Saturday, 15 July 2006

Paleosols and Environmental Changes in Southeastern European Steppes during Second Part of Holocene.

Vitaly A. Demkin and Tat'ana S. Demkina. Institute of Physicochemical and Biological Problems of Soil Science, RAS, Institutskaya, 2, Pushchino, Moscow region, Russia

Paleosols buried under archaeological monuments (kurgans) of Eneolothic Epoch, Bronze Age, Early Iron Age, and Middle Ages within steppe zone allow us to obtain the information about soil development and paleoenvironmental changes. The soil evolution in Southeastern European Steppes witing the last 6000 years can be described as follows. During the fourth Millennium BC, in the watershed areas of southern Russian steppes the soil with the absence of solonetzic features, high humus content, and low salinity were spread. During the third Millennium BC, a significant change in the soil-forming conditions induced increasing aridity resulted to alkalinization and dehumification of soil as well as accumulation of carbonates, soluble salts, and gypsum in the upper 1-m thick soil layer, with corresponding changes in the trophik structure of the soil microbial communities occurred. The boundaries of soil-geographical zones shifted slightly to the northwest. At the end of the third Millennium BC, the processes of soil degradation were combined with intensive water and wind erosion induced by not only natural but also anthropogenic reasons. As a result, at the end of third Millennium BC the watershed areas and high terraces of rivers were covered by extra-arid calcareous nonsolonetzic saline soils having no analogues in the modern soil cover. But period of extremely drought climate condition was not long. At the beginning of second Millennium BC environmental conditions were similar to those of modern one. At that time increasing humus content occurred and solonetzic features appeared due to secondary exchangeable sodium accumulation. Within the period of 500 BC - 400 AD the soil-forming conditions varied significantly; thus increased humus content and heightened activity of soil microbial communities took place at first and forth centuries AD induced by higher precipitation. Within periods of 500-200 BC and 100-300 AD the climate was more arid. A significant transformation of paleosols happened during the Golden Horde epoch (700-600 AD): the content of soluble salts and gypsum decreased, soil carbonates were redistributed, humus content increased. This time characterized by the highest microbial activity and reduced solonetzic features due to leaching exchangeable sodium. An annual precipitation rate was 50-70 mm higher then modern one.

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