New materials on the Nặm Mặn Formation, Mường Tè area
Bùi Phú Mỹ, Đoàn Nhật Trưởng,
Nguyễn Đình Hữu,
Nguyễn Văn Hoành, Nguyễn Văn Lồng
The Nặm Mặn Formation (T3c-n nm) was established in 2001 by authors of the Geological and Mineral Map of the Mường Tè map sheet group at 1:50.000 scale . According to these geologists, this Formation is composed of conglomerate, gritstone, sandstone, shale, marl and limestone, 150-200 m thick. It rests unconformably upon granite of the Pu Si Lung Comphex (γC1 pl) and under the Suối Bàng Formation (T3n-r sb). Sediments of the Nặm Mặn Formation contains Carnian and Norian bivalves and Middle-Late Triassic foramiferas and hexacorals. On the other hand, the Formation was correlated to the Pác Ma Fm with the remark that the Nặm Mặn is younger.
In March-April of this year, the authors of this article carried out the field survey of the study of Formation stratotype. Two fossil collections were obtained. Corals have been yielding the Late Carnian age, while bivalves – Norian. The formation is composed of terrigenous and carbonate sediments. It is the lowest part of the Suối Bàng Formation.
Người biên tập: Vũ Khúc