New discovery on grit- and pebble-bearing cherty shale in the lower part
 of the Thiên Nhẫn Formation in the Hà Tĩnh Province

Dương Văn Huấn

The Thiên Nhẫn Formation, distributed mainly on the territory of Hà Tĩnh Province, was established by Dovzhikov et al. [2] and dated as Early-Middle Triassic. Its main composition consists of cherty shale interbedded with chert-clay shale, fine-grained polymictic sandstone, siltstone and clay shale, with usually thin seams of manganese hydroxide of from tens cm to tens m in thickness. Recently, radiolarian fossils were found in cherty shale beds, allowing geologists to date the Thiên Nhẫn Formation as Late Devonian [3]. Lately, polymictic grits and pebbles lying in abundance in the lower part of the formation were discovered with a thickness of 400-600 m. This is a new discovery, but it still is not enough studied for clarifying the forming setting of the Thiên Nhẫn Formation and the geological history of the North Trung Bộ region during Devonian.

Người biên tập: Vũ Khúc