Ban Nguon Fm

Period:

Devonian

Age Interval:

Early Devonian, D₁bn, (9, 11)

Province:
West Bac Bo

Type Locality and Naming

Upstream course of the Song Mua River, in the section lying 1-2 km upstream from Ban Nguon Village.

Synonym: Điệp Bàn Nguồn: Nguyễn Xuân Bao et al 1969 (D₂ẹ); Phan Cự Tiển et al. 1977 (D₁), Dương Xuân Háo et al. 1980 (D₂e), Tống Duy Thanh et al. 1968, 1988 (D₁). Séríe de Ban Cai: Dcprat J. 1914 (Dinantien); Dussault L. 1929 (D₃-C₁); Saurin E. 1956 (Dinanticn). Sẻrìe de Ban Thoc'. Dussault L. 1929 (Dj-C₁), Saurin E. 1856 (C₁t). Eifeiian (part.): Dussault L. 1929; Sau rin E. 1956; Dovjikov A.E. et al. 1965; Dương Xuân Hào et al. 1968, 1973, (tầng Mia Lé); 1975; Nguyễn Vĩnh 1977 (Các írậm tích Eifcli)

Lithology and Thickness

Claystone and Sandstone: Stratotype (total of 380 m): (1). Grey, medium- to thick-bedded quartz-rich sandstone interbedded with black-grey clay-bearing sandstone and black clayey shale containing micro-bands of sandstone, 120 m thick. (2). Black clayey shale and sand-bearing siltstone interbedded with sandstone and quartz-rich sandstone; locally sandstone beds have a thickness of about 25 m. Thickness: 160 m. (3). Quartz-rich sandstone and clay-bearing sandstone interbedded with black clayey shale, 50 m thick; shale intcrbeds yield Euryspirifer tonkinensis and Posidonia sp.. (4). Calcareous-clayey, locally sand-bearing siltstone, 50 m thick.

Lithology Pattern:

Sandy claystone

Relationships and Distribution

Lower contact

Conformable upon the Song Mua Fm.

Upper contact

Conformable under the Ban Pap Gr.

Regional extent

Based on the sections exposed in the Ban Nguon, Nga Hai, Ban Thoc and Hoa Binh - Tu Ly areas in the lower course of the Song Da River and in a narrow band extending from Mo Tom to Ban Ngui on the right side of the Song Da River. [Note: coeval Ta Khoa Fm is in parts of the lower (SE) Son La Province portion of the same area.]

GeoJSON

null

Fossils

Favosites ex gr. goldfussi, F. aff. alpina, F. cf. gregalis, F. sp., Gephuropora aff. vietnamica, Squameofavosites aff. kolymensis, Sqf. attenuatus, Sqf. sp., Emmonsia aff. crassa, Pachyfavosites aff. bystrowi, P. cf. vilvaensis, P. sp., Thamnopora sp., Striatopora sp., Parastriatopora sp., Cladopora sp., Yacutiopora suoinhoensis, Roemeripora sp., Caliapora macroporosa, C. aff. crassimuralis, C. sp., Coenites cf. vermicularis, C. sp., Natalophyllum sp., Heliolites aff. vulgaris, H. aff. barrandei, Chaetetipora sp. and stromatoporoids, auloporids.

[Figure: Bản Nguồn Fm: Brachiopod fossil (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

Age

Early Devonian according to the fossils. [Assigned ages to conformable overlying and underlying formations constrain it as middle Early Devonian.]

Age Span:

Beginning stage:

Lochkovian

Fraction up in beginning stage:

0.5

Beginning date (Ma):

415.70

Ending stage:

Lochkovian

Fraction up in the ending stage:

1.0

Ending date (Ma):

412.40

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).