Phong Chau Fm

Period:

Paleogene, Neogene

Age Interval:

Chattian-Burdigalian; N₁, (12, 13)

Province:
Vietnam Offshore North

Type Locality and Naming

Hanoi Depression and North Song Hong Basin (north Red River Basin). The type section is located borehole GK. 110 drilled in the Phong Chau Commune area, Dong Hung Disữict (Thai Binh) from 1820 to 3000 m (N = 20“35’; E = 106°14’). It was named by Palustovitch B. and Nguyen Ngoc Cu.

Synonym: Hệ tầng Phong Châu: Palustovitch B., Nguyễn Ngọc Cư 1972; Trịnh Dánh 1985, 1989, 1993, (in Vũ Khúc vànnk. 2000); Phan Trung Điền 2000. Điệp Phang Châu: Sevostianov K.M. 1977; Skorduli V.D. 1982; Lê Văn Cự 1987; Phan Huy Quynh 1984; Đỗ Bạt’ Phan Huy Quynh 1986, 1993, 2000; TOTAL 1991; IDEMITSU 1994

Lithology and Thickness

Upper (Burdigalian) is dominated by Shale; Lower (Chattian-Aquitanian is dominated by Siltstone). The continuous intercalation of light grey to greenish-grey, well cemented, fine-grained sandstone and very thin-bedded (some mm to cm) silty sandstone of ocular, lentiform structure, named as “striped beds”. The sandstone cement consists mainly of carbonatc (25%). Accessory minerals comprise much glauconite and pyrite. The thickness of the formation ill this borehole reaches 1180 m. It is composed of interbedded sandstone, silty sandstone and claystone bearing coal traces or thin interbeds of limestone (boreholes GK.103-TH, 1Ơ3-HOL). The sandstone is grey to dark grey colored, fine- to medium-grained, locally coarse-grained, with medium to well sorted grains and carbonate cement. The claystone is light to dark grey and light chocolate colored, parallel- to wavy-bedded, and composed mainly of kaolinite and illite. The thickness of the formation changes from 400 to 1400 m.

Lithology Pattern:

Siltstone

Relationships and Distribution

Lower contact

Unconformable upon the Dinh Cao Fm and older sediments.

Upper contact

Unconformably (15.5 Ma unconformity) below the Phu Cu Fm

Regional extent

The Phong Chau Fm is distributed mainly in the Khoai Chau - Tien Hai Band (borehole GK.I00) and, possibly, in the Bac Bo Gulf (borehole GK.103-TH).

GeoJSON

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Fossils

Betulapollenites, Pỉnuspolỉenites, Quercidites, Selaginella, Pteris, Acrostichum, Alnipollenites, Tsugapolleniies, Polypodiacaeiosporites, Florschuetzia levipoli that allow to recognize the Betula-Alnipollenites Assemblage and the Florschuetzia levipoli Zone of Early Miocene age.

Age

Lower siltstone-rich is 26-21 Ma = Chattian-Aquitanian. Upper clay-rich is 21-15.5 Ma (Burdigalian)

Age Span:

Beginning stage:

Chattian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

27.29

Ending stage:

Burdigalian

Fraction up in the ending stage:

1.0

Ending date (Ma):

15.99

Depositional setting

Upper is a shallow-sea facies, capped by a Sequence-boundary major reflector (15.5 unconformity). Lowre is also shallow-sea facies.

Depositional pattern:

Additional Information

Compiler:

Discussion notes from Prof. Tran Nghi (2019); 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).