GEOLOGICAL EXPOSURES
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GEOLOGICAL EXPOSURES |
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Several interesting geological exposures occur within the Kirstenbosch Gardens. Localities are superimposed on the map of gardens that visitors usually purchase and subsequently use to navigate around the various trails. Browse the geological sites below to get a description of what you are looking at. |
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| [1] Ferricrete-cemented talus breccia, containing angular blocks of sandstone derived from erosion of the Graafwater Formation strata upslope. The yellow colour comes from the ferruginous cement exposed during trail construction. Silvertree trail above the reservoir approaching junction with Contour Path. |
[1] Ferricrete-cemented talus breccia, containing angular blocks of sandstone derived from erosion of the Graafwater Formation strata upslope. Silvertree trail above the reservoir approaching junction with Contour Path. |
[2] Ripple marks preserved on an exposed bedding plane of red siltstone, Graafwater Formation. Contour Path south of Nursery Ravine. |
[2] Some of the red siltstones in the Graafwater Formation retain delicate ripples produced in pools along the course of the ancient river |
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[3] Ripple marks preserved on an exposed
bedding plane of red siltstone, Graafwater Formation. Here the wide surface
of the slab has been worn almost smooth by hikers. Contour Path south
of Nursery Ravine. |
[3] Periodic drying of the desert rivers
not only generated the red colour, bit also produced these polygonal patterns
related to the development of mud cracks |
[3] A bedding surface of red Graafwater
siltstone often shows polygonal patterns related to the formation of mud
cracks |
[3] The red Graafwater beds show cross
bedding formed during deposition from ancient streams, while the colour
was imposed by desert conditions |
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| [4] Steplike outcrops
of siltstone strata, Graafwater Formation. Contour path approaching Vaalkatkloof
stream from the south. |
[5] Nursery Ravine
at the junction with the Contour Path. |
[5] Contour Path
on the north side of Nursery ravine. The dolerite dyke crops out within
the dotted lines beside the trail. |
[5] Strong weathering
of the dolerite causes the rock to become practically indistinguishable
from the other brown boulders in Nursery Stream, but the fresh blue-grey
material is preserved in the interior |
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[5] Under microscope
(field of view = 3mm) the dolerite can be seen to contain tiny crystals
of feldspar (white), pyroxene (brown) and magnetite (black) |
[6] Flaggy outcrops of Graafwater siltstone form the south wall of Nursery Ravine, immediately below the Contour Path. | [7] Thicker beds of sandstone within the Graafwater Formation. Nursery Stream below the Contour Path. | [8] Basal contact between sedimentary strata of the Graafwater Formation and the underlying Cape Granite. Waterfall on the Vaalkatkloof Stream at its junction with Nursery Stream. |