Cryo-Geomorphological Evolution of Soils on Islands of Terekhol Lake, Tyva, Southern Siberia

Specific soils on calcareous lacustrine sediments have been described on the islands in the Terekhol Lake, Terekhol'skaya intermontane trough of the Tuva Upland. The islands themselves originate from frost heaving cycles as shown by their relief and interfacial analysis of litho- and biostratigraphy of dated cores sampled in the bottom of the lake and on the islands. Soils of two altitude-age groups (generations) of islands have been studied. Younger islands (400-1700 cal yrs BP) have relative heights above the lake level below 2.5 m and an active layer 0.6-1.5 m thick. Histic Cryosols (Limnic, Drainic) were found there. Soils are well drained now and have no relation with the lake waters. The central elevated parts of older, and higher islands (4000-5000 cal yrs BP; 2.5-4.5 m, active layer about 1.5 m thick) are under dry-steppe phytocenoses on Calci-Mollic (Histic) Cryosols (Limnic, Calcaric, Gypsiric). The following evolution phases of islands and their soils were reconstructed. The lacustrine sediments were raised from the sedimentation zone to remain in subaerial conditions, where Histic Cryosols were formed. Owing to heaving, an admixture of limnic material was included in them. Further heaving resulted in the isolation of soils from the lake waters, the sedimentation completely stopped, and pedogenesis slowly shifted toward that inherent to well-drained conditions under dry-steppe vegetation. Histic horizons got degraded and transformed to mollic ones, the permafrost table moved deeper, carbonates, gypsum and soluble salts were leached from the upper horizons.