Frasnian–Tournaisian (Late Devonian to Earliest Carboniferous) lithostratigraphy and biostratigraphy of Hainan Island, South China

Abstract

Sedimentary successions of the Frasnian–Tournaisian (Late Devonian to Earliest Carboniferous) and their spatial distributions in the Hainan Island, South China are critically reviewed based on updated information of the previously published data and newly obtained fossils. The Upper Devonian strata are assigned to the Frasnian Lanyang Formation and Famennian Changjiang Formation, which are distributed in north‐western Hainan Island. The Lanyang Formation is represented by limestone, siltstone, slate, and intercalated with tuff, and yields tentaculites: Polycylindrites sp., stromatoporoids, and tabulate corals. The Changjiang Formation yields abundant conodonts Palmatolepis gracilis sigmoidalis and Polynodosus germanus, typical of Famennian assemblages, and the associated faunas include corals, radiolarians, foraminifers, and calcareous algae of Famennian age. Of these, corals are assignable to the upper Famennian Cystophrentis Zone of South China. The strata of the Tournaisian Jishi Formation are categorized into two types, typically exposed in the Shilu and Jinbo areas, respectively, both of which are located north to the Gancheng‐Wanning Fault. The lower Jishi Formation yields brachiopods Unispirifer (Unispirifer) extensus, Unispirifer sp., Schuchertella magna, and gastropods. The middle Jishi Formation yields conodonts: Siphonodella isosticha and S. levis, brachiopods: Unispirifer (Unispirifer) forbesi, Atylephorus tornacensis, coral: Pseudouralinia irregularis, trilobite: Weberiphillipsia linguiformis, ostracods, bryozoans, and foraminifers. The conodonts are assignable to the zonation equivalent to the Siphonodella sulcata Zone, implying the Devonian–Carboniferous boundary is placed at the base of the middle part of the formation. The upper part of the Jishi Formation yields abundant brachiopods characterized by Mesochorispira subgrandis, Atylephorus tornacensis, and Marginatia huaqiaoensis. The presence of corals Cystophrentis, Pseudouralinia, Zaphrentites, and Kueichowpora, and trilobite Hunanoproetus, endemic to South China from the Changjiang and Jishi formations implies that the Hainan Island was palaeobiogeographically close to the South China Block of the Tethyan Realm, rather than of Gondwana affinity during the Late Devonian and Tournaisian. Identification of Xinanosprifer flabellum and Homotoma sp., typical of early Silurian from the ‘Nanhao Formation’ previously assigned to the Tournaisian suggests that no Carboniferous strata are distributed in southern Hainan Island and the area south of the Gancheng‐Wanning Fault.