Geology Reference
In-Depth Information
10
Formation and Collapse of the Kalahari Duricrust
['African Surface'] Across the Congo Basin,
with Implications for Changes in Rates
of Cenozoic Off-Shore Sedimentation
Bastien Linol, Maarten J. de Wit, Francois Guillocheau, Michiel C.J. de Wit,
Zahie Anka, and Jean-Paul Colin
{
10.1
Introduction
margins, and to the east by the East African Rift System
(EARS). Their relatively flat interior is covered by an exten-
sive Upper Cretaceous-Cenozoic succession of sand dunes,
pan-lacustrine sediments and alluviums with hard-caps
(duricrusts) of calcrete, silcrete and ferricrete, collectively
named the Kalahari Group (SACS,
1980
). This succession
reaches a maximum thickness of about 500 m, but across
southern and central Africa is generally less than 100 m
thick, representing one of the world
The Congo Basin (CB) of central Africa lies at about 400 m
above mean sea level (amsl), and is linked to the south,
across a central African drainage divide, to the high interior
Kalahari Plateau (KP) at ca. 1,100 m amsl (Fig.
10.1
). The
CB and KP are flanked by distinct marginal escarpments
along the South Atlantic and southwest
Indian Ocean
s most extensive, long-
lived condensed stratigraphic sequences.
The Kalahari Group directly overlies Precambrian base-
ment of the Kalahari and Central African Shields
(Fig.
10.1b
), late Paleozoic to mid-Mesozoic sequences of
the Karoo Supergroup including Lower Jurassic flood
basalts in southern Africa, dated at 178-183 Ma (the
Stormberg Group; Jourdan et al.
2007
), and Cretaceous
volcanics and dykes in Namibia, dated at 127-132 Ma (the
Etendeka Group; Miller
2008
). By contrast, across the CB,
the Kalahari Group overlies Upper Jurassic to Upper Creta-
ceous red sandstones (e.g. the Kwango Group) ranging in
thickness between about 300 m and 1,000 m (Linol
2013
;
Kalahari Group marks a subcontinental scale peneplanation
surface that is commonly referred to as the
'
'
(e.g. King
1963
; Partridge and Maud
2000
; Haddon and
McCarthy
2005
; Decker et al.
2013
), developed as a result
of extensive denudation and uplift following the break-out of
Africa from Gondwana during the opening of the Indian and
South Atlantic Oceans, and the onset of the Kalahari epeiro-
geny (de Wit
2007
). However, the precise age-range of this
elevated, mega-denudation surface remains uncertain
because the stratigraphy of the overlying Kalahari Group is
poorly characterized, including many internal and local
unconformities and abundant silcretes, calcretes and ferri-
cretes that are difficult to date and correlate regionally.
Moreover, because large parts of this Kalahari succession
'
African Surface
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