Boreskov

PP‐52EARLY PROTEROZOIC BIOMORPHIC STRUCTURES IN SIBERIAAND PROBLEMS IN SEARCHING EXTRATERRESTRIAL LIFEKolesnikov A.V.Novosibirsk State University, Novosibirsk, RussiaMicrotectonically deformed metacrysts in the Lower Proterozoic Butun Formation of theUdokan Group (Transbaikalia, Siberia) are remarkably biomorphic in their appearance.Hollow column, or sheath‐like metacrysts, in particular if there are less resistant secondaryminerals in the core, often weather out as tubular structures. Metasomatic mono‐ andpolymineral fridges in the weathered out metacrysts are often misinterpreted as externalwalls. Microtectonic deformation transforms abutting metacrysts and druses of metacrystsinto variously curved and branching objects, whereas the deformed metacrysts themselveshave rounded faces and cylindrical shapes. Prolonged metamorphism leads to fragmentationof the metacrysts by transversal microcracks that become filled with secondary mineralresembling septa and monoseriate arrangement of tubular structures. Growth‐relatedcorrugated morphology of the metacrysts can be taken for growth‐lines of tubular objects.Petrographic and SEM study of metacrysts from the Butun Formation confirmed thepresence of two types of biomorphic structures. (1) Metacrystalline aggregates of lawsonite(occurs at low‐T, medium to high‐P conditions) and associated secondary minerals havecolumnar shape and square cross‐section, sometimes with rounded corners as a result ofmicrotectonic deformation. Lawsonite. These aggregates were described as metazoan fossilsUdokania problematica. (2) Metacrystalline aggregates of olivine (high‐T and high‐P) andaccessory minerals heavily deformed by microtectonics. These aggregates were described asmetazoan fossils Udokania leitesi. Despite the mineralogy and relying solely on the shape,Udokania is currently regarded as the oldest metazoan fossils. These biomorphic structurespose problems in terms of pattern recognition: in brief, when do shapes become significant?The example with Udokania is especially relevant for atrobiology because just such imagesmight be returned from the unmanned vehicular exploration of other planets. It is worthrecalling therefore that in the future exobiologists may be faced with a similar set ofconundrums that even today face us with certain terrestrial fossils. This study was supportedby the RAS Program “Biosphere origin and evolution”.225