Xinji Fm
Type Locality and Naming
The type section of the Xinji Formation is Xinji section, measured by the Henan Regional Survey Team in 1982. The section lies 2.5 km northwest of Xinji Village, the seat of Xinji Township, Lushan, Pindingshan, central Henan Province (112°59’02”E, 33°48’23”N). In the type section, the formation is 14.85 m thick. The Xinji Formation was named by Henan Regional Geological Survey Team (1964). The name is derived from Xinji Village, Lushan County, northwest of Pindingshan City, central Henan Province. Originally the formation was erected as Xinji Phosphoric Formation for the basal part referred previously to the Chushatung Formation in a 1962 manuscript by the Henan Institute of Geology. It was renamed Xinji Formation by the Henan Regional Geological Survey Team (1964).
Synonym: （辛集组）
Lithology and Thickness
The Xinji Formation is a phosphoric clastic sequence. In the type section, the formation comprises three lithologic beds, from bottom up: (1) greyish green, thick-bedded, glauconitic quartz-sandstone with a phosphate-rich breccia of 10 cm thick (0.25 m thick); (2) dark grey, phosphoric fine-grained sandstone with hummocky cross bedding (2.00 m); and (3) purplish red sandstone with rich ripple marks on bedding surface (12.60 m).
Relationships and Distribution
Lower contact
The Xinji Fm rests disconformably on either the Ediacaran Dongpo Fm in western Henan and eastern Shaanxi provinces or the Ediacaran Luoquan Fm in the Zhongtiaoshan Mountain, southwestern Shanxi Province. The Xinji Fm is occasionally in disconformable contact on the Mesoproterozoic formation in central Shanxi Province (to the north and east of Shuiyu and Shuiyou). The underlying Dongpo Fm is probably Ediacaran in age.
Upper contact
The Xinji Fm is overlain conformably by the Chushatung Fm everywhere in Henan, Shaanxi and Shanxi provinces, with its lower boundary defined by the appearance of limestone at the base of overlying Chushatung Fm.
Regional extent
The Xinji Formation is mainly exposed in the Shanxi-Henan-Shaanxi and the Xuzhou-Huibei areas of North China Region, distributed in western and west-central Henan Province (Lingbao, Lushan, Fangcheng, and Yexian counties), southeastern Henan Province (Queshan and Gushi counties); southwestern and eastern Shaanxi Province (Longxian, Qishan, Qianyan, and Luonan counties and northern Shangzhou District of Shangluo City), in southwestern Shanxi Province (Ruicheng County and Yongji City), central Shanxi Province (Shuiyu, and Shuiyou villages) and in the northern Ningxia Hui Autonomous Region (Helan County). The thickness varies significantly, ranging from 4.5 m to 80 m.
GeoJSON
Fossils
The type section yields no fossils but in western Longxian County, western Shaanxi, the middle and upper parts of the formation contain trilobites Estaingia zhoujiaquensis, E, shaanxiensis, and Longxianaspis latilimbatus. Trilobite Estaingia is also reported from the formation in south-central Henan, where it is associated with small shelly fossils including hyolithid Parakorilithes mammilatus; monoplacophorans Anabarella drepanaida, and Mellopesma rostratum, M. brevicosta, Bemella costa, and Yochelcionella chinensis; gastropods Pelagiellu adunca, and Xinjispira simplex; bivalve Pojetaia runnegari etc. In addition, the formation in western Henan fields also trilobite Bergeroniellus sp. (He et al., 1984). In Jinshan Village, Helan County, the Ningxia Hui Autonomous Region (Helan County), the basal part of the formation yields trilobite Bergeroniellus.
Age
Depositional setting
Additional Information