Longjing Fm

Its base in the type area marked by purple red conglomerate is separated from the underlying Dalazi Fm and shows an unconformable contact with the latter. See regional extent for contacts in other regions.

Its top is unknown in the type area; but is overlain by Paleogene basalt in the Mudanjiang basin. See regional extent for contacts in other regions.

The present formation occurs in the Yanji, Fudong and Dadianzi basins of Jilin. In the Yanji basin, it occurs in Chaoyangchuan, Yanji city, Toudao and Longjing, where the lower part of the formation is composed of purple conglomerate and gravel-bearing sandstone while the upper part sandstone interbedded with siltstone. It ranges from 190 to 420 m in thickness. It lies unconformably on the Dalazi Fm, and its top is overlain unconformably by the Hunchun Fm in the Qinchaguan area. It is 127 m thick in the Fudong basin and 200 m in the Dadianzi basin. The strata equivalent to this formation are called the Sipingshan Fm and the Hailang Fm in Heilongjiang, which were considered to be synonymous with the Longjiang Fm during the Inner Mongolia Conference on Stratigraphic Sorting held in December of 1993. The Qixinghe Fm and the Yanwuo Fm erected by the Daqing Oilfield in the Sanjiang basin in 1985 belong to the same horizon as that of the Longjing Fm and were attributed to the latter. It occurs in NE direction in the Mudanjiang, Muling and Sanjiang faulted basins, covering a largest area in the Mudanjiang basin. It lies unconformably on the Houshigou Fm consisting of yellow brown gravel-bearing arkose, and is overlain disconformably by the Paleogene basalt. In the Muling basin, its exposed thickness is rather small, but the characteristics of its rock assemblage are similar as compared to that in the Mudanjiang basin.