Geoscience Reference
In-Depth Information
Landscape C: The Thames and tributary estuaries
The intricate pattern of tidal channels and islands that is so typical of this Landscape
extends from the Blackwater Estuary in Essex (Fig. 219) to the Medway and the Isle
of Sheppey in Kent. The Landscape has formed by the flooding of river valleys by the
recent (Flandrian) rise in sea level. The bedrock of the estuary is London Clay, but this
is buried under large thicknesses of recent marine, estuarine and freshwater muds.
Sea level has risen by over 100 m worldwide in the last 20,000 years, since the
end of the last (Devensian) cold episode of the Ice Age. Sea-level rise relative to the
local land surface may have been even higher in this particular area, due to a seesaw
effect between the northwest and the southeast of Britain: northern and western Bri-
tain have been rising since they are no longer being depressed by the weight of the ice
sheets; meanwhile, south and east England, on the other end of the 'seesaw', have been
gradually subsiding.
FIG
219.
Maldon (Fig. 215,
c1
) on the upper Blackwater estuary. (Copyright Dae Sasitorn
& Adrian Warren/www.lastrefuge.co.uk)
The idea that this area may recently have been tilted eastwards at the same time
as worldwide sea level was rising is supported by the sedimentation pattern of the re-
gion. Over the last 10,000 years, more than 30 m of marine and estuarine sediment has
accumulated where Canvey Island (
c2
) now is, whereas at Tilbury (
c3
), 20 km further
up the Thames, only 10 m of sediment has accumulated. During the last 10,000 years,
a number of peat beds formed further up the Thames, representing distinct phases of
