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Sangxiu Formation
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Sangxiu Fm base reconstruction

Sangxiu Fm

Period: 
Cretaceous

Age Interval: 
Early Cretaceous, (11a,b) K1sx


Province: 
Xizang (Tibet)

Type Locality and Naming

Himalayan North Belt. The Sangxiu Formation was erected by Wang Naiwen, Liu Guifang and Chen Guoming. The section for the designation is at the Sangxiu hill of the Kadong Village of the Nagarze County, Xizang (90°07′E; 28°05′N). The reference section is from the Gongboxue to Bajiutang through the Shelangre mountain (91°00′E; 28°06′N).

[Figures: Type section of Sangxiu Formation in Kadong of Nagarze County, southern Xizang (Tibet)[


Lithology and Thickness

The Sangxiu Formation is divided into two members. Lower member is built up by gray and blue gray macrocrystalline and microcrystalline andesite with gray siliceous shale, with a thickness of 50 m. Upper member gray and grayish green silty shale with thin-bedded sandstone, richly bearing ammonite fauna, with a thickness of 150 m.

[Figure: Lower part of Sangxiu Formation in type section of Nagarze County]

[Figure: Upper part of Sangxiu Formation in type section of Nagarze County]


Lithology Pattern: 
Volcanics


Relationships and Distribution

Lower contact

The base of the formation lies conformably on gray silty and calcareous shale at the top of the underlying Kadong Fm, which is about 200 m thick. Locally, underlain by Weimei Fm.

Upper contact

Overlain by Jiabula Fm (revised interpretation by Dangpeng Xi, Xiaoqiao Wan et al. (2019,

Regional extent

The present formation occurs in the Duoque, Gongboxue and Rongduo of the Nagarze County, Xizang. It is 200-250 m thick.


GeoJSON

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Fossils

The shale beds of the lower part of the Sangxiu Formation in Nagarze yield the nannofossils Tubodiscus verenae, Diazomatolithus lehmanii, Calcicalathina oblongata, Speetonia colligata, Polycostella senaria, Manivitella pemmatoidea and Watznaueria barnesae, and ammonites Haplophylloceras aff. strigile, H. substrigile, Pterolytoceras exoticum, Phylloceras serum, Neocosmoceras subhooker, N. aff. hystricoidum, Colliptychoceras walkeri, C. calliptychus, C. constrictus, Thurmanniceras kingi, Sarasinella nagarzensis, Neocomites theodorfi, N. montanus, N. indomontanus, Kilianella cf. leptosoma, K. roubaudi, Olccostephanus cf. sublaevis, Valanginites xizangensis, etc. The fossil group of the Sangxiu Formation is similar to that from the lower part of the Jiabula Fm in Gyangze. Although the abundance of the species is relatively lower. By fossil correlation, the age of this fossil assemblage is assigned as Early Cretaceous.


Age 

The Jurassic-Cretaceous boundary is between the Sangxiu Fm and Weimei Fm (figure). It is a potential sequence to study the key marine J-K boundary of China.

Age Span: 

    Beginning stage: 
Berriasian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
143.10

    Ending stage: 
Valanginian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
132.60

Depositional setting

It is quite persistent in lithology and belongs to normal neritic deposition accompanied by volcanic eruption.


Depositional pattern:  


Additional Information


Compiler:  

Wan Xiaoqiao