Bien Dong Fm
Type Locality and Naming
Southern offshore plus southern Song Hong Basin. Bien Dong = Vietnamese name "East Sea" for the South China Sea. The name Bien Dong has been given to this formation based on the correlation of Pliocene sediments in the whole continental shelf of the Bien Dong with those described by Le Van Cu (1982) from the Cuu Long and Nam Con Son Depressions as Bien Dong "Suite". Holostratotype: borehole GK.15-IX drilled in the Cuu Long Basin, at a depth of 250 to 650 m (10°25', 108°21).
Synonym: Hệ tàng Biền Đông: Lẽ Văn Cự 1982; Đỗ Bạt 1985, 1993, 2000. Hệ iầng Cừu Long (part.): Ngô Thường San 1982. Diệp Hiến Dông: Lê Vãn Cự 1982. Hệ lầníỊ mến Dóng: Lc Đỉnh Thám 1992, 1994,1998; Sladen C., Hoang Ngoe Dang (BP) 1995, 1977; Phan Trung Điền 2000; Trịnh Dánh {ỉn Vũ Khúc ei al. 2000). - Pliocene: Lamcrs E. (Shell) 1992; Do Bat 1993. - Bac Bo Group (part): Morris J. 1993.
Lithology and Thickness
In its stratotype the formation is composed mainly of grey clay, silt, some light grey soft marl and grey, loose, fine- to medium-grained, medium-sorted, medium- to well-rounded, mainly quartz sand, bearing small limestone bodies. Claystone and sand components of the formation contain abundant foraminifera, molluscs, bryozoans, etc. The thickness of the formation in this borehole reaches 325 m.
In the Nam Con Son Basin, the characteristic section of the Fm is about 1300 m thick (in the depth of 600-1900 m), including mainly grey, yellowish sand, silt and clay containing forams, mollusks, bryozoans, etc. In uplifted areas situated to the east of the basin, reef carbonate rocks are rather continuously developed.
In the Malay – Tho Chu Basin, the Bien Dong Fm is widely distributed and has a relative stable thickness in the depth of about 400-600 m. Its characteristic sediments consist of grey clay and silt, interbedded with loose, mainly fine-grained sand, containing many marine fossils as in the Nam Con Son Basin.
Relationships and Distribution
Lower contact
Unconformably upon the Quang Ngai Fm (south Song Hong Basin), upon the Nam Con Son Fm (Nam Con Son Basin), Dong Nai Fm (Cuu Long Basin) or Minh Hai Fm (Malay Basin).
Upper contact
Quaternary (no details)
Regional extent
Malay Basin (Tho Chu Basin), Cuu Long basin, Nam Con Son Basin, south Song Hong Basin [See Additional Information]. The Bien Dong Formation covers completely the whole southern part of the Red River Basin. In general, the scction of the formation in different areas does not differ from the stratotype section, reflecting a similar developmental stage of deposition in this region.
GeoJSON
Fossils
Palynomorphs collected in the formation include: Florschuetzia meridionalis, Fl. Levipoli (without Fl. trilobata - index species of the Pliocene Florschuetzia meridionalis Assemblage,), Dacrydium, Carya, Dipterocarpidites, Stenochlaena, Chenopodium, Rhizophora, abundant Pinus and Pteris, belonging to the Dacrydium - Florschuetzia meridionalis Zone. There still are many dinoflagellates. Foraminifcra include abundant remains of Pseudorotalia, Asterorotalia, in addition there still arc Ammonia, Quinqueloculina, Operculina, Lenticulina, Eponides, Elphidium, Nonion, Globigerinoides trilobus, Gl. ruber (N18-N23), Gl. obliquus (N17-N21), Globorotalia margaritae (N18-N20) belonging to the Pliocene N18-N20 Zones. In many places test linings of foraminifcra have been found. Nannoplankton comprise Ceratolithus rugosus, Cyclococcolithus formosus, Discoaster argutus, Discoaster broweri, Calcidiscus macintyrei, Reticulofenestra pseudoumbilica belonging to the Pliocene NN12-NN15 Zones.
Age
Depositional setting
The depositional environment of the Bicn Dong Formation in this area belongs to from shallow- to deep-marine facies related to the development of the continental shelf of the Bicn Dong (East Viet Nam Sea or South China Sea).
Additional Information
GeoJSON:
Fossils:
Palynomorphs collected in the formation include: Florschuetzia meridionalis, Fl. Levipoli (without Fl. trilobata - index species of the Pliocene Florschuetzia meridionalis Assemblage,), Dacrydium, Carya, Dipterocarpidites, Stenochlaena, Chenopodium, Rhizophora, abundant Pinus and Pteris, belonging to the Dacrydium - Florschuetzia meridionalis Zone. There still are many dinoflagellates. Foraminifcra include abundant remains of Pseudorotalia, Asterorotalia, in addition there still arc Ammonia, Quinqueloculina, Operculina, Lenticulina, Eponides, Elphidium, Nonion, Globigerinoides trilobus, Gl. ruber (N18-N23), Gl. obliquus (N17-N21), Globorotalia margaritae (N18-N20) belonging to the Pliocene N18-N20 Zones. In many places test linings of foraminifcra have been found. Nannoplankton comprise Ceratolithus rugosus, Cyclococcolithus formosus, Discoaster argutus, Discoaster broweri, Calcidiscus macintyrei, Reticulofenestra pseudoumbilica belonging to the Pliocene NN12-NN15 Zones.
Age:
The Bien Dong Fm has been referred to the Pliocene on the basis of its fossil assemblages, and because it rests unconformably upon the Dong Ngai Fm.
Age span:
Beginning stage: Zanclean
Fraction up in beginning stage: 0.0
Beginning date (Ma):
Ending stage: Piacenzian
Fraction up in ending stage: 1.0
Ending date (Ma):
Depositional setting:
The depositional environment of the Bicn Dong Formation in this area belongs to from shallow- to deep-marine facies related to the development of the continental shelf of the Bicn Dong (East Viet Nam Sea or South China Sea).
Depositional-pattern:
Additional Information
The scismic profiles of this formation are easy to correlate with those in the north (Bac Bo Gulf) and in the south (Phu Khanh, Cuu Long and Nam Con Son Basins). They are composed of beds of parallel or nearly parallel and horizontal reflections, of great amplitude, good continuity related to open shallow- to deep-marine clay and silt sediments. At the base of this member an eroded truncation surface and the onlap attitude have been clearly seen, related to the unconformity between the Bien Dong Fm and Quang Ngai Fm.