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Xiala Formation
Click to display on map of the Ancient World at:
Xiala Fm base reconstruction

Xiala Fm

Period: 
Permian

Age Interval: 
P2 (48), late Guadalupian Epoch (late Middle Permian)


Province: 
Xizang (Tibet)

Type Locality and Naming

The type section is located in the Xiala area of the Angjie Mt. about 12 km to the east of the Yongzhu Country, Shenzha County, Tibet. It was named by Xia Daixiang and Xu Zhongxun in 1979, and was issued to the public by Xia Daixiang in 1983.


Lithology and Thickness

Limestone. Composed of cherty concretion-bearing massive limestone, dolomitic limestone and purple bioclastic limestone, with a thickness of over 700 m.


Lithology Pattern: 
Limestone


Relationships and Distribution

Lower contact

Conformable contact with the underlying Anjie Fm (or Langmaria Fm)

Upper contact

Unconformable contact with the overlying Cretaceous strata in type section; but next higher unit in region is either the local Jiazhanong Fm (Changhsingian) or Mujiucuo Fm (Changhsingian; Shuzhong Shen et al, 2019; but not in Permian lexicon)

Regional extent


GeoJSON

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Fossils

Yields abundant biological fossils among which the Fusulinids is represented by Chusenella, Nankinella and Verbeekina; the Brachiopods are such as Purdonella, Tschernyschewia, Dictyoclostus, Pugnax, Costiferina, Chonetinella; Corals are represented by Asserculinia, Cyathocarinia, Iranophyllum, Axpinnophyllum, Ipciphyllum, Wentzelellites; and Foraminifera are represented by Pachyphloia, Hemigordiopsis, etc., whose features are similar to those of the fauna from the Maokou Fm in the Tethyan region.


Age 

late stage of the Middle Permian = late Guadalupian Epoch (late Middle Permian). [But Permian lexicon chart shows as extending through early Middle Permian, because it was cited as conformable on Artinskian-age Anjie Fm]. Shuzhong Shen et al (2019; Permian integrated stratigraphy and time scale) stratigraphic column has this Xiala Fm extending from mid-Xiangboan (ca. 80% up in Kungurian) through Wuchiapingian (used here).

Age Span: 

    Beginning stage: 
Kungurian

    Fraction up in beginning stage: 
0.8

    Beginning date (Ma): 
276.16

    Ending stage: 
Wuchiapingian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
254.24

Depositional setting


Depositional pattern:  


Additional Information

Permian Lexicon (2017) chart shows Ria Fm as either a synonym or regional variation of this Xiala Fm.


Compiler:  

Wang Yujing

GeoJSON estimate by Longgang Ye and Yuyin Li (Chengdu Univ. Tech. students)