Stratigraphic Division And Comparison And Sedimentary Facies Analysis Of Middle-late Permian In Northeast Chongqing Area

Northeast Chongqing Area locates in the basal reverse belt of Dabashan Mountain and Micang Mountain in the Yangtze landmass, in which early Permian formation is in absence with interim and late Permian stratum extensively developed. Through the investigation of northeast Chongqing area, based on the data about the rocks and creatures obtained from the stratum section survey in the research center and combined with previous publications, this paper makes the multi-stratigraphic subdivision towards the stratum in the study area plus sedimentary facies analysis on the interim and late Permian stratum and then achieves the depositional model of the interim and late Permian stratum in the study area.There are three measured sections and three observed profiles in this paper which are the middle and upper permian series stratum section survey of houses in the mountain in Tangfang village, Wuxi County in Chongqing Municipality, the middle and upper permian series stratum section survey in Hongchiba region of Wenfeng town, Wuxi county in Chongqing Municipality, the middle and upper permian series stratum section survey in Osmanthus power station in Changgui town of Wuxi, the middle and upper permian series observed profile in Xianrui, Wuxi county, the middle and upper permian series observed profile in Shuanghe, Chengkou County and the middle and upper permian series observed profile in Tianba Village of Wuxi County respectively. According to section of research results, it is concluded that the stratigraphic lithology and rock assemblage characteristics of research area. It divides the study area into three parts based on the lithology and rock assemblage characteristics which are north phase region referred to as the north part of Xianyi town in Chengkou County-Wenfeng town in Wuxi County, of which the rock formation are divided into Liangshan formation, Qixia formation, Maokou formation, Gufeng formation, Wujiaping formation and Dalong formation; south of the line mainly exists Liangshan formation, Qixia formation, Maokou formation, Gufeng formation, Wujiaping formation and Changxing formation and the nearby are mainly transitional phase region of which the rock formation are divided into Liangshan formation, Qixia formation, Maokou formation, Gufeng formation, Wujiaping formation, Changxing formation and Dalong formation.Based on the fossil types, characteristics, outcropped strata and distribution of ancient organisms in the study area’s layer, three brachiopods combination zone, three coral class combination zone, one fusulinids combination zone and one ammonites combination zone have been established in the Northeast Chong qing. They are peduncle Orthotichia-Linoproductus combination zone, peduncle Cryptospirifer omenshanensis-Monticulifera sinensis combination zone, peduncle Squamularia grandis-Oldhamina squamosa combination zone, coral Hayasakai a-Polythecalis combination zone, coral Tachylasma Grabau-Huangophyllum Tsen g combination zone, coral Waagenophyllum-Liangshanophyllum combination zon e, fusulinids Chusenella-Verbeekina combination and ammonoid PseudotirolitesHuananoceras combination zone.Type and content of biological fossils is very rich in the study area and b ased on the fossil records and outcropped strata, the classification of chronostra tigraphic can be made. The general shortage of the lower permian series in the study area leaves no comparison basis of classification. In this paper, Liangsh an and Qixia formation correspond with Qixian-xiangbo stage of Yangxin series,Maokou and Gufeng formations correspond with maokou stage, Wujiaping for mation corresponds with Loping series Wujiaping stage, and Changxing formati on and Dalong formation correspond with Changxing stage of Loping series.Sedimentary facies analysis has been done based on the lithostratigraphy and biostratigraphy in the study area and divides the middle and upper permian system formation in the northeast Chongqing into shoreline sedimentary system, the carbonate platform sedimentary system, carbonate ramp depositional systems and shoreline sedimentary system during which the shoreline sedimentary system mainly are barrier coast phase and it can divide more specifically into barrier island subfacies, lagoon subfacies and coastal swamp subfacies according to the sediment lithologic. The carbonate platform sedimentary system can be divided into carbonate platform facies, carbonate rock basin facies while carbonate platform can be subdivided into restricted platform subfacies and open platform subfacies and platform marginal subfacies with carbonate rock basin facies further into deep and shallow basin subfacies and carbonate rock in gentle slope system can be further divided into deep gentle slope and gentle shallow slope facies. Based on the study on the middle and upper ermian system formation in the northeast Chongqing, this paper established the sedimentary facies model of the middle and upper ermian system in northeast Chongqing and believes that sedimentary model in the study area is carbonate rock platform edge gentle slope pattern, besides, the sedimentary facies mode pattern has been summarized in this paper.