Chongdui Fm
Type Locality and Naming
Yarlung Zangbo suture zone. Chongdui is located 18 km southeast of Xigaze City, Tibet Autonomous Region. Cao Ronglong (1981, Scientia Geologica Sinica) named the Chongdui Formation in the Chongdui- Qunrang area, Xigaze City.
Lithology and Thickness
Wu Haoruo (1984) described the southern edge of the Xigaze basin margin, the lower-most beds were placed in the Chongdui Formation. They are comprised by pelitic, siliceous and silty rocks with minor sandstone and conglomerates. Radiolaria are frequent in the siliceous rocks, and planktonic foraminifera occur in a thin-bedded limestone intercalation within the upper part of the formation (Wan et al., 1998). Wu Haoruo subdivided the formation into 3 parts: Lower part dominated by high-siliceous content flysch sediments; Next part is low-siliceous content flysch sediments; and Top part is organic-carbon-rich sediments.
[Figure: Type section of Chongdui Formation in Chongdui Village of Xigaze, Xizang (Tibet)] |
Relationships and Distribution
Lower contact
It rests conformably on the Anren Fm or on the Yarlung Zangbo Ophiolite Fm.
Upper contact
It is unconformably overlain by the Liuqu Fm. In the Xialu Valley the reddish, bedded early Cretaceous radiolarites are conformably overlain by a sequence of black shales intercalated with greenish grey siltstone turbidites.
Regional extent
The sediments occur in the south side of the Xigaze forearc basin, southern Xizang (Tibet). The Chongdui Formation only outcrops discontinuously between the forearc basin and the Indus-Yarlung ophiolite belt.
GeoJSON
Fossils
Planktonic foraminifera Rotalipora sp. was found in the Naxia area, and limited larger foraminifera Orbitolina sp. occurs in the sandy conglomerates of Qunrang section. It is indicated that the Chongdui Formation is possibly of late Albian to early Cenomanian age.
Age
Depositional setting
It represents the toe of the forearc sedimentary prism.
Additional Information