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Shagou Formation

Shagou Fm

Period: 
Neogene

Age Interval: 
Pliocene, N2. , (20b)


Province: 
Yunnan

Type Locality and Naming

The reference section is located northward to the Shagou Village, Yuanmou County, Yunnan. In 1961, Zhou Mingzhen named the otter-bearing fossil bed as Shagou Formation, but did not give the stratotype section and related data. In 1978, You Yuzhu et al. gave a relatively definite definition of this formation.


Lithology and Thickness

Lower part is grayish purple sands and sandy mudstone with lignite beds; Upper part is variegated (pink, grayish green, grayish yellow and light purple) mudstone (or clay). It is rich in calcareous matter and gypsum. The base is grayish brown sandy conglomerate. The formation is 30-50 m thick.


Lithology Pattern: 
Sandy claystone


Relationships and Distribution

Lower contact

Unconformable contact with the underlying pre-Sinian schist and gneiss in type section. Regionally, the next older unit is the Xiaohe Fm?

Upper contact

The top is variegated mudstone (clay), which has a disconformable contact with a light purple and grayish yellow sand bed with cross bedding of the Yuanmou Fm [Quaternary]

Regional extent

It is distributed in Yuanmou County, and its comparable deposition Ciying Fm is placed in Qujing, Kunming and Yuxi, Yunnan. The formation is mainly exposed at Shagou, Gantang and Yangliu Village of the Yuanmou basin and Tieshan, Huxi and Leilao of the Baguo basin. In the Banguo basin deposits are slightly coarse in grain size, coal being rarely contained.

It is comparable to the Ciying Fm in the Yuzhou basin of Qujing. It is also comparable with the Tuobuka Fm in Tangdan, but which has been considered as synonymy of Ciying Fm. The Ciying Fm is from Qujing, Kunming and Yuxi, Yunnan.


GeoJSON

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Fossils

In the Yuanmou basin, in addition mammal fossils such as otter and Mammut, there are also mollusk and plant fossils; in the Banguo area there are Stegotetrabelodon primitium, Stegolophodon banguoensis and Chilotherium yunnanensis.


Age 

Since Zhou Mingzhen (1961) correlated the Ciying Fm fossil bed with the Dhak Pathan Fm bed of the Siwalik Gr Series of the Indian subcontinent and assigned its age to late Pliocene, the Shagou Formation has been long ascribed to the upper Pliocene. However, in the concept of the modern stratigraphic time, it is generally considered that the Dhak Pathan bed is late Miocene (5.5–8.5 Ma). In addition, other mammal fossils contained in this formation is difficult to explain that its age is actually late Pliocene. The age of the formation once compared with that of Zhaotong Fm, the latter recently has been determined as the latest Miocene (Ji et al., 2015). Therefore, the accurate age of the Shagou Formation remains to be further studied. Before its age is finally defined, it seems appropriate to assign its age to Pliocene.

Age Span: 

    Beginning stage: 
Zanclean

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
5.34

    Ending stage: 
Gelasian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
1.80

Depositional setting

The formation belongs to lacustrine-swampy deposits


Depositional pattern:  

Additional Information


Compiler:  

Tao Deng, Sukuan Hou, J.Z. Qigao, Q. Li, Q.Q. Shi, B.Y. Sun, S.Q. Wang, F.X. Wu