Arenigian acritarchs from the Daping section (Yangtze Gorges area, Hubei Province, Southern China) and their palaeogeographic significance
详细信息 查看全文
文摘
A rich acritarch assemblage (called HD2) from the Arenigian Dawan Formation of the Daping section (Yangtze Gorges area, Hubei Province, Southern China) is described. The new data supplied by the study of this assemblage support the previous opinion that the Upper Yangtze Region should be included within the Mediterranean (Peri-Gondwana) acritarch Paleoprovince. But, compared with this scenario, the picture resulting from the above data seems to be more complicated. Actually, the HD2 assemblages have a mixed composition, even if they show a prevalent Mediterranean character. Some Australian and Baltic affinities were also observed. The extension of the Mediterranean acritarch biofacies up to the Yangtze Platform during Arenigian times is attributed to a cool periantarctic (that is peri-Gondwana) oceanic current first flowing along the subpolar margin of Gondwana and after rising northwards up to South China. The proposed scenario implies that the above mentioned peri-Gondwana current branched northwest of Southern China, giving also origin to a progressively warmer current, then descending up to Baltica. The palaeobiogeographical implications of this oceanic current pattern are discussed. Nine new species are described: Baltisphaeridium fragile, Ordovicium yangtzeense, Peteinosphaeridium armatum, P. exornatum, P. robustiramosum, P. tenuifilosum, Pirea baculifera, P. levigata, and Striatotheca rugosa. Six previously described species are revised: Ampullula? erchunensis (Fang Xiaosi, 1986) Tongiorgi, Yin and Di Milia, comb. nov., emend., Barakella rara (Lu Li-chang, 1987) Tongiorgi, Yin and Di Milia, comb. nov., emend., Costatilobus? rhabdocladius (Lu Li-chang, 1987) Tongiorgi, Yin and Di Milia, comb. nov., emend., Costatilobus? striatum (Lu Li-chang, 1987) Tongiorgi, Yin and Di Milia, comb. nov., emend., Rhopaliophora mamilliformis Lu Li-chang, 1987, emend., and Veryhachium symmetricum Lu Li-chang, 1987, emend.