Bild 1

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The basement relief in South Sweden its
development and relation to the tectonic and
climatic history during the Phanerozoic
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What questions need to be answered ?

• What does the relief look like ? Different types,
  spatial distribution etc. Descriptive approach.
  Maps, DEM, field work.
• When was the relief formed ? Problem of dating.
  Geological constraints.
• How was the relief formed ? Which and where are
  the indicators of process ?

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Problem 1 The geology Shield areas such as the
Fennoscandian consists mostly of Precambrian
rocks of different types. This is a problem when
trying to date different landforms especially in
formerly glaciated shields, since the hiatus
between the Precambrian bedrock and the
Quaternary cover represents a considerable amount
of time, often more than 1 Ga.
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Problem 2 The fact that Scandinavia and South
Sweden was repeatedly glaciated during the
Quaternary give rise to problems. First, older
weathering mantles and sedimentary cover rocks
have been eroded away. Secondly, the landforms
may in different amount have been reshaped by
glacial erosion. Indeed many writers consider the
knob and basin topography typical of glaciated
shields a result of differential glacial erosion.
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How does the relief look like ? Maps of different
kind make it possible to distinguish different
landforms and landscape types in the Precambrian
rocks. This shaded relief map is based on digital
elevation data
we can see plains in different parts
Here we have hilly relief of different kind
We may also see individual forms such as
Valleys
Residual hills
Tectonic landforms
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The age of different landforms Can be judged by
using the relation to the sedimentary cover rocks
bordering the area
Lower Palaeozoic sedimentary rocks cover the
shield in the eastern and northern part of the
area
Mesozoic sedimentary strata cover the shield in
the south and in the west
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Now we are able to describe the relief
topographical dataset and we also have a
chronological control by using the geology By
mapping the entire area along E-W and N-S
profiles it is possible to differentiate the
bedrock relief in southern Sweden
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Two E-W profiles and two N-S profiles. What do
they show ?
1) An inclined flat surface emerge from below
Lower Palaeozoic (Cambrian) rocks in the east and
north the relief was formed before the Cambrian
2) An inclined undulating surface emerge from
below Mesozoic (Jurassic Cretaceous) rocks in
the west and south the relief was formed before
the Jurassic and Cretaceous
3) Stepped horisontal surfaces in the central
part is separated by erosional scarps from the
inclined surface in the east and cut off the
inclined surface in the south and west these
surfaces are thus formed after the Mesozoic, i.
e. they are of tertiary age
4) In some places the sub-Cambrian surface is
fractured and tilted in different blocks
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This is the position of the previously shown
profiles
Exhumed sub-Cambrian Peneplain in the north and
east
Exhumed Sub-Mesozoic relief in the west and south
Stepped Tertiary palaeoplains in the central part
Dissected part of the sub-Cambrian peneplain
Tornquist Tectonoc Zone
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The sub-Cambrian Peneplain
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The sub-Cambrian Peneplain emerging from the
Cambrian sandstone along the Småland coast is
extremely flat. Even landforms in the Quaternary
deposits are seen in the relief, as for instance
the esker on the map to the left. Some prominent
residual hills occur, as for example Blå Jungfrun
(lower right) in Kalmarsund.
View of the peneplain from Aboda Klint, south of
Högsby, southeastern Sweden.
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The sub-Cambrian Peneplain viewed from Omberg,
Östergötland
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Slätter det subkambriska peneplanet
The extremely flat surface at Nordkroken, very
close to the Cambrian cover forming the base of
Halleberg in the background.
The sub-Cambrian surface at Råbäck, Kinnekulle,
Västergötland
Cambrian conglomerate
Precambrian gneiss
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Sub-Mesozoic Relief of different types
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The relief in northeastern Skåne and in Blekinge
Joint valley landscape
Undulating hilly relief
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Undulating hilly land in the northern part of the
Kristianstad Plain
Precambrian bedrock hills protrude through the
Cretaceous sediments
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At the old clay pit at Blaksudden. The
Precambrian basement found beneath the Cretaceous
sediments is weathered to clay
minerals (kaolin mainly). The weathering mantle
is thich and reaches over 50 m at some places.
This suggests that deep weathering that occurred
before deposition of the Cretaceous sediments
formed the basement relief in this area.
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At Kjugekull it is evident that the weathering
mantle was partially eroded before the Cretaceous
sea transgressed over the area since Cretaceous
sediments rest directly on the granite surface.
Many of the landforms, also quite small pits and
hollows are formed prior to the late Cretaceous.
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Sprickdalslandskap
Joint valley landscapes are found within the
sub-Mesozoic relief on the west coast and in
Blekinge. The photo shows part of Bohuslän. The
structural control is evident in joint valley
landscapes, which typically consists of joint
aligned valleys and basins.
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Joint valley landscape on Tjörnekalv, Bohuslän
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The join valley landscape in Blekinge has lower
relative relief than in Bohuslän and is also
characterised by N-S trending valleys
Remanats of kaolin found within joints suggests
that the joint valley landscape in Blekinge was
formed during the same weathering phase as the
undulating hilly relief.
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Deep clefts with rounded weathering forms are
abundant within the sub-Mesozoic relief. These
examples are from Bohuslän (above) and Halland
(right).
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The plains of central south Sweden
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The South Småland Peneplain is extremely flat and
is interrupted only by scattered residual hills.
Lunnabacken from where the photo below is taken
is one example. The photo is taken northwards
towards the South Småland Peneplain
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Stepped palaeoplains dominate the central part of
the South Swedish Highlands. The photo below is a
view to the east fromIsaberg, Hestra. The
different levels is quite easily recognized.
200 m level
Sub-Cambrian Peneplain
South Småland Peneplain
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Joint valley landscape in Östergötland and
northeastern Småland
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The relief in this area is highly controlled by
the bedrocks structure as can be seen in the
maps below which show the distribution of steep
slopes (left) and the direction of bedrock hills
(right).
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Reliefens ålder och bildningssätt
Gravelly saprolites are common to find in this
area (see next slide also) and is closely related
to landforms such as joint valleys, steep slopes
and boulders. The weathering here is thus of
another type than is found within the joint
valley landscapes in Bohuslän and Blekinge.
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The gravelly saprolites are found in dissected
part of the sub-Cambrian Peneplain. Uplift and
dissection of the peneplain probably occurred in
Neogene (end Tertiary) and caused new relief in
this area.
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SUMMARY OF EVENTS
In late Precambrian the basement was denuded to a
flat surface with scattered residual
hills Throughout the Cambro-Silurian and
probably also the Devonian, thousands of metres
of sediments was deposited on the denuded
basement During the Jurassic/Cretaceous parts of
the basement was uplifted and the Cambro-Devonian
was eroded. The climate was warm and kaolinitic
weathering along joints and fracture zones formed
joint aligned landscapes and undulating hilly
landscapes In Late Cretaceous most of the
weathering mantle was eroded and was succesively
Late Cretaceous sediments were deposited on the
basement In the Tertiary (Miocene) the basement
was uplifted again, however, the Tertiary climate
was drier for most of the time and plains
developed at different by pediplanation processes