Geo&Bio (Dec 2020)
Diversity of the Vendian fossils of Podillia (Western Ukraine)
Abstract
Diversity ofVendian fossil associations is a common feature. The diversity depends on many factors: firstly, physical conditions in the basin, in which animals lived (i.e. depth of the sea, its oxygenation state, temperature, salinity, hard or soft bottom, wave activity, and currents); secondly, biological conditions (members of the association, nutrition, bioturbation, presence of enemies, laws of evolution, etc.). Fossils represent remains of different soft-body animals (with radial, bilateral, and triradial symmetry) as well as algae, microfossils, bacteria and fungi. Bacteria (cyanobacteria) and micro-algae formed mats, which served as food resource for animals. Only some of the animals had special organs for eating bacterial mats. The eating tracks were discovered in the White Sea and Australian Ediacaran sections. Facies changes determined the sequence of fossil associations. The lithological succession reflects changing water depth and oxygenation conditions. Different conditions favored different fossil associations (communities). Fifteen species of imprints and animal tracks are described. The diversity of imprints, tracks, and sedimentary rocks is illustrated on photos. In previous articles, new species of vendobionts from the Vendian of Ukraine were described and imaged. More than two thousand samples are stored in the Geological Department of the National Museum of Natural History NAS of Ukraine. The samples need more detailed study including statistic treatment and description. There are some species, which are similar with those from the Ediacaran of Russia and Ediacaran species from the ancient sea basins (paleobasins) of others continents (Gondwana and Laurasia), but there are dozens of species, which are different. Among the reasons of the differences, in our opinion, are paleogeographical controls, which were linked with climate and in accordance with facies distribution. The Cryogenian (Snowball Earth) period (720–635 millions of years ago) was followed by Ediacaran (635–542 millions of years ago). Predominantly carbonate sedimentary rocks (limestones and dolostones) are typical for the Ediacaran successions of East Siberia and some regions of China. The carbonate accumulations are associated with warm or even tropical climates. The almost entire absence of carbonate sedimentary rocks in the Ediacaran sequence of Podillia is a possible testimony of temperate climate, which established after glaciations of the Cryogenian age in Baltica. The food resource for the Ediacaran animal communities were likely bacterial mats and plankton. Attention should be paid to animal remains and bacterial mats found in a large quarry on the left bank of the Dniester River near Novodniestrovsk, which has potential for discoveries of new species of Ediacaran animals.
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