Dat Do Fm
Type Locality and Naming
Holostratotype = Dat Do Beach, on the western side of Nam Du Island, Gulf of Thailand, Kien Oiling Province (E = 9°41'; E = 104°22'). The formation was first described by Nguyen Huu Hung in the report “Stratigraphy of Phancrozoic in the Southwest Viet Nam Region” (Trinh Dzanh et al. 1988).
Synonym: Hệ tầng Đất Đô'. Nguyễn Hữu Hùng (in Trịnh Dánh ei al. 1998); Tống Duy Thanh, VQ Khúc 2000; Nguyễn Hữụ Hùng, Trần Minh Khang 2001 (Permi muộn). Hệ tầng Nơm Du (part.): Nguyễn Kinh Quốc et al. 1981 (S - D); Vũ Khúc, Bùi Phú Mỹ et al.1 990 (PZ1.2). Hệ tầng Hòn Ngang (part.): Nguyễn Ngọc H oa et al. 1991 (C?). Hệ tầng Hòn Chông (part.): Nguyễn Ngọc Hoa et al. 1996 (D - C1)
Lithology and Thickness
Sandstone and Siltstone: (1). Black-grey, motley, brown-violet-weathering siltstone, 60 m thick. The clastic component is 66%, with quartz - 55-57%, usually in the form of well-rounded small fragments (0.050.08 mm). Fragments of claystone and chert occupy 3-5%; they are well rounded with a size of about 0.1 mm. Apart from these, among the clastic components there are fragments of green tourmaline with high interference. The cement is 40%, mainly clay, together with sericite, and chlorite impregnated with ferric hydroxide. (2). Yellow-brownish, strongly compressed, fine- to medium-grained sandstone alternating with siltstone with a thickness of 10-20 cm. The clastic composition is about 65% with quartz playing the main role with a size range of 0.25-0.35 mm and good roundness. The cement is 5% consisting of sericite, Mid chlorite with some aphanitic chert and carbonate impregnated with dirty-brown ferric oxide. Thickness: 120 m. (3).Yellowish, fine-grained claystone and siltstone, 60 m thick, composed mainly of oriented clay minerals and oriented sericite. Siltstone is composed of small, well-rounded grains of quartz (0.01-0.05 mm), with rare prisms of green tourmaline.
Relationships and Distribution
Lower contact
Relationship with the underlying Ha Tien Fm has not been determined.
Upper contact
The formation has tectonic contact with the Middle Triassic Hong Ngang Fm volcanics. Regionally, next younger unit is the early Triassic Hon Duoc Fm volcanics
Regional extent
Nam Du Fm exposed on Nam Du Island to the sandstone beds containing Devonian flora of the Hon Chong Fm and calcareous shale containing brachiopods and crinoids of the Chua Hang Fm to form the Hon Chong Fm of Devonian - Early Carboniferous age, while the fclsic cffusivcs exposed on Nam Du Island were attributed to the Hon Ngang Fm of Triassic age.
GeoJSON
Fossils
The species of Compressoproductus sp., Neospirifer and Beecheria and the productids are not older than Carboniferous and not younger than Permian. The crinoids Pentagonocyclicus sp., Cyclocydicus sp.; the bivalve Sanguỉnoỉites cf. modiomorphoides and bryozoan Fenestella cf.
Age
Depositional setting
Additional Information