition pattern.