THE POSSIBLE MESOPROTEROZOIC OXYGEN OASIS OF THE ARCTIC SIBERIA

Mesoproterozoic Era extends for the most of the “boring billion”, the interval of the Earth’s history characterized by tectonic stability, climatic stasis, stable carbon isotope curve, and slow tempo of biological evolution. The oceans of this time are predominantly reconstructed as euxinic (oxygen and nutrient-depleted). However, the more diligent geochemical investigations of this time interval resulted in a more nuanced picture of the world ocean, which included oxygen oases. Here, we present the results of a new geochemical investigation of Mesoproterozoic rocks from Arctic Siberia, which indicate the presence of dissolved oxygen in the water column during its accumulation.

Our study is based on the sample collection from the Arymas, Debengda, and Khaipakh formations of the Sololi Group of the Olenek Uplift. Rb-Sr and K-Ar globular phyllosilicates ages of ~ 1.30 Ga, 1.28 – 1.26 Ga, and 1.17 – 1.12 Ga respectively suggest the Mesoproterozoic age. Each of these formations composed of mixed carbonate-siliciclastic successions. Together they constitute the ~1.5 km of rocks. For now, the analyzed collection includes 56 samples, taken from the siliciclastic intervals of the formations (23 from the Arymas Fm., 11 from the Debengda Fm., and 22 from the Khaipakh Fm.). The preliminary results of iron speciation analysis demonstrate that during those 200 Ma the shallower waters of the basin (glauconitic siltstones with rare fine sand channels) were predominantly oxic, and deeper/distal parts of the basin (black shales and siltstone intervals in between stromatolitic carbonates) show the ferruginous signal. Those intervals followed each other, and present in each of the studied formations. The oxic intervals of the succession are characterized by various microbial structures, including the “string of beads” Horodyskia. Thus, it is highly plausible, that the microbial communities were the sources of the locally produced oxygen. Such oxygen oases could act as a cradle for appearing eukaryotes during this time, which are also found in this succession ( specifically, Osculosphaera sp., Lophosphaeridium sp., Satka favosa, Dictyosphaera aff. macroreticulata, Germinosphaera sp., Valeria lophostriata).

The research was funded by RFBR # 19-05-01006, 18-05-70110, and government contract 0331-2019-0002 (Ministry of Education and Science of the Russian Federation).