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Aershan Formation
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Aershan Fm base reconstruction

Aershan Fm

Period: 
Cretaceous

Age Interval: 
earliest Cretaceous, (17d)


Province: 
Inner Mongolia

Type Locality and Naming

Erlian Basin.


Lithology and Thickness

Based on lithological characteristics, the Aershan Formation is divided into two fining-upward successions, named as the Lower and the Upper Aershan formations. The Lower Aershan Formation rests on the Jurassic strata with an angular unconformity (named as T11 in seismic reflection sections), and comprises two intervals. The lower interval with a maximum thickness of ca. 433 m, is a succession of coarse-grained sediments, dominated by alluvial fan and braided channel conglomerate and pebbly sandstone. The upper interval with a maximum thickness of ca. 650 m, is mainly made up of thick lacustrine mudstone, interbedded with a few thin layers of siltstone, sandstone and intermediate-basic volcanic rocks.

The Upper Aershan Formation, with a maximum thickness of ca. 680 m, overlies the Lower Aershan Formation with an angular unconformity (named as T10 in seismic reflection sections), and is characterized by coarse-grained sediments, mainly made up of alluvial fan and braided channel conglomerate, pebbly sandstone, and sandstone. Fine-grained sediments, dominated by fluvial and lacustrine alternating beds of sandstone, siltstone and mudstone, are recognized in the upper part of the Upper Aershan Formation in the center of some sub-basins."


Lithology Pattern: 
Sandstone


Relationships and Distribution

Lower contact

The Lower Aershan Formation rests on the Jurassic strata (e.g., Hugejiletu Fm) or the early Cretaceous Xinganling Gr with an angular unconformity (named as T11 in seismic reflection sections).

Upper contact

Regional extent

Erlian Basin


GeoJSON

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Fossils

It yields spores, pollen grains and ostracods.


Age 

[The summary chart in Guo et al. (2019; Fig. 14) based on their dating is 138 Ma (above 1 myr unconformity) to 132 Ma (followed by very brief unconformity); hence, using GTS2020, the age span implies late Berriasian to earliest Hauterivian.]However, the entire Bayanhua Gr is placed into only the Aptian-Albian by Kosenko et al. (2021), who did not reference Guo et al.'s study. Therefore, until this conflict is resolved, the age model for the Erlian Basin stratigraphy by Guo et al. (2019) is used here.

Age Span: 

    Beginning stage: 
Berriasian

    Fraction up in beginning stage: 
0.95

    Beginning date (Ma): 
137.97

    Ending stage: 
Hauterivian

    Fraction up in the ending stage: 
0.1

    Ending date (Ma):  
131.99

Depositional setting


Depositional pattern:  


Additional Information


Compiler:  

Guo, Z.X. et al. (2019, Early Cretaceous tectonostratigraphic evolution of the Erlian Basin, NE China, Marine and Petroleumm Geology, 110: 539-564)