Ha Giang Fm
Type Locality and Naming
Vi Xuyen section, Ha Giang Province (N = 22°49’; E = 104°57’). Tran Van Tri et al. 1977.
Synonym: - Lame de Ha Giang: Bouret R. 1922 et al. (Devonian). Hệ tầng Hà Giang-. Trần Văn Trị. 1977 (Middle Cambrian); Phạm Kim Ngân 1980,1986, (Middle Cambrian); Vũ Khúc, Bùi Phú Mỹ et al. 1990 (Cambrian); Nguyễn Đình cần el «/. 1994 (Middle Cambrian); Lương Hồng Hược et al 1994 (Middle Cambrian); Lê Văn Giang et al. 1997 (Middle Cambrian); Hoàng Thải Sơn et al 1998 (Middle Cambrian); Hoàng Quang Chi et al 2000 (Middle Cambrian); Tống Duy Thanh in Vũ Khúc et al 2000; Hoàng Xuân Tình et al. 1976 (Hệ tầng - Middle Cambrian). Série de Coc Pat Deprat J. 1915 (Cambrian). Schistes lustrés: Bourret R. 1922; Hệ tầng Pha Long (part): Dovjikov A.E. et al. 1965 (Lower Cambrian); Hệ tầng Nà Hang (part): Dovjikov A.E. et al. 1965 (Proterozoic); Hệ tầng Chạm Chu: Dinli Thế Tân et al. 1987 (Middle Cambrian).
Lithology and Thickness
Claystone (metamorphosed to Schist and Phyllite) with interbeds of Limestone. The total thickness of the formation in the Vi Xuyen section reaches about 2,100 m (ranges from 500 m in Luc Yen area to 2500 m in Bac Ha, Lao Cai areas). The lithological composition of the formation is as follows (in ascending order): (1). Quartz-biotite schist containing garnet, staurolite, sericite-chlorite schist containing carbonaceous material, lenses of marble limestone, about 600 m thick. (2). Grey brecciated limestone interbedded with sericite schist, 100 m thick. (3). Sericite schist containing carbonaceous material ("shungite"), phyllite (metamorphosed claystone), limestone, 400 m thick. (4). Algae-bearing oolitic limestone interbedded with calcareous phyllite, 400 m thick. (5). Clay-sericite schist interbedded with silty shale and limestone lenses, 300 m thick. (6). Claystone, calcareous siltstone interbedded with fine-grained limestone, oolitic limestone containing abundant trilobites and inarticulate brachiopods, 500 m thick.
Relationships and Distribution
Lower contact
The lower boundary of the Ha Giang was not characterized. "Pseuo-conformity" onto the An Phu Fm of the Song Chay Gr (latest Neoproterozoic-early Cambrian)
Upper contact
The Ha Giang Fm conformably underlies the Upper Cambrian Chang Pung Fm,
Regional extent
Exposed in the Vi Xuyen and Bac Quang areas (Ha Giang Province), Luc Yen (Yen Bai Province), Bac Ha and Murong Khurong (Lao Cai Province). In the Lang Quang - Bac Xao area the presence of quartz-amphibole-feldspar schist has been observed by many authors.
GeoJSON
Fossils
Trilobites, brachiopods and algae. In the Bac Ha area (Lao Cai Prov.), Trilobites of Middle Cambrian have been found, such as Yohoaspis cf. pachycephala, Ptychoparia sp., Palaeobolus sp.; plus Brachiopods of Lingulella tangshiensis, Palaeobolus sp., and Westonia sp.
Other fossils (fron entry in Tong-Dzuy Thanh and Vu Kuc (Eds., 2011) include Archaeohystrichosphaeridium aff. acanthaceum, Favososphaeridium sp., Zonosphaeridium sp., Leiosphaeridia sp., Nucellosphaeridium sp., Orygmatosphaeridium sp. etc.
Age
Depositional setting
The terrigenous - carbonate sediments containing trilobites, brachiopods, and algae show that the Ha Giang Fm was formed in a shallow-marine basin, which was joined with the South China region in the Early Paleozoic.
Additional Information