Phu Cu Fm
Type Locality and Naming
Hanoi Depression and North Song Hong Basin (north Red River Basin). The type section is located borehole GK.2 drilled in Phu Cu Townlet (Hung Yen) at 960 to 1180 m (N = 20°44’; E = 106°12’). It was named by the Phu Cu Fm on the basis of drilling materials from borehole GK.2 (960-1180 m) situated in the Phu Cu Structure of the Ha Noi Depression.
Synonym: Hệ tầng Phù Cừ: Golovenok V.K., Lê Văn Chân 1966; Golovenok V.K., Kisliakov V.N. 1970; Phan Trung ĐiỀn 2000; Trịnh Dánh (ìn Vũ Khúc et al. 2000). Điệp Phù Cừ: Sevostianov K.M. 1977; Trịnh Dánh 1975, 1979, 1995; Phạm Hồng Quế 1981; Lê Văn Cự 1985, 1987; Đỗ Bạt, Phan Huy Quynh 1984, 1986, 1992,2000; TOTAL 1991; IDEMITSU 1994.
Lithology and Thickness
Dominated by clay-silt offshore. It is composed of sandstone, silty sandstone, coal seams and, locally, thin interbeds of carbonate. Sandstone is light to greenish-grey colored, fine- to medium-grained, locally, coarse-grained (borehole GK.104-QN), medium to well-sorted, generally thin-bedded, lentiform, wavy, sometimes of massive structure; it contains siderite concretions, locally, glauconite (boreholes GK.100, 102, 110, 104, 204, 107-PA ). Its cement is rich in carbonate, but poor in clay. Silty sandstone is light to dark grey colored, containing some carbonate, a little plant debris and lignite (borehole GK. 103-TH) and some thin interbeds of carbonate (boreholes GK.103-TH, 107-PA). The thickness of the formation is from 1500 to 2000 m.
Relationships and Distribution
Lower contact
Major unconformity (15.5 Ma unconformity) upon the Phong Chau Fm
Upper contact
Unconformable below the Tien Hung Fm.
Regional extent
Distributed over the whole Ha Noi Depression, having a small thickness in the Dong Quan area, but strongly developed in the Bac Bo Gulf.
GeoJSON
Fossils
Florschuetzia trilobata, FI. levipoli, Fl. semilobata, Tsugapollenites, Acrostichum, Pteris, Pinuspollenites, Dacrydium, Quercidites, Carya, Ilex, Liquidambarx Alnipollenites, Lygodium, Juglans, Magnastriatites howardi belonging to the Tsuga - Fl. semilobata - Alnipollenites - Fl. trilobata Assemblage of Middle Miocene age, accompanied by many dinoflagellates.
Foraminifera from the Phu Cu Fm in Balanus-bearing sandstone include Elphidium, Ammonia, Cibicides, Globorotalia mayerii, Orbulina universa. In silty claystone interbeđđed with sandstone, they consist of benthonic forms, such as Ammonia, Trochammina,. Cýcỉammina, Elphidium and Cloborotalia.
Age
Depositional setting
Deltaic plain to shallow-sea environment.
Additional Information