Saturday, 15 July 2006

Development of Vertisols of Northern Caucasus River Valleys During the Last 5500 years.

Alexander V. Borisov1, Andrey B. Belinsky2, and Sergey V. Lyakhov2. (1) Institute of Soil Science Problems, Institutskaya, 2, Pushchino, Russia, (2) State Enterprise “Nasledie”, pr. K.Marksa, 56, Stavropol, Russia

The macromorphological and chemical properties of three paleosols buried under kurgans of different ages have been studied. The kurgans were created at the Eneolithic Epoch (5500 BP), Middle Bronze Age (3900 BP), and Early Iron Age (1900 BP). All studied objects were located in the Kuban river valley. The modern soils are deep, calcareous, clayey, dark colored soils (Vertisols order in Soil Taxonomy) with gilgai relief. Comparative analysis of paleosoils buried under the kurgan mounds in different historical epochs, enables us to obtain information about changes in soil properties overtime. Paleosoil of Eneolithic Epoch buried at 5500 BP had not slickenside zone; the paleosoil surface under kurgan embankment (around 0.2 ha) had not gilgai microrelief. The paleosoil had low salinity and thick dark colored humus accumulation zone; the surface horizons had medium, granular structure; cracks extend down to the 65-70 cm deep. Paleosoil buried at the Middle Bronze Age (3900 BP) meet criteria for the Vertisols order of Soil Taxonomy. The first slickenside horizon occurred at the depth of 45 cm; intersecting slickensides formed parallelepipeds with their long axes tilted 30-45O from the horizontal; cracks cut through the slickenside zone to the 90-100 cm deep. Gilgay microrelief consisted of microhighs 10-12 cm above adjacent microlows, with spacing of 2-4 m between laterally adjacent microhighs and microlows. The paleosoil was moderately alkaline; the surface horizons had subangular blocky structure. Paleosoils of Early Iron Age (1900 BP) was strongly alkaline with exchangeable sodium percentage of 15-18; the upper horizon was light gray, fine, granular structure. Horizon B was dark grayish brown, medium, prismatic in the microhighs pedons, and black, granular or subangular blocky structure in microlows pedons. The slickensided horizon was at the depth of 55 cm, with the short, solitary slickensides occurring. The data obtained allowed us to suggest that the soils of river valleys in Northern Caucasus had not morphological and chemical properties typical for the Vertisols till 5500 BP. After that the Vertisols of this region have been modified under the influence of climate condition changes.

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