Devonian fish (Placodermi, Antiarcha) from Tra Ban Island (Bai Tu Long Bay, Quang Ninh Province, Vietnam) and the question of the age of the Dô Son Formation

Abstract

Remains of an Asterolepis-like antiarchan placoderm fish are reported from the top part of the sandstone series of the Tra Ban Island (Quang Ninh Province, Vietnam), which are referred to the Dô Son Formation. This sandstone series is overlain by the well-dated Late Givetian–Frasnian Trang Kenh Formation, which constrains the top part of the Dô Son Formation to the Middle Devonian, and most probably the Givetian, as suggested by the presence of a large Asterolepis-like antiarch. This would agree with the fish and plant assemblage previously recorded from the upper part of the Dô Son Formation at Dô Son. The question of the age of the base of the Dô Son Formation is raised by the discovery of Late Silurian or Early Lochkovian plant, arthropod and fish remains at Dô Son. The Dô Son Formation now appears to be composed of two members, Late Silurian (or Early Lochkovian) and Givetian in age, respectively. Recent field observations suggest that the two members are separated by an unconformity. The meaning of the Devonian terrigenous deposits in the eastern part of Vietnam and south China is briefly discussed.