A newly discovered Ediacaran biota containing Arkarua-like fossils from the Irkineeva Uplift, East Siberia

Liu A.G. ¹, Brasier M.D. ², Bogolepova O.K. ³, Raevskaya E.G. ⁴, Gubanov A.P. ³

¹Department of Earth Sciences, University of Cambridge, Cambridge, U.K.,; ²Department of Earth Sciences, University of Oxford, Oxford, U.K.; ³ CASP, Cambridge, U.K.,; ⁴ Geologorazvedka, St. Petersburg, Russia

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Macroscopic fossils from the new Ediacaran Period include some of the most enigmatic organisms known [1], including intriguing forms such as Arkarua adami Gehling 1987, once tentatively regarded as an echinoderm ancestor [2]. We here report a wholly new fossil assemblage of this aspect from the Irkineeva Uplift, East Siberia, Russia, together with additional biological impressions from within nearby Riphean units.

Reconnaissance in the shallow marine to alluvial successions of the Taseeva Series reveals specimens here attributed to Arkarua adami, as well as Beltanelliformis minutae McIlroy et al. 2005 [3] (of either prokaryote or protistan affinity), and an impression that we compare with the more typically Phanerozoic ichnofossil Bergaueria cf. perata Prantl 1945 [4]. These specimens are found within the Aleshino and Moshakov formations, alongside various microbial mat fabrics, and the microbially-induced sedimentary structure ‘Arumberia’ [5]. If accepted, this assemblage would prove consistent with a Late Ediacaran age for the Taseeva Series; significantly younger than previously thought.

Further specimens have been discovered within the Sukhoy Pit Series, formerly considered to be of Middle Riphean (Mesoproterozoic) age [6]. Alongside an assemblage of simple leiosphaerid acritarchs occurs a collection of large (>50 mm) discoidal markings, here assigned to the taxon Nimbia occlusa Fedonkin 1980 [7]. Given their position in the stratigraphy, and previous lithostratigraphic correlations, it seems likely that the units in which they occur are of pre-Ediacaran age. Acritarch assemblages thus far obtained from the sequence are, unfortunately, insufficient to accurately constrain their age further. Variation in the ellipticity of these Nimbia impressions is consistent with their formation by microbial (e.g. prokaryote) growth [8], and we make no claim for their metazoan origin.

The new finds from the Irkineeva Uplift add to the already diverse array of Russian Ediacaran material, and they provide fresh insights into the biology and taphonomy of the Ediacaran biota. Further exploration of the Irkineeva region is planned, which will hopefully aid attempts to correlate Meso- and Neoproterozoic successions across the Siberian Platform.

Fig. The Riphean Kartochka Formation, Irkineeva River, East Siberia, Russia

References:

1.Fedonkin, M. A., Gehling, J. G., Grey, K., Narbonne, G. M. and Vickers-Rich, P. 2007. The Rise of Animals: Evolution and Diversification of the Kingdom Animalia. John Hopkins University Press, Baltimore 326 pp.

2.Gehling, J. G. 1987. Earliest known echinoderm - a new Ediacaran fossil from the Pound Subgroup of South Australia. Alcheringa, 11, 337-345.

3.McIlroy, D., Crimes, T. P. and Pauley, J. C. 2005. Fossils and matgrounds from the Neoproterozoic Longmyndian Supergroup, Shropshire, U.K. Geological Magazine, 142, 441-455.

4.Prantl, F. 1945. Two new problematic trails from the Ordovician of Bohemia. Academie tchèque des sciences, Bulletin International, Classe des sciences mathematiques et naturalles et de la medicine, 46, 49-59.

5.Callow, R. H. T., McIlroy, D. and Brasier, M. D. 2011. John Salter and the Ediacara Fauna of the Longmyndian Supergroup. Ichnos, 18, 176-187.

6.Mel’Nikov, N. V., Yakshin, M. S. et al. 2005. Summary. In N. V. Mel'nikov (ed). Stratigraphy of Oil and Gas Basins in Siberia. Book 1: Riphean and Vendian of Siberian Platform and its plaited border. Novosibirsk Academic Publishing House Geo, Novosibirsk, 324-393 pp.

7.Fedonkin, M. A. 1980. [New Precambrian Coelenterata from the North of the Russian Platform]. Paleontologicheskij Zhurnal, 1980 (2), 7-15. [In Russian]

8.Grazhdankin, D. and Gerdes, G. 2007. Ediacaran microbial colonies. Lethaia 40, 201-210.

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