Soil organic matter of the Kuchiger thermal field (Barguzin Basin, Transbaikalia): forms and intra-profile distribution

Coastal ridges with turbated soils are formed among the marsh massifs in the north- west of the Barguzin basin in area of gas-hydrothermal fluids discharge. The morphological structure of the soils reflects a combination of endogenous, cryogenic and turbation processes. The profile contains a large number of disordered layers, spots, vertical, subvertical or horizontal stripes, wedges, fragments of soil layers, etc. The profile formula is presented by the following system: TUR[A-H-Q-IMP]s - IMP@,s - Qimp - IMP2 - Q2imp. A rich diversity of microforms of soil organic matter has been established on the crest of the diapiric ridge (collision zone) both within the horizons and along the profile. They are represented by black granules, flake-clump aggregates, semi-decomposed and charred plant tissues, clay- organic complex aggregates, fine-silty organic interlayers, scaly aggregates and organoclay cutans. The upper turbated layer is dominated by semi-decomposed plant tissues, flake-clot clusters, black granules, and rare fine-silty organic layers. The micromorphological structure of the impregnated layers at depths of 90-95 and 145-150 cm differs. The upper layer is characterized by a large number of brown clay-organic complex aggregates, large black organo-mineral aggregates with sandy grains cracked into sharp-angled fragments. In the lower impregnated horizon, fine-silty organic matter and flake-clump aggregates are found. The presence of black granules is noted in both layers. The presence of undecayed brown roots and black carbonaceous organic residues has been noted in the quasi-clay horizon (Qimp). In the lowest horizon of the exposed profile (Q2imp), subparallel layering is pronounced.The article contributes to the theory of soil formation in conditions of intracontinental riftingwith unloading of geofluids.