Russian research institute for cultural and natural heritage, Moscow
PALEO-GEOGRAPHY OF KOBYLIKHA FORTRESS
Kobylikha hillfort was located in the lower reaches of the Pechora river at the southern boundary of the tundra zone. Its confinedness to a large plain resulted in the appearance alongside with the typically tundra alluvial lowland landscapes of the intrazonal open forests.
The hillfort was located in the southern part of Gorodetsky lake, 4 km south of Pustozersk on 4-5 m high shore. Most of it was destroyed by wave processes, and the rest was matted, overgrown with shrubs, tall grass groups, and, along the steep slope - with trees. The slope was covered with dense moss and shrubs groups. The excavations revealed the absence of permafrost in the hillfort.
This tectonic origin lake depression appeared in place of a relatively sunken recent tectonic land block. In its modern form the lake depression was formed in the end of the Neo-Pleistocene. The appearance of the lake was related to a subsequent rise of the land and regression of the sea. At that time it was below the waters of the deeply cutting into the land sea gulf. At present the depression is rather large, the central part is 4-6 m deep, maximum depth is 16 m.
Analysis of the cartographic materials and literature allowed to reproduce the lake's paleo-geography.
In the Boreal and during the Atlantic time in the course of the climate warming and the transgression of the sea there was a period of the high flood alluvium accumulation. According to the radiocarbon analysis data the age of the high flood sediments was 9.2-7.3 thousand years. During the Boreal period the sea coast was overgrown with birch forests. During the Holocene climatic optimum about 6.5-5.0 thousand years ago the sea level was the highest – +3-5 m. A significant part of the Pechora valley in the Gorodetsky lake area below the first flood-plain terrace ledge could have been flooded and was similar to the present day delta section in the Korovjya Guba area. The sporo-pollen analysis data indicated that the climate at that time was warmer than during the formation of the first flood-plain terrace, since the quantity of arboreal pollen increased from 12-14% to 40%. The spruce forests at that time moved far north and came close to the Pechora Sea coast. The cooling during the sub-Atlantic period resulted in a significant drop of the sea level to be followed with a rise, which continues to this day.
In the beginning of the 2nd millennium AD there was a period of climate warming. Apparently the lake level was higher than the present. Beginning from the middle of the 13th century a cooling (the Little Ice Age) started occasionally interrupted by short – 30-40 years - warming periods. In the warming periods there was an active erosion of the shores under the effect of thermo-abrasive processes. One of such warming periods was a cause of the hillfort's destruction. In spring the flood-land was covered with water, water also rose to the terrace slope, since its temperature was higher, the frozen soil thawed and the shore collapsed. In this way the shore continued thawing and crumbling in the warm periods. The floodwater carried away the sand, which led to an inevitable destruction of the hillfort which could not be stopped by its inhabitants.