Yajiang Fm
Type Locality and Naming
The named section is located 2 km north to Xiadu Village, Yajiang County, Sichuan Province. It was named by Fan Jiasong in 1960 and first publicly cited by the Sichuan Regional Stratigraphic Table Compilation Group in 1978.
Synonym: In 1977, the aeronautical reconnaissance team of Sichuan Geological Bureau named the stratum with the same lithology, horizon and distribution as the Yajiang Fm as the Huanhe Fm.
Lithology and Thickness
The Yajiang Formation is mainly composed of clastic rocks, which can be divided into three parts from bottom to top. Lower part is mainly the interbeds of dark gray sandstone and the same color killas in different thickness. Middle and Upper parts are mainly dark gray and black slate with little fine feldspathic quartzose sandstone. There are ripple marks and hieroglyphic moulage on sandstone layer. The total thickness is 3364 to 4750 m.
Relationships and Distribution
Lower contact
The bottom conformable contact to the underlying Xinduqiao Fm is marked by the first appearance of pyrite-bearing sandstone. In same Yajiang county is the Lianghekou Fm that is coeval with the upper Xinduqiao Fm according to the schematic stratigraphic column.
Upper contact
The top boundary is not clear.
Regional extent
The lower part of this formation is widely distributed, such as Malancai Mountain in Xinlong County, Sichuan province, Dagai and Xinduqiao in Kangding, while the middle and upper parts are only distributed in the vicinity of Yajiang County.
GeoJSON
Fossils
Bivalve: Halobia subrugosa-H. superbescens layer can be established in the lower part of this formation and Pergamidia layer can be built in the upper part.
Age
Additional Information