Gambadongshan Fm
Type Locality and Naming
Himalayan South Belt. The section for the designation is about 4 km southeast of the Gamba County, Xizang. The reference section is about 8 km southeast of the Gamba County, Xizang. The Gambadongshan Formation was erected by Wang Yigang, Sun Dongli and He Guoxiong in 1980.
In 1974 Wen Shixuan designated the shale and sandy shale with thin-bedded marl and sandstone, bearing Cretaceous fauna, as the Gamba Gr in the Gamba area. Wang Yigang et al (1980) divided the Gamba Gr in ascending order into the Gambadongshan Fm (Valanginian-Albian), the Chachiela Fm (Albian-Cenomanian), and the Gambachunkou Fm (Cenomanian-Coniacian or Santonian). China Stratigraphic Chart (2014) and Wan Xiaoqiao (1985) described the Gambadongshan Fm as a unit dominated by black shales, which characterized by the deposition of Oceanic Anoxic Event during Barremian-Aptian of the Early Cretaceous.
Lithology and Thickness
The Gambadongshan Formation is mainly represented by dark shale, interbedded with gray marl, gray black and dark gray thin-bedded shale with thin-bedded limestone yielding nodules. It is persistent in lithology and varies considerably in thickness, ranging roughly from 100 to 300 m.
Relationships and Distribution
Lower contact
The conformable base consists of black shale, differing from the underlying brownish grey siltstone of the Gucuocun Gr (Gucuocun Fm).
Upper contact
It underlies conformably under the Chaqiela Fm.
Regional extent
It occurs in Gamba and Tingri, Xizang.
GeoJSON
Fossils
The formation yields ammonites Pterolytoceras sp., Protanisoceras mereanum, Hypacanthohoplites sp., Dimorphoplites tethydis, etc. and foraminifera Dorothia levis, Globorotalites brotzeni. Three ammonite horizons (Pterolytoceras bed, Parahoplites bed, Cleoniceras-Dipoloceras- Perviquieria bed in ascending order), which roughly refer Berriasian-Aptian age to the formation.
Age
Depositional setting
It is of bathyal facies.
Additional Information