Con Son Fm

Period:

Neogene

Age Interval:

Middle Miocene; N₁², (27)

Province:
Vietnam Offshore south

Type Locality and Naming

Cuu Long Basin. The type section is established within borehole 15B-1X drilled in the Con Son Structure from a depth of 1583 to 2248 m (E = 10°4’; E = 107°58’).

Synonym: Hệ tầng Côn Sơn (part.): Ngô Thường San 1981, 1988; Phan Trung Điền 2000.

Diệp Côn Sơn (part.): Đỗ Bạt 1986, 1993,2000. Hệ íầng Vàm Cỗ (part.): Lê Văn Cự 1992.

Lithology and Thickness

Lower part is formed mainly by grey, white grey, thick-bedded to massive, fine- to coarse-grained sandstone sometimes containing pebble and grit (holes 17-DD, R-4, R-6, Wolf-1 and15-G) with poor to medium sorting and roundness. Sandstone usually contains fragments of foraminifcra and sometimes glauconite and many coal fragments. The sediments are weakly cemented by clay and carbonate. The major part of the sandstone has good porosity and permeability, and possibly contains petroleum-bearing beds of high quality. Upper part gradually changes into fine-grained sandstone interbedded with claystone, carbonate clay, or locally, greenish-grey, chocolate, yellow-brown motley- colored limestone interbeds (holes Wolf-1, 15-G and Dragon-6), coal-bearing clay and lenses or thin beds of black brown coal.

Lithology Pattern:

Sandstone

Relationships and Distribution

Lower contact

Conformably upon the Bach Ho Fm

Upper contact

Unconformably overlain by the Dong Nai Fm

Regional extent

The formation largely occurs in the Cuu Long Basin.

GeoJSON

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Fossils

Dacrydium, Florschuetzia meridionalis, FI. ỉevỉpoỉi, Fi. trilobata, FI. semilobata, Magnastriatites howardi, Acrostichum, Slenochlaena palustris, Carya, Alnipollenites, Triletes, Eugeisonia insignis, Calophyllum, Brownlowia, Ahingia and Polypodiaceiosporites, many dinoflagellates and foraminiferal linings. Nannofossils are rare, with a large stratigraphic range, such as: Calcidiscus marcintyrei, C. leptopus, Thoracosphaera tuberosa, Umbilicosphaera sibogaef oliosa.

Age

Middle Miocene.

Age Span:

Beginning stage:

Langhian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

15.99

Ending stage:

Serravallian

Fraction up in the ending stage:

1.0

Ending date (Ma):

11.63

Depositional setting

It is interpreted as a alluvial - coastal plain through delta (Rhizophora facies) to shallow-marine (Operculina-Lepidocyclina- Myogypsina facies).

Depositional pattern:

Additional Information

Compiler:

Tran Van Tri and Vu Khuc (Editors; Geology and Earth Resources of Viet Nam, General Dept. of Geology and Minerals of Viet Nam; completed in Dec., 2011), with additional details from Tong-Dzuy Thanh and Vu Khuc (Editors; Stratigraphic Units of Viet Nam, 2^nd edition; 2011; English edited by A. Boucot).