中国科学院南京地质古生物研究所机构知识库

We report an unusual instance of macrofossil pyritization in the Precambrian: three-dimensionally pyritized internal molds of chuarids from the late Neoproterozoic Lantian formation (similar to 550-600 Ma) in southern Anhui Province, South China. These chuarid internal molds are composed almost entirely of iron oxide pseudomorphs after pyrite framboids (5-20 mum in diameter) and polyhedra (1-2 mum in diameter) pyritization probably occurred near the water-sediment interface during authigenesis. The internal molds are typically enveloped by a diagenetic quartz rim. Furthermore, about half of the Lantian chuarid population display medial split excystment structures, suggesting that the Lantian chuarids are eukaryotic megacysts rather than colonial prokaryotes. Applying a similar megacyst interpretation to other Proterozoic chuarid populations may not be straightforward, largely because of the lack of diagnostic features in most chuarids. Chuarids tin particular those in sole Chuaria assemblages) may therefore represent a polyphyletic group of diverse eukaryotic land perhaps prokaryotic) origins, although the Chuaria-Tawuia association may represent a biologically and biostratigraphically coherent group. (C) 2001 Elsevier Science B.V. All rights reserved.