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The oldest flora of the South China Block, and the stratigraphic bearings of the plant remains from the Ngoc Vung Series, northern Vietnam |
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| Authors: | Paul Gonez Hung Nguyên HuuPhuong Ta Hoa Gaël ClémentPhilippe Janvier |
| Institution: | a Palaeobiogeology, Palaeobotany, Palaeopalynology, Department of Geology (B18), University of Liège, allée du 6 aout, Sart Tilman, 4000 Liège 1, Belgium b Vietnam National Museum of Nature, 18 Hoang Quoc Viet Str., Hanoi, Viet Nam c Vietnam National University, Department of Geology, 334 Nguyên Trai Street, Thanh Xuan, Hanoi, Viet Nam d Muséum National d’Histoire Naturelle, UMR-CNRS 7207 CR2P, Bâtiment de Paléontologie, CP 38, 47 rue Cuvier 75231 Paris cedex 05, France |
| Abstract: | Several outcrops of the Late Silurian and Devonian of the Ngoc Vung Series, northern Vietnam, yielded plant remains. The Late Silurian localities delivered the earliest known flora of the South China block. Although the fossils are fragmentary, they complement our knowledge about the global composition of the flora. The major components of the flora are plants with dichotomous habit and terminal bivalvate sporangia, which are close relatives to zosterophylls, and zosterophylls. Plants with possible euphyllophyte affinities and bryophytes are occasionally present. This floral composition is similar to that of the rich, younger South China block assemblages from the Posongchong and Xujiachong Formations of China, considered Pragian in age. The South China block flora is therefore likely to have been dominated by zosterophylls and pre-zosterophylls at least from the Late Silurian to the Pragian (i.e. a 20 million years long period). It also strengthens the hypothesis that more derived plants were present on eastern Gondwana earlier that elsewhere, in the first steps of tracheophyte evolution. The Devonian localities of the Ngoc Vung Series delivered a thick fibrous stem fragment and a basal euphyllophyte. These latter plant remains provide some stratigraphic data. The large stem fragment is consistent with an Eifelian age for the Duong Dong Formation (part of the Ngoc Vung Series), as suggested by the brachiopod fauna. The accompanying basal euphyllophyte displays a combination of characters (axes 3-4 mm wide and lateral branchings) that is also consistent with an Eifelian age, but possibly more characteristic of the Emsian flora. It is therefore suggested that the stratigraphic range of the Duong Dong Formation might be extended down to the Emsian. |
| Keywords: | Early land plants Zosterophylls Late Silurian Basal euphyllophyte Early Devonian Phytogeography Vietnam |
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