Weald-Artois Anticline
The Weald-Artois Anticline is a geological structure running between the regions of the
Weald in southernEngland andArtois in north easternFrance .The
anticline uprose during theAlpine orogeny in the lateOligocene to middleMiocene , resulting in achalk 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 theThames andRhine to theNorth Sea , resulting in a largeproglacial lake to the northeast of the ridge. To the southwest, low-lying land connected the island that is nowGreat Britain to continentalEurope . Overtopping of this ridge at two separate times resulted in the severing of this peninsular connection. The firstglacial 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 theStraits 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 andSurrey has been greatly eroded, with the presumed chalk surface removed to expose older,Lower Cretaceous rocks and a small area ofUpper 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-facingescarpment s, theNorth Downs andSouth Downs . In Artois the chalk remains except in a small area aroundBoulogne-sur-Mer andDesvres , where mainlyUpper Jurassic deposits are exposed. ["Carte Géologique de la France", BRGM, Orléans]References
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