Guanjiagou Fm

Southeast corner of Gansu. The name Guanjiagou Fm derived from the Guanjiagou Stage named by the Tianshui Team of Gansu Bureau of Geology, in 1961. Qin Feng and Gan Yiyan renamed it as the Guanjiagou Formation in 1976. The typical section is situated at Guanjiagou in Wenxian County of Gansu Province.

Synonym: （关家沟组） , Tao Hongxiang et al. (1993) proposed that the Guanjiagou Formation should be renamed as the Guanjiagou Group and subdivided into four formations of ascending order, a Huangluba Fm of pebbly slate and phyllite; a Dishuiya Fm of conglomerate, pebbly slate and tuffaceous slate; a Guanjiaba Fm of slate, pebbly slate intercalated with limestone, and a Haozidian Fm of medium-thick bedded limestone and siliceous dolomite. However, most researchers consider that these subdivisions can be used as four members, because the divisions cannot be used for large regional correlation.

The Guanjiagou Fm is composed of two sets of tillite intercalated with a set of slate. Lower part consists of gray and greenish gray till of pebbly and sandy slate, and massive till of meta-conglomerate and dark gray silty slate. Middle part is dark gray to black meta-siltstone and silty slate. Upper part is dominated by gray to greenish gray massive till of conglomerate, and a till of pebbly-sandy argillite and pebbly sandstone. It is about 1268 to 4897 m thick.

The cements contain abundant microplants, dominated by Laminarites antiquissimus, Trachysphaeridium cultum, Nucellosphaeridium sp., Bavlinnella faveolata, Micrhystridium sp., Leiopsophosphaera sp., Leofusa bicornuta, L. solida, Nostocomorpha cf. prisca, Taeniatum crassum, Zonosphaeridium sp., Synsphaeridium conglutinatum etc.