Yanchang Gr
Type Locality and Naming
Type locality lies in the area from Suide to Yanchang in northern Shaanxi; the reference locality is located in Qishuihe, Tongchuan, Shaanxi. M. L., Fuller, and F. G., Clapp, named it “Yanchang Facies” in 1926. Pan Zhongxiang changed its name into “Yanchang Stratum” in 1934, and determined its geological age as the Late Triassic. The Yanchang Group in The National Stratigraphic Multiple Division and Comparative Study of Lithography in Shaanxi Province in 1994 contains Tongchuan Fm, Yongping Fm and Wayaobao Fm. Hujiacun Fm is classified into Yongping Fm. "A more detailed division of the Yanchang "Formation" has been used in oil and gas exploration by petroleum companies. In this division, the Yanchang is divided into 10 oil-bearing members, which are named as Chang-1 to Chang-10. Among them, the Chang-4 and Chang-5 are usually difficult to distinguish and is regarded as one member, called Chang-4+5). The Chang-7, characterized by thick oil-bearing shales, is the most
widely and stably distributed bed of the Yanchang Formation." (from Deng S, Lu Y, Luo Z, Fan R, Li X, Zhao Y, Ma X, Zhu R, Cui J. 2018. Subdivision and age of the Yanchang Formation and the Middle/Upper Triassic boundary in Ordos Basin, North China. Science China Earth Sciences, 61, 21 pp. https://doi.org/10.1007/s11430-017-9215-3. ]. The black-shale-rich Chang-7 Mbr is the Yongping Fm of the Yanchang Gr in the stratigraphic terminology of this Lexicon. [See Additional Information below for additional discussion.]
Synonym: Yanchang Fm
Lithology and Thickness
The Yanchang Gr is a set of coal-bearing and oil-bearing rock series composed of gray-green, yellow-green sandstone and black-gray mudstone. See each formation description for detailed characteristics.
Relationships and Distribution
Lower contact
Conformable with conformable in contact to underlying Ermaying Fm.
Upper contact
Unconformable with the overlying Fuxian Fm of lower Jurassic.
Regional extent
GeoJSON
Fossils
Producing the famous Tongchuan flora: Tongchuanophyllum-Danaeopsis magnifolia and Yanchang flora: Danaeopsis fecunda-Bernoullia zeilleri.
Age
Depositional setting
Additional Information
Synonym: Yanchang Fm
Lithology and Thickness:
The Yanchang Gr is a set of coal-bearing and oil-bearing rock series composed of gray-green, yellow-green sandstone and black-gray mudstone. See each formation description for detailed characteristics.
Lithology-pattern: Clayey sandstone
Relationships and Distribution:
Lower contact:
Conformable with conformable in contact to underlying Ermaying Fm.
Upper contact:
Unconformable with the overlying Fuxian Fm of lower Jurassic.
Regional extent:
GeoJSON:
Fossils:
Producing the famous Tongchuan flora: Tongchuanophyllum-Danaeopsis magnifolia and Yanchang flora: Danaeopsis fecunda-Bernoullia zeilleri.
Age:
Tong et al. (2019; Triassic integrative stratigraphy and timescale of China; Science China: Earth Sciences, 82: 189-222) indicate that it is upper Anisian through middle Rhaetian.
Age span:
Beginning stage: Anisian
Fraction up in beginning stage: 0.75
Beginning date (Ma):
Ending stage: Rhaetian
Fraction up in ending stage: 0.75
Ending date (Ma):
Depositional setting:
Depositional-pattern:
Additional Information
In 1959, Gan Kewen and others renamed the "Yanchang Series", and divided 5 lithological members and included the lower strata of the "Wayaobao Coal System" built by Pan Zhongxiang. In 1980, the Institute of Geology of the Chinese Academy of Geological Sciences named the first and second members of the Yanchang Series as the Tongchuan Fm, and the age was Middle Triassic; The third, fourth, and fifth members are named "Yanchang Fm", and their ages are the Late Triassic. Regional Geology of Shaanxi Province combined Tongchuan Fm, Hujiacun Fm, Yongping Fm and Wayaopu Fm as Yanchang Gr, in which, Tongchuan Formation equal to the first and the second member of Yanchang Gr; Hujiacun Fm, Yongping Fm and Wayaopu Fm (Wayoaboa Fm) equal to the third, fourth and the fifth member correspondingly.