Erlian Fm

Unconformably over the underlying Upper Carboniferous Benbatu Fm. Regionally, the next older unit is the Saihan Fm. The unconformity between the Saihan and Erlian formations is named as T2 in seismic reflection sections.

Its top is marked by gravel-bearing sandy mudstone and lies disconformably under the overlying Eocene Manerdingha Fm.

The Upper Cretaceous Erlian Formation was locally deposited in a few sub-basins in the northwestern basin. The present formation occurs in the Yanchi area of Eren and is exposed sporadically only in the northern part of the Hailar area and is mostly overlain. In the Songgendalai area, the formation consists primarily of turmeric and gray white sandy conglomerate and siltstone, and its upper part is built up by break red sandy conglomerate, gravel-bearing sandstone and clayey sandstone with gray white sandy marl, without fossils and in a thickness of about 120 m. In the Dersihaolega-Gunchaabu area, the formation is built up by gray yellow siltstone and mudstone with both the top and the base unknown, about 92 m thick, with floras and sporopollen grains. In Baiyintuga, the base of the formation is built up by purple red and gray green clayey conglomerate; the lower part gray blue massive mudstone interbedded with gravel-bearing clayey siltstone; the upper part brown yellow sandy mudstone; and the top part red mudstone with thin-bedded medium-grained sandstone and grit. The formation is 114 m thick. Down the boreholes in the Xinbarag Zuoqi area, the lower part of the formation is represented by gray sandy mudstone and clayey siltstone with pink clayey siltstone, fine sandstone and conglomerate; while the upper part break red clayey siltstone, sandstone, mudstone with fine sandstone and gravel-bearing sandstone. The formation is about 335 m thick.