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Yangxi Formation

Yangxi Fm

Period: 
Paleogene

Age Interval: 
Early Eocene (21a)


Province: 
Hubei

Type Locality and Naming

Jianghan Basin - NW. The type section is located at Laoyashan ~2 km west of Yangxi Township, southeast of Yidu County, Hubei, and the reference section is located at Gongjiachong, Dangyang County-Baiquesi, Zhijiang County. It was named by P.T. de Chardin and C.C. Young in 1935–1936.


Lithology and Thickness

Lower part is brownish yellow, brownish red, purplish red and yellow green sandstone and muddy sandstone and sandy mudstone with grayish white or grayish yellow sandstone and marlstone, containing calcareous concretions, the base of which is light brown sandy conglomerate and conglomerate with sandstone. Upper part consists of grayish purple, purplish red, grayish white and brownish red limestone and marlstone, with brownish red, grayish black and grayish green muddy sandstone, the base of which is brownish yellow or brownish red sandy mudstone and grayish green mudstone with purplish red or grayish purple marlstone. The thickness is about 100–150 m and ranges from about 100 to 520 m to the east of Songcikou and at Dongyuemiao, Dangyang.


Lithology Pattern: 
Clayey sandstone


Relationships and Distribution

Lower contact

The formation has a conformable or disconformable contact with the underlying Paomagang Fm.

Upper contact

The formation has a conformable or disconformable contact with the overlying middle Eocene Pailoukou Fm.

Regional extent

It is mainly distributed at Yidu, Songzi and Dangyang, and similar horizons are probably exposed at Nanzhang and Jingmen.


GeoJSON

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Fossils

The formation contains abundant fossils. The ostracods are represented by the assemblage mainly of Cypris-Limnocythere-Sinocypris; the gastropods are Bithynia lordostoma, Australorbis odhneri etc. The vertebrates mainly include fishes, birds (Songzia heidangkouensis) and the mammals Coryphodon zhichengensis and Asiocoryphodon cf. conicus. In addition, there are the charophyte fauna mainly of Peckichara-Grovesichara and sporopollen.


Age 

According to paleomagnetic measurements, this formation originated in the chrons C24r to C22n, and the paleolatitudes during the formation of the strata were 21.23º–21.25º (Zhang Shiben et al., 1992). The Yangxi Fm covers C24r-C22n; therefore its age was initially determined as 54.9-50.5 Ma according to the older Geologic Time Scale (Zhang Shiben et al., 1992). According to the revised Geologic Time Scale (Gradstein et al., 2012), the geologic age of Yangxi formation should be 55.5-49 Ma. From the paleomagnetic and fossil features, it is thought that the age of the Yangxi Formation should be early Eocene.

Age Span: 

    Beginning stage: 
Ypresian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
56.00

    Ending stage: 
Ypresian

    Fraction up in the ending stage: 
0.8

    Ending date (Ma):  
49.66

Depositional setting

This formation refers to lacustrine deposit.


Depositional pattern:  

Additional Information


Compiler:  

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