TWO TYPES OF PRESERVATION IN THE KHATYSPYT LAGERSTÄTTE, THE OLENEK UPLIFT, THE SIBERIAN PLATFORM

The Ediacaran Khatyspyt Formation of the Siberian Platform preserves a Lagerstätte characterized by soft-bodied organisms, including macroalgae. Three fossiliferous intervals have been recovered: two of them with Ediacara-like organisms and one with macroalgal fossils.

The Ediacara-like assemblage shares some elements with the Avalon biota from Newfoundland. It consists mostly of two groups: Frondomorpha and Rangeomorpha. Some of these organisms are epibenthic and known to have holdfast-like anchoring structures. They are preserved as a result of authigenic carbonate cementation in intervals of finely laminated nodular limestones. This taphonomic window (Khatyspyt-type) is a taxonomically poor.

From the other hand the Khatypyst Formation also contains a taxonomically rich assemblage of carbonaceous compression fossils, most of which represent macroalgal fossils. This Miaohe-type taphonomic window includes 9 informal morphological groups of 10 in which carbonaceous compression fossils can be categorized. This assemblage is preserved in silicified finely to medium laminated carbonate rocks.

Nevertheless that some of fossils (such as Ediacaria, Charniodiscus, Mawsonites) are found in both above-mentioned types of preservation in the Khatyspyt Formation, usually every type of preservation is characterized by distinct fossils. So we can see that preservation was selective. However, the presence some of organisms in both assemblages is leading to the fact, that during the Khatyspyt time Ediacara-like organisms and macroalgae lived together and were parts of one biota. But the reason for such selective preservation is hidden in different types of organism’s tissues. Due to preservation of organic matter of marcoalgae, it is detected that they had decomposers on their surface such as different types of bacteria and even some trichomes. But the early silicification of carbonate material was a reason for their preservation, which had effect as mummification. The Ediaraca-like organisms also had an early cementation but induced by decaying, not by silica. Macroalgae usually fully decayed before preservation in such condition. Vice versa the Ediacara-like organisms were not preserved in silicified cement because silica limited the required cycle of elements.