Koksayi Fm
Type Locality and Naming
The Koksayi Formation was named by No.3 Team of No.8 Xinjiang Party of Regional Geological Survey (1962-1963) based on the 1:50 000 scale geological survey, and was published by Xinjiang Compiling Group for Regional Stratigraphic Scale (1981). It’s name came from the Koksayi River in Tuoli County, northern Xinjiang. The type section is at area between the Koksayi River and Suye River, on the southern slope of Mayili Hill (83°34′55″E, 45°10′08″N).
Synonym: (科克萨依组) ; Kekeshayi Fm, Kekesayi Fm
Lithology and Thickness
The formation is divided into two subformations. The lower subformation is dominated by variegated felsite and tuff intercalated with basic lava and tuffaceous siltstone, sandy limestone and abundant jasper rock, and is 2187 m thick. The upper subformation recorded a thickness of 1593 m, with a lower part composed of basaltic porphyrite, andesite, tuffaceous lava with spilite intercalations, and an upper part of fine-crystalline dacitic tuff, tuff breccia, intermediate-acid tuff, chert and felsite. It has a total thickness of 3780 m thick in the type area.
Relationships and Distribution
Lower contact
Lower boundary is covered in the type section. Regionally, it conformably overlies the Tulongguoyi Fm of middle Ordovician.
Upper contact
Its upper boundary is cut by a fault in the type section. Regionally, the next younger unit is the Qargaye Fm of lower Silurian.
Regional extent
It is exposed mainly at Mayili Hill area.
GeoJSON
Fossils
Gastropod Macurites cf. orientalis, M. manitobensis from the top of the lower subformation.
Age
Depositional setting
This unit came from volcanic eruption in the deep-sea environments.
Additional Information