Heishuihe Fm
Type Locality and Naming
No type section was assigned when the formation was erected. An auxiliary section, the Liuhe section, was proposed by Yang et al. (1991) as representative section of the formation. The section is measured along the rural highway at Liuhejie Town in Liuhe Township, Ziyang County (108°31’ 30” E, 32°18’23” N). The Liuhejie lies about 24 km south of Ziyang Town. The Heishuihe Formation was named by the Third Research Section of the Chinese Academy of Geological Sciences (1963). The name is derived from Heishuihe River in Ziyang County, Ankang City, southern Shaanxi Province.
Synonym: （黑水河组）
Lithology and Thickness
The Heishuihe Formation is a pure carbonate sequence. In the auxiliary section, the formation is 621.6 m thick, and can be roughly divided into three parts: Lower part consists of mainly dark grey limestone breccia, dark grey thin-bedded limestone intercalated with thin-bedded laminated limestone bearing limestone lenses (314.7 m); Middle part consists of mainly thick-bedded muddy dolomitic limestone, thin-bedded laminated limestone with interbeds of limestone breccia (153.2 m); Upper part consists of mainly argillaceous striped limestone, sandy limestone, dolomitic limestone, and interbeds of limestone breccia (153.7 m).
Relationships and Distribution
Lower contact
The formation with thick-bedded limestone breccia at base is conformably rests on the underlying Baguamiao Fm
Upper contact
It is conformably overlain by the Gaoqiao Fm with silty laminated limestone at base, which becomes shaly bedded limestone after weathering.
Regional extent
The Heishuihe Formation is exposed in the Jiangbei Slope Area of South China Region, distributed mainly in southern Shaanxi Province (Yuxihe and Liuhe of Ziyang County; Huangbogou of Langao County; Foyebian, Shuanghe and Maoping of Pingli County, and Wencaigou of Zhenping County). Extending northeastward, the formation increases the muddy and sandy contents, and significantly increases the interbeds of limestone breccia, but decreases its thickness gradually. The formation has maximum thickness at Jiangxijie of Pingli County, about 975 m, becoming 654 m thick at Raoxihe of Ziyang County, and 192 m thick at Taishanmiao of Pingli County.
GeoJSON
Fossils
The lower part, at the level about 50 m above the base of the formation in the auxiliary section, yields trilobites Fenghuangella laochatianensis laochatianensis [=Fenghuangella. cf. F. modesta sensu Yang et al., 1991] and Eoshengia? sp. [=Shengia sp. indet. Sensu Yang et al., 1991].
Age
Depositional setting
Additional Information