·
The Karoo Super Group of Permian age consists of
the Dwyka Formation, Ecca Group and Beaufort Group.
·
The Beaufort group overlies the Ecca group and
consists of alternating mud-stone (red in places) and sandstone.
·
It sub-divides into the lower Abrahamskraal
Formation (1 500m-2 000m thick) and an upper Teekloof formation (±1400m thick)
with the boundary arbitrarily at the base of the so-called “Poortjie
Sandstone”.
·
This formation consists of mud-stone (red in
places), sandstone and thin greenish cherty beds.
·
The sandstone's represent river channel deposits
and the mud-stones, floodplain deposits.
·
The cherty beds were originally ash fall tuffs,
although the presence micro-cross-lamination suggests subsequent transportation
by water onto the floodplains.
·
Jurassic-age dolerite extensively intrudes the
Beaufort Group as dykes and sheets. Inclined sheets form crescent shaped or
concentric intrusions that are clearly visible on the Middle- and Upper
Plateau.
·
The sills range from a few meters to over 100m
in thickness.
·
The dolerite causes a metamorphosis effect on
the adjacent host rocks.
· Mud-stone altered to horn fells and the sandstone's develop a quarzitic appearance.
·
Deposits of Quaternary age include river terrace
gravel, calcrete, alluvium and debris.
·
Terrace gravel consists of fairly well-rounded
cobbles and boulders composed largely of dolerite.
·
The terrace gravel shows clearly along the banks
of the Gamka River where sharp profiles occur.
·
These gravels are partly calcrete cemented and
occur on terrace remnants that now lie from a few meters to a maximum of 30m
above the general land surface.
·
Calcrete occurs directly on bedrock and has also
formed extensive deposits within some larger areas of alluvium, attaining a
maximum thickness of a few meters.
·
The alluvium embraces both alluvial slopes
(sheet wash) and alluvial valley (channel-related) deposits, with the former
predominating in the Lammertjiesleegte and the latter dominating in the
Stolshoek areas of Karoo National Park.
·
Vegetation types are closely linked to soil
type, soil depth, rockiness, slope and aspect.
·
Finer soil types with smaller grains (such as
clay) generally retain moisture better than coarse-grained soils.
·
In soils with very high clay content water may
be retained so well that it is unavailable for absorption by plant roots.
·
Clay also forms a compacted surface more easily,
causing water to run off rather than penetrate deeply into the soil.
·
Deep soil, if it is too sandy does not retain
water as well as rocky soils.
·
Vegetation growing on rocky soils is therefore
more resilient to the effects of drought and grazing.
·
Deep Karoo soils are very easily eroded by wind
and water if denuded of a healthy vegetation layer, leading to even more
degraded veld with poor fodder production for herbivores.
Soils
·
The dominant soil-forming processes have been
rock weathering, the formation of orthic topsoil horizons and, commonly, clay
alleviation, giving rise typically to lithucutanic horizons.
·
Soil forms that are typical of these processes
are Glenrosa and Mispah.
·
Any other soil form can however also be found in
these land types.
·
Oakleaf soil forms, deep or shallow, developed
by rock weathering also occur in upland sites.
·
The steep slopes, middle plateau and Puttersvlei
(upper plateau) areas of Karoo National Park, excluding the northern most
corner, fall into the Ib land type.
·
Surface rock with underlying soil or rock covers
sixty to eighty percent of these areas.
·
The parent material of the slopes consists of
mudstone, siltstone and sandstone with some dolerite intrusions, and typically
Mispah or Glenrosa soil forms.
·
Dolerite covers most of the middle plateau, with
an influence of mudstone, siltstone and sandstone closer to the upper slopes.
·
Fertile soils occur on this flat plateau with
little erosion save where the deep red soils gradually erode from a natural
basin.
·
Dolerite rocks cover most of the Puttersvlei
section of land type Ib, with the underlying sandstone appearing in terraces,
descending in a northerly direction.
·
The northernmost corner of the upper plateau
occurs in land type Db.
·
Prismacutanic and/or pedocutanic diagnostic
horizons characteristically dominate this land type.
·
Non-red B horizon, duplex soils cover more than
half the land area.
·
The local area is underlain by rocks of the
Karoo Super Group.
·
These are mostly sediments with some later
igneous intrusions.
·
Sediments are rocks formed by the erosion of
older rocks, which have been deposited by and in water (rivers, lakes and seas
and wind).
·
Igneous rocks are related to volcanoes.
·
Most of Karoo rocks are sediments deposited in a
huge inland fresh water lake/sea in the middle of the super continent of
Gondwanaland (South America, Antarctica, Australia, Africa, India).
Philippolis is in the Beaufort Group:
·
It mainly consists of sandstones and purple
shales.
·
The sandstones hold all the underground water of
the Karoo area.
·
It’s also world known for the early dinosaurs
and mammal fossils.
·
Intruded into the Beaufort sediments are
dolerite sheets, dykes (vertical) and sills (horizontal).
·
These are basaltic in composition and are the
feeders for the Drankensberg basalt levels.
·
These are very hard rocks that have a dark black
colour on the outside resulting in then being called “ysterklip” by locals.
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180 my
|
Stormberg
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Volcanoes basalt for as of
Drakensberg
|
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Clarens
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Wind deposited mostly – in Sahara
desert
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Red Beds
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Red coloured sandstones and shales
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Beaufort
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Dark to purple mudstones and white
sandstone
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Ecca
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Black shales and very fine weeds,
sand stone
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300 my
|
Dywka Tillite
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Deposited by glaciers and melting
icebergs 300 million years (my) ago
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