Hon Duoc Fm

Gulf of Thailand.. Holostratotype - on the eastern and southern sides of the Hon Duoc Islet (N = 10°18'; E = 104°20'). The fonnation bears the name of an islet of the Hai Tac Archipelago, Kien Giang Province, lying in the Gulf of Thailand.

Synonym: - Hệ tầng Hòn Đước: B.i Minh T.m, Đặng Trần Huy.n (in Trinh D.nh et al. 1997 - Trias sớm); Trương C.ng Đượng et at. 1997 (Permi muộn - Trias sớm); Vũ Kh.c (<>1 Vũ Kh.c et al. 2000 - Trias sớm). - Hệ iầng Nam Du (part.): Nguyễn Kinh Quốc (in Vũ Kh.c, B.i Ph. Mỹ et al. 1990 - PZ1.2). - Hệ tầng Hòn Ngang (part.): Nguyễn Ngọc Hoa e! aỉ. 1995 (Trias sớm); Nguyễn Xu.n Đao et ai, 1994,2000 (Anisi).

Volcanics and Chert: The stratotype is composed of thin-bànded cherty shale of different colours: white-pinkish, white-grey and black-grey exposed near the eastern and southern edges of the islet. North-south the Hon Duoc Formation changes from andesito-dacite to rhyolite in the composition of the volcanics. These rocks are usually accompanied by sedimentary chert, possibly corresponding to a deep-water facies. The hypostratotype is: (1). Dark green to black-grey, massive or poorly-bedded andesite-dacite and dacite-andcsite occurring mainly in the southeast of the islet; thickness: approximately 250 m. (2). Tuffs, mainly andesito-dacitic tuff, with some rhyolitic and rhyodacitic tuffs. They are usually red-brown, brown-violet to dark violet coloured, thick-bedded (50-60 cm). Thickness: approximately 300 m. The total thickness of the formation in this section reaches about 550 m.

No fossils have been found in the Hon Duoc Formation.

In a given level one can correlate the Hon Duoc Fm with the Lower Triassic Song Hien Fm in East Bac Bo, which is a volcano-sedimentary formation having a composition from mafic to felsic, interbedded with terrigenous sediments containing Early Triassic faunas