Lan Pang Fm

Song Hein Basin. The type section is located along the Lan Pang Stream, near Lan Pang Village situated near Highway No.lA, 5 km NW of the Bac Son Townlet, Bac Son District, Lang Son Province (N = 21°54’; E = 106°18’).

Synonym: Diệp Lân Pảng: Nguyễn Kinh Quổc, Đặng Trần Huycn (in Nguyễn Kinh Quốc, Đặng Trần Huyên 1991), Vũ Khúc (in Vũ Khúc et al. 2000 --Hệ tầng).

Clayey Limestone: (1). Light grey quartz gritstone, quartz sandstone bearing some feldspar grading upwards into dark grey, thin-bedded clayey shale with some interbeds of marl, about 50 m thick. (2). Thin-bedded clayey limestone, dark grey, thin-bedded (some to 12 cm) clayey shale and marl interbedded with grey tuffaceous sandstone, tuifaccous gritstone, 40 m thick. (3). Black-grey to light grey, medium- to thick-bedded limestone, 80 m thick. (4). Grey, thin-bedded marly shale, interbedded grey marl and clayey shale, about 50 m thick. The total thickness of the formation in this section reaches 220 m.

In the Ban Chuc - Coc Lao area, the Lan Pang Fm occupies the tops of high mounts, and also rests unconformably upon clayey shale of the Song Hien Fm. The section includes 2 members. 1. Quartz conglomerate and gritstone, medium-bedded polymictic sandstone grading upwards to silty clayey shale and marly shale, about 30 m thick. 2. Grey to black-grcy, thick-bedded limestone, about 90 m thick. The total thickness of the formation in this section reaches about 120 m.

Ammodiscus cf. semicontractus, Earlandia mesozoica, Glomospira sp., Glomospirella sp.. ; Glomospira sp., Nodosaria sp.. Leiophyllites sp., Phyllocladiscites sp. or Sturia sp., Norites sp. and bivalves Pleuromya cf. musculoides.