FIRST FINDINGS OF HORODYSKIA IN THE MESOPROTEROZOIC ROCKS OF ARCTIC SIBERIA

Horodyskia was originally discovered from the Mesoproterozoic Appekunny Formation (~ 1.46 Ga), Belt Supergroup, Montana, USA, and described as a “string-of-beads” structure preserved on the bedding surfaces. It was subsequently found in the Stag Arrow and Backdoor formations of Western Australia (1.46 – 1.07 Ga) and in the Cassiterite Creek Quartzite of Tasmania (1.30 – 0.80 Ga). The nature of Horodyskia has been the subject of an ongoing debate with affinities ranging across abiotic structures (tool mark), prokaryotic colonies, fungi, brown algae, trace fossils, and eumetazoans. Here, we present new findings of Horodyskia this time in the Arctic region of Siberia, Russia.

In the Arctic Siberia Horodyskia occurs in 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 thу Mesoproterozoic (Riphean) age. Each of these formations represented by mixed carbonate-siliciclastic successions. Horodyskia is found exclusively in the siliciclastic parts of the formations, in glauconitic sandstones and siltstones. The collection has 770 samples (strings of more than 3 beads).

Our preliminary results favor the placement of the Siberian material into H. williamsii, because “the beads” become progressively closer to each other with increasing diameter of “the beads”, and they are not infilled with quartz as H. moniliformis. Statistical analyses do not show any significant differences between measured parameters (width and length from the beginning of one bead to the beginning of the next one) of Horodyskia in three Siberian formations, thus all the samples most probably represent the same object. Based on the appearance of Siberian Horodyskia at the particular stratigraphical levels (which roughly cover 200 million years of the Earth history), we can conclude, that no matter the nature of these structures, they were strongly facies dependent. It is preserved only in the glauconitic channelized sandstones and siltstones with microbial structures. Thus, they were formed/preserved only in very shallow marine environments with low sedimentation rates.

The research was funded by RFBR # 19-05-01006, RSF # 17-17-01241 and government contract 0331-2019-0002.