Baoding Fm
Type Locality and Naming
Named by Sichuan Province Regional Stratigraphic Table Compilation Group in 1978. The type location is located in the Hongshiyan area about 5-7 km east of Baoding, Dukou City, Sichuan.
Synonym: Baoding Fm refers to the Daqing Fm, which was named by Zeng Fan-ren in 1945, and was later changed to Daqing Fm by the survey team of Yunnan Geological Bureau (1966). The strata are between the Jurassic Fengjiahe Fm and the gray coarse grains of the underlying Upper Triassic Daziaidi Fm (Daqiaodi Fm). However, because the Daqing Fm is a foreign body (homonym) with the Middle Ordovician Daqing Fm named by Guo Wenkui Yechizheng (1942). Therefore, in 1978, the regional stratigraphic compilation group of Sichuan changed the name of Daqing Fm to Baoding Fm, which is dated to the late Late Triassic.
Lithology and Thickness
It is mainly composed of gray-green, gray-yellow and gray-white conglomerate, sand, conglomerate, fine conglomerate, siltstone, mudstone shale and coal seam. Lower part is conglomerate sandstone and coal seam, and the Upper part is interbedded with sandstone, siltstone and mudstone. In the Baoding area, the thickness is 424 to 1352 m.
Relationships and Distribution
Lower contact
The bottom of super-thick layered conglomerate is in pseudo-conformable contact onto the top of the underlying Daziaodi Fm (Daqiaodi Fm) (thick conglomerate interbedded with thin siltstone).
Upper contact
The top is in conformable contact with the grey-green light gray mudstone or sandy mudstone at the bottom of the overlying Fengjiahe Fm of early Jurassic (in northwest Yunnan; region of column TJ100) or Yimen Fm of early Jurassic (in southernmost Sichuan, region of column TJ77).
Regional extent
The lithology of this Formation varies greatly, and it is widely distributed in Panzhihua area. In Baoding area and southwest Sichuan, the thickness without coal in the upper part of this formation is generally greater than 1000 m. In the Yanbian Banbian Street Qinghe Gage area, the thickness is 1700~1900 m. The formation is equivalent to the Ganhaizi Fm and Shezi Fm in central Yunnan.
GeoJSON
Fossils
Rireticopteris—Pterophyllum longifolium plant assemblage, mainly composed of Dictyophyllum nathorsti, Clathropteris meniscioides etc.; Bivalves: Trigonodus rablensis, Utschamiella cf. elliptica, Unionites sp.; conchostracans: Euestheria minuta, E. dazuensis; Ostracod: Gomphocythere? subelliptica etc.
Age
Depositional setting
It is interpreted as continental coal-bearing deposit.
Additional Information