Mang Yang Fm
Type Locality and Naming
The type section is located Mang Yang Pass on Highway N21.4, Gia Lai Province (N= 13°58’; E= 108°47’). It was named by Nguyen Kinh Quoc 1985.
Synonym: ỉlệ tầng Mang Giang: Nguyễn Kinh Quốc 1985 OV 2); Vũ Khúc et al. 1986; Vũ Khúc 1990, {I Vũ Khúc et al. 2000). - Hệ tầng Mang Yang: Trần Tính et al. 1998. - Hệ táng Măng Giang ịparí.y, Nguyền Kinh Quốc (in Vũ Khúc, Bùi Phú Mỹ et al. 1990). - Rhyoỉiie: Lacroix A. 1937; Saurin E. 1956. - Hệ tằng Chư Klin: Nguyền Kinh Quốc 1985.
Lithology and Thickness
Felsic volcano-sedimentary beds, mainly formed in a marine setting. Conglomerate, Sandstone and Volcanics. Mang Yang Pass section: (1). Polymictic gritstone, sandstone interbedded with dark grey clayey shale and siltstone, 80 m thick; containing palynomorphs Dictyophyllidicites sp., Peltoidespora sp., Monoculcites sp., Lophotriletes sp.. (2). Quartz conglomerate, gritstone and sandstone, grey to greenish-grey calcareous siltstone, 310 m thick, containing poorly preserved plant remains. (3). Medium- to fine-grained sandstone, grey to violet-grey calcareous siltstone, 300 m thick; calcareous siltstone yields the marine bivalves Palaeoneilo yanjiensis and Neoschizodus sp. of Anisian age and plant remains (Rhodea sp.). (4). Quartz-cherty conglomerate and gritstone, coarse- to medium-grained sandstone, violet-grey siltstone, 680 m thick; siltstone yields Calamites sp. (5). Sandstone containing volcanic clasts, quartz sandstone, grey to dark grey siltstone, 275 m thick. (6). Porphyritic rhyolite, tuffaceous sandstone interbedded with grey to greenish-grey siltstone, 180 m thick. The total thickness of the formation in this section reaches 1825 m.
Relationships and Distribution
Lower contact
Unconformably upon the various older formations. In the Mang Yang area where its basal conglomerate unconformably lies upon Archean crystalline schists of the Kail Nack Gr; in the Chu Klin area - upon Upper Paleozoic andesite of the Dak Lin Fm; while in the Cu Mong Pass area the formation is penetrated and homfelsed by biotite granite of the Van Canh Complex having an isotopic age of 210 ±1 Ma (Late Triassic). Regionally, the Chu Prong Fm of Late Permian is the next older unit (according to the stratigraphic columns in Tran Van Tri and Vu Khuc (2011).
Upper contact
Disconformable upper contact to overlying formations: Bin Som Fm in Middle Trung Bo region, Dray Linh in northern South Trung Bo region
Regional extent
The Mang Yang Fm occurs in the coastal area of Central Trung Bo from the valley of the Song Bung River and the lower course of the A Vuong River in the west of Quang Nam Province through the areas of Cu Mong Pass, Mang Yang Pass and An Khe Pass to the north of the Ninh Hoa area. Besides, there still are scattered exposures of the formation on the Tay Nguyen Highland, from the Plci Breng area on the Victnamese-Laotian border to the Chu Klin area of the Buon Don District, Dak Lak Province.
GeoJSON
Fossils
Trigonodus tonkinensis, T. trapezoidalis, T. keuperinus, T.zhamoidai, Hoernesia magnissima, Costatoria gold/ussi, C. ngeanensis, C. aff. proharpa), Langsonella cf. minima), Aviculopecten sp., Entolium sp
Age
Depositional setting
Additional Information