The Present Day Drainage Patterns of the Congo River System and their Neogene Evolution - Geology and Resource Potential of the Congo Basin - page 317

of the Northern Bat´k´ Plateau System of the basin western
margin (see Table 15.2 and Figs. 15.3 and 15.4C ).

dominant fault control. Additionally much of this zone
corresponds to the Precambrian basement (Deffontaines
and Chorowicz 1991 ), which incorporates a portion of the
West Congolian orogenic belt making it probable that tec-
tonics, lithological structures and rock differences, have
resulted in a trellis drainage forming. Subsequent tectonic
activity may have modified the rivers further.

15.3.3.1 Luangwe System (P7 in Fig. 15.3 )
The southern plateau areas, which incorporates the Luangwe
basin and associated tributary catchments in the southern
Basin has dominantly parallel drainage pattern. The bound-
ary zone varies from parallel to sub-parallel and it covers a
region that has been suggested to have remnants of an upper
Jurassic drainage network (Cahen 1954 ). The parallel drain-
age is associated with the transition zone of the low gradient
slopes of the northern extent of the Kalahari Plateau to the
basin of Cuvette Central . The parallel pattern suggests
uniform lithology which allows the river to flow along the
greatest slope, as seen to the south of Kasai (Zernitz 1932 ;
Deffontaines and Chorowicz 1991 ).

15.3.5.2 Sembe-Ouesso (T10 in Fig. 15.3 )
This pattern is controlled by numerous south-north trending
faults, with several NNE trending faults, with the rivers
flowing on Precambrian basement. Dolerite outcrops further
add to the structural control of this trellis pattern. Therefore
the Sembe-Ouesso drainage network is predominantly con-
trolled by the directionality of the faults, and the underlying
lithology.

15.3.5.3 Kwango Valley (T11 in Fig. 15.3 )
The Kwango Valley, found along the southern margin of the
CB exhibits a trellis pattern drainage pattern. Here the
Kwango River flows in a north-west direction, compared to
parallel, north flowing rivers of adjacent Luangwe System to
the east. Incision into the Precambrian basement by the
Kwango River appears to have caused the diversion and
breakup of the longer parallel streams into several shorter
rivers. Thus the Kwango River trellis pattern, at least in the
eastern region close to the Luangwe System, likely
represents a modification of a parallel drainage that existed
on the tilted plateau, previous to incision by the Kwango
River. Furthermore, its location on the margin of the West
Congolian orogenic belt has resulted in the western part of
the Kwango Valley developing a strong trellis pattern,
shaped by structural control in this region. The Kwango
Valley drainage therefore is dominantly a modified parallel
network with subsidiary structural control.

15.3.4 Sub-parallel

15.3.4.1 Northern Bat ´ k ´ Plateau System (Sp8 in
Fig. 15.3 )
The Northern Bat´k´ Plateau System comprises of many
near linear rivers, flowing across a NE dipping plateau (see
Table 15.2 and Figs. 15.3 and 15.4D ). The combination of
the a strong NNE flow direction and the linearity of the
rivers with connections between parallel rivers being short
suggests a degree of fault control. The location of the plateau
to the Atlantic margin, lead Karner and Driscoll ( 1999 )to
suggest a Gondwana break-up origin of these rivers. These
rivers may have begun flowing basinward due to flexural
rebound associated with Gondwana break-up, that
established numerous, short rivers toward the interior basin
(Karner and Driscoll 1999 ) and these patterns have been
maintained to present day.

15.3.5 Trellis

15.3.5.4 Lufupa System (T12 in Fig. 15.3 )
Forming the southern margin of the Congo Basin the Lufupa
trellis drainage system comprises of the easterly flowing
Kasai River in the west and the northerly flowing upper
Congo (Lualaba) River in the east. The Lufupa system thus
forms the main portion of the Congo-Zambezi Watershed.
The western part of this trellis network, around the Kasai
River, may contain the remnants of late-Cretaceous rivers
(Cahen 1954 ) and thus it inherited to some degree. Whereas,
the presence of folded schists and tillites of the Kanga-
System (Upper Precambrian) and tectonics (indicated by
three major fault scarps) (De Dapper 1988 ) in the eastern
half of the trellis drainage are the likely controlling factors
on the drainage pattern.

There are five instances where trellis drainage was
identified, with this drainage type occurring mainly along
the peripheries of the central basin (see Table 15.2 and
Figs. 15.3 and 15.4E ).

15.3.5.1 Southern Bat ´k ´ Plateau System
(T9 in Fig. 15.3 )
The Southern Bat ´ k ´ Plateau System differs from the North-
ern Bat´k´ Plateau System in that the rivers in the region are
shorter, with more right angles and flow directly into CR.
The geometry of the rivers and the consistent directionality
of many of the river segments, being WWN, reveal a