Xintiangou Fm
Type Locality and Naming
It was named by Sichuan Aerogeological Survey Team in 1977. The naming locality is situated in Xintiangou Village, Beibei District of Chongqing City. The Xintiangou Formation is absent in the original Chinese edition of “Stratigraphical lexicon of China”. The current information is based on Bureau of Geology and Mineral Resources of Tibet Autonomous Region (1997).
Synonym:
Lithology and Thickness
It is mainly composed of yellowish green, purplish red with dark grey mudstones and silty mudstones, intercalated with fine-grained sandstones, siltstones and bioclastic limestone lenses. It is divisible into 3 parts. The lower and upper parts are mainly composed of varicolored mudstones. The middle part is mainly composed of black claystone. Its total thickness is 200 m.
Relationships and Distribution
Lower contact
It is in conformable contact with the underlying Ziliujing Fm.
Upper contact
It is in conformable contact with the overlying Shaximiao Fm (Xiashaximiao Fm)
Regional extent
It is distributed in the middle and eastern parts of Sichuan Basin. The triple-division of lithology is regionally stable in the middle part of basin. The thickness is about 200 m in Hechuan of Chongqing City, increasing east- and northwards to 350-490 m in Dachuan of Dazhou City and Wanzhou of Chongqing City. Lithology changes obviously in the south region along the Yangtze River between Fengdu and Wushan. The varicolored beds in the lower and upper parts disappear gradually and change into a set of grey, black shales without division mark, intercalated with sandstones and shelly limestone, with a thickness of 170-300 m. It is eroded in different extent in the west of Sichuan Basin, with erosion increasing from the east to the west. Only the lower part is preserved in Suining, Yongchuan and Jiangjin areas, with a residual thickness of 50-150 m, but the triple division is still visible. Only the quartz-sandstones and lime conglomerates lenses can be found westward to Zigong and Weiyuan area, with a residual thickness of 0-70 m, and lithology changes significantly. The massive lithic feldspar-sandstones of the overlying “Guankou Sandstones” (or “Lianggaoshan Sandstones”) are regionally significant as a mark of macro division.
GeoJSON
Fossils
It yields abundant fossils such as bivalves Pseudocardinia, Psilunio and Unio, ostracods Darwinula and Metacypris, “conchostracans” Euestheria and Shizhuestheria, and spore-pollen. Some vertebrate fossils also occurred in Chongqing.
Age
Depositional setting
Additional Information