Feixianguan Fm

Named by Zhao Yazeng in 1929, Yin Zanxun (1937) first introduced the named place: Feixianguan, 15 km north of Guangyuan County, Sichuan. It was named "Feixianguan Shale", and was divided into the lower purple shale and the upper purple shale interbedded with thin-bedded tuffs, and was dated as Triassic. In 1933, Li Chunyu used the Fei Xian Guan Formation for the first time and dated it to the Early Triassic. 1936, Ding Wenjiang and A. W. Grabau founded the Yelang Series and divided it into the "Baoan Shale", "Yulan Shale", and "Yulan Shale" from the bottom up. "Baoan Shale", "Yulongshan Tuff", "Feixianguan Shale" and "Sanqiao Tuff", and dated it as Late Triassic. In 1939, Hou Defeng renamed the Feixianguan Shale as Feixianguan Fm and divided it into "Wangjiaba Formation "In 1962, Zhao Jinke and others changed the name to "Feixianguan Group" to represent the mixed phase of purple shale and tuff in the area of Zitong, Sichuan. In 1964, Chen Chuzhen et al. divided the "Feixianguan Shale" into the upper Tongjiezi Fm and the lower Feixianguan Fm. Wang Zunzhou et al. (1992) argued that the Feixianguan Fm should be consistent with the meaning of "Feixianguan Shale". The present study follows it, but believes that the age should be early Triassic.

Synonym: Feisienkuan Fm

It is dominated by a set of marine purple-red and dark purple shales, mudstones and sandstones, interspersed with marl and tuffs. The stratigraphic section is divided into four members from bottom to top: First member is dominated by gray-purple, purple-red and gray-green sandy mudstone. Second member is dominated by gray-purple and purple mud shales with a few mud tuffs and bioclastic tuffs. Third member is dominated by purple-red and purple-gray mud shales with mesoscopic tuffs. Fourth member is dominated by purple-gray and purple-red mud shales with a few mud tuffs and mesoscopic tuffs. The total thickness is 465 m.

The group is rich in bivalve fossils, and four assemblages can be built from the bottom up: (1) Pseudoclaraia wangi assemblage; (2) Claraia stachei assemblage; (3) Claraia aurita assemblage; (4) Eumorphotis multiformis assemblage. The first section of the Feixianguan Formation can also be divided into four odontoclastic assemblages from the bottom up: (1) Hindeodus minutus assemblage; (2) Hindeodus parvus assemblage; (3) Isarcicella isarcica assemblage; (4) Neogondolella carinata assemblage.

This formation is a shallow marine deposit.