Xiagou Formation
| Xiagou Formation Stratigraphic range: Early Cretaceous | |
|---|---|
| Type | Geological formation |
| Unit of | Xinminpu Group |
| Underlies | Zhonggou Formation |
| Overlies | Chijinpu Formation |
| Lithology | |
| Primary | Mudstone |
| Location | |
| Region | Changma Basin, Gansu |
| Country |
 |
| Type section | |
| Named for | Xiagou |
The Xiagou Formation is the middle strata of the Xinminpu Group. It is named for its type site in Xiagou, in the Changma Basin of Gansu Province, northwestern China and is considered Early Cretaceous in age. It is known outside the specialized world of Chinese geology as the site of a Lagerstätte in which the fossils were preserved of Gansus yumenensis, the earliest true modern bird. The laminated yellowish mudstones of the Xiagou Formation are the lithified remnants of varves that were laid down as extremely fine silt settled to the bottom of a tranquil freshwater lake. The result was dense anoxic bottom sediment, where the lack of bacteria slowed the processes of decay, preserving uncompressed fossils in details that include feather impressions and remnants of the webbing between the bird's toes.
The age of the formation has not yet been confidently determined. The underlying Chijinpu Formation is likely the same age as the Jehol Group due to the presence of similar fossils, meaning that the Xiagou Formation is probably slightly younger than the Jehol biota, dating to around the mid Aptian age.[1]
Paleobiota
The Xiagou Formation is particularly noted for its high diversity of ancient birds. These include both modern birds close to the ancestors of living species, and related lineages now entirely extinct:
- Dunhuangia cuii Wang et al., 2015
- Feitianius paradisi O'Connor et al., 2015
- Qiliania graffini Ji et al., 2011
- Changmaornis houi Wang et al., 2013
- Gansus yumenensis Hou & Liu, 1984[2]
- Jiuquanornis niui Wang et al., 2013
- Yumenornis huangi Wang et al., 2013
Other fossils from the Xiagou will permit detailed recreation of an Early Cretaceous lake ecology. There are fossils of abundant fish fauna, Charophyta and ostracods.
See also
- List of fossil sites (with link directory)
References
- ↑ You, Hai-lu; Lamanna, Matthew C.; Harris, Jerald D.; Chiappe, Luis M.; O'Connor, Jingmai; Ji, Shu-an; Lü, Jun-chang; Yuan, Chong-xi; Li, Da-qing; Zhang, Xing; Lacovara, Kenneth J.; Dodson, Peter; Ji, Qiang (2006). "A Nearly Modern Amphibious Bird from the Early Cretaceous of Northwestern China". Science. 312: 1640–1643. doi:10.1126/science.1126377. PMID 16778053.
- ↑ Weishampel, David B; et al. (2004). "Dinosaur distribution (Early Cretaceous, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 553-556. ISBN 0-520-24209-2.
Further reading
- "Early Cretaceous Ostracods From The Xiagou Formation In Xiagou, Gansu Province" in Acta Micropalaeontologica Sinica part 2, 2005
- Bureau of Geology and Mineral Resources of Gansu Province,Regional Geology of Gansu Province (Geological Publishing House, Beijing, 1989), pg. 692