Pyritized chuarids with excystment structures from the late NeoproterozoicLantian formation in Anhui, South China

We report an unusual instance of macrofossil pyritization in the Precambria n: three-dimensionally pyritized internal molds of chuarids from the late N eoproterozoic Lantian formation (similar to 550-600 Ma) in southern Anhui P rovince, South China. These chuarid internal molds are composed almost enti rely of iron oxide pseudomorphs after pyrite framboids (5-20 mum in diamete r) and polyhedra (1-2 mum in diameter) pyritization probably occurred near the water-sediment interface during authigenesis. The internal molds are ty pically enveloped by a diagenetic quartz rim. Furthermore, about half of th e Lantian chuarid population display medial split excystment structures, su ggesting that the Lantian chuarids are eukaryotic megacysts rather than col onial prokaryotes. Applying a similar megacyst interpretation to other Prot erozoic chuarid populations may not be straightforward, largely because of the lack of diagnostic features in most chuarids. Chuarids tin particular t hose in sole Chuaria assemblages) may therefore represent a polyphyletic gr oup of diverse eukaryotic land perhaps prokaryotic) origins, although the C huaria-Tawuia association may represent a biologically and biostratigraphic ally coherent group. (C) 2001 Elsevier Science B.V. All rights reserved.