Geology Reference
In-Depth Information
Fig. 10.7 Sieved-residues of sample—106-107 m from the Ngami-2 borehole (Fig. 10.6c ). ( a ) Ostracode shell fragments dated at ca. > 50 ka by
14 C method, and ( b ) charophyte stems
Hardpan
'AFRICAN SURFACE'
Poorly consolidated red sandstones
Fig. 10.8 Northernmost extension of the KP (ca. 1,100 amsl) in the
southwest CB (ca. 400 amsl). A hardpan of silcrete and calcrete (
[the
] across red sandstones of the Kwango Group.
This distinct pedogenic unit at the base of the Kalahari Group can be
correlated with similar calcretes in Botswana and Namibia
'
African Surface
'
'
Poly-
morph Sandstones
'
) overlies
a
regional peneplanation surface
10.4.1 Silcrete and Calcrete Boulders on Flats
and River Terraces of the Kwango Valley
the lower sequence of the Kalahari Group (the
'
Polymorph
Sandstones
), and are displaced lower down along the slopes
(Fig. 10.9a ). In the lower-lying Kwango Valley, at
elevations between 400 m and 600 m amsl, remnant outcrops
of red sandstones form flat erosional surfaces devoid of
silcrete or calcrete caps (Fig. 10.9b ). These are commonly
covered with residual blocks of silcrete and calcrete
(0.5-5 m in diameter), and often best preserved within the
'
The Kwango Valley is deeply incised into the Kwango
Group red sandstones along the northern flank of the KP in
the southwest CB (Fig. 10.2 for location). Along the scarp at
the upper part of the KP, large blocks of silcretized
sandstones (5-15 m in diameter) have broken-away from
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