Characteristics of the Siberian coal basins permafrost: An example of Ytymdja depression

Ytymdja depression is one of the Mesozoic structures with discovered large coal deposits of the Aldan Upland. Lack of industrial development and farness from agglomerations explain the knowledge gap about the environmental conditions of the Ytymdja depression. A field monitoring network with existing deep boreholes was absorbed to investigate permafrost conditions and to assess potential impacts of local factors and climate change. This paper describes analyse temperatures at the depth down to 240 m by these boreholes with air and ground temperatures of the Ytymdja depression to determinate permafrost conditions. The research was carried out in a 1800 km² area of the South Yakutia, Siberia, using satellite imagery-based classification. The field investigations and analysis of ground temperatures indicated that permafrost underlies of the ground entire area of Ytymdja depression, but likely absent under large rivers. Permanent negative temperatures have been detected in the borehole, which shows evidence of the existing of widespread permafrost conditions nowadays in the coal basins in Siberia. Permafrost temperatures vary between -3.1 °C and -1.5 °C at 35 m below the surface, and annual ground temperatures at 1 m depth ranged from -4.9 °C to -1.2 °C. Thermal conductivity of rocks determined by individual core samples varies from 1.1 to 2.9 W m^-1 °C^-1 with geothermal heat flux in the permafrost zone of 0.02 W m^-2 and an increase in the zone below permafrost to 0.03 W m^-2. Spatial modelling for the entire territory of the Ytymdja depression deduced a continuous permafrost distribution with a thickness between 106 and 251 m. The considerable thickness of permafrost probably prevents the emission of greenhouse gases from coal seams into the atmosphere, but detailed studies in this direction have yet to be carried out.