Khon Lang Fm

Period:

Triassic

Age Interval:

Anisian, T₂a, (4, 5)

Province:
East Bac Bo

Type Locality and Naming

The type section is located from Lung Khoang through Khon Lang to Cuom Duoi villages, Van Quan District, Lang Son Province (N = 21°50’; E = 106°33’). It was named by the Khon Lang, in accordance with the stratotypic area name.

Synonym: Điệp Khôn Làng: Đặng Trần Huyên, Nguyễn Kinh Quổc (in Nguyễn Kinh Quốc et al. 1991); Vũ Khúc (Hệtầng: in Vũ Khúc et al. 2000). Rkyolite: Bourret R. 1922 (Trias); Patte E. 1927 (Virglori-Cami). Hệ Jura không phân chìa: Jamoida A.I., Phạm Văn Quang (in Dovjikov A.E. et al. 1965). Tầng Ryolit Tam Đảo: Nguyễn Nghiêm Minh 1968 (Trias trung - thượng). Diệp Na sảm (part.): Phạm Đình Long 1975. Hệ tầng Lũng Trâu: Trịnh Thọ (in Vũ Khúc, Trịnh Thọ 1975); VQ Khúc 1990. Diệp Sông Hiến (part.): Phạm Đình Long 1975; Nguyễn Kinh Quốc (in Vũ Khúc, Bùi Phú Mỹ c. 1990). Bậc Anisi: Phạm Đức Lưưiig ((in Trần Vỉín Trị et al 1977); Vũ Khúc, Trinh Thọ (in Dương Xuân Hảo et al.. 1980). Hệ tầng Tam Lang: Nguyễn Công Lư ợng (in VQ Khức, Bùi Phú Mỹ et al. 1990) (Jura thượng - Creta hạ). Hệ lang Tam Đào: Ngô Quang Toàn (Jura thượng- Creta hạ) Hệ tầng Bình Liêu: Trần Thanh Tuyền et al. 1992; Vũ Khúc, Đặng Trần Huycn 1995. Hệ tầng Pò Hèn: Trần Thanh Tuyền 2001. Hệ tầng Tiên Y én: Trần Thanh Tuyền 2001.

Lithology and Thickness

Sandstone and Volcanics: The Lung Khoang - Cuom Duoi section is composed of 3 members: (1). Conglomerate, gritstone, medium-grained sandstone with lenses of grey marl and interbeds of thin-bedded clayey shale, 3-5 m thick. (2). Greyish, thick-bedded porphyritic rhyolite, rhyodacite and dacite interbedded with lenses of tuff, volcanic agglomerate, and 250-300 m thick. (3). Dark grey tuffaceous silty sandstone interbedded with black-grey, yellowish-grey, thin- bedded (4-9 cm) siltstone and clayey shale, 25-30 m thick.

Lithology Pattern:

Lava

Relationships and Distribution

Lower contact

Unconformably on Upper Permian limestone of the Dong Dang Fm or Lower Triassic shale of the Lang Son Fm.

Upper contact

In Au Chao Basin, it conformably underlies black limestone of the Diem He Fm in the Lang Son area, and the Na Khuat Fm - in Binh Lieu and Tam Dao areas. Regionally in Lang Son region, the next younger unit is the upper-Lower Triasic Bac Thuy Fm. Regionally in Quang Ninh area, the next younger unit is the Norian Hon Gai Fm.

Regional extent

Quang Ninh Basin – the pre-Norian sediments are restrictively distributed alng a fault in the northern margin of the basin (BinhLieu – Tien Yen areas; and form the Tam Dao Range in the NW of Hanoi City); and their assignment as "Khon Lang Fm" is based on their correlation to exposures in the adjacent Au Chau Basin. In that Au Chau Basin, the Khon Lang Fm is exposed largely in the Bho Bai – Khon Lang areas of Lang Son Province.

GeoJSON

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Fossils

Bivalves of Neoschizodus laevigatus, Costatoria praenapengensis, C. sp., Hoernesia chobaiensis, Unionites sp.. Costatoria praenapengensis, Plagiostoma sp., Entolium sp., Palaeonucula sp..

Age

Anisian, based on the fossils. Overlain by the Diem He Fm of Late Anisian in northern Au Chao Basin constrains age of Khon Lang Fm in that area? Prof. Dan Tran Huyen (May, 2019) indicated that the volcanism of Vietnam is mainly late Anisian; with Early Anisian being mainly a gap (used here).

Age Span:

Beginning stage:

Anisian

Fraction up in beginning stage:

0.3

Beginning date (Ma):

245.13

Ending stage:

Anisian

Fraction up in the ending stage:

0.8

Ending date (Ma):

242.51

Depositional setting

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).