Microstructure and Mineral Composition of Long-Cultivated Permafrost Affected Soils from the Yamal Experimental Agricultural Station (Salekhard, Yamal-Nenets Autonomous Okrug)

The results of investigations into the microstructure and mineralogical composition of long-term arable permafrost-affected soils from the Yamal Experimental Agricultural Station are presented to elucidate the peculiarities of their formation under synlithogenic agropedogenesis. The methodology encompassed micromorphological analysis of thin sections, X-ray diffraction analysis, and semi-quantitative assessment of mineral phases. The arable horizon (0–30 cm) exhibits a high degree of pedality and close porphyric c/f distribution of the groundmass. Aggregation processes are attributed to prolonged accumulation of allochthonous organic matter coupled with clay formation in the arable horizon. The latter is explained by intense physical weathering of the parent material, accompanied by additional degradational transformations under low pH conditions. The dominant mineral phases in the clay fraction of the arable horizon are those of smectite (44–45%) and chlorite-kaolinite (41–42%). This mineralogical phenomenon arises from concurrent smectitization and chloritization processes affecting micas inherited from the parent material.