Yourmeinak Fm
Type Locality and Naming
Aksu-Kalpin region. The Yourmeinak Fm was named Gao Zhenjia (1981). The type section is located west of Kalakz Yourmeinak village, south of Wushi County, Xinjiang Weiwuerzhu Zizhiqu (Xinjiang Uygur Autonomous Region). The reference section is located at near of Sugetbulak, south of Wushi County, Xinjiang Weiwuerzhu Zizhiqu (Xinjiang Uygur Autonomous Region). Lowest formation of the Wushinanshan Gr.
[Figure: The Yourmeinak Fm in the Aksu area is composed of diamictite (section and field photos by Kuang Hongwei, 2019)]
Synonym: （尤尔美那克组）
Lithology and Thickness
The Yourmeinak Fm consists mainly of a series of typical terrestrial glacial deposits (ortho-till), which is purple red massive diamictite (glacial conglomerate), with thin interbeds of purple red, gray-green sandstone, siltstone, silty slates and slate. Some dropstones have usually been found in the interbeds. There is one layer of boulder conglomerate in the bottom of the formation. A large range of glacial features, such as: scratch, indentation, fracturing, and some forms of saddle and lantern shapes have been found on the glacial pebbles. The cement is argillaceous. In the lower part of the section, there are unstable gray-green siltstone and sandstone. The distinct basal ice pavement with flute marks, scratches and chatter marks is well preserved in the underlying erosional surface onto the Qiaoenbulak Group. The thickness ranges from 10-80 m.
Relationships and Distribution
Lower contact
The Yourmeinak Fm disconformably or unconformably overlaps on the different formations of the Qiaoenbulak Gr, of which the uppermost unit is Dongwu Fm. At Aksu, it overlaps the Aksu Gr (early Neoproterozoic?)
Upper contact
The top is unconformably overlain by the Sugetbulak Fm.
Regional extent
Aksu-Kalpin region. The distribution of the Yourmeinak Fm is rather limited in a triangular area among Aksu-Wushi-Kalpin. It thins and disappears westward. It is well developed in the South Hills of Wushi and southward to Kalakz Yourmeinak, Sugetbulak and Qiaoenbulak.
GeoJSON
Fossils
Microplants: Asperatopsophosphaera umishanensis, Leiopsophosphaera densa, Trachysphaeri dium planum, T. incrassatum.
Age
Depositional setting
Additional Information
According to the isotopic age of 740 Ma (U-Pb) from lower part of the overlying Sugetbulak Fm, the age of Yourmeinak Fm tillite is roughly the same as the Nantuo Fm tillite, which belongs to Nanhuan System.