Yurtus Fm
Type Locality and Naming
The type section of Yurtus Formation is the Sugautbulak Phosphorite Mine (No.VI) section, located at the Mining Area, near Yurtus Hill in Wushi County, Xinjiang Uygur Autonomous Region (79°27’45” E, 40°51’47” N). The section lies about 80 km southwest of Aksu City, and was measured by the Gao Zhenjia and colleagues from the Institute of Geology. Xinjiang Bureau of Geology in 1981. In the type section, the formation is about 14 m thick. The Xiaoerbulak Formation was named by Qian and Xiao (1984). The name is derived from Yurtus Hill near the Sugaitbulak Spring, about 80 km southwest of the Aksu City, the seat of Aksu Prefecture, Xinjiang Uygur Autonomous Region.
Synonym: （玉尔吐斯组）
Lithology and Thickness
The Yurtus Formation is phosphoric and siliceous sequence, consisting mainly of black phosphoric-uraniferous-vanadiferous siliceous rock, marlstone, carbonaceous shale, siltstone and dolomite, intercalated with thin-bedded limestone.
Relationships and Distribution
Lower contact
The Yurtus Fm is in disconformable contact with the underlying Qigbluk Fm of Ediacaran. The lower boundary is marked by a disconformable plane.
Upper contact
It is conformably overlain by Xiaoerbulak Fm. The upper boundary is defined by the appearance of the thin-bedded limestone at the base of the Xiaoerbulak Fm.
Regional extent
The Yurtus Formation is exposed in the Bachu-Kalpin Area of Tarim Region, distributed, as known from outcrops and exploratory borings, in Aksu, Kalpin, Qipan, Subexi, Wensu, Wushi, and Zanbile cities and counties etc. The thickness of the formation varies between 11 and 35 m.
GeoJSON
Fossils
The Yurtus Formation yields diverse small shelly fossils, including Chancelloriid: Archiasterella pentactina Sdzuy, Allonia cf. tripodophora Dore & Reid, Chancelloria sp.; Zhijinitid: Zhijinites sp., Parazhijinites sp., Cambroclavus bicornis Qian & Xiao); Conodont-like fossils: Hertzina？sp., Protoherzina？cultrata Missarzhevsky, Jiangshanodus？triangulus Mambetov & Missarzhevsky; Tubular fossil: Hyolithellus tenuis Missarzhevsky, H. sp., Paragloborilus spinatus Qian & Xiao, P. sp., Conotheca sp., Torellella sp., Tiksitheca sp.; Globulal fossil: Olivooides？sp.; Coeloscleritophora: Halkieria mira Qian & Xiao; Monoplacophoral fossil: Bemella sp., Igorella sp.; Operculum of Hyolitha: circothecid hyolithid; Tommotiid Lapworthella sp.; Sponge: Polycladium yurtusensis Qian & Xiao; and unclassified small shelly fossils: Aurisella tarimensis Qian & Xiao etc.
Age
Depositional setting
Additional Information
Based on the founding of small shelly fossil from the lower part of Xiaoerbulak Fm, Qian and Xiao (1984) split the Xiaoerbulak Fm up into two parts with naming the basal part of Xiaoerbulak Fm as Yurtus Fm and restricting Xiaoerbulak Fm to its upper part. Cai (1999) merged it back with the reduced Xiaoerbulak Fm to the original concept of the formation. However, despite the newly erected Yurtus Fm is obviously based on biostratigraphic content, the formation does have individual property in lithology with phosphoric and siliceous sequence that differs from the carbonate sequence of Xiaoerbulak Formation, and therefore Yurtus Fm is here accepted as a valid unit.