Xin’ertai Fm
Type Locality and Naming
Type section of the Xin’ertai Formation is the No 10 section measured along the old highway, south of Kensayis Mountain Pass, in Guozigou Huocheng County, Xinjiang Uygur Autonomous Region (81°10’06”E, 44°28’24”N). It is the same section shared as auxiliary section by the underlying Guozigou Fm. The section lies about 52 km northeast of the seat of Huocheng County, Xinjiang Uygur Autonomous Region and was measure by the Joint Team of Regional Geology Survey Team of Xinjiang Uygur Autonomous Region and Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences in 1974. The section spams the Cambrian-Ordovician boundary. The Xin’ertai Formation was first published by Hou Hongfei et al. (1979). The name is derived from Xin’ertai, a platform on the hillside in the Guozigou Canyon, Huocheng County, Ili Kazak Autonomous Prefecture, Xinjiang Uygur Autonomous Region. The name was first appeared a 1978 manuscript by the Joint Team of Xinjiang Regional Geological Survey Team, Geological Bureau of Uygur Autonomous Region, and The Stratigraphic Brigade of the Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences. This formation spans the Cambrian-Ordovician boundary.
Synonym: （新二台组）; see Additional Information
Lithology and Thickness
The Xin’ertai Formation is basically a clastic sequence, consisting of dark grey and grey, siliceous and argillaceous and calcareous siltstone, siliceous rock, intercalated with shale and thin-bedded limestone. In the type section, the formation is 141 m thick. In the type area, the Xin'ertai Formation has a recorded thickness of 200-305 m.
Relationships and Distribution
Lower contact
The Xin’ertai Fm is in conformable contact on the siliceous, muddy banded limestone of the underlying Guozigou Fm
Upper contact
The Xin’ertai Fm is in conformable contact by the siltstone of the overlying Kekesaleixi Fm (Koksaleixi Fm) of Middle Ordovician.
Regional extent
The Xin’ertai Formation is exposed in the west of Middle Tianshan-Beishan Region, distributed at Guozigou of Houcheng County, at Kokirqin of Jinghe County, and in the area of Sayram Lake.
GeoJSON
Fossils
This formation yields graptolites, trilobites, brachiopods and conodonts. The lower part of the formation yields trilobite Hysterolenus oblongus, Parabolinella sp., and Niobella sp., and the middle and upper parts yield graptolites Anisograptus, Cardiograptus, Didymograptus, Isograptus, Oncagraptus, Tetragraptus and Triograptus etc. As integrated by Cai (1999), the Xin’ertai Formation embraces eight biozones, including the lowermost trilobite Hysterolenus Zone, which spans the Cambrian-Ordovician boundary, and seven successive Ordovician graptolites, in ascending order, the Adelograptus Zone, the Anisograptus-Triograptus Zone, the Tetragraptus (Etagraptus) approximatus Zone, the Tetragraptus fruticosus Zone, Didymograptus deflexus Zone, Isograptus maximodivergens Zone, and Cardingraptus-Oncograptus upsilon Zone. The lower part of the formation is assigned to the trilobite Hysterolenus Zone (Cai, 1999). The lower part of the biozone is Cambrian in age, and the upper part is correlatable with conodont Cordylodus lindstromi Zone (Zhou et al., 1990), which spans Cambrian-Ordovician boundary (Dong and Zhang, 2017).
Age
Depositional setting
The lithology and fauna indicate a restricted and starved basin setting and an anoxic bottom water condition for the formation.
Additional Information
Lithology and Thickness:
The Xin’ertai Formation is basically a clastic sequence, consisting of dark grey and grey, siliceous and argillaceous and calcareous siltstone, siliceous rock, intercalated with shale and thin-bedded limestone. In the type section, the formation is 141 m thick. In the type area, the Xin'ertai Formation has a recorded thickness of 200-305 m.
Lithology-pattern: Siliceous limestone
Relationships and Distribution:
Lower contact:
The Xin’ertai Fm is in conformable contact on the siliceous, muddy banded limestone of the underlying Guozigou Fm
Upper contact:
The Xin’ertai Fm is in conformable contact by the siltstone of the overlying Kekesaleixi Fm (Koksaleixi Fm) of Middle Ordovician.
Regional extent:
The Xin’ertai Formation is exposed in the west of Middle Tianshan-Beishan Region, distributed at Guozigou of Houcheng County, at Kokirqin of Jinghe County, and in the area of Sayram Lake.
GeoJSON:
Fossils:
This formation yields graptolites, trilobites, brachiopods and conodonts. The lower part of the formation yields trilobite Hysterolenus oblongus, Parabolinella sp., and Niobella sp., and the middle and upper parts yield graptolites Anisograptus, Cardiograptus, Didymograptus, Isograptus, Oncagraptus, Tetragraptus and Triograptus etc. As integrated by Cai (1999), the Xin’ertai Formation embraces eight biozones, including the lowermost trilobite Hysterolenus Zone, which spans the Cambrian-Ordovician boundary, and seven successive Ordovician graptolites, in ascending order, the Adelograptus Zone, the Anisograptus-Triograptus Zone, the Tetragraptus (Etagraptus) approximatus Zone, the Tetragraptus fruticosus Zone, Didymograptus deflexus Zone, Isograptus maximodivergens Zone, and Cardingraptus-Oncograptus upsilon Zone. The lower part of the formation is assigned to the trilobite Hysterolenus Zone (Cai, 1999). The lower part of the biozone is Cambrian in age, and the upper part is correlatable with conodont Cordylodus lindstromi Zone (Zhou et al., 1990), which spans Cambrian-Ordovician boundary (Dong and Zhang, 2017).
Age:
Latest Niuchehean (= latest Cambrian) through Middle Ordovician.
Age span:
Beginning stage: Cambrian Stage 10
Fraction up in beginning stage: 0.8
Beginning date (Ma):
Ending stage: Darriwilian
Fraction up in ending stage: 1.0
Ending date (Ma):
Depositional setting:
The lithology and fauna indicate a restricted and starved basin setting and an anoxic bottom water condition for the formation.
Depositional-pattern:
Additional Information
The Xin'ertai Formation is derived from the Xin'ertai Group proposed by the Comprehensive Group of Stratigraphy of Xinjiang Team of Regional Geological Survey and Institute of Geology, Chinese Academy of Geological Sciences in 1974. Before the symposium on the geology of northern geosyncline, the Comprehensive Group of Stratigraphy of Xinjiang Party of Regional Geological Survey and Institute of Geology, Chinese Academy of Geological Sciences restudied the Xinertai Gr, and divided it into Xin'ertai Fm, Fenggou Fm, Talejihe Fm and Kekesaleixi Fm, in ascending order, a suggestion was followed by Xu Jie (Hsü S.C.) and Huang Zhigao (1979) and Hou Hongfei et al. (1979). In 1978-1979, Xiang Liwen and Zhang Tairong found the Tremadocian trilobites from the limestone in the top of the Upper Cambrian Guozigou Fm, and established the Sailimu Fm. Xiao (1990) suggested that the information for establishing the Sailimu Fm is not sufficient, and abandoned it. Considering the similar lithology of the Fenggou Fm and the Xin'ertai Fm, the present book includes the former in the latter.
Xu and Huang (1979) suggested that the graptolite fauna is mixed because of the possible drifting of the planktonic fauna. Chen Xu remeasured the type section, and collected samples bed by bed. They suggested that the zoning of the graptolite fauna is clear.