Zhongbei Fm

In 1978, the Second Geological Team of the Tibet Geological Bureau named the Middle and Lower Triassic in the Lazi area as the Zhongbei Gr. The named section is located in Dongshan, Zhongbei Township, Lazi County, Tibet.

Synonym: In 1962, the Tibetan Comprehensive Examination Team of the Chinese Academy of Sciences named the Triassic system in the Lazi area of Tibet as the "Lazi Group" (later used for the Cretaceous system by Wu Haoruo (1977)). In 1963, the South Tibet Geological Team of the Tibet Geological Bureau divided the strata into the upper Langjie Fm and the lower Qiangdui Fm (the strata in the latter named place have been proved to be Jurassic and Cretaceous). In 1974, the Tibetan scientific expedition team of the Chinese Academy of Sciences named the strata as the Jilong Gr. In 1978, the Second Geological Team of Tibet Geological Bureau named the middle and lower Triassic part of the strata as the Zhongbei Gr. In 1983, the Lower and Middle Triassic in Qiongguo area of Zhongba County was named Qiongguo Gr by the regional survey team of Tibet Bureau of Geology and Mineral Resources (1∶1 million Xigaze area survey report), which was later adopted by Tibet Bureau of Geology and Mineral Resources (1993).

Mainly gray, dark gray thin-bedded sandstone, shale and thin-bedded limestone interbedded, the upper shale contains pyrite nodules. Its visible thickness is 76 to 86 m.

Bivalves: Claraia sp., Claraia concentrica dingjiensis, C. sp., Leptochondria sp., Eumorphotis sp., Pseudoclaraia cf. limaica, Myoconcha gastrochaena Ammonoids: Anasibirites kingiamus, Keyserlingites subrobustus. And the arrow petrochemical stone: Asteroconites sp.