Khao Loc Fm

Lectotratotype: Khao Loc - Pac Xum Section, Quan Ba District, Ha Giang Province (N= 22° 58', E= 104° 54'), selected and proposed by Ta Hoa Phuong and Le Van Giang (1998). Ta' Hoa Phuong and Le Van Giang (1998) proposed a lectostratotype section beginning from the primary school of the Minh Tan Commune, situated 1.5 km northwest of Khao Loc Mt, and extending eastwards to the upper course of the Pac Xum River. The section terminates in a confluence in the upper course of the Pac Xum River.

Synonym: Đá vôi Khao Lộc\ Vasilèvskaia E.D. (ỉ« Dovjikov A.E. et al. 1965) (D₂e-gv); Tong-Dzuy Thanh- 1967 (D₁- D₂e); Tống Duy Thanh 1976 (D₁-D₂). Điệp Mường Chà (part.): Tạ Hoàng Tinh 1971 (Di-D₂e). Điệp Khao Lộc: Hoàng Xuân Tình et al. 1976 (D₁-D₂e); Hệ tầng Khao LỘC'. Tống Duy Thanh et al. 1986, 1988 (D₁-D₂); Ta Hoà Phưomg, Lê Văn Giang 1998 (D₁-D₂), Vũ Khuc et al 2000 (D,-Dj); Khao Loc Fm: Tống Dzuy Thanh 1993 (D₁-Dj), Tong-Dzuy Thanh et al. 1995 (Dr D₂); Tạ Hoà Phương, Baudu-Suire, Lê vãn Giang 1996 (DI -D₂).

This is a unique Devonian formation in Viet Nam, in that it is mainly Limestone with minor claystone that spans the Early Devonian through Givetian of Middle Devonian. The lectostratotype (total thickness in this section reaches 980 m) consists of the following succession. (1). Dark grey, yellow-grey, red-brown weathering marl and clay shale, 15 m thick; containing in abundance vertebrates, such as: Acanthothoraci gen. et sp. indet, Youngolepis cf. precursor belonging to the Polybranchiaspis liaojaoshanensis - Dongfangaspis qujingensis Assemblage. (2). Black-grey limestone interbedded with clayey limestone, 60 m thick; containing in abundance Amphipora sp. indet. and the corals Squameofavosites enormis, Sqf. vanchieni. (3). Black-grey, thin- to medium-bedded limestone interbedded with marl and black clayey chert, 65 m thick. (4). Black, thin- to medium-bedded limestone interbedded with cherty limestone, clayey limestone and marl, 40 m thick. (5). Grey, medium- to thick-bedded limestone, locally with interbeds of cherty limestone or clayey limestone, about 800 m thick; scattered in the member there are many remains of large Amphipora sp. and Favosites polyforata.

[Figure: Khao Lộc Fm: Landscape of fairy breasts (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

Collected the following Vertebrates: Youngolepis praecursor, Polybranchiaspis liaojaoshanensis, Acanthothoraci gen. et sp. indet.. Along the trend of this exposure, about 500 m northeast of it, the following Vertebrates were identified: Minicrania lissa, Laxaspis yulongsus and Heteroyunnanolepis qujingensis (Janvier Ph., Ta Hoa Phuong 1999). And from about 40 m higher than the “fish”-bearing beds marly shale exposed on the road from Tong Vai to Ban Thang village the Brachiopods Howittia wangi and Howellella ex gr. crispa occur.

[Figure: Khao Lộc Fm: Fossils of the fish Polybanchiaspis liaojaoshanensis; Khao Lộc Fm (D1-2 kl), Quản Bạ District, Hà Giang Prov. (Photo Ph. Janvier)]