The lower part of the Dawan Formation (lower Arenig) from both the Huanghuachang and the Daping sections (Yangtze Platform, Hubei Province, South China) has yielded rich acritarch assemblages dominated by the "cold water taxa" which are characteristic of the high latitude Perigonwanan (or "Mediterranean") Acritarch Paleoprovince. New findings show that the top of the Dawan Formation (uppermost Arenig) is characterized by a very different scenario. Here, elements of the Perigondwanan microflora are missing, while the phytoplankton communities have typical "Baltic" affinities. This change in the microfossil composition within the Dawan Formation may be attributable to a variety of different constraints, such as a modification in the pattern of oceanic currents (influenced by changing paleogeography) or sea level fluctuations (related to eustatic cycles).

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