Geology Reference
In-Depth Information
CENTRAL «CUVETTE» and PLATEAUS
SURROUNDING RELIEFS
(Katanga, Kamina, Kasai, Lunde, Kwango, Batéké)
(Cameroon Highlands, Ubangian Rise, East African Dome, Atlantic Swell)
Kwango
Cuenza
Pediments
Congo
base level
Atlantic
base level
Katanga
Present-day
Fluvial terraces
Pediment Z
Z
c
Z
a
Iron duricrust 4
Pediment Y
Y
c
Y
kc
Y
a
Iron duricrust 3
Pediment X
X
c
X
kc
X
a
V
kc
V
a
Pediment V
V
c
Pediment W
W
kc
W
a
W
c
Lower Planation Surface (
l
)
Iron duricrust 2
Upper Planation Surface 2 (
u2
)
Laterite «Top Grès polymorphes»
Gravel beds
Iron duricrust 1
Upper Planation Surface 1 (
u1
)
«Grès polymorphes» Fm - Yangambi Fm
Laterite «Top Cretaceous sediments»
Cretaceous
Fig. 14.11
Relative chronology of the sediments and landforms of the CB and surrounding highs
identified with reasonable confidence. It crops out along a
crescent from the Cameroon highlands crossing the
Ubangian Rise and the Blue Mountains to finish on the
southern Itombwe Plateau. Southward, in Katanga and on
the Angola Plateau, this surface merges either with Upper
planation surface 1 (Katanga) or with the Lower plana-
tion surface (Angola). In Katanga, this surface could be
equivalent of the uppermost iron duricrust (iron duricrust
2) located above the
Gabon) to the Ubangian Rise and the northern East Afri-
can Dome (Ituri). To the east (Ituri), the Lower planation
surface is a pediplain with few preserved weathering
profiles that passes to the west (north Gabon-south
Cameroon) into a large highly weathered pediplain
(with iron duricrusts). Toward the southeast (middle and
southern East African Dome and Katanga), this surface is
highly degraded by younger pediments (mainly X).
Along the central African Atlantic Swell, the Lower
planation surface is only preserved on the high relief of
Gabon-Congo, the Chaillu Massif. In Angola, because of
the absence of spatial continuity with Katanga or Gabon,
the summit planation surface may be the Upper planation
surface 2 or/and the Lower planation surface.
Pediments V (V
a
V
c
V
kc
) and W (W
a
W
c
W
kc
)
record both a
narrowing of the pediplains and the emergence of differ-
ent local base levels and different pedi-valleys drainages,
labelled V
a
and W
a
for the South Atlantic Ocean base
level, V
c
and W
c
for the Congo base level and V
kc
and
W
kc
for the Kwango-Cuenza large pedi-valleys to
pediplains. No V and W pediments were identified
along the western flank of the East African Dome, but
some forms attributed to the degraded Lower Surface
Gr
`
s Polymorphes
Fm.
Congolese Surface (C)
covers the Central CB (dissected
planation surface) and the Bat
´
k
´
and Kwango/Lunde/
Kasai/Kamina Plateaus (this etchplain is covered by the
surficial sediments of the
“
”
“
”
Fm).
On the Congolese flank of the Ubangian Rise, the
Congolese Surface merges with Upper Surface 2 (
u2
) and
with the Lower Surface (
l
). In Katanga, the Congolese Sur-
face corresponds to the iron duricrusts 1 and 2 of Alexandre
(
2002
)
.
The Congolese Surface (
C
) is then contemporaneous
with the Upper planation surfaces (
u1
and
u2
) and then
represents a long-lasting planation surface.
Lower planation surface (l)
is the dominant form in the
northern half of the mapped area. It continuously extends
from the northern Central African Atlantic Swell (North
Sables ocres
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