Đặc điểm cổ sinh thái và phân bố cảu hóa thạch răng nón, vỏ nón trogn các trầm tích D3-C1 ở một số vùng thuộc bắc bộ.

Abstract

In Bac Bo region the Da-Cj sediments, containing pelagic fossil groups Conodonts
and Tentaculites, belong to deep facies type and are mainly of calcareous, silicic and
terrigen-silicic composition. Based upon the features of sediments and their distribution,
one can find that they mainly were formed in the deep and narrow troughs, which are
possibly of tectonic origin and located in the carbonate platform areas. Among them the
next typical rock types can be distinguished: 1) Lens- and nodul-shaped, grey or
multicoloured, griotte clayey limestones (the Toe Tat Formation in the Ha Lang, Dong Van
areas; the Suoi Nho Formation in the Northwestern of Bac Bo 2) Striped limestones (the
uppermost part of the Trang Kenh Formation in the Kinh Mon area). 3) Cherts and shales
(the Bang Ca Formation in the Ha Lang area, the Phuc Son Formation in the Ham Rong
area); 4) Medium- to thin-bedded limestones, clayey limestones, siliceous limestones (the
uppermost part of the Si Phai Formation in the Dong Van area, the lowemost part of the
Pho Han Formation in the Cat Ba isle; 5) Thin-bedded or banded black limestones, siliceous
limestones (the intermediate part of Pho Han Formation in the Cat Ba isle.