Xiaotangzi Fm
Type Locality and Naming
The Xiaotangzi Fm refers to the first Marine member of the former Xujiahe Fm. The named section is located in Xiaotangzi near Xujiahe River to the north of Guangyuan City, Sichuan Province. The reference section is located at Mount Emei (Emeishan), Sichuan. The Xujiahe coal measure established by Zhao Yazeng and Huang Jiqing in 1931, and was renamed Xujiahe Fm by Chen Chuzhen in 1964. In 1974, the Mesozoic Emei Conference of Southwest China redefined the definition of Xujiahe Fm, and the first lower member (Marine member) of the Xujiahe Fm was separated and named Xiaotangzi Fm. It was first publicly cited by the Sichuan Regional Stratigraphic Table Compilation Group in 1978.
Synonym: Xiaoshuitang Fm [as used by Tong et al. (2019, Triassic integrated stratigraphy and timescale in China, Science China: Earth Sciences, v. 62, no. 1]
Lithology and Thickness
The formation is mainly composed of gray mudstone, sandy mudstone interbedded with the siltstone and the fine sandstone, with quartz sandstone and coal in the lower part.
Relationships and Distribution
Lower contact
The basal claystone of the Xiaotangzi Fm is pseudo-conformational contacted to the underlying gray dense dolomite of the middle Triassic Leikoupo Fm or dark gray lithic quartz sandstone of the Kuahongdong Fm of the Carnian (lower-Upper Triassic).
Upper contact
This formation is pseudo-conformational contacted to the overlying boulder bed of Xujiahe Fm.
Regional extent
This formation is widely distributed in the western part of Sichuan Basin, and is developed in Dayi and Chengdu. At Wuzhong Mountain of Dayi, the formation is up to 1050 m thick, thinning rapidly to the north, 320 m thick at Mianzhu and Hanwang, and only 150 m thick at Guangyuan. It decreases sharply to the south and even dies out, and turns into continental facies sedimentation in the east.
GeoJSON
Fossils
This formation contains the bivalve Burmesia lirata-Costatoria napengensis assemblage zone, and conchostracans, etc. Continental strata contains plant fossil Dictyophyllum, Taeniopteris, etc.
Age
Depositional setting
Additional Information