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Abstract
Christensen, Leif: Faststående og omlejrede Saale-morånelersaflejringer. Et eksempel fra Szdding-området, Vestjylland. Geografisk Tidsskrift 82: 91–94. Copenhagen, Dec. 1, 1982.
In situ clayey till materials on the Skovbjerg Bakkea, western Jutland can be recognized by crop-marks revealing pseudomorphs of ice-wedge polygons in orthogonal, random orthogonal and hexagonal patterns. The tills inside these polygonal patterns have high shear-strength values as measured by vane tests. Remoulded fossil solifluction deposits of till origin reveal stripes and deformed polygonal patterns in the crops. High strength as measured by vane are encountered below fossil solifluction deposits 4 meters below ground.
SUMMARY
It is commonly accepted, that »Bakkeeerne«—the landscape of Saalian drift and meltwater deposits in western Jutland- have experienced active periglacial modification throughout the Weichsel glaciation, when the ice-shetts extended to the Main Stationary Line in Central Jutland. Solifluction probably associated with frozen ground—gelifluction (Washburn, 1973)—has reduced the lower slopes in angle and extended the slopes in length, while the upper parts of »Bakkeøerne« suffered erosion and retreat and near-stable slopes were ultimately attained.
In engineering-geological mapping of soft bottom areas in selected regions in western Jutland it is important to recognize between in situ glacial drift materials and remoulded fossil solifluction materials of till origin deposited downslope. There is however a big problem, because the solifluction deposits have lost their topographic forms.
The outline of pseudomorphs of ice-wedge polygonal patterns as revealed by differential crop-markings on air-photographs in western Jutland (Svensson, 1963 and 1972 and Christensen 1973, 1974 and 1978) can help in recognizing between in situ and remoulded materials. Usually hexagonal, orthogonal and random orthogonal patterns are found on the smoothed surface of »Bakkeeerne« consisting of in situ glacial drift materials. Downslope—where remoulded materials accumulate to some depths—the crop-patterns are transformed into oriented orthogonal patterns and stripes.
A study area composed of clayey glacial tills on the southern slopes of Skovbjerg Bakkeø have been mapped in large scale 1:10.000 and 1:4.000. This area reveals a high concentration of pseudomorphs of ice-wedge polygonal patterns (Svensson 1972 and Christensen 1978).
In the study area apparent strength parameters for clayey and silty materials are determined by vane-tests in two borings. The glacial deposits preloaded by advancing Saalian glaciers will normally be rather strong and incompressible.
The fossil solifluction deposits of till origin have not been preloaded by ice. These deposits are sandier than the in situ deposits. Strong and incompressible glacial tills are registered below the fossil solifluction deposits 4 metres below ground level.