Paleosols in red-colored sediment complex in the Pre-Sayan Basin (Southeastern Siberia)

The red-colored deposits of the Mikhailovka section, formed during the filling of the erosional landform formed during the main phase of neotectonic uplift (late Pliocene – early Pleistocene) in the south of the Irkutsk amphitheater are analysed. There is a pedocomplex consisting of three soils of varying preservation, formed during phases of decreasing activity of exogenous processes of relief formation. The upper parts of the soil profiles are characterized by biogenic structuring and contain biogenic forms of secondary carbonates. The middle horizons show orientation of clay and contain flowing forms of carbonates, which indicates the mobility of ferruginous-clay and carbonate micromass in periods of different moisture. Analysis of the δ13С values of soil organic matter, as well as δ13С and δ18О of carbonate accumulations indicates a significant role of pedogenesis in the genesis of the carbonates and indicates of the soil formation on red-colored sediments under a hydrothermal regime comparable to the modern one in the study area. At the same time, the observed isotopic equilibrium between carbonates and soil organic matter suggests a lower contrast of hydrothermal regimes in the intra-annual cycle and a longer duration of the growing season. Soils formed at red-colored deposits show signs of cryogenesis at the macro and micro levels, indicating a trend toward climate cooling during transition from pedogenic to morpholithogenic stages.