Middle Devonian-Tournaisian rocks and biota on Hainan Island, South China

On the basis of new paleontological data, the sequence and distributions of the Middle Devonian-Tournaisian rocks on Hainan Island have been sorted out for the first time. The Devonian rocks include the Middle Devonian Jinbo Formation and the Upper Devonian Changjiang Formation, which are distributed in northwestern Hainan Island. The Jinbo Formation is represented by 631 m of littoral facies deposits, and was intruded by the Yanshanian granite in the base. The presence of chitinozoans Eisenackitina caster, Funsochitina pilosa, and Lagenochitina amottensis indicates the Givetian in age. The Changjiang Formation is made up of 140 m of neritic facies rocks, and contains the Famennian conodonts Palmatolepis gracilis sigmoidalis, Polygnathus germanus, and corals Cystophrentis kalaohoensis. The Devonian-Tournaisian transition beds, the lower part of the Jishi Formation, are composed of 61–129 m sandstone and siltstone, with gastropods Euomphalus spp. and brachiopods, and marked by conglomerate with the underlying Devonian rocks. The middle-upper part of the Tournaisian Jishi Formation consists of 100–251 m clastic and carbonate rocks, containing abundant corals Pseudoularinia irregularis, conodonts Siphonodella isosticha, trilobites Weberiphillipsia linguiformis, and brachiopods. On the basis of the occurrence of Xinanosprifer flabellum and Homotoma sp., the Nanhao Formation in southern Hainan Island is now regarded as the Lower Silurian, instead of the previously designated Lower Carboniferous. It is confirmed that no Carboniferous rocks occurred in the area south to the Gancheng-Wanning Fault.