Depositional environments of the Ediacaran succession in the Zimnie Gory, White Sea region: new insights into the habitat of the Ediacara biota

The Ediacara biota (580-542 Ma) marks the first global appearance of large architecturally complex organisms in the palaeontological record. Zimnie Gory in the White Sea region is one of the major localities of the Ediacara... [ view full abstract ]

The Ediacara biota (580-542 Ma) marks the first global appearance of large architecturally complex organisms in the palaeontological record. Zimnie Gory in the White Sea region is one of the major localities of the Ediacara biota in the world. Previously the depositional environments of the Ediacaran siliciclastic succession in the Zimnie Gory have been interpreted as estuarine and marine prodelta settings. However, new observations from the outcrops, coupled with laboratory research, revealed numerous features which do not fit this model, and rather suggest that the deposits containing the Ediacaran impressions were formed on a tidal flat.
The fossil-bearing beds in the Zimnie Gory recorded evidence for bidirectional palaeocurrent pattern (bimodal-bipolar direction of cross bedding, herringbone cross bedding and reactivation surfaces), alternating bedload and suspension sedimentation (lenticular, wavy and flaser bedding, high content of clay pellets, flat pebbles and chips and numerous clay drapes within sandstones) and subaerial exposure (rill marks, mini-ripples and flat-topped ripples, polygonal pattern of mat-like surfaces and possible mud cracks). Channel forms often have terraced walls and are filled with flaser-bedded sandstones with numerous layers of flat clay pebbles and chips. Apart from the tidal deposits, the Zimnie Gory section has subtidal and shallow-water deposits formed above the wavebase and between storm- and fairweather wavebase, which do not contain any Ediacarans.
In view of numerous evidence of in situ preservation of the Ediacara biota and traces of their activity found in the same layers, these results mean that the Ediacarans in the Zimnie Gory lived on a tidal flat. This widens our image of the habitat of the Ediacara biota and affects our knowledge on the lifestyle, behaviour, taxonomy and ecology of these organisms.