Majiagou Fm
Type Locality and Naming
The type section is at Majiagou in Kaiping 15 km northeast of Tangshan City, Hebei. The Majiagou Fm is derived from the Majiagou Limestone proposed by Sun Yunzhu (Y.C.Sun) and Yang Zhongjian (C.C. Young) in 1922.
The Majiagou Limestone was referred to the Actinoceras-bearing limestone overlying the coral-bearing limestone (present Liangjiashan Fm) and underlying the Carboniferous. Zhang Wentang (1949) divided it into two parts, which was named the Lower Majiagou Fm and Upper Majiagou Fm respectively by Wang Hongzhen in 1953. Wang's suggestion was subsequently followed by Zhang (1962). In 1975, Chen Junyuan named the strata equivalent to the Lower Majiagou Fm in Central Shandong as the Bei'anzhuang Fm, and the strata equivalent to the Upper Majiagou Fm as the Majiagou Fm. The present book follows Chen Junyuan's (1975) suggestion.
Synonym: (马家沟组)
Reference Section:
The reference section is at Hupinao in Cixian, Hebei (Hebei Bureau of Geology and Mineral Resources, 1989).
Lithology and Thickness
The Majiagou Fm is dominated by thick-bedded to massive limestone, leopard limestone, dolomitic limestone intercalated with dolomite, argillaceous limestone, with a base of brecciated dolomitic limestone and dolomite. In the type area, it recorded an incomplete thickness of 274-370 m.
Relationships and Distribution
Lower contact
It can be distinguished from the underlying Bei'anzhuang Fm by the thin-bedded dolomitic limestone and brecciated dolomite at the base. On the basis of the cycle analysis, a possible sedimentation hiatus has occurred during the deposition between the Majiagou Fm and the underlying strata. Therefore, the contacts between the Majiagou Fm and the underlying strata are probably disconformable. In north Anhui region (Ordov column 36), the next older unit is the Sanshanzu Fm of latest Cambrian through mid-Ordovician. In Shanxi and near Beijing (Ordov columns 31 and 35), it overlies the Liangjiashan Fm of late-Early Ordovician.
Upper contact
It can be distinguished from the overlying Fengfeng Fm by the thin-bedded argillaceous limestone and brecciated dolomitic or argillaceous limestone at the base of the Fengfeng Fm. On the basis of the cycle analysis, a possible sedimentation hiatus has occurred during the deposition between the Majiagou Fm and the overlying strata. Therefore, the contacts between the Majiagou Fm and the overlying strata are probably disconformable. In the central exposures, the Majiagou Fm is disconformably overlain by the Fengfeng Fm, but in the northernmost and southernmost exposures, it is disconformably overlain by the Carboniferous (e.g., Hutian Fm).
Regional extent
With a persistent lithology, the Majiagou Fm is widely exposed in Hancheng of Shaanxi and northern Shaanxi (100-200 m thick), most Shanxi (138-558 m thick), Kaiping in Tangshan (274 m thick incompletely) and Pingquan to west ranges in Handan (100-370 m thick) of Hebei, areas north of Xiwo in Xin'an-Xiaotian in Gongxian-Queshan of Henan (70.5-322.3 m thick), southern Jilin (250 m thick), Taizihe (284-558 m thick), Fuzhouwan (399-548 m thick) and western part (200 m thick) of Liaoning, areas east of Jinan-Jining of Shandong (214 m thick incompletely) and Xuhuai district (56-147 m thick).
The Wuyangshan Fm and Tuyu Fm in Shandong (Shandong Bureau of Geology and Mineral Resources, 1991), Cixian Fm in Hebei (Hebei Bureau of Geology and Mineral Resources, 1989), Dazhai Fm in Xuzhou of Jiangsu (Jiangsu and Shanghai Compiling Group for Regional Stratigraphic Scale (1978) and Upper Majiagou Fm in other areas are equivalent to the Majiagou Fm.
GeoJSON
Fossils
On An's et al. (1983, 1990) studies, the Majiagou Fm in North China includes four conodont zones, in ascending order, Plectodina fragilis zone, Acontiodus ? linxiensis-Eoplacognathus suecicus zone, Plectodina onychodonta zone and Aurilobodus serratus zone. Among them, the first one is seen in Tangshan of Hebei, Gongxian and Bo'ai of Henan (Pei et al., 1987). Additionally, cephalopods of Stereoplasmoceras pseudoseptatum assemblage and Tofangoceras paucirannutatum assemblage have been found from the Majiagou Fm. From the conodont, the Majiagou Fm is equivalent to the Pseudamplexograptus confertus zone to the lower part of the Husterograptus teretiusculus zone.
Age
Depositional setting
Additional Information