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Yehucheng Formation

Yehucheng Fm

Period: 
Paleogene

Age Interval: 
late Early Eocene to early Early Oligocene, (6c)


Province: 
Gansu

Type Locality and Naming

Lanzhou-Xining region. The naming section is located in the vicinity of Yehucheng-Fenghuangcun, Yongdeng County, Lanzhou basin, Gansu. Named by the Regional Geological Survey Party, Gansu Bureau of Geology in 1984.

Synonym (or equivalent): Mahalagou Fm (in adjacent Qinghai sub-basin). Former larger lacustrine setting was disrupted by late Cenozoic tectonics; hence different sub-basin names for the same strata.


Lithology and Thickness

Primarily red mudstone with sandstone; the base, nodular sandy marlstone or sandy conglomerate beds; rich in gypsum and mirabilite.


Lithology Pattern: 
Gypsiferous claystone


Relationships and Distribution

Lower contact

The formation has a conformable contact with the underlying Eocene Xiliugou Fm.

Upper contact

The formation has a conformable contact with the overlying Neogene (called Xiejia Fm in Qinghai subbasin side).

Regional extent

The formation is mainly distributed in the Lanzhou basin, being 198–831 m thick, and in the Longzhong basin it is 33 m thick.


GeoJSON

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Fossils

It yields the charophytes Sphaerochara, Pseudolatachara and Gyrogona and the ostracods Ilyocypris, Cyprinotus and Candona.


Age 

Previously the age of the Yehucheng Formation is assigned to Oligocene (Zheng et al., 1999), and is now assigned to late Early Eocene (mid-Ypresian) to early Early Oligocene by Y.Q. Wang et al. (2019, Paleogene chapter of China Integrated Stratigraphy and Timescale); but they seem to have merged with previous underlying Xiliugou Fm?

Age Span: 

    Beginning stage: 
Ypresian

    Fraction up in beginning stage: 
0.7

    Beginning date (Ma): 
50.45

    Ending stage: 
Rupelian

    Fraction up in the ending stage: 
0.5

    Ending date (Ma):  
30.60

Depositional setting


Depositional pattern:  


Additional Information


Compiler:  

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