Lanchengqu Gr

Liang Dingyi et al named it in 1991. The named sections are located in Qusong Rekala-Donggangqu and Jiangyema-Angzhang, Zada County, Tibet.

It is mainly carbonate rocks and clastic rocks, interbedded with siliceous rocks and volcanic rocks, and can be divided into three groups from bottom to top: lower, middle and upper formations. Lower formation is composed of yellow crystalline limestone or purplish red "red ammonite limestone", the former (Qusong area) is 16 m thick, the latter (Jiangyema, Angzhang, Duowugou) is 1~80 m thick. Middle formation is dominated by black and black-green slate with thin layers of argillaceous limestone or marl, and some sections are interbedded with siliceous slate with thickness greater than 350~700 m. Upper formation is composed of gray-white quartz sandstone, gray-green and gray-purple feldspar quartz sandstone, hard sandstone and siltstone interbedded with radiolarian siliceous rock and basic volcanic rock, with over 1500 m.

Synonym: Lanchenquxia Fm

There are ammonoids, bivalves, conodonts, belemnite and other fossil and relic fossils.

Lower part contains ammonoids Proptychites lawrencianus, Flemingites griesbachiformis; Conodonts Neogondolella nevadensis, Neospathodus homeri, N. bransoni; Bivalve Claraia hubeiensis-Promyalina assemblage; Middle part contains bivalves Longidaonella cf. obtusa, L. aff. semicordiformis, Daonella indica; Upper part is dominated by radiolarians, among which Rikivatella was dominant, besides Pseudoheliodiscus sp., Paraonaella aff. gemmata, Gorgansium sp., Hemicryptocapsa zandaensis, Dictyomitrella equicamerata, D. bicyclica, Sethocapsa cf. cometa; And bivalve Daonella sp. and belemnite Belemnopsis.

Lower part represents the deep-water shelf environment, while the Middle and Upper parts represent the deep-sea environment and are the turbidite deposits.