Saturday, 15 July 2006

Evolution Of Ecosystems Of The Central Siberia in the Upper Pleistocene (paleopedological data).

Galina A. Demidenko, Krasnoyarsk State Agricultural Univ, Mira Str., 88, Krasnoyarsk, Russia

The northern part of Central Siberia is strongly impacted by permafrost and the soil forming processes in the Pleistocene occurred under its effect. That time external condition of natural environment led to formation of peculiar natural substances - paleosoils. The climate changing during all geological periods and ages was the main factor of the process. Paleosoils have been studied on archaeological sites within the Middle Yenisei basin in southern taiga (Priangara plateau). The multi-layer archaeological site Ust- Kova lies on the left bank of R.Angara, immediately over the R.Kova mouth. The R Angara second terrace joins the R Kova second-plain terrace with in the digging site area. The soil-forming zone of the Ust-Kova pedocomplex comprises two soils;both with the preserved A horizon. In the lower buried soil, the A horizon (150-180 cm from the day surface) is represented by a dark-brown humified loam. The parts of plant roots are ferruginated, showing abundant coaly inclusions and features of solifluction. From morphological description, the A horizon has a typically chernozem-lake humus. The A horizon of the upper buried soil (120-127 cm from the day surface) is a dark-grey or brown humified loam having suffered loam having suffered solifluction. The horizon is ferruginated, carbonised, gleyed; it contains carbonaceous inclusions. Micromorphologically,the A horizon of the upper buried soil is a typical chernozem-like humus. The A horizon in the lower and upper buried soils are quite similar both morphologically and geo-chemically. It may thus be assumed that the lower and upper buried soils of the Ust-Kova pedocomplex have formed in the steppe conditions after the chernozem-like soil pattern. The two-member structure of soil-forming zones is no longer revealed in the Ust-Kova pedocomplex which shows strong secondary carbonation, and is slightly feriferrous. In single sample of the pedocomplex`s buried soils, spore-pollen spectra have been found which indicate vegetation of cold steppe areas.

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