Houshigou Fm

The base of the formation marked by conglomerate is distinguished from sandstone of the underlying Muling Fm.

The top of the formation is unknown. Next younger regional unit is the Hailang Fm of mid-Late Cretaceous.

The present formation occurs in the intramontane or piedmont basins of Mudanjiang-Hegang. In the Muling and Gonghe basins in the southern part, only the upper sandstone member is observed, called the Xiachengzi Fm by Yang Yueyu et al, yielding abundant floras and faunas, lying disconformably on the underlying Dongshan Fm, ranging from 550 to 1390 m in thickness. In the Jixi basin, the present formation is exposed together with coal measures, and its lower member is quite persistent in thickness, ranging from 300 to 450 m. The upper member is well developed in the northern part with a thickness of about 700 m, dominated by sandstone and shale. In the southern part, it is quite thin about 300 m thick and is dominated by sandstone. In the Mudanjiang basin, the conglomerate member of the formation is about 700 m thick and the upper sandstone member is widespread, locally with coal streaks, ranging from 110 to 1500 m in thickness. The formation overlies the Paleozoic and its upper part is overlain unconformably by the Longjing Fm. In the Boli basin the upper part of the formation is called the Jinsha Fm (1979) and recalled as the Houshigou Fm during the stratigraphic sorting in 1994 where the lithology is quite fine, the conglomerate member is not developed, 30-40 m thick, while the sandstone member is built up by mudstone and multi-layers of tuff, 2500 m thick. In the vicinity of Jiamusi, the conglomerate member of the formation is about 100 m thick and lies unconformably on the Dongshan Fm. In the Hegang basin, the present formation occurs in SN-oriented bands in Hegang, Xingdong, and the Yadan river domain. In Hegang the present formation is exposed together with coal measures, showing coarse-fine cyclic structure; the conglomerate member is not so developed, 1216 m thick, lying disconformably with the underlying Dongshan Fm. In Dongxing and along the Yadan River, the lower conglomerate member is about 600 m thick, intercalated with lenticular thin coal seams; and the upper member is 1400 m thick and contains more than 20 thin coal beds.