Formation and Collapse of the Kalahari Duricrust [‘African Surface’] Across the Congo Basin, with Implications for Changes in Rates of Cenozoic Off-Shore Sedimentation - Geology and Resource Potential of the Congo Basin - page 200

propose the following simple model of regional excavation
(subterranean erosion) and collapse of this Kalahari cara-
pace, remnants of which are now found in many lower-lying
Cenozoic to Recent deposits of the CB (Fig. 10.12 ):
1. Jurassic-Cretaceous northeast-derived aeolian red
sandstones of the Kwango Group were deposited across
central Africa (and eastern Brazil), forming a giant
Gondwana desert under arid conditions (Myers et al.
2011 ; Linol 2013 ; Chap. 13 , this Topic). The sandstones
remained largely unconsolidated (Fig. 10.12a ).
2. With the onset of more humid conditions at the end of the
Cretaceous and during the early Cenozoic, Kalahari
silcretes and calcretes formed a thick layer of hard-cap
rocks across most of the basement of the KP and the red
sandstones of the CB, and is here named the

JURASSIC - CRETACEOUS
Aeolian sand dunes deposition (desert)

Kimberlites

a

END CRETACEOUS
Peneplanation and weathering (hot, humid)

'

Kalahari

(Fig. 10.12b ).
3. Increasingly wet conditions, following the Paleocene-
Eocene thermal maximum (e.g. Zachos et al. 2001 ),
resulted in fluvial activity across the Kalahari Surface,
excavating and eroding preferentially underlying poorly
consolidated (soft red) sandstones of the Kwango Group,
creating subsurface karsts topography (Fig. 10.12c ).
4. Accelerated erosion in the CB removed an estimated
volume of 0.5 x 10 6 km 3 of red sandstones that ultimately
led to the demise of the Kalahari Surface during sustained
riverine erosion and to re-deposition of giant boulders of
silcrete and calcrete (Fig. 10.12d ). The most recent
deposits trap Stone Age artefacts and alluvial diamonds
concentrates.
In summary, a prolonged period of peneplanation and
weathering at the end of the Cretaceous formed a thick
carapace (the Kalahari Surface) across the KP and the CB.
This was followed by rapid subterranean erosion and
'

Surface '

Kwango Group
unconsolidated red-beds
ca. 500 000 km 3

b

OLIGO-MIOCENE
Increased surface and subterranean fluvial activity (wet)

Caves

of the CB during wetter times that must have
generated large volumes of sediment to an off-shore sink
after the opening of the South Atlantic Ocean.

flushing '

c

RECENT
Silcrete and calcrete boulders re-deposition (wet)

10.6 Off-Shore Sedimentation History
of the Congo Fan

The Congo deep-sea fan is one of the largest submarine fan
systems in the world (ca. 300,000 km 2 ; Fig. 10.13 ),
formed on the continental margin of west-equatorial Africa

Alluvial
diamonds

d

the Kwango red-beds into the off-shore Congo Fan. A calculated
volume of 0.5 million km 3 sediments removed on-shore closely
matches the estimated off-shore accumulation of 0.7 million km 3 of
Oligocene to Recent sediments

Fig. 10.12 Regional model of formation and collapse of the Kalahari
hard-cap (the ' Kalahari Surface ' ) across the CB, and re-deposition of