Kuahongdong Fm
Type Locality and Naming
The Southwest Geoscience Institute named it in 1964. It was first publicly cited by the Southwest Stratigraphic Palaeontology Bulletin in 1975. The named section is located in Kuihong Dong near Longmen Dong, Tianjin Township, West Emei, Sichuan. In 1931, Yin Zanxun created the name "Marine a Halobia" in Emei, Sichuan, to represent the Ladinian strata of the area. In 1939 Xu renamed it "Halobia Beds". Later, Xu Deyou and Chen Kang (1944) renamed it "Ladinic Layer". In 1964, the Southwest Institute of Geology questioned the Middle doubted the "Halobia Beds" belonged to Triassic Ladinian. Then they renamed it Kuahongdong Fm, and defined its age as Late Triassic Norian.
Synonym: Hongdong Fm. [Tong et al. (2019, Triassic integrated stratigraphy and timescale in China, Science China: Earth Sciences, v. 62, no. 1) implied the overlying Xiaotangzi Fm encompassed the Kuahongdong Fm in their composite Sichuan Basin column.]
Lithology and Thickness
In the named section, the formation is interbedded with dark gray medium to thick-bedded sandy limestone, thin-bedded limestone, argillaceous limestone, gray-black calcareous mudstone and marl. The thickness is 22.4 m.
Relationships and Distribution
Lower contact
A layer of conglomerate is generally developed at the bottom. On different levels of Lower Triassic to Middle Triassic, it is conformable or pseudo-conformable.
Upper contact
The top boundary is marked by the disappearance of thick-bedded sandy limestone. It is conformably underlying the Xiaotangzi Fm of Upper Triassic, and it is pseudo-conformable in some areas
Regional extent
It is mainly distributed in Rongjing, Emei, Leshan, Ebian, Qianwei, Muchuan, Jiangyou, Mianzhu, Mabian, Dayi and other places west of Longquan Mountain in the southwest of Sichuan Basin, with a thickness of 24 to 91 m.
GeoJSON
Fossils
There are abundant multi-phyla fossils, mainly bivalves and brachiopods, followed by ammonoids and foraminifera, in addition to crinoids, ostracods, archstones and sporopollen. Bivalves: Burmesia lirata, Halobia sp. Ammonoids: Dionites sp., Trachyceras sp. and Sirenites sp.
Age
Depositional setting
The formation belongs to mixed marine carbonate rocks and clastic rocks.
Additional Information