Boulder clay , also known as block clay , is that part of the ground moraine material that emerged from the calcareous boulder clay through superficial weathering . Boulder clay can also arise primarily from the deposition of lime-free moraine material.
It consists mainly of sand and silt . The clay content is subject to strong fluctuations. The glacial , mostly non- stratified sediment can be interspersed with rock fragments , blocks and other bed load components.
If the source material of the glacier sediment did not have any lime content, a lime-free sediment is created which, due to the lack of lime content, cannot be called marl , but otherwise has all the properties of the till.
In the case of glacial till, the originally present lime content is gradually reduced by weathering (especially solution ), in many cases until it is completely decalcified. The degree of decalcification decreases from top to bottom, and in deeper areas it can even lead to re-precipitation of lime with concretion . However, due to the soil formation and rooting that began after the Ice Age with the accompanying good drainage, the upper soil area is usually completely free of lime. The color of the boulder clay changes with the transformation into boulder clay from the previous gray to blue to ocher yellow to brown ( browning ).
- Hans Murawski: Geological Dictionary . 8th edition. Enke, Stuttgart 1983, ISBN 3-432-84108-6 , pp. 80 .
- Fritz Scheffer : Textbook of soil science / Scheffer / Schachtschabel. Revised and expanded by Hans-Peter Blume, among others, 15th edition. Spektrum, Heidelberg, Berlin 2002, ISBN 3-8274-1324-9 , p. 470 f.