Longmen Fm
Type Locality and Naming
It was named by Wang Zhuquan, Ji Rongsen in 1933. The naming section is located on the slope of the Beishan Hill, Longmen Village of Mentougou District, Beijing City, with its reference section being situated at Yuejiapo Village of Mentougou District. Uppermost formation in Mentougou Gr.
Synonym: （龙门组）
Lithology and Thickness
Composed of an alternating layers of grey-black and black siltstones and carbonaceous siltstones together with grey and green-grey sandstones and pebble-bearing gritstones, intercalated with grey conglomerates and coal seams. Its thickness in the naming section is of 160 m, while in its reference section is of 395.5 m.
Relationships and Distribution
Lower contact
Its basal conglomerates (2-10 m thick) are developed extensively and steady, being in a disconformable contact with its underlying Yaopo Fm
Upper contact
It is in a disconformable contact with its overlying Jiulongshan Fm. However, Huang (2019) states "the Longmen Formation (the so-called Jiulongshan Formation in northern Hebei Province)", therefore this equivalence (?) would also imply a disconformable upper contact with the Tiaonjishan Fm.
Regional extent
The formation is distributed in the area of West Hills of Beijing, with a remarkable lateral variation both in its lithology and thickness. In the area of the Jiulong Mt and Daliang area of Xiangyu Region the formation consists largely of siltstones and sandstones, intercalated with many layers of conglomerates, with its thickness getting greater on the southern slope of the Jiulong Mt, and reducing both to the east and north; as with the maximum thickness being of 395 m at Yuejiapo; easterly to the west of Sleeping Buddha Temple, only of 69 m; and northerly to the vicinity of Jiuyuan Garden, of 103 m, while in the area of North Ridge it is 300-395 m thick, and at Qianjuntai-Datai it is 150-160 m thick.
GeoJSON
Fossils
It yields plant fossils as represented by Todites denticulate, T. williamsoni, Clathropteris pekingensis, Cladophlebis aff. scariosa, Pterophyllum sp., Anomozamites sp., Nilssoniopteris vittata, Elatocladus manchurica and Podozamites sp.
Age
Depositional setting
Additional Information