Boreskov

PP‐5EDIACARAN SOFT‐BODIED ORGANISMS AND MACROPHYTES:TWO SIDES OF ONE COIN?Bykova N.Trofimuk Institute of Petroleum‐Gas Geology and Geophysics, Novosibirsk, RussiaThere are two fundamentally different types of Proterozoic macrofossil preservation:casts (molds) usually attributed to soft‐bodied organisms and carbonaceous compressionsinterpreted as macrophytes. That some of the casts (molds) of soft‐bodied organisms havemorphological analogues among carbonaceous compressions has long been appreciated(Zhu et al., 2008), but the full scale of this phenomenon is revealed in a Konservat FossilLagerstätte discovered in the Arctic Siberia (Grazhdankin et at., 2008). The Upper VendianKhatyspyt Formation cropping out along the Khorbusuonka River of the Olenek Uplift(northeast of the Siberian Platform) is characterized by two types of macrofossilassemblages: (1) casts and molds of soft‐bodied organisms (about 600 specimens) and (2)carbonaceous compressions of macrophytes (about 250 specimens). The soft‐bodiedorganisms are represented by rangeomorphs and frondomorphs, as well as microbialcolonies, however the frondomorphs and microbial colonies can also be preserved ascarbonaceous compressions, whereas the rangeomorphs are restricted to fossil assemblageswith moldic preservation. Preservation of certain soft‐bodied organisms in a style which istypical for macroscopic algae suggests that at least in frondomorphs their macrophytenature cannot be entirely excluded. This has important implications for interpretation of theAvalon biota of Newfoundland, the oldest fossil assemblage of Ediacaran soft‐bodiedorganisms, which is also represented by frondomorphs and rangeomorphs. The Avalon biotais interpreted as deep‐sea communities that inhabited continental slope below the photiczone (Clapham et al., 2003); however, if frondomorphs are just seaweeds, then the Avalonbiota is irrelevant to understanding the metazoan evolution. In any case, a possibility shouldnot be excluded that casts, molds and carbonaceous compressions could represent differentmodes of preservation of the same organism, not necessarily a metazoan.139