- London-Brabant Island
The London-Brabant Island goes under a number of names such as London Island, London Platform, London-Brabant Massif, Wales-Brabant Massif or, in French texts, Anticlinal ardennais du Brabant, Terre de St-Georges et du Brabant or Bloc du Midland et du Brabant. It was an anticlinal ridge extending from the
Rhineland to the sites ofEast Anglia and the middle Thames. In a sense, it still exists but in Britain, it is buried. It was part of theterrane ,Avalonia .Compass points mentioned below relate to the modern orientation of the island.
Formation
To state events very simply, the rocks of which it is formed are mainly of the
Precambrian ,Cambrian ,Ordovician andSilurian but the anticlinal folding came with theCaledonian Orogeny at the end of the Silurian and in the earlyDevonian , when the continent was drifting through the southernlatitude s. As it passed through the dry latitudes represented today by theNamib Desert 1, it was eroded and thesoil s becameLaterite represented by theOld Red Sandstone which shows its presence in the red soils of Devonshire. The strata, particularly of the Precambrian are complex. They are also poorly understood because they are beyond the reach of mostborehole s.The Carboniferous
The period from which the island has exercised most economic influence on modern Europe was the
Carboniferous . As the continent was drifting past theEquator , on the island's shores, there grew a richtropical forest swamp . On the island's southern shore, it left theDinantian ,Namurian and Westphaliancoal field s ofFrance ,Belgium and western Germany. See [http://de.wikipedia.org/wiki/Aachener_Revier Aachener Revier] (in German).To its northwest, the thinner crust between it and the
Market Weighton Axis was crumpled between the blocks leaving low ridges of wet land between strips of water such as theWidmerpool Gulf . On the wet land, the coal fields ofLeicestershire ,Nottinghamshire andDerbyshire were deposited. These extend further east but are now at ever greater depth. At the modern eastYorkshire and northLincolnshire coast for example, their upper surface is at about 2km depth. These Carboniferous beds are part of a system linking with those of Westphalia, around the north side of the island. On the northNorfolk coast, the line of the Carboniferous shore roughly coincides with the modern one.2The Permian and Triassic
As the continent drifted northwards, away from the Equator, through the latitudes represented today by the
Sahara desert , the erosion was renewed. This time, the lateritic soils are represented by theNew Red Sandstone and the red soils of Leicestershire andRutland .The early Permian was the time of the height of the Variscan earth movements as the crust to the south was crushed against the island. The great disturbances seen at the surface in
Brittany , theArdennes and theRhineland also lie below the Paris Basin. They fade out in the gentleranticline of the downs and Weald of southern England which overlies the edge of the island. The axis of this anticline is normally called the northern Variscan front. However, the chalk of the downs is Upper Cretaceous, so the process continued well after the Permian. The point in the present context is that the stability of the island contrasts with the relatively unstable crust to its south, which was forced into a long mountain ridge.To the north, economically important things were happening. Western Britain was pushed up as part of the Variscan Orogeny while the east of Britain, including the island began to subside leaving a broad basin, north of the island and south of Scandinavia. This formed a shallow sea in a very dry climate. Desert sands and salt basins were a result but there are also mudstones. This provided the alternating porous and imperveous rocks which have trapped the gas escaping when the coal measures, below were subjected to
geothermal heat . This has left a group of gas fields off the Norfolk coast. That is to say, off the coast of the island.Rhaetic Transgression
In the early
Jurassic , the Rhaetic sea flooded much of thePermian plain. On the margin of the London-Brabant Island, the estuarine conditions which left theLower Estuarine Series prevailed for a while before the sea rose so as to deposit theLincolnshire Limestone s before falling again so that theUpper Estuarine Series was left. Again the sea rose to deposit theBlisworth Limestone , theBlisworth Clay and theUpper Jurassic clays.The same general pattern occurred in France leaving the Paris Basin flooded from Anjou to Luxembourg.
Cretaceous
By the
Cretaceous the island had sunk much further in relation to the sea level. Before the end of the period, the British end was buried inUpper Cretaceous chalk. This happened because the Pacific Ocean bed swelled up causing the world’s seas to rise but also, the process released much carbon dioxide. That caused global warming, melted the ice caps and was slowly converted to calcium carbonate which was precipitated in the water.Modern existence
It is now best viewed as a block of dense crust floating deeply sunk into the mantle and overlain with less dense superficial rocks. It depresses the boundary of the crust and the mantle (
Mohorovičić discontinuity , commonly Moho) to depths greater than 40 kilometres as against a figure at the top of thecontinental shelf of about thirty and less than fifteen below oceanic depths.3The map shows that there is some tendency for such seismic activity as there is in the region, to occur around the margin of the massif. It was into this pattern that the
2008 Lincolnshire earthquake , marked by an orange star, fell.ee also
*
Geologic time scale
*Proterozoic References
*Cameron, T.D.J. "et al". "The Geology of the Southern North Sea" (1992) ISBN 0-11-884492-X
*Dercourt, J. "Géologie et Géodynamique de la France" 3rd. edn. (2002) ISBN 2-10-006459-2
*Dercourt, J. "et al". "Carte Géologique de la France à l'Échelle du Millionième" ISBN 2-7159-2158-6
*Gallois, R.F. "Geology of the Country around King's Lynn and The Wash". (1994) ISBN 0-11-884495-4
*Glennie, K.W. ed. "Introduction to the Petroleum Geology of the North Sea" 3rd. edn. (1990) ISBN 0-632-02711-8Footnote
*Note 1: Reference to modern climate regions is intended to be helpful in envisaging events but although the basic climate zones persisted throughout the story, the changing configuration of the continents had a great and changing effect on the configuration of the climate zones.
*Note 2: Gallois, Figure 9 shows how the overlying strata lie in relation to it in north Norfolk.
*Note 3: Dercourt, Figure 6.2.
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