Huobachong Fm
Type Locality and Naming
The type section is located at Huobachong about 25 km southwest of Gejiu, Yunnan Province. It was named by the Meng Xianmin in 1935. When named, it was called "Huobachong coal seam", which refers to the strata rich in bivalves and plant fossils in the uppermost part of the Triassic in southeastern Yunnan. In 1959, Chen Chuzhen and others renamed the Huobachong Formation, representing the middle and late Late Triassic sediments.
Synonym:
Lithology and Thickness
It is mainly composed of gray-white, gray-brown, yellow, green-purple variegated fine sandstone, siltstone, mudstone, shale, fine conglomerate intercalated with carbonaceous shale and coal seams. The thickness is 900 m.
Relationships and Distribution
Lower contact
At the bottom, the gray-yellow medium and thick quartz fine sandstone is conformable contact with the gray-brown silty shale at the top of the underlying Upper Triassic Niaoge Fm (at Gejiu) or the Banan Fm (Guizhou). At Dongchuan, Yunnan, it is unconformable above the Leikoupo Fm.
Upper contact
The top is false conformable contact with the overlying Cenozoic in most places; or below the lower Jurassic Xialufeng Fm at Dongchuan, Yunnan; or (as implied by Tong et al., 2019) below the Erqiao Fm of upper Rhaetian in northern Guizhou.
Regional extent
Yunnan-Guizhou. This group is mainly distributed in Luoping, Kaiyuan, Shizong, Jianshui, Gejiu and other places. The thickness varies greatly, ranging from 200-1000 m. In Gejiu Huobachong is 900 m, in Kaiyuan Niaoge is only 200 m, and the thickest is 1000 m in Nanpanjiang.
GeoJSON
Fossils
Bivalves: Trigonodus cf. keupermus, Yunnanophorus boulei, Unionites postera, Myophoria (Costaroria) napengensis, Burmesia lirata, Plant: Neocalamites sp.
Age
Depositional setting
It is interpreted as marine-terrestrial alternate deposits.
Additional Information