SUMMARY

New fiding of radiolarians and graptolites in Son La, West Bac Bo

Trần Văn Trị, Nguyễn Văn Can, Nguyễn Cẩm,
Nguyễn Văn Hoành, Bùi Công Hóa

The band of banded chert extending in the NW-SE direction along road from Sơn La to Sông Mã, in the section lying between Bản Có and Nà Viễn villages, does not belong to any existed formation exposed this area. Therefore, it is described as a new stratigraphic unit, “Bản Có Formation” in this paper. The stratotyppe includes 3 members as follows: 1) Marlaceous shale interbedded with gray clayish-cherty shale and shale, > 180 m thick; 2) Gray, dark-gray, thin-bedded, banded chert, containing the radiolarians Albaillella pardoxa? Deflandre Albaillella sp. and spherical algae(?), ≈ 120 m thick; 3) Gray calcaro-cherty shale interbedded with dark-gray clayish-cherty shale, > 160 m thick. The above radiolarian fossils were determined by Prof. Wu Haoruo, Institute of Geology and Geophysics, Chinese Academy of Sciences, giving the Early Carboniferous age, possibly Tournaisian.

Apart from this, in the Kết Hay area the graptolites Demirastrites triangulatus (Harkness) and Diplograptus cf. modestus (Lapworth) have been collected. They allow to affirm the Early Silurian age of the Kết Hay Formation.

Ngày nhận bài : 17-01-2005
Người biên tập: Vũ Khúc