Lashizhong Fm
Type Locality and Naming
The type section is at Tuoluogai in Jiamusu west of Lashizhong on the southernmost Gangder Hill in Wuhai, Inner Mongolia. The Lashizhong Fm is derived from the green Lashizhong Series proposed by Guan Shicong and Che Shuzheng in 1955. In 1959, Mu Enzhi studied the graptolites from the series, and named it the Lashizhong Fm. The type section is exposed incompletely. Fu Lipu et al. (1993) considered the Beishan section of the Lashizhong Fm, west of Gongwusu, as the type section, and restricted the formation to turbiditic sandy shale bearing graptolite. At the same time, they renamed the light green shale in the lower part of Gongwusu Fm of Chen Junyuan et al. (1984) in area east of Hermaori Youth farmland the Hermaori Fm.
Synonym: (拉什仲组）
Lithology and Thickness
The formation is dominated by grayish green sandstone and shale, intercalated with bioclastic limestone in the upper part. In the type area, the Lashizhong Fm recorded an incomplete thickness of 139 m.
Relationships and Distribution
Lower contact
The type section is covered or cut by fault at the lower boundary, and the contact between the Lashizhong Fm and the underlying strata is not known. On the lithology, An et al. (1990) included the black shale bearing N. gracilis in the underlying Wulalik Fm. Surface between No.1 and No.2 beds is probably a transformation boundary of sequence, and is a disconformity.
Upper contact
The type section is covered or cut by fault at the upper boundary, and the contact between the Lashizhong Fm and the overlying strata is not known in the type section. Regionally, it is conformably overlain by the Gongwusu Fm.
Regional extent
This formation is seen on the southernmost Gangder Hill, Hanggaijing and Shanghaimiao in Otog Qianqi, Inner Mongolia. In southernmost Gangder Hill, it recorded an incomplete thickness of 138 m, and in last two places, it is 108 m thick incompletely.
GeoJSON
Fossils
It yields graptolite Climacograptus (C.) bicornis. An et al. (1990) suggested that strata in the southernmost Gangder Hill is only the lower part of the Lashizhong Fm, and in Lashizhong exposed is its middle and upper part which yields graptolite of C. (C.) bicornis assemblage. N. gracilis has been reported from the black shale of the No.1 bed at the base.
Age
Depositional setting
Additional Information