Yardangshan Fm
Type Locality and Naming
The type section of the Yardangshan Formation is the Yardangshan section. It is situated south of Kuruktag Mountain, Yuli, Bayingolin, Xinjiang Uygur Autonomous Region, close to Tuanjiecun Village or about 75 km south of Qinggir Village (88°58’E, 39°47’N). The section is measured by Zhong and Hao (1990) from the Institute of Petroleum Geology of Yunnan-Guizhou-Guangxi Petroleum. Also, the section is very close to the section measured at Yardangshan by the Xinjiang First Regional Geological Survey Team in 1982, which was published by An and Zhang (1986). In the type section, the formation is 54.47 m thick. The Yardangshan Formation was named by Lin et al (2001). The name is derived from Yardangshan Hills in Yuli (Lopnur) County, Bayingolin Mongolian Autonomous Prefecture, Xinjiang Uygur Autonomous Region.
Synonym: （雅尔当山组）
Lithology and Thickness
The Yardangshan Formation is principally a carbonate and silicate sequence with interbeds of clastic rocks. Lower part of formation, 19.21 m thick, consists of dark grey dolomite and black chert with a layer of thick-bedded pebbly dolomitic sandstone, 4.62 m thick, at the base and a layer, 3.2 m thick, of dark yellowish green, fine-grained gabbro-diabase at the top. Upper part, 35.26 m thick, consists of black, argillaceous siliceous rock and siliceous shale, alternated with greyish black dolomite, dolomitic limestone, and mudstone.
Relationships and Distribution
Lower contact
The Yardangshan Fm rests disconformably on the underlying Hangeerqiaoke Fm of Ediacaran. The lower boundary of the formation is marked by the disconformable plane characterized by the pebbly dolomitic sandstone of the Yardangshan Fm overlies on the tillite of the Hangeerqiaoke Fm
Upper contact
It is conformably overlain by the Mohershan Fm. The upper boundary of Yardangshan Fm is defined by the appearance of thick-bedded limestone at the base of the Mohershan Fm. The Yardangshan Fm in southern Kuruktag is conformably overlain by the Torsuqtagh Fm.
Regional extent
The Yardangshan Formation is exposed in the east of South Tianshan Area of Tarim Region, distributed in the south slope of the Kuruktag Mountain, and the Charchaq and Yaerdangshan mountains (hills).
GeoJSON
Fossils
The sandstone at the base of the Yardangshan Formation yields acritarch Micrhystridium regulare; other parts of the formation yields small shell fossils including Allonia erromenosa, Archiasterella pentina, Eomyclopsis sp., Lotouchella sp., Onychia sp. and Protospongia sp., trilobite and brachiopod fragments, and sponge-spicules Protospongia sp. and Kiwetinokia sp.
Age
Depositional setting
Additional Information
Previously the strata occupied by the Yardangshan Formation in South Kuruktag were assigned to Xishanbulak Fm and Xidashan Fm is by Zhong and Hao (1990). The type locality of the Xishanbulak Fm and Xidashan Fm is in North Kuruktag area, and these two formations were now merged by Cai (1999) to return back to its original concept of Zhang et al. (1959), which is not supported by Lin et al (2001) and by this book as well. Lin et al (2001) considered the strata assigned to Xishanbulak Fm and Xidashan Fm in the South Kuruktag area are hard to be separated, thinner in thickness, and bear less volcanic rock. Based on these differences in lithological assemblage from the Xidashan Fm of North Kuruktag, they erected the Yardangshan Fm for the early Cambrian of South Kuruktag area.