Erqiao Fm

The age is Norian-Rhaetian. It was named "Erqiao Sandstone", which refers to the interbedded carbonaceous shale and sandstone with a thickness of tens of meters. The layer is located between the overlying Jurassic Qianling Fm sandstone and the underlying Triassic Sanqiao Fm. The age is late Triassic. In 1933, Sixingjian set its time as the Rhaetian. In 1944, Le Senpi and Jiang Rong introduced the "Second Bridge Sandstone". In 1959, Wang Yu and Chen Chuzhen were renamed the Erqiao Formation. Later, the Nanjing Institute of Geology and Paleontology placed the Qianling sandstone in the Erqiao Fm, which expanded the meaning of the Formation and changed its age to the middle and late Late Triassic. The latter is the meaning of the second bridge group currently used. However, Tong et al. (2019, Triassic integrated stratigraphy and timescale in China, Science China: Earth Sciences, v. 62, no. 1) assign as late Rhaetian; with Norian through early Rhaetian as the underlying Huobachong Fm or coeval Sanqiao Fm.

This formation is a continental-brick water deposit with stable lithology and large thickness variations.