Ermaying Formation
The Ermaying Formation is a geological formation of Anisian (Middle Triassic) age in north-central China. It is found across much of the Ordos Basin, at outcrops within the provinces of Shaanxi, Shanxi, and Inner Mongolia. It is composed of up to 600 m thick sequence of mudstone and sandstone, overlying the Heshanggou Formation and underlying the Tongchuan Formation. In the southern part of the Ordos Basin, the Zhifang Formation is equivalent to the Ermaying Formation.
| Ermaying Formation | |
|---|---|
| Stratigraphic range: Anisian ~ | |
| Type | Geological formation |
| Sub-units | Two Members |
| Underlies | Tongchuan Formation |
| Overlies | Heshanggou Formation |
| Thickness | Up to 600 metres (2,000 ft) |
| Lithology | |
| Primary | Mudstone, sandstone |
| Other | Tuff |
| Location | |
| Coordinates | 37°26′15″N 110°39′06″E |
| Approximate paleocoordinates | 38.2°N 90.5°E |
| Region | Shaanxi, Shanxi, Inner Mongolia |
| Country | China |
Ermaying Formation (China) Ermaying Formation (Shanxi) | |
The Ermaying Formation is divided into two members, each with a distinctive assemblage of tetrapod fossils. A 2013 study used SHRIMP U-Pb radiometric dating to assign an imprecise age of 245.9 ± 3.2 Ma for the upper member. A 2018 study assigned a more precise age of around 243.53 Ma based on three ash samples near the base of the upper member. This would indicate that the Upper Ermaying Formation is no older than the late Anisian stage.
A few studies apply the name "Ermaying Formation" to a sedimentary unit in the Yanshan belt, a fold-thrust belt northeast of Beijing. In the Yanshan belt, reported exposures of the formation are dated to the Late Triassic, lying below the Early Jurassic Xingshikou Formation. The Yanshan belt exposures are also known as the Huzhangzi Formation, an alternative name proposed to reflect their chronological and geographic divergence from exposures in the Ordos Basin.