Acritarch biostratigraphy of the Lower-Middle Ordovician boundary (Dapingian) at the Global Stratotype Section and Point (GSSP), Huanghuachang, South China

The Lower to Middle Ordovician Dawan Formation has been investigated palynologically at Huanghuachang, South China (Global Stratotype Section and Point of the base of the Dapingian, first Global Stage of the Middle Ordovician Series) with the aim of identifying the biostratigraphical potential of acritarch assemblages for the recognition of the Lower-Middle Ordovician boundary, recently defined by the first appearance of the conodont Baltoniodus? triangularis. For comparison, the nearby Daping section has also been sampled. Based on their first appearances, some of the taxa recorded may be useful for recognition of the Lower-Middle Ordovician boundary in sections where conodonts, graptolites or other fossils are absent. While the genera Barakella and Liliosphaeridium are indicators of the base of the Dapingian, Stelomorpha is a diagnostic genus present in the boundary interval because species of this genus first appear both below and above the GSSP. Other diagnostic taxa useful for long-distance correlation, which include Orthosphaeridium and Dicrodiacrodium, first appear higher in the Dapingian. Several of the stratigraphically significant taxa are typical of the peri-Gondwanan palaeobioprovince, while others also occur outside of the Gondwana palaeocontinent. The acritarch successions recovered from the South China Plate at Huanghuachan2 and Daping can therefore be correlated with sequences known from other peri-Gondwanan areas. In addition, correlations are also possible with other palaeocontinents, in particular with Baltica.