Cenozoic Landscape Evolution in and Around the Congo Basin: Constraints from Sediments and Planation Surfaces - Geology and Resource Potential of the Congo Basin - page 285

Few radiometric dates are available from this area (see
age arguments on Table 14.4 ). The only dated rocks
intersecting the planation surfaces are the volcanic rocks of
the Bukavu (or South Kivu) Volcanic Province (Kampunzu
et al. 1998 ). Only Pediment Xc can be dated by cross cutting
of its upstream incised network of rivers on the Lugulu
basaltic flow that belongs to the initial episode of the Bukavu
Volcanic Province (Lubala et al. 1984 ; Kampunzu et al.
1998 ), made up of pre-rift tholeiitic to transitional basalts.
The upstream part of the incised river network fitting to
pediment X c is younger than 5.9

to the youngest, (1) Congolese Surface ( C, Cd ), (2) Congolese
Surface degraded by the Lower planation surface ( Cdl ), (3)
degraded Lower planation surface ( ld ), (4) Pediments X ( X c ,
X f ), (5) Pediment Y ( Y c ) and (6) incised channels.
The only available age constraints are from relative
relationships with (1) dated sediments of the “ Gr`s

polymorphes ” Fm (Alexandre 2002 ) and (2) dated supergene

“ (Decr´eeta. 2010 —see arguments on

Table 14.5 ). From this we deduce that all the studied landforms
described above are younger than Paleogene (and probably
Eocene). Pediment X c is older than 10.3

cobalt caps ”

0.3 Ma. 0.1 Ma and Y c

(and may be Z c ) were shaped between 10.3 and 3.66 Ma.
The three large depressions or plains of the Upemba/
Kamalondo, Lufira and Lake Mweru (

14.5.2.4 South-Central: Katanga, Kamina/Kasai/
Lunde/Kwango Plateaus and Central CB
(S DRC, Zambia, Angola)
This domain of plateaus (Plate 1) stretches from the southern
side of the CB (i.e. the northern limit of the Kalahari Plateau)
to the transitions with the East African Dome (Mporokoso
Plateau, northern-eastern Zambia) and with the Angolese
Plateau (Bi ´ Plateau). This is the Congo-Zambezi divide
that define the boundary between two local base levels, the
Ubangi-Likouala Swamps to the north and the Chobe—
Okavango Swamps (Okavango and Machili Rifts), to the
south (see also Flugel et al., Chap. 15 , this Topic).
These plateaus and the CB correspond to the Congolese
Surface (Plate 2 and 14.5.1.3 ), buckled along an E-W trending
long wavelength (

Moero)/Luapala
Swamps (Plates 1 and 2) were interpreted as rifts (e.g.
Mortelmans 1953 ). Our study suggests that only the
Mweru Lake is an asymmetrical rift (Chorowicz 2005 ),
bordered by the NW Lake Mweru Fault, present-day sharp
escarpment. The other ones, the Luapala Swamps, the Lufira
Plain and the Upemba/Kamalondo Depression are not rifts
as indicated by the absence of significative sediments, but
pediments (pediments X c ). In this area, the only active fault
is the Upemba Fault, old geological structure (Mortelmans
1953 ), reactivated after the formation of the Congolese Sur-
face (maximum vertical displacement: 600-700 m) and prior
to X c . The Marungu, Kibara, Biano, Kundelungu and
Mporokoso Plateaus (Fig. 14.9 Ka1) form a large block
bounded to the NW by the Upemba Fault and titled toward
the SSE (long wavelength deformation:

¼

100 km) antiform. In the Central CB, the
Congolese Surface cuts across from the southern plateaus to the
Lukenie River (Plate 1), Archean rocks (Kasai Craton) and Late
Cretaceous red sandstones (Kwango Gp), and from the Lukenie
River to the Uele, Itimbiri and Congo Rivers, the lacustrine
Paleogene (Eocene?) sediments (see 14.4.2 and 14.4.4 ).
The Congolese Surface is dissected by incised valleys
(Kamina-Kasai-Lunde-Kwango Plateaus and Central CB) and/
or pediments (Katanga, Mbuji-Mayo area—not mapped here;
but see Roberts et al., Chap. 9 , this Topic, for more information).
Along the southern flank of the CB , the plateaus are
deeply incised by northward facing valleys. All these incised
rivers and channels fit to the local base level corresponding
to the Ubangi-Likouala Swamps. Two arguments indicate
that this incised drainage was initiated at time of formation
of pediment X c : (1) The present-day Congo River between
Kisangani and Mbandaka is located on the outlet of pedi-
ment X c (see 5.2.3.); (2) Along the eastern side of the CB,
following the N-S trending X c pediplain, the dissection of
the Kamina Plateau, incised by several rivers, starts with
pediments X c (Plate 2).
The Kalahari flank of the plateaus is deeply incised by
valleys, mainly on the Angolese Plateau. The rivers fit to the
local base level of the Chobe Swamps (Plate 1) filled by the
recent Kalahari Sands (younger than the

100 km).

14.5.2.5 Southwest: Angola Plateau and the
Central African Atlantic Swell, South
of the Congo River (Angola, SW DRC)
This domain (Plate 1) extends from the Angolese Plateau to
the Congo River and includes, from west to east (1) the
Atlantic Ocean coastal plain, (2) the Angolese coastal
Escarpment and (3) the Angolese Plateau passing northward
into the large stepped pedi-valleys to pediplains of the
Cuanza ( Kwanza) and Kwango present-day Rivers with

two troughs, the Cuanza-Luando (Cuanza large pedi-valley)
and Cassange (large pedi-valley) Troughs.
Here we focus on the Kwango and Cuanza large pedi-
valleys to pediplains. The successive planation surfaces are
labelled with the subscript kc for Kwango-Cuanza.
Six landforms are defined (Plate 2, Fig. 14.9 An, see
description on Table 14.6 ), from the oldest to the youngest,
(1) Upper planation surface 1 ( u1u ), (2) undifferentiated
Upper planation surface 2 and Lower planation surface
( u2lu ), (3) Pediments V ( V kc ), (4) Pediments W ( W kc ) (5)
Pediments X ( Xk c ) and (6) Pediment Y ( Yk c ).
The N-S trending Kwango large pedi-valley to pediplain
(600 to 700 km long) that feeds into the Congo River south
of the Bat ´ k ´ Plateau, is a type-case of pediment system
( 14.5.1.5 , Fig. 14.8 ).

¼

“ Sables ocres ” Fm,

here upslope incised).
In the Katanga area, six landforms are defined (Plate 2,
Fig. 14.9 Ka, see description on Table 14.5 ), from the oldest