Bai Dinh Fm
Type Locality and Naming
Vietnam-Laos border in Quang Binh Province. Holostratotype - along the small Cao Ai Stream, Bai Dinh - Y Leng area, situated near the Mu Gia border pass on the Vietnamese-Laotian border (x = I7°45’; y = I05°46’). Pham Huy 'Thong et al. 2000. The stratotype is in the valley of the small Cao Ai Stream, Bai Dinh - Y Leng area, situated on the right side of the Road Ne 9.
Synonym: - Hệ tầng Bãi Dinh'. Phạm Huy Thông el al. 2000. - Creta không phân chia-. Mareichev A.M. 1965 (in Dovjikov A.E. ei aỉ. ¡965); Vũ Khúc 1977 (in Trần Văn Trị et ul. 1977). - Hệ tầng Mụ Giạ (part.): Trần Đức Lương, Nguyễn Xuân Bao el al. 1988; Vũ Khúc, Lê Thị Nghinh 1996; Vũ Khúc et aỉ. 2000.
Lithology and Thickness
Marine sediments with Jurassic fauna in its upper part grading upwards into continental red beds. The stratotype sequence (350-430 m thick) is: (1). Calcareous conglomerate grading upwards into grey, dark grey calcareous siltstone, sandstone with some interbeds of greenish-grey argillaceous limestone, 80 m thick. Conglomerate pebbles consist mainly of limestone, poorly rounded, one to several centimeters in size; cement of calcareous sandstone; some limestone pebbles yield Late Paleozoic foraminifera. (2). Light violet-grey siltstone, quartz sandstone interbedded with thin-bedded grey limestone, oolitic limestone and some black-grey argillaceous shale, 180-200 m thick. (3). Chocolate-colored, violet-grey siltstone, some brownish sandstone, 100-150 m thick; siltstone contains fresh-water bivalves, such as Nakamuranaia sp., and Peregrinoconcha sp., and palynomorphs Conioptens aff. divaricata, Davallia aspera, Lycopodium subrotundum, Laevigatosporites sp., and Protoquercus sp. of Jurassic age.
Relationships and Distribution
Lower contact
Unconformable on Upper Paleozoic limestone (Cam Lo Fm) in the type locality. Regionally, the next older unit is the Dong Trau Fm volcanics of late Anisian age.
Upper contact
Under the Upper Jurassic-Lower Cretaceous Mu Gia Fm in this area.
Regional extent
The Bai Dinh Formation is limited to the Vietnamese-Laotian border area, which includes the eastern margin of the large Mesozoic Nam Theun Depression in Middle Laos. In the distribution area of the Cretaceous Mu Gia Fm. This was the first finding of Lower Jurassic marine sediments north of the 17th parallel.
GeoJSON
Fossils
From above described tripartite section, grey calcareous sediments of the lower and middle parts (1 and 2) clearly belong to the marine facies. Regrettably, no fossils occur in these members, but similar beds on the other side of the Viethamese-Laotian border yield marine bivalves belonging to the genera Pleuromya, Cuspidaria and Coniomya, often met with in the Lower Jurassic of the region.
Age
Depositional setting
Marine Lower Jurassic grading upwards into Middle Jurassic continental red beds.
Additional Information