Geology of the Netherlands and Flanders

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The geology of the Netherlands and Flanders can be clearly divided into two parts:

One consequence of this situation is that nowhere in the world is this division of research as clear as it is here.

overview

Flanders and the Netherlands are in the north of the Ardennes , the western part of the Rhenish Slate Mountains . Like a large part of Denmark and Northern Germany, they consist of unconsolidated , very young ( Quaternary ) sediments on the surface .

Due to the proximity of the low-lying part of the European continent , the basin of the North Sea , the Netherlands and Flanders rarely rise much higher than 30 m above the sea beyond. The rivers that flow into the North Sea today, such as the Rhine with its tributaries, the Meuse , the Scheldt , the Ems and other smaller rivers, have supplied a large amount of sediment, which has led to the formation of a large delta , the Rhine -Maas-Deltas .

As a result, solid rocks rarely come to the surface. More than 80% of the Netherlands have sediments that are less than a million years old. The geological situation is thus similar to that which can be found in many geologically young subsidence areas, and older rocks are almost everywhere hidden in the deeper subsurface.

Deposits close to the surface

Quaternary sediments are mostly called "soil types" or "soil types" in the Netherlands. Which sediment occurs in the soil largely determines today's parcelling and land use , and thus the landscape .

Ice edge locations (pre-glacial and Saale glacial)

In sections of the major rivers in the Netherlands and in some places in the far east of the country, sediments come to the surface that are older than the penultimate ice advance, the Saale glacial (between 380,000 and 150,000 years ago). In the west and middle of the Netherlands, these pre-glacial gravels and sands only come to the surface when they are dammed up by the drifting action of the glaciers in the so-called ice edge layers . Examples of large ice margins are the Utrecht ridge , the Veluwe and the Salland ridge . Boulder clay was left behind by the glaciers along the outside of the ice edge layers .

Deck sand and loess (Vistula glacial)

In the last section of the Ice Age, the Vistula Glacial (approx. 110,000 to 11,000 years ago), just like in the earlier glacials, a large part of the seawater was deposited as ice in the ice sheets that completely covered areas at higher latitudes such as Scandinavia . In contrast to the Saale glacial, the ice sheet did not reach the Netherlands. However, a large part of the North Sea (which is no deeper than 30 m in most places) was dry due to the lowering of the sea level. The dry area had a polar desert climate , where the wind had free rein. In the regions in the south of today's North Sea, the wind deposited ( aeolian ) sand, the so-called deck sand . The further south you go, the smaller the grains carried by the wind, so that the deck sand becomes finer and finer towards the south. Approximately in the south of the Roermond - Antwerp line , the deck sand changes into loess , a type of soil made up of well-sorted, fine grains.

Aeolian sediments such as deck sand and loess have the property of balancing out the relief of the landscape by gradually covering depressions and bends in the slope. That is why the deck sand in the northern Netherlands lies in a wedge shape against the ice edge layers.

Clay deposits, ice edge layers and fens (Holocene)

In the stretches of land along the coast ( provinces of Groningen , Friesland , Noord-Holland , Zuid-Holland , Zeeland , West Flanders and East Flanders ), the surface layers of soil consist mainly of clay deposits . In the west of the Netherlands, the clays are being replaced by fens . Both were deposited after the glaciers retreated and sea levels began to rise ( transgression ). This happened in two major cycles:

  • This was followed by a period of rapid sea level rise and warmer climates . This period is called the Atlantic (8,000 to 6,000 years ago). The sea washed over a large part of the Netherlands, the swamp gave way to an inland sea with lagoons in which clays were deposited. These clays are called old blue clay . In many places, the base bog was torn away by waves, so that it is no longer all underground.
  • The Atlantic was followed by the less warm period of the subboreal (approx. 6000 to 3000 years ago), in which the sea retreated somewhat. The lagoons grew back together to form swamps in which a new layer of bog was deposited. These deposits, known as Hollandveen , come to the surface in some areas in North and South Holland and in the province of Utrecht . In many places they have been dug up to be used as fuel. This created lakes .
  • The Sub-Atlantic followed the sub-boreal , in which the sea level rose again. In some places the water broke through the row of dunes and formed a lagoon or an inland sea. An example of this is the Flevomeer , which was roughly on the site of today's Flevoland . In the coastal regions behind the dunes, clay was deposited again, the so-called young sea clay . At the same time, the higher young dunes formed on the banks .

River clay

Throughout the Quaternary, river or floodplain clay was deposited where rivers flowed. In the cold periods the rivers carried more water than in the warm periods and formed intertwined courses ( intertwined river ). In the warm periods such as the present Holocene come meandering rivers before. The amount of water in the rivers was higher during the ice ages.

In the course of time the Rhine, the IJssel , the Scheldt and the Meuse have relocated their lower reaches in the Dutch coastal plain several times. That is why river clay can be found in some places in the underground where no river flows today. At the same time, a network of old (sandy) river ridges remained underground in the river basin. Before the Saale glacial, for example, the Rhine flowed northwards from where Arnhem is today , instead of westwards as it does today. The course of the river later shifted due to the formation of the ice edge of the Veluwe.

A little further south, the rivers are in a "more solid" position in a valley , like the Meuse in Limburg . Here river clay occurs only in a strip along the river.

High moor

Raised moors formed on the high ice edge layers . These cover a large area there; in the rest of the Netherlands the fen is more widespread. The raised bog, however, is not limited to ice-edge areas; it can also form on other higher, less permeable soils, such as in the High Fens .

Rocks in the deep underground

The rocks in the Dutch, North Belgian and North German subsoil are broadly comparable with those in other places in Western Europe . Some of the rocks listed here and known only from the subsurface occur on the surface in the Ardennes.

Pre-Variscan base

The base is formed by early Paleozoic rocks, which are older than the Variscan mountain formation (around 390 to 300 Ma ago ). These are usually located several kilometers depth in the southern Netherlands and Flanders soar in the so called Brabant Massif to the surface, so that they in some valleys Nordbelgiens minded are.

Carbon

Carboniferous rocks only come to the surface in a few places in the extreme southeast of Limburg. They are deposited on the edges of the Variscan Mountains in shallow coastal swamps. After the plants growing there died and were covered by sand and silt, initially lignite and later hard coal formed, which was the basis for mining in South Limburg until the 1970s .

Permian and Triassic

In the south of today's North Sea there was a shallow inland sea in the Permian . This was filled in the Rotliegend and Buntsandstein with degradation products of the Variscan Mountains, sandstones and conglomerates , from the south. They are completely absent in the south of the Netherlands and Belgium. Towards the north, where the sea was deepest, these layers are thicker. They serve as reservoir rocks in which crude oil and natural gas from the carbon below could collect.

Impermeable layers were deposited on these porous rock layers, for example through the retreat of the sea in the Zechstein and Keuper evaporites (mainly salt ) and limestone in the Jura . These rocks have ensured that in many places in the Dutch underground oil and natural gas could not escape and are now economically viable. The salt from the Zechstein and Keuper has formed enormous diapirs ( salt domes ) under Northern Germany, the North Sea and the Netherlands, where these layers were most thick .

Jurassic and chalk

During the Jura and the Cretaceous the mountains in the south were almost completely eroded . Both the Netherlands and Belgium were covered by a shallow sea. Especially at the end of the Chalk period, thick layers of limestone were deposited here. These come to the surface at the edge of the Ardennes, for example near Maastricht , where the lime is mined in the large quarries of ENCI Holding . The well-exposed and fossil-rich limestones around Maastricht gave the Maastrichtium , the highest level of chalk, its name. In Limburg the chalk lime is called marl , although it contains little clay and silt . In some places dry natural gas has formed in chalk rocks , which has been covered by limestone and is degradable.

Tertiary

Tertiary sediments emerge in some places in the south of the major rivers. Sands and clays alternate. In most places, these tertiary sediments were covered with deck sand or loess. Today, the tertiary sediments overlay the chalk layers on the northern edge of the Brabant massif and sink to the north under the Quaternary sediments of central Netherlands. Remnants of tertiary deposits on the High Fens show that the tertiary deposits reached further south than they do today. In the far east of the Netherlands, these sediments also come to the surface in isolated places in Twente and the Achterhoek .

literature

  • JHA Bosch, P. Cleveringa, T. Meijer: The Eemian stage in the Netherlands: history, character and new research. In: Geologie & Mijnbouw / Netherlands Journal of Geosciences. Volume 79, No. 2/3, 2000, pp. 135-145.
  • P. Cleveringa, T. Meijer, RJW van Leeuwen, H. de Wolf, R. Pouwer, T. Lissenberg, AW Burger: The Eemian stratotype locality at Amersfoort in the central Netherlands: a re-evaluation of old and new data. In: Geologie & Mijnbouw / Netherlands Journal of Geosciences. Volume 79, No. 2/3, 2000, pp. 197-216.
  • Kurt M. Cuffey: Substantial contribution to sea-level rise during the last interglacial contribution from the Greenland ice sheet. In: Nature . Volume 404, April 2000, pp. 591-594. doi: 10.1038 / 35007053
  • P. Harting: Le système Éemien. In: Archives Néerlandaises Sciences Exactes et Naturelles de la Societé Hollandaise des Sciences (Harlem). Volume 10, 1875, pp. 443-454.
  • P. Harting: Het Eemdal en het Eemstelsel. In: Album of the Natuur. Volume 1886, 1886, pp. 95-100.
  • G. Spaink: De Nederlandse Eemlagen, I: Algemeen overzicht. (= Wetenschappelijke Mededelingen Koninklijke Nederlandse Natuurhistorische Vereniging. Volume 29). Amsterdam 1958. OCLC 522282169 .
  • RJ Van Leeuwen, D. Beets, JHA Bosch, AW Burger, P. Cleveringa, D. van Harten, GFW Herngreen, CG Langereis, T. Meijer, R. Pouwer, H. de Wolf: Stratigraphy and integrated facies analysis of the Saalian and Eemian sediments in the Amsterdam-Terminal borehole, the Netherlands. In: Geologie en Mijnbouw / Netherlands Journal of Geosciences. Volume 79, 2000, pp. 161-196.
  • JH Van Voorthuysen: Foraminifera from the Eemien (Riss-Würm-Interglacial) in the Amersfoort I (Locus Typicus) borehole. In: Mededelingen Geologische Stichting NS. Volume 11, 1958, pp. 27-39.
  • Roland Walter among other things: Geology of Central Europe . 5th, completely revised edition. Schweizerbarth'sche Verlagsbuchhandlung, Stuttgart 1992, ISBN 3-510-65149-9 .
  • WH Zagwijn: Vegetation, climate and radiocarbon datings in the Late Pleistocene of the Netherlands. Part 1: Eemian and Early Weichselian. In: Mededelingen Geologische Stichting NS. Volume 14, 1961, pp. 15-45.

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