Vorobyev, and 5 co-authors, report that studies on the Yamal crater formed as a result of a cryogenic eruption of a water-gas fluid were carried out. The structure and variations of the composition of the geochemical field along the section of the upper horizons of permafrost are considered on the basis of field work, including the drilling of boreholes near the crater. The obtained regularities of the distribution of chemical elements, and gases between the mineral component of the soil and meltwater, suggest that permafrost at the site of the funnel are the remains of a sub-lake paleo-talik, from which mineralized water and gases were expulsed into the yet unfrozen reservoir that previously existed at this place. The component composition of gases suggests that they are products of biochemical processes similar to those that occur in modern peatlands. The δ13C value for methane extracted from the sediments of the near-contact zone of the Yamal crater was found to be -76%. The predominance of high molecular weight normal alkanes in frozen bitumen indicates that the original organic substrate which was buried contained remains of higher vegetation. The Yamal funnel was formed by the sediment’s “explosion” while the water-gas fluid was released. The volume of the ejected sediment amounted to about 220 thousand m3.
The trends of gas distribution in permafrost samples from boreholes drilled around the Yamal crater discussed in this work show that the processes responsible for generation of the exploded gas are largely similar to those in modern paludal environments. Partitioning of some major and trace elements between the mineral and ice components indicates that deeper ice-rich rocks in the northern part of the profile may belong to the sublake paleo-talik. Gas from the talik was expulsed by the freezing front into a yet unfrozen zone of sediments beneath the pingo and was made part of a water and gas fluid.
Judging by the compositions of the mineral and gas components of permafrost, the crater is located at the edge of the freezing talik. The elements had been partitioning between the liquid and solid phases for a few thousand years while the talik was freezing, and biogenic reactions transformed organic matter. As a result, high-molecular compounds of peat and mud communities converted to fulvic and humic acids, while bacteria metabolized organic matter and formed CO2, CH4, and H2, the main gas species found in ice-rich sediments within the frozen paleo-talik. The results obtained for the upper part of the section for drilled boreholes confirm the presence of cryogenic gas separation during the freezing of a closed thawed rock mass. The gas composition transformations have their own specifics for different depths of the section. Thus, according to estimates of the internal pressure in the talik before the explosion, favorable conditions are created in the lower part of the talik for the formation of carbon dioxide gas hydrates.
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