ИСТИНА

Ice-rich permafrost exposures containing massive tabular ground ice (MTGI) and ground ice wedges (GIW) were investigated in coastal exposures of Kara Sea at Gydan, Taymyr and Yamal Peninsulas. The sediments enclosing large ice bodies can be characterized by two distinct layers. The lower layer is presented by clays formed in marine and shallow shelf anaerobic environments with large input of terrestrial organic material. These sediments were frozen epigenetically, have high salinity and methane content. The sediments of the upper layer are mostly terrestrial sands formed in aerobic conditions and were frozen syngenetically (simultaneous with sedimentation) and contain slightly decomposed organic material. The change in sedimentation occurred under conditions of lower sea level and cold climate. The MTGI of the lower strata were formed under conditions of epigenetic freezing of talik waters of shallow sea and syngenetic freezing of strata of tidal zone. The GIW of the upper layer were formed under condition of frost cracking of the exposed sea shelf around 50K BP in Western Taymyr and 35-40K BP in Western Yamal. Unlike ice complex of Eastern Siberia, the ice-rich terrestrial sediments of Western Siberia are not as widespread and mostly attributed to large lake drained basins, topographic depressions or fluvial terraces and less than 12 m thick. The sediments are also characterized by lower organic material compare to Eastern Siberia. The presence of MTGI and GIW allows to make paleo reconstructions of climatic and environmental conditions in the Kara Sea Region and to evaluate the role of massive ice deposits in development of dangerous cryogenic processes, thermokarst, coastal erosion rates and methane emissions from permafrost. This research was funded by RFBR according to the research project № 18-05-60080, the lab analyses were supported by RFBR project 18-05-60004