GEOLOGICAL INFORMATION about chalk from Lägerdorf
|Schleswig Holstein is a young land which was formed by the period and the post-glacial periods. Together with a large part of Northern Germany and almost the whole of Denmark it would have been sea bed, if the periods of Cenozoic had not considerably increased its structure. However, the subsoil consists of solid rocks which connect the mountainous regions of Central Germany and the rock caves of Scandinavia.
The gypsum mountain of Segeberg and the rock island Helgoland are monuments of this subsoil and rise above the younger deposits. Near Elmshorn and Lägerdorf the old mountains are right under the earth's surface. Chalk is an important part of this subsoil. For Lägerdorf it is of special importance. A number of petrifications show that these are sea deposits. The chalk sea the northern and southern coast of which was approximately 300 km away from Lägerdorf, extended from the Baltic countries to the Atlantic. For this reason similar chalk can be found on the island Rügen, near Hemmoor a.d. Oste, in Belgium, in the Champagne, and near Dover.
The sea must have had subtropical living conditions and is supposed to have been not deeper than 1,000 m. It had oceanic character due to the lack of the clay-arenaceous rinsing masses of the surrounding lands, which were typical for the prehistoric shallow waters. The main quantity of the deposits does not consist of fragments of bigger life-forms, but of microscopic lime particles of tiny sea organisms, unicellular organisms with cilicaries, unicellular rhizopods, plankton algae with a lime shell, and lime tinsel of sea bacteria).
In many million years the chalk deposits became enormous layers. Often it took an entire millennium to form 1 - 2 cm of sediment. Supposing that 2 cm per millennium is the medium sedimentation velocity, 400 m write chalk - this layer package results from the different profile sections for the open minings in Lägerdorf and Kronsmoor - deposited in approximately 20 million years. This period was also established by advanced physical determinations of the age.
The water temperature was constant and came to 18 - 20 degrees Celsius. During this long period of time the life-forms of the chalk sea passed different developmental stages. Here the most important exponents, the index fossils, are to be mentioned. It had been proven, that the chalk near Lägerdorf comprises only deposits from the Sénon (youngest formation of the upper chalk). The index fossils are remains of prehistoric octopuses (limy shell of the cover of octopuses) They differ by the shape of the conical pit and the top.
Furthermore sea urchins are often present. In most cases they are filled with chalk, however, often they are silicified. The forms are different: heart-shaped, ball-shaped and small, halved ellipsoid. Sea urchins of the same kind show different developmental stages. The orifices of the body are distributed both symmetrically and asymmetrically. There are only fragments of shells and sea urchins. Furthermore skeletons of dinosaurs of the Jurassic period are said to be found in Lägerdorf. There were silicious sponges and other life-forms with silicious skeletons in the chalk sea, too. You still find traces of silicious skeletons of the sponges, however, the silicate framework is now replaced by brown iron ore. The silicious mass of the sponges and of other life-forms disolved in long periods of time and was then separated as jelly and enriched again.
The formations of the flints are supposed to have developed as a result of the dewatering of the jelly. In Lägerdorf they occur in so-called flintbanks when chalk is won. These flintbanks divide the chalk into many layers, thus enabling the geologist to perform a good classification. Compared with other deposits, chalk in Lägerdorf does not contain too many flints and fossils. For this reason it is a raw material with an extremely high quality. The CaCO3 content comes to app. 96 - 98 %. The chalk deposits in Lägerdorf and Kronsmoor consist of solid chalk, i. e. it has a connection to the chalk mountains extending under the whole of Schleswig-Holstein.
In Lägerdorf there is a flatly strained vault which was brought up from the depth by means of the elevation of the salt dome to the earth's surface during the middle Tertiary; it is streaked with fragments, polished by inland ice, and covered by a thin morainic layer. The thickness of the chalk profile determined until now with certainty amounts to 250 m. Boring in the pit resulted in chalk being determined at 200 m. Furthermore, already a 4 % brine was detected which proves the existence of the salt dome under the chalk. In Lägerdorf the spoil layer above the chalk is 3 - 10 m. The minable area comes to app. 10 km².
In the remaining area of our district and land, chalk can be found in a number of different depths. To the west of Krempe it is at a depth of 30 to 40 m, near Büttel at 350 m, and near Hamburg even at more than 800 m under mean sea level. Near Heide where chalk is also not very deep enormous salt rock layers starting at 504 m under the chalk were opened by means of a deep drilling of 1,600 m.
The deposits of the Cenozoic clearly differ from those of chalk. They predominantly consist of marls, clays, pebbles, and sands, and apart from some deposits of the Paleogene, they are soft and loose. The Holstein Gestein originated in the Neogene and can also be found in Itzehoe. This is a sand stone which is rich in shells; many boulders of it can be found in our clay and sand pits. This is sand strengthened by ironcarbonate which contains a variety of different and well preserved sea shells and snails. Deposits of mica clay from earlier lap formations also belong to this formation.
The surface formation of our homeland goes back to the Diluvium with several periods of glaciation and of the decrease of ice. The two earliest glaciations passed over the area of the district Steinburg, while the following one caused the formation of the end moraine lines near Itzehoe. The last glacial period only reached Mittelholstein and its snow waters split the moraine landscape which had many tops. In those days the network of waters was fundamentally formed. Enormous masses of snow water - the so-called Urstör - washed out the Störbett of today, separated the geest island of Münsterdorf from the mountain ridge to the north of the Störtal, and formed the precipices near Itzehoe and Kellinghusen. The geest island of Münsterdorf is not too high, app. 8 km long, and about 3.5 km wide. In the east it is limited by the Breitenburger and Rethwischer Moor, in the south by the Rethwischer and Neuenbrooker Marsch, in the west by the Krempermarsch which, together with the Münsterdorfer Störmarsch, forms the end in the north.
That the geest island of Münsterdorf is an original island was made evident to us during the big storm tide in 1962, when the Stördeich (the Stör-dike) broke and the surges dashed against the old beach line at the edge of the village Münsterdorf. Today the Nordoer Dünen still show the former sandy beach. Due to a slow but clear lowering of the whole land the North Sea could gradually reach the geest borders. At the end of the last glacial period it still was approximately 20 - 60 cm higher than today. The change between land and sea in our homeland took place very slowly during long periods of time.
Since these changes can hardly be measured in lifetimes of human beings, all we can see toady is an instantaneous picture of this development.
Further geological formations, earth and primeval times, are not known in Schleswig-Holstein, but maybe they exist in big depths. They occur in boulders of Northern Europe.
(Source: Lägerdorfer Chronik II)
Cenocoic Alluvium (present time and post-glacial period)
|since 20,000 years||exisiting|
|Diluvium (glacial period)||1 million years||exisiting|
|Tertiäry||60 million years||exisiting|
|Middle ages||upper chalk||50 million years||to be found near Lägerdorf|
|lower chalk||30 million years||to be found near Lägerdorf|
|Jurassic||35 million years||exisiting|
|Trias (variegated sandstone)||40 million years||Helgoland|
|Antiquity||Perm||40 million years||to be found near Elmshorn and Segeberg, together with chalk it forms the mountain subsoil|