Tra Tan Fm

Period:

Paleogene

Age Interval:

Middle to Late Oligocene; E₃^2-3, tt (29, 27)

Province:
West Nam Bo, Vietnam Offshore south

Type Locality and Naming

The type section is located established within Hole GK.15A-1V drilled on the Tra Tan Structure at a depth of 2535-3038 m (E = 10°4’; E = 107°58’).

Synonym: Hệ tầng Trà Tảtt: Ngô Thường San 1981, 1993; Lê Văn Cự 1982; Phan Trung Điền 1985; Đỗ Bạt 2000. Điệp Trà Tân (part): Đồ Bạt 1986, 1993.

Lithology and Thickness

White-grcy, fine- to medium-grained sandstone with carbonate cement, grading upwards into brown and black siltstone and claystonc with thin coal seams, locally containing glauconite. These sediments were subjected to late catagcncsis stage alteration. The logging curve is characterized by very high electrical resistance in the lower part, but low in the upper part, as for the gamma line it is the reverse. The total thickness of the formation in this borehole is 503 m.

Lithology Pattern:

Clayey sandstone

Relationships and Distribution

Lower contact

Conformably upon the Tra Cu Fm

Upper contact

Unconformably under the Bach Ho Fm (Cuu Long Basin offshore) or unconformably below the Ben Tre Fm (West Nam Bo).

Regional extent

West Nam Bo, and Cuu Long Basin (offshore).

GeoJSON

null

Fossils

Magnastriatites howardi, Crassoretitriletes nanhaiensis, Potamogeton, Pinuspollenites, Verrucatosporites, Triletes, Tsuga and Florschuetzia trilobata, Onagranaceae with Jussiena, Alnipollenites, Carya, Tricolpites, Cicatricosisporites and Verrutricolporites pachydermus. The formation contains much amorphous organic matter of sapropcl form, which was formed under anoxic lacustrine conditions. This condition was named by Morlcy the “sapropcl facies” when analyzing the boreholes of Lot 15. Besides, there still are fresh-watcr algae, such as Pediastrum and Bosidinia.

Age

Middle-Late Oligocene age has been determined in accordance with the spores and pollen.

Age Span:

Beginning stage:

Rupelian

Fraction up in beginning stage:

0.7

Beginning date (Ma):

29.27

Ending stage:

Chattian

Fraction up in the ending stage:

1.0

Ending date (Ma):

23.04

Depositional setting

It is interpreted as a alluvial, deltaic, marshy-!agoonal to shallow-marine 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).