Geology Reference
In-Depth Information
Fig. 15.3
Present day drainage
patterns of the CB, elevations and
major drainage patterns including
C
contorted,
T
trellis,
D
dendritic,
Sd
sub-dendritic,
P
parallel,
Sp
sub-parallel,
R
rectangular,
RA
rectangular-angulate (
white
lines
). Refer to Table
15.1
for
pattern descriptions and
Table
15.2
for drainage pattern
classification. River courses
generated from the SRTM DEM
V4 250 m (Reuter et al.
2007
and
Jarvis et al.
2011
)
beginning of the twentieth Century the CR experienced a
near constant flow (Laraque et al.
2001
). During the 1960s,
the CR recorded a discharge exceeding the previous 40 years
average, which was followed by a 10 % drop in its interan-
nual discharge in the 1990s which may be related to the high
degree of variability of rainfall over central Africa over
decadal and centennial time scales (Nicholson
2000
;
Laraque et al.
2001
). Owing to differential denudation
between high and low relief of the CB, development in the
drainage network will occur different rates throughout the
basin (Pinet and Souriau
1988
).
The first order geomorphology of the CB can be attributed
the interplay between the geodynamics that have led to
Africa
the cratonic areas, as evidenced by widely distributed
Palaeogene sediments over continental Africa (Seranne et al.
2008
). These surface processes, in turn are linked to climatic
factors, with past effects of this climatic signal being pre-
served in the sedimentary record (e.g. Linol et al., this vol-
evidence of important geomorphic and tectonic events. These
events include breaching of pre-existing barriers (pertinently
the Atlantic Rise) and expansion of the CRS, especially along
its southern margins by drainage capture events. The latter
have been most important in significantly increasing the total
area of the southern catchment.
Evidence of first order events of the CB
s Cenozoic devel-
opment, including fluvial changes and climatic and
geodynamic signals are indicated in the offshore terrigenous
sedimentary evidence (Lavier et al.
2001
). The Oligocene saw
large amounts of sediments transported into the Lower Congo
Basin, a consequence of late Cenozoic uplift and formation of
the Congo River, forming the Cenozoic Congo deep sea fan
(Anka and S´ranne
2004
; Seranne et al.
2008
;Ankaetal.
'
'
s bimodal topography (Fig.
15.1a
), controls of tecton-
ics (uplift and rifting) and surface processes. The latter have
resulted in incision and erosion of valleys around the basin
margins, with concomitant deposition of thick lacustrine and
fluvial sediments and autogenic river rearrangements, some-
times across drainage divides (Fig.
15.2
). For example, during
the Palaeogene there was extensive reworking, transport and
deposition of sediments within Africa, with limited erosion of
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