Hulusitai Fm
Type Locality and Naming
The type section of Hulusitai Formation is the Taosigou section, located at the middle of Taosishan Hill, north of Taosigou Valley, west of Shitangjing Mining Area, Dawukou District, Shizuishan City, Ningxia Hui Autonomous Region (106°16’E, 39°13’N). It lies about 5 km west of Shitangjing Mining Area or 4 km northeast of Hulstai Town, and was measured by Zhou Zhiqiang in 1976. In the type section the formation is 200.70 m thick. The Hulusitai Formation was named by Du (1950). The name is derived from Hulstai Village in Hulstai Township, Alxa Zuoqi (Left Banner), Alxa League, Inner Mongolia Autonomous Region. The original Mandarin name given by Du (1950), translated from Mongolian, is different from the official Mandarin name of the village in Chinese characters (呼鲁斯太). Du (1950) originally called the unit Hulusitai Bed for entire Cambrian strata in the area of northern Helanshan Mountain. Lu (1962) renamed the unit Hulusitai Formation by restricting it to partial strata of “early Middle Cambrian age” of Du’s Hulusitai Bed. The revised concept of the formation by Lu (1962) has been widely used by subsequent authors.
Synonym: （胡鲁斯台组）; Abuqiehai Fm (see Additional Information)
Lithology and Thickness
The Hulusitai Formation is a carbonate and fine clastic sequence. Lower part consists of yellowish grey medium- to thick- bedded sandy limestone intercalated with greyish green and purplish red shale, medium- to thick- bedded oolitic limestone, and greyish, thin-bedded argillaceous striped limestone. Middle part consists greyish green shale intercalated sandy limestone, bioclastic limestone, and dark grey, thin-bedded argillaceous oolitic limestone. Upper part consists greyish white, thin-bedded limestone with interbeds of edgewise conglomeratic limestone; and Top part is greyish green sandstone and purplish red, greyish green, brownish red shale.
Relationships and Distribution
Lower contact
The Hulusitai Fm is in conformable contacts with the underlying Taosigou Fm. The lower boundary of the formation is defined by lithologic change from the dolomite of underlying Wudaotang Fm to the sandy limestone at the base of the Hulusitai Fm.
Upper contact
The Hulusitai Fm is in conformable contacts with the overlying Sanshantzu Fm (Shanshanzi Fm; Sandaokan Fm). The upper boundary by lithologic change from greyish shale to the thin- to thick-bedded dolomite, at the base of the overlying Sanshantzu Fm.
Regional extent
The Hulusitai Formation is exposed in the Western Margin Area of North China Region, restricted in the middle and northern sections of the Helanshan Mountain, northern Ningxia (Helan and Pingluo counties and Yinchuang and Shizuishan cities) and the area of adjacent southwestern Inner Mongolia (Alxa Left Banner, Wuhai City and Zuozishan Mountain). The upper boundary of the Hulusitai Formation is notably diachronous. As reported by Shen in Gu (1996) and Yuan et al. (2016), the uppermost part of the formation in the type section contains Koptura, Bailiella and Crepicephalina that suggests it belongs to lowermost of Wangcunian Stage, whereas at Suyukou, south of the type section, and at Gangde’er Hill of Wuhai, north of the type section, the uppermost part contains Cyclolorenzella, Damesella, and Jiulongshania, all of which suggest that part belongs to upper Guzhangian Stage.
GeoJSON
Fossils
Hulusitai Formation yields diverse polymerid trilobites in the type section (Shen in Gu, 1996), including Bailiella, Holanshania, Inouyops, Iranoleesia, Kootenia, Leiaspis, Luaspides, Metainouyia, Monanocephalus, Pagetia, Parachittidilla, Parainouyia, Pseudinouyia, Solenoparia, Solenoparia (Plesisolenoparia), Sunaspidella, Zhongtiaoshanaspis, Zhuozishania, antagmids, ordosiids, proasaphiscids, and ptychoparids. In other localities the formation yields also additional trilobites Blackwelkderia, Cyclolorenzella, Damesella, Jiulongshanian, Poshania, and Taitzuia, etc. (Yuan et al., 2016). Conodont Cordylodus proavus and trilobite Calvinella were reported from the uppermost of the formation. Conodont Cordylodus proavus and trilobite Calvinella were reported from the uppermost strata of the formation at Qianggangling-Xialingnangou section of Alxa Left Banner, Inner Mongolia (Bureau of Geology and Mineral Resources of Ningxia Hui Autonomous Region, 1990), indicating the upper boundary of the formation in that section is at middle of Niuchehean Stage, close to the base of Ordovician.
Age
Depositional setting
The formation belongs to open shallow sea and littoral tidal flat setting.
Additional Information
Lithology and Thickness:
The Hulusitai Formation is a carbonate and fine clastic sequence. Lower part consists of yellowish grey medium- to thick- bedded sandy limestone intercalated with greyish green and purplish red shale, medium- to thick- bedded oolitic limestone, and greyish, thin-bedded argillaceous striped limestone. Middle part consists greyish green shale intercalated sandy limestone, bioclastic limestone, and dark grey, thin-bedded argillaceous oolitic limestone. Upper part consists greyish white, thin-bedded limestone with interbeds of edgewise conglomeratic limestone; and Top part is greyish green sandstone and purplish red, greyish green, brownish red shale.
Lithology-pattern: Limestone
Relationships and Distribution:
Lower contact:
The Hulusitai Fm is in conformable contacts with the underlying Taosigou Fm. The lower boundary of the formation is defined by lithologic change from the dolomite of underlying Wudaotang Fm to the sandy limestone at the base of the Hulusitai Fm.
Upper contact:
The Hulusitai Fm is in conformable contacts with the overlying Sanshantzu Fm (Shanshanzi Fm; Sandaokan Fm). The upper boundary by lithologic change from greyish shale to the thin- to thick-bedded dolomite, at the base of the overlying Sanshantzu Fm.
Regional extent:
The Hulusitai Formation is exposed in the Western Margin Area of North China Region, restricted in the middle and northern sections of the Helanshan Mountain, northern Ningxia (Helan and Pingluo counties and Yinchuang and Shizuishan cities) and the area of adjacent southwestern Inner Mongolia (Alxa Left Banner, Wuhai City and Zuozishan Mountain). The upper boundary of the Hulusitai Formation is notably diachronous. As reported by Shen in Gu (1996) and Yuan et al. (2016), the uppermost part of the formation in the type section contains Koptura, Bailiella and Crepicephalina that suggests it belongs to lowermost of Wangcunian Stage, whereas at Suyukou, south of the type section, and at Gangde’er Hill of Wuhai, north of the type section, the uppermost part contains Cyclolorenzella, Damesella, and Jiulongshania, all of which suggest that part belongs to upper Guzhangian Stage.
GeoJSON:
Fossils:
Hulusitai Formation yields diverse polymerid trilobites in the type section (Shen in Gu, 1996), including Bailiella, Holanshania, Inouyops, Iranoleesia, Kootenia, Leiaspis, Luaspides, Metainouyia, Monanocephalus, Pagetia, Parachittidilla, Parainouyia, Pseudinouyia, Solenoparia, Solenoparia (Plesisolenoparia), Sunaspidella, Zhongtiaoshanaspis, Zhuozishania, antagmids, ordosiids, proasaphiscids, and ptychoparids. In other localities the formation yields also additional trilobites Blackwelkderia, Cyclolorenzella, Damesella, Jiulongshanian, Poshania, and Taitzuia, etc. (Yuan et al., 2016). Conodont Cordylodus proavus and trilobite Calvinella were reported from the uppermost of the formation. Conodont Cordylodus proavus and trilobite Calvinella were reported from the uppermost strata of the formation at Qianggangling-Xialingnangou section of Alxa Left Banner, Inner Mongolia (Bureau of Geology and Mineral Resources of Ningxia Hui Autonomous Region, 1990), indicating the upper boundary of the formation in that section is at middle of Niuchehean Stage, close to the base of Ordovician.
Age:
Mid Wuliuan to Middle Niuchehean (top limit ranges among this region from base-Guzhangian to mid-Niuchehean); (middle to late Cambrian)
Age span:
Beginning stage: Wuliuan
Fraction up in beginning stage: 0.5
Beginning date (Ma):
Ending stage: Jiangshanian
Fraction up in ending stage: 0.75
Ending date (Ma):
Depositional setting:
The formation belongs to open shallow sea and littoral tidal flat setting.
Depositional-pattern:
Additional Information
After Du (1950) erected Hulusitai Bed near Hulstai Town in north section of Helanshan Mountain, for entire Cambrian strata in northern part of Helanshan Mountain, Guan and Che (1955) proposed Abuqiehai Series, which is also for entire Cambrian strata of Helanshan-Zuizishan Mountain area. The Zuizishan lies immediately north of the Helanshan Mountain. These two units are actually synonymous because both are extremely similar in lithology to each other. Subsequently Lu (1962) renamed former unit Hulusitai Formation and the latter unit Abuqiehai Formation and used the former formation as representative of local “early Middle Cambrian”-aged strata of the Helanshan-Zuizishan Mountain region and the latter formation representative of local “late Middle Cambrian”-aged strata there. Lu’s formations actually are chronostratigraphic units than lithological ones. Xiang in Compiling Committee for Chinese Stratigraphic Lexicon et al. (1999) abandoned the Abuqiehai Formation by regarding it a junior synonym of Hulusitai Formation. Xiang’s concept is followed in this book.