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Geologic structure in southern England and northern France
The
Weald?Artois Anticline
, or
Wealden Anticline
, is a large
anticline
, a geological structure running between the regions of the
Weald
in southern
England
and
Artois
in northern
France
. The fold formed during the
Alpine orogeny
, from the late
Oligocene
to middle
Miocene
as an uplifted form of the
Weald basin
through
inversion
of the basin. The
folding
resulted in
uplift
of about 180 metres (590 ft),
[1]
though concurrent
erosion
may have substantially reduced the actual height of the resulting
chalk
ridges.
As is the case with all anticlines, older rock strata are found in the core of the structure. These are in this case
Upper Jurassic
and
Lower Cretaceous
strata. The western part of the ridge (the Weald of
Kent
,
Sussex
and
Surrey
in England) has been greatly eroded, with the presumed chalk surface removed to expose older, Lower Cretaceous rocks (
Wealden Group
) and a small area of Upper Jurassic
Purbeck Beds
.
[2]
On the French side of the English Channel more
Upper Jurassic
rocks crop out in a small area around
Boulogne-sur-Mer
and
Desvres
.
[3]
At the flanks of the anticline outcrops of the (younger) Upper Cretaceous
Chalk
occur. The chalk survives as a rim of inward-facing
escarpments
, forming the
North Downs
and
South Downs
. The Chalk forms characteristic white
cliffs
on both sides of the English Channel, an example being the
White Cliffs of Dover
.
Formation of the Strait of Dover
[
edit
]
The
Strait of Dover
is geologically speaking a very young feature, which cuts through the much older Weald?Artois Anticline. The anticline continues uninterrupted in the subsurface of the Strait of Dover and English Channel.
Gupta
et al.
argue that the section of the anticline between Britain and France was destroyed by two megafloods caused by the breaching of
proglacial lakes
. The first occurred around 450,000 years ago during the
Anglian Glaciation
(
MIS
12). It did not fully destroy the anticline although there was sporadic connection between the English Channel and the North Sea during periods of high sea level. The second megaflood occurred around 160,000 years ago during the
Wolstonian
/
Saalian
glaciation (MIS 6), after which Britain would be an island during periods of high sea level.
[4]
During the
most recent glacial period
, lowering of sea levels joined the British Isles once more to the continental mainland of
Europe
via
Doggerland
, until about 6500?6200 BCE.
References
[
edit
]