Lauenburg clay
Lauenburger clay is a fine-grained basin sediment .
Origin of the designation
The Lauenburger Ton got its name after the town of Lauenburg / Elbe , which is located on the right bank of the Elbe at river km 570. From Lauenburg the right bank of the Elbe belongs to Schleswig-Holstein . There are several occurrences of Lauenburg clay in and around the city. One of them was cut in the course of the new construction of the Elbe-Lübeck Canal (opening in 1900 as a replacement for the Stecknitz Canal, which had existed since 1348 ). Since then this clay has been called Lauenburger clay.
Origin of the Lauenburger clay
At the end of the Elster Ice Age, the Lauenburg clay settled in hollow forms previously carved out by the ice with the meltwater as basin sediment. Since the fine clay particles in the meltwater stayed in suspension for longer than the sandy parts (they have a lower sink rate ), the basin sand first settled at the bottom and especially near the glacier and only then did the basin clay. At a greater distance from the edge of the glacier, only basin clay sedimented.
Since the prerequisites for the formation of Lauenburg clay (excavated hollow forms, clay particles in the meltwater) represented a special situation under ice age conditions, Lauenburg clay only occurs locally, but not over an area like a ground moraine . The above The end of the Elster Ice Age can be dated to around 380,000 years before our era. The Elster Age deposits were then covered again during the Saale Ice Age and u. U. again during the Vistula Ice Age in the areas north of the Elbe, which were directly affected by the last glaciation.
This chronological sequence of the icing does not mean that the respective deposits can be found neatly stacked on top of one another. The proximity of the Lauenburg clay layers to the surface, especially near Lauenburg, can be explained by the fact that the glacier ice loosened clods of clay during the later cold ages, dragged them away and pushed them up. In addition, the deposits of the later Ice Age (s) can be of very different thickness or even completely absent, so that one can then look at the older layer as if through an opening.
Investigation methods to determine the clay deposits
To determine whether there is clay, silt or sand , a grain size analysis is used first . Clay has a grain size of <0.002 mm, whereby one speaks only of grain size - in reality the clay minerals have a flake-like and not a granular shape. A grain class has always been referred to as clay when the clay content is over 45%, the rest is then made up of different proportions of silt and sand.
In the Lauenburg area, geological mapping was carried out by hand drilling to a depth of 2 m before 1914. Occurrences of Lauenburg clay, Holstein clay and tertiary clay were already recognized (see Section 4). Since 1969, geoelectric measurements have been carried out there to better understand the deposits .
“A largely horizontally layered subsurface can be examined using electrical direct current, provided that the individual layers have sufficiently large conductivity differences and thicknesses. If direct current is supplied to such a substrate via two electrodes , a characteristic voltage distribution is created, which is measured with suitable probes. [...] The strength of the direct current flowing between the electrodes and the voltage measured at the probes result in an average rock resistance. [...] By comparing the measured curve with the theoretically calculated one, the specific resistances, thicknesses and depths of the recorded layers are determined.
The following resistance ranges were determined and assigned:
- 25 - 80 ohmmeter : glacial till (water-saturated)
- 15 - 25 ohmmeters: tone, silty; silt in places
- 5 - 15 ohmmeter: tone "
Differentiation of the Lauenburg clay from other clay deposits
Lauenburg clay is weakly silty clay with a finely distributed weak lime content, but without fossils such as mussel and snail shells, because it is a basin deposit in its current interior. The tone is black to gray, e.g. T. red. In the case of gray shades, it often has a small proportion of fine sand.
Holstein clay has mussel and snail shells because it is the marine deposit of a warm period. This clay is also weakly silty with a finely divided weak lime content, but it is not black, but gray, e.g. T. red. In the case of light gray shades, the silt content is often greater, the fine sand proportion low.
Lauenburger clay and Holstein clay can be closely interlinked (socialized). This is explained by the fact that the Lauenburg clay was formed towards the end of the Elster Ice Age (see above). As the ice masses melted, the sea level rose, so that basins with Lauenburg clay were flooded in the warm period between the Elster and Saale glaciers, the Holstein interglacial , and then sea deposits formed over the Lauenburg clay. This idea is all the easier when you consider that z. B. the occurrence of Lauenburger clay west of Dalldorf (approx. 10 km north of Lauenburg) extends down to 1 m below sea level.
Tertiary tone is weakly silty, black, e.g. Sometimes red, mostly lime-free, but with remains of mussels and snail shells.
Occurrence of Lauenburger clay
Occurrences of Lauenburg clay are not only limited in terms of area, as already mentioned, but also in number. On the geological overview maps 1: 200,000, sheets CC 3118 Hamburg-West and CC 3126 Hamburg-Ost, that is the North German lowlands from Delmenhorst / Lower Saxony in the west to Dömitz / Elbe in the east, from Hamburg in the north to Walsrode / Lower Saxony in the south, a total of approx. 15300 km², just 20 occurrences are recorded, namely six between Lauenburg and Dalldorf, in the district of Lüneburg near Rettmer, in the district of Rotenburg / Wümme near Basdahl, southeast. Hesedorf, near Deinstedt, Ober Ochtenhausen, south. Ostereistedt, northeast. Zeven, near Hainhorst west of Visselhövede and between Visselhövede and Wittorf, in the district of Osterholz near Vollersode, Hülseberg, Garlstedt, Osterholz-Scharmbeck and Worpswede. A deposit near Breetze in the Lüneburg district no longer reaches the surface due to soil degradation.
Use of the Lauenburger clay deposits
Lauenburger clay has long been used by brickworks in z. Sometimes deep pits are mined because it is ideal for making bricks. If the clay obtained is particularly pure, it must be stored with sand or boulder clay.
Drainage is often a particular problem in clay pits, as the clay has formed in basins as described. During mining , the clay prevents the surface water from draining away , so that the water must often be drained away with pumps. Only when the clay has been fully exploited and more water-permeable layers underneath have been reached can water seepage be expected again. If, however, clay still remains in the subsoil at the end of mining or if the groundwater level has already been reached or fallen below, permanent water surfaces can form. Careful dismantling planning is required to take into account all the related aspects and this is prescribed in the nature conservation and landscape management laws of the federal states.
Bibliography
- ^ Hansjörg Küster : The Elbe . CH Beck, Munich 2007, p. 220.
- ^ A b c d Klaus-Dieter Meyer : Geological natural monuments in the Lüneburg district in: Yearbook of the Natural Science Association for the Principality of Lüneburg eV , Vol. 36, 179–196, Lüneburg 1983.
- ↑ a b Fritz Scheffer , Paul Schachtschabel : Textbook of soil science . 10. through Ed. By P. Schachtschabel, Enke, Stuttgart 1979.
- ↑ a b c d e f g K. Picard, D. Hölbe: Expert opinion of the Geological State Office Schleswig-Holstein on clay deposits near Lauenburg / Elbe v. 10.10.1969, report no. 69/49.
- ↑ a b Geological overview map 1: 200,000, sheet CC 3118 Hamburg-West, Federal Institute for Geosciences and Raw Materials , Hanover 1976
- ↑ a b Geological overview map 1: 200,000, sheet CC 3126 Hamburg-Ost, Federal Institute for Geosciences and Raw Materials, Hanover 1977