Weald-Artois Anticline

The Weald-Artois Anticline is a geological structure running between the regions of the Weald in southern England and Artois in north eastern France.

The anticline uprose during the Alpine orogeny in the late Oligocene to middle Miocene, resulting in a chalk ridge eventually reaching a height of about 180 metres. [ [http://www-qpg.geog.cam.ac.uk/research/projects/tertiaryrivers/neog.html Tertiary Rivers: Neogene (Miocene and Pliocene)] , Cambridge Quaternary, Cambridge University]

During the Pleistocene an ice sheet blocked the flow of rivers including the Thames and Rhine to the North Sea, resulting in a large proglacial lake to the northeast of the ridge. To the southwest, low-lying land connected the island that is now Great Britain to continental Europe. Overtopping of this ridge at two separate times resulted in the severing of this peninsular connection. The first glacial lake outburst flood occurred approximately 425,000 years ago, resulting in a waterfall of up to a million cubic meters per second that gouged out the Straits of Dover and flooded the low-lying land. The second, which may have been larger than the first, occurred approximately 225,000 years ago and finally severed the slender peninsula. [cite web |url=http://www.nature.com/news/2007/070716/full/070716-11.html |title=The megaflood that made Britain an island |author=Schiermeier, Quirin |work=Nature |date=2007-07-18|accessdate=2008-01-31] [cite web |url=http://environment.newscientist.com/article/dn12289-dambusting-megaflood-made-britain-an-island.html |title=Dam-busting "megaflood" made Britain an island |date=2007-07-18 |author=Marks, Paul|work=New Scientist|accessdate=2008-01-31]

During the most recent, Devensian glacial period, lowering of sea levels joined the British Isles once more to the continental mainland of Europe.

The eastern part of the ridge, the Weald of Kent, Sussex and Surrey has been greatly eroded, with the presumed chalk surface removed to expose older, Lower Cretaceous rocks and a small area of Upper Jurassic Purbeck Beds. [Gallois R.W. & Edmunds M.A. (4th Ed 1965), "The Wealden District", British Regional Geology series, British Geological Survey, ISBN 011884078-9] The chalk survives only as a rim of inward-facing escarpments, the North Downs and South Downs. In Artois the chalk remains except in a small area around Boulogne-sur-Mer and Desvres, where mainly Upper Jurassic deposits are exposed. ["Carte Géologique de la France", BRGM, Orléans]

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