Dongmaolong Fm
Type Locality and Naming
Ma Fubao, Wang Xiulin and Che Yi were named in 1984. The named section is located in Dongmaolonggou, about 40 km west of Shanglaxiu, Yushu County, Qinghai Province. The purple-red clastic rock group of the original Jiezha Gr. Lowermost formation in Jiezha Gr.
Synonym:
Lithology and Thickness
Mainly purple clastic rocks. Lower member is composed of gray-purple siltstone, feldspar quartz sandstone, and conglomerate, and the bottom is yellow-brown conglomerate, with a thickness of 251 m. Middle member is composed of gray siltstone, fine sandstone intercalated with marl, and the lower section intercalated with carbonaceous mudstone and coal line. Unstable iron-bearing and siliceous claystone with a thickness of 257 m is seen. Upper member is composed of variegated sandstone, argillaceous siltstone intercalated with feldspar quartz sandstone, and the top calcareous sandstone and marl are increased, with a thickness greater than 372 m.
Relationships and Distribution
Lower contact
The yellowish-brown conglomerate at the bottom is unconformably lying on the Upper Permian feldspar quartz siltstone. Regionally, next older unit is the Benpulong Fm of Middle Triassic.
Upper contact
The top with variegated sandstone and calcareous sandstone is in conformity contact with the overlying Xiaoqiacuo Fm.
Regional extent
The purple-red clastic rock group of the original Jiezha Group, which is widely distributed in the southern part of Zhiduo County, Qinghai Province, Zaduo, Nangqian and other places. The area in Shanglaxiu is dominated by variegated sandstone, and the upper part of the group is interposed by neutral lava, tuff, and volcanic breccia in the upper part of the group in Xia Yase and Dengkong. The thickness is greater than 1000 m; to Dasumang, Niangla and other places, The lower part is incompletely exposed, and the upper part is dominated by gray siltstone and sandstone, with carbonaceous shale, coal line and unstable thin coal seams, marl and limestone, occasionally with siderite nodules, partially with pyroclastic rocks, thick Most of them are above 1200 m; south of Zhaqu River, they are distributed intermittently, and the thickness is obviously thinner, mostly below 500 m.
GeoJSON
Fossils
Most of the fossils produced are concentrated in the upper part, with bivalves and brachiopods as the majority, followed by ammonoids and plant fossils. Bivalve fossils include Unionites trapezoidalis, Myophorigonia gemaensis, Trigonodus carnolicus, T. sanabergeri are the most prosperous；from bottom to top, ammonoids can be divided into: Frankites —Maclearnoceras zone and Trachyceras cf. aon zone; Plants are more developed in genera such as Equisetites, Pterophyllum, Danaeopsis etc.
Age
Depositional setting
This group is dominated by marine settings and is the purple-red clastic rock group of the original Jiezha Gr.
Additional Information
See “Jiezha Group”