Van Huong Fm

Upper formation of the Do Son Gr. Stratotype in the Ba Vi Mt in the Van Huong Ward area, on the western side of the Do Son Peninsula. Previous hypostratotype for "Do Son Fm" (previous name) was situated on the southwestern side of the Do Son Peninsula, extending from the southwestern slope of Do Son Mt through Hoa Chat Hotel to the Van Huong Harbour.

Synonym: Uppermost part of former Do Son Fm (now elevated to Do Son Gr). - Grès de Do-son (part.): Lantenois H. 1907; Saurin E. 1956 (D), 1958 (D₁). - Bậc Eifel (part.): Jamoida A.I. (in Dovjikov A.E. et al. 1965; 1972). - Hệ tầng Kiến An (part.): Nguyễn Quang Hạp 1967 (S₂). - Điệp Sóng Cầu (part.): Trần Văn Trị, Nguyễn Đình Uy 1975, 1977 (Dt). - Hệ tầng Đồ Sơn (part.): Nguyễn Công Lượhg et al. 1980 (D₁); Tống Duy Thanh et al. 1986; Vũ Khúc, Bùi Phú Mỹ et al. 1990 (D₁); Ngô Quang Toàn 1994 (D₃-C₁); Tống Duy Thanh (in Vũ Khúc et al. 2000) (D); Nguyễn Hữu Hùng et al. 2004 (D₁-D₂gv); Tống Duy Thanh, Tạ Hoà Phương 2005 (D₂gv-?Djfr); Nguyễn Hữu Hùng, Tạ Hòa Phương, Nguyễn Thị Thủy 2007 (D₂gv). - Do Son Fm (part.): Tong-Dzuy Thanh et al. 1988 (part. D₁); Long J. et al. 1990 (D₂gv-D₃); Tong-Dzuy Thanh, Janvier Ph. eì ai 1992 (D₂gv-D₃fr); Jfanvier Ph. et al. 2003 (S₂?-D₃).

On Do Son Peninsula, it is 70 m of medium- to thick-bedded gritstone, usually cross-bedded quartzitic sandstone. Former Do Son Fm hypostratotype description: (1). Conglomerate and gritstone interbedded with light-colored, cross-bedded sandstone. Pebble composition consists mainly of opaque-white quartz, pinkish quartz-rich sandstone, black chert, greenish-grcy siltstone; diameter of pebbles reaches 1-2 cm; their roundness is good. Cement consists mainly of light-colored quartz-rich sandstone. This member unconformably covers the member of black, brown-violet weathering, clay shale of the Van Canh Fm. Thickness: 10 m. (2). Opaque-white, thick-bedded quartz-rich sandstone. These beds have a sloping attitude, with average dip of 10“, plunging south-southwestwards. In the exposure located on the southwestern slope of Do Son Mt many imprints of flora belonging to the Lepidodendropsis group as well as spores have been collected. Towards the southeast direction, this sandstone member extends to Van Huong Harbour, just to the seawater surfacc. This is also the well-known exposure yielding many lepidodendrids. Farther in the southeast, 100 m west of the foot of “Bao Dai Villa” Hill, J. Long et al. (1990) and Janvier Ph. et al. (1998) collected remains of fishes of D₂gv-D₃ age. The total thickness of the Fm in this section reaches ~75 m.

Fish fossils of Givetian - Bothriolepis-Vietnamaspis, and Lepidodendropsis.

[Figure: Vạn Hương Fm: Plant fossils (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

Lithological, geochemical and paleontological analysis show that sediments of the Do Son Fm were formed in fluvial and deltaic environment