Reconstruction of the Climate of the Medieval Epoch Based on Soil and Geochemical Studies of Kurgans of the Srostki Culture in the South of Western Siberia

摘要

The environmental diversity of Altai region is of great interest for researchers. There are many monuments of cultural heritage in the region, which are still poorly studied by natural scientific methods. Paleosols and background soils of the large Srostki-I necropolis of the Early Medieval epoch was examined by pedological and geochemical methods with the aim to trace changes in the soil properties over time and to apply these data for reconstruction of the paleoclimate. This group of kurgans is located in Biysk district of the Altai region and, according to the radiocarbon method, dates back to 890 +/- 105 - 975 +/- 85 AD (calibration 1 delta). Paleosols of the Medieval epoch are characterized by a weaker leaching of carbonates in the middle part of the profile, lower accumulation of biophilous elements (P, S, Co) in the upper horizons, and lower values of the weathering index Al2O3/(CaO + MgO + Na2O + K2O) in comparison with the background surface soils. Thus, in the period before the kurgans' construction, these paleosols were formed under somewhat drier climate in comparison with the present time. However, the similarity of these paleosols and background surface soils in their morphological properties, reconstructed humus content, and averaged values of weathering indices Al2O3 . 100/(Al2O3 + CaO + MgO + Na2O + K2O) and Rb/Sr, as well as Mn/Sr, Mn/Al, and Mn/Fe indices characterizing the degree of biological activity attest to humidization of the paleoclimate during the period of construction of the kurgans. Among highly hazardous pollutants of the first toxicity class, the studied soils are enriched with As and Cd (in comparison with natural abundances of these elements in the lithosphere). In general, regional soils and parent material are enriched with As, Ni, Zn, Ba, and Sn, though the concentrations of these heavy metals in the soil profiles remain below the corresponding maximum permissible concentrations. The accumulation of toxic substances under the impact of anthropogenic pollution in the profiles of studied soils does not exceed the permissible values. The concentrations of heavy metals in the background surface soils are no higher than those in the medieval paleosols. The application of GIS technology demonstrated that 21 settlements and 130 necropolises of the Srostki community (second half of the 8th-12th centuries AD) were localized on fertile soils of leveled areas near large lakes and rivers (the Ob, Katun, Biya, Alei, and other rivers) and within wide valleys at the confluence of small streams with larger water bodies.