Ban Hang Fm
Type Locality and Naming
An Chau and Song Hien basins. The type section is located that section along the Ky Cung River at Ban Hang Village, Dinh Lap District, Lang Son Province (N = 21°38’, E = 107°08’). Nguyen Cong Luong 2000 . It was named by that Cretaceous continental red beds were first described with clear distinction from Jurassic red beds in the work “Geology of North Viet Nam” (1965) based on the observation of the cuesta form of topography in the Dinh Lap area of Cretaceous red beds lying unconformably upon older Mesozoic formations..
Synonym: Hệ tầng Bản Hang Nguyễn Công Lượng (in Vũ Khúc el al.) 2000. Hệ Creía: Jamoida A.I., Phạm Văn Quang (in Dovjikov A.E. el al.) 1965; Vũ Khúc (in Trần Văn Trj el al.) 1977. Hệ tầng Mụ Giạ (part.): Trằn Đức Lương, Nguyễn Xuân Bao el al.1988.
Lithology and Thickness
Ban Ang to Ban Hang Villages section is about 600 m of: (1). Conglomerate, gritstone with intcrbcds of chocolate, thick-bedded polymictic sandstone that grade upwards to red-brown, violetish-grey clayey siltstone interbeddedwith red-brown sandy siltstone containing lime concretions, 200 m thick. (2). Red-brown siltstone with some interbeds of clayey and sandy siltstone, 400 m thick; with fresh-water bivalves.
In the Bac Quang area: 1. Thick-bcddcd (1-2 m) polymictic conglomerate interbedded with gritstone, calcareous gritstone, 170 m thick. Conglomerate pebbles are poorly- to medium-rounded of quartz, quartzite, granite and limestone; the cement is violet-brown silty claystone. 2. Gritstone with interbeds of violet-brown sandstone, 80 m thick. 3. Violet-brown, thick-bedded (0.4 - 0.5 m) polymictic sandstone, 50 m thick. 4. Gritstone with interbeds of brownish sandstone, 90 m thick. 5. Chocolate siltstone and silty claystone, calcareous silty sandstone with lenses of gritstone, 120-160 m thick. The total thickness of the formation in this section reaches about 500-550 m.
Relationships and Distribution
Lower contact
Unconformably upon the Early-Middle Jurassic Ha Coi red continental formation, that has been observed along the Dinh Lap - An Chau car road, 1 km from Dinh Lap, as well as in the Gia Bay Bridge area, in Thai Nguyen City; as in the Yen Binh Commune area - upon the Middle Triassic Yen Binh Fm. Or unconformable on Triassic formations
Upper contact
Next younger regional unit are the Cao Bang Fm conglomerates within fault-produced troughs of Eocene age.
Regional extent
The Ban Hang Fm is distributed mainly in the An Chau Synclinorium, in the Ban Hang, Tien Phi, Ban Tan, Dinh Lap, Khon Quan and Khau Sam Chom areas. In addition, there are some small exposures around Thai Nguyen City, as in Nui Phao Mt, along the Song Cau River from Son Cam to the Iron and Steel Combine, and some small areas in Yen Binh Commune, Tuyen Quang which have been preliminarily attributed to this formation
GeoJSON
Fossils
Cyotrigonioides aff. C. longus. In former field studies no fossils have been found in the Ban Hang Fm. Recently Nguyen Xuan Khien el al. have collected a fresh- to brackish- water bivalve determined by Dang Tran Huyen as Cyotrigonioides aff. C. longus of Early Cretaceous age in these red beds in the Po Hang, Dinh Lap area.
Age
Depositional setting
Additional Information