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Xiaotun Formation

Xiaotun Fm

Period: 
Paleogene

Age Interval: 
Late Eocene , (20b)


Province: 
Yunnan

Type Locality and Naming

The naming section is located at Anren Village and Xiaotun, Lunan County, Yunnan. Named by Zheng Jiajian in 1978.


Lithology and Thickness

A sequence of fluvio-lacustrine deposits consisting of alternating beds of brownish red, thick-bedded muddy sandstone and sandy mudstone, locally containing pebbly sandstone; in sandstone there are occasionally mudstone patches. Its thickness is >40 m at Anren Village and Xiaotun and up to 50 m or so west of Lunan City and southwest of Lumeiyi.


Lithology Pattern: 
Sandy claystone


Relationships and Distribution

Lower contact

It is probably disconformably underlain by the Middle Eocene Lumeiyi Fm.

Upper contact

It is mostly overlain by the Quaternary. Regionally, the next younger unit is the Xiaolongtan Fm.

Regional extent

The formation is mainly exposed on the western margin of the Lunan basin.


GeoJSON

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Fossils

This formation contains very scarce fossils and fossil groups, but its characters are remarkably different from its underlying Lumeiyi Fm. Of these fossils the most important ones are the mammals Gigantamynodon giganteus, which is close to G. cessator in the Late Eocene Erden Obo Fm (=Eerdengaobao Fm), their difference only lying in that the size of the former is slightly bigger. The similar species are also found in Middle to Late Eocene strata at Caijiachong, Qujing.


Age 

Therefore according to the stratigraphic sequence and correlation with the fossiliferous horizons in adjacent areas, the age of the Xiaotun Fm is Late Eocene. The age of this formation was suggested to be Ealy Oligocene in the past (Zheng et al., 1999), but Wang et al. (2019) inferred it was Late Eocene.

Age Span: 

    Beginning stage: 
Bartonian

    Fraction up in beginning stage: 
0.9

    Beginning date (Ma): 
38.04

    Ending stage: 
Priabonian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
33.90

Depositional setting

It is interpreted to a sequence of fluvio-lacustrine deposits.


Depositional pattern:  

Additional Information


Compiler:  

Tao Deng, Yuanqing Wang, Qian Li, et al.