Badong Fm
Type Locality and Naming
Richthofen named it in 1921. The named section is located in the county seat of Badong, Hubei Province.
Synonym: Patung Fm
Lithology and Thickness
The formation is a combination of carbonate rocks and clastic rocks. From bottom to top, it can be divided into four members: First member is grey, dark grey marl, dolomitic limestone, limestone with shale, and the bottom is hydromica clay rock (mung bean rock = Green Bean horizon of volcanic ash). Second member consists of purplish red mudstone, calcareous mudstone, silty mudstone, siltstone intercalated with gray-green calcareous mudstone and fine sandstone (equivalent to the Lujiagou Fm and Xinlingzhen Fm). Third member is mainly composed of thin layer micritic limestone, light gray and grayish yellow, intermingled with micritic limestone and calcareous mudstone (equivalent to "Baotahe Fm"). Fourth member is mainly composed of purplish red medium to thick calcareous mudstone, shale and siltstone, with dark gray and light gray medium to thick laminated dolomite at the top, containing argillaceous microcrystalline dolomite (equivalent to the "Yuan'an Fm" and "Shuijiawan Fm"). The total thickness is 355~1416 m.
Relationships and Distribution
Lower contact
The bottom boundary is marked by "Mung Bean Rock". Concordant contact with the underlying Lower Triassic Daye Gr.
Upper contact
The top boundary is marked by the disappearance of dolomite. Overlain (above a hiatus) by either the Shazhenxi Fm or coeval Jiuligang Fm of Norian. [However, regionally, the Badong Fm is also overlain by the Yingzuishan Fm.]
Regional extent
The formation is mainly distributed in western Hubei, northwestern Hunan, eastern Sichuan and northern Guizhou. The lithology of this formation in northwest Hunan is mainly purplish red sandstone and mudstone, with a small amount of carbonate rocks interbedded. The maximum thickness is 2118 m in Hongjiaguan, Sangzhi. From Hongjiaguan to the south and east, the thickness decreases sharply, and only tens of meters to Yinjiachong area of Shimen. Preserved in the first to fourth member of western Hubei, with a thickness of 848 to 1416 m. Most of the four members in eastern Sichuan and northern Guizhou are not completely preserved.
GeoJSON
Fossils
This group is rich in ammonoids, bivalves, conodonts, foraminifera, phyllopodophytes, plants, wheatophytes, palynology, and hypogenic fossils. Progonoceratites-Beyrichites assemblage and Noetlingites-Semiornites assemblage can be established in the second, third and second member, respectively. Leptochondria illyrica-L. ubillyrica bivalve assemblage was widely distributed in the first to the third sections. From the first to the second segments, there is a phyllopoda fauna represented by Xiangxiella. The Annalepis Zeilleri-Neocalamites meriani plant assemblage is still produced in the middle and upper part of this group.
Age
Depositional setting
It is shallow sea and semi-closed marine deposits. The middle and upper part is sedimentation of coastal marsh facies.
Additional Information