Gejiu Fm

Named by Meng Xianmin and others in 1936. The named section is located in the Jinlao Tin Mine, Yunnan; the reference section is located in Mazheshao, Kaiyuan, Yunnan.

Synonym: Kochiu Fm

It is mainly dolomite and can be divided into five units from bottom to top: First unit is dominated by gray and dark gray medium- to thick-bedded smectite, mud crystal, bright crystal tuff and bioclastic tuff, interbedded with dolomitic tuff, with yellow shale and sericite "green bean rock" at the bottom (263.6 m). Second unit is dominated by dark gray and dark gray smectite tuff, gray dolomitic tuff interbedded with [text missing in submitted English version]. The third unit is dominated by gray and dark gray thick-bedded smectite to fine-grained smectite dolomite and sand-chip dolomite, interbedded with algal dolomite (147.2 m). Fourth unit is gray medium-bedded mud-crystal-bearing dolomite tuff, mud smectite tuff and mud smectite dolomite tuff interbedded with bioclastic debris (14.2 m). Fifth unit is light gray to dark gray thick-bedded to massive smectite dolomite, with the upper part interbedded with thickly laminated residual agglomerate, fine and smectite dolomite interbedded with lamproite dolomite (487.6 m).

Fossils are scarce, the first and second sections produce conodonts Neospathodus germanicus, N. cf. kockeli, etc.; bivalves Leptochondria illyrica, Costatoria goldfussi mansuyi, Bakevellia costata, etc.

This formation is saline shallow water sediment.