Xishanyao Fm
Type Locality and Naming
Junggar and Turfan-Hami Basins. It was named by the Geological Survey Division of the Petroleum Administration of Xinjiang as the Xishanyao Horizon in 1956, and was first cited publicly by the Compiler
Jingeng Sha (coordinator) Group for the Regional Stratigraphic Chart of Xinjiang in 1981, and was renamed as the Xishanyao Formation at the same time. The naming locality is situated at Xishanyao to the west of Urumqi City, Xinjiang. Uppermost formation in Shuixigou Gr.
Synonym: （西山窑组）
Lithology and Thickness
It is composed of grey, grey-green, grey-yellow and purple sandstones and carbonaceous mudstones, intercalated with coal beds and siderite thin layers, and representing an important coal-bearing stratigraphic unit. It commonly is 600-1000 m thick.
Relationships and Distribution
Lower contact
Conformably overlies the Sangonghe Fm
Upper contact
The formation is in a conformable contact with the overlying Toutunhe Fm
Regional extent
The formation is distributed in the Junggar Basin and its surrounding mountainous areas, as well as in the Tulufan-Hami Basin. In the Junggar Basin it is exposed essentially in the areas of Toutun River-Zini Spring, Karamay-Heshituoluogai, Sangequan-Jiangjun Temple, and southern foothill of the Karamaili Mts, while in the Tulufan-Hami Basin it is exposed in the areas of Korjie, Yingtaoguanzi, Meiyaogou, Ortang-Kokoya, Subashi, Shanshan, Qiketai and the Greater South Lake, with its scattered exposures being found as well as on the southern and northern margins of the Yili Basin. The lithology of the particular formation is more or less consistent in various regions, but with a greater changeable thickness, as shown by its variation in a range from 600 m to 1000 m on the southern margin of the Junggar Basin, and being of 6-150 m already in the Karamay region.
GeoJSON
Fossils
It yields plant fossils such as Coniopteris hymenophylloides, C. tatungensis, Equisetites ferganensis, Podozamites lanceolatus, Phoenicopsis angustifolia and Czekanowskia rigida, as well as bivalve fossils as represented by Pseudocardinia tuvaensis, P. turfanensis, P. aff. ovalis, Ferganoconcha subcentralia, F. sibirica and Sibireconcha sp.
Age
Depositional setting
It is interpreted as a fluvial-lacustrine environment.
Additional Information
Age:
Schematic strat column in previous "red Chinese Lexicon" implies that the Xishanyao Fm is Aalenian below a "Bajocian" Toutunhe Fm, but that Toutunhe Fm is now re-assigned as mid-Oxfordian through Kimmeridgian. Diying Huang (2019; Jurassic integrative stratigraphy and timescale of China. Science China: Earth Sciences, v. 62) re-assigns this Xishanyao Fm as Bathonian through mid-Oxfordian.
Age span:
Beginning stage: Bathonian
Fraction up in beginning stage: 0.0
Beginning date (Ma):
Ending stage: Oxfordian
Fraction up in ending stage: 0.5
Ending date (Ma):
Depositional setting:
It is interpreted as a fluvial-lacustrine environment.
Depositional-pattern:
Additional Information
Compiler
Jingeng Sha (coordinator)