Gegenaobao Fm

The type section is located at Gegen’aobao, Erjizhuolsu, Zhumuqin Banner, Dongwu, Inner Mongolia. It was named by Xie Tonglun in 1963, and was cited officially by the 1^st Geological Survey Party under the Bureau of Geology of Inner Mongolia in 1972.

Synonym: Gegen'aobao Fm

Volcanics and volcaniclastics. Composed mainly of lavas and is gradually changing upward into the predominance of volcaniclastic rocks, and simultaneously with a gradual increase in the amount of normal sedimentary rocks. Its basal part is composed of volcaniclastic rocks, thick-bedded chloritized andesitic porphyrite, intercalated with volcanic breccia. Its lower part is composed of grey clastics-bearing andesite, tuffaceous fine-grained sandstone and siltstone. Its middle part is composed of interbeds of black-grey sandy conglomerate, conglomerate and black tuffaceous siltstone. Its upper part is composed of dark-green and dark-grey lithoclastic and crystal-clastic tuffs and yellow medium-grained feldspar-rich sandstone, intercalated with coarse-grained sandstone and micro-conglomerate. Thickness is over 2000 m.

The paleobiocoenosis of the formation is possessed of local salient features. Yields Brachiopods that should be assigned to the Gegenella gegenensis-Jakutoproductus excellens assemblage, including Grandaurispina pustule, Kiangsiella subcircularia, Haplospirifer typica, Licharewia neosibirica, Parareticularia spiriferiformis. It also yields plant fossils (phytolite) such as Noeggerathiopsis, as well as Gastropods as represented by Bellerophen.

It is interpreted as volcanics and volcaniclastics deposits.