The Present Day Drainage Patterns of the Congo River System and their Neogene Evolution - Geology and Resource Potential of the Congo Basin - page 315

individual drainage patterns will now be discussed in more
detail. Figure 15.3 indicates the extent and location of the
various drainage patterns for the CRS and Table 15.2
provides the names and map codes of each drainage type
and an example of the drainage pattern from the CB is
illustrated in Fig. 15.4 .

Central (see Table 15.2 and Figs. 15.3 and 15.4B ). Several
of these zones are associated with areas of locally outcrop-
ping resistant lithologies and structure, in a region that is
dominantly alluvial in nature. Abrupt changes in flow direc-
tion in zones of transition from one dendritic to sub-dendritic
patterns reveal the presence of NE-SW and ESE-WNW
trending faults (Deffontaines and Chorowicz 1991 ). Addi-
tionally, to the south, the Luk´mi´ and Kasai Rivers have
parallel interfluves that suggest the modification of river
patterns by a horst block or tilted block (Deffontaines and
Chorowicz 1991 ). The abrupt change in river direction of the
Congo River near Kisangani, the middle section of the
Sankuru River and also in the lower Kasai to the south
such structural controls, which have experienced vertical
movements since the Cenozoic (Figs. 15.1 and 15.5 ;
Deffontaines and Chorowicz 1991 ). The regular, trending
to parallel drainage pattern of the lower Kasai River in the
south, may indicate a distinct, major block tilted northwards
(Deffontaines and Chorowicz 1991 ).

15.3.1 Dendritic Patterns

In the CB there are three regions exhibiting dendritic
patterns and four exhibiting sub-dendritic patterns (see
Table 15.2 and Figs. 15.3 and 15.4A ):

15.3.1.1 Northern Oubangui System
(D1 in Fig. 15.3 )
This large, northern area of the basin appears to correspond
to the underlying Precambrian basement (Chap. 2 , this
topic). The occurrence of fractured, weathering resistant
Proterozoic quartzitic sandstones provides localised struc-
tural control on some tributaries (Runge 2007 ).

15.3.2.2 Western Congolian Wetlands
(Sd4 in Fig. 15.3 )
The drainage pattern of the rivers flowing south into the CR
just before it crosses the Equator for a second time is sub-
dendritic. This drainage zone corresponds to a large,
inundated region of dominantly Holocene alluvium that
forms the Western Congolian wetlands. A combination of
low gradients and mosaics of very dense tropical rainforest
and swamplands has prevented the establishment of den-
dritic drainage. This can be seen in the multi-branching
meandering form of Likoula aux Herb ´ s River (a tributary
of the lower Sangha River, Fig. 15.5 ) as it flows through the
wetlands. Parts of the region have be influenced by
neotectonics (namely Lac T´l´ (Master 2010 ) which has
likely further inhibited the development of a dendritic pat-
tern through network reorganisation.

15.3.1.2 Cuvette Central (D-Sd2 in Fig. 15.3 )
The drainage pattern of the Cuvette Central is dominantly
dendritic, although several large extents of interleaved sub-
dendritic drainage patterns are present. Cahen ( 1954 )
suggested a Neogene to early Quaternary age for the large
portions the Cuvette Central dendritic pattern and that
portions of present day channels of the Sangha, Oubangi
and Congo Rivers that flow through the Western Congolian
wetlands, along with the Lukemie River, are related to the
formation of Malebo (Stanley) Pool (Fig. 15.5 ). These
sections thus represent the youngest part of the network
(Cahen 1954 ). It is likely that portions of the Cuvette Central
have been superimposed, flowing along inherited older
trends (Deffontaines and Chorowicz 1991 ).

15.3.1.3 Upper Malagarasi System (D3 in Fig. 15.3 )
The upper Malagarasi system exhibits a dendritic pattern.
The dendritic pattern lies predominantly on Tanzanian cra-
tonic region, in the shallow basin region south of Lake
Victoria. The tectonic stability and broadly uniform lithol-
ogy this region would have allowed for the uninterrupted
development the Malagarasi system.

15.3.2.3 Lindi System (Sd5 in Fig. 15.3 )
This small zone of sub-dendritic drainage occurs in the
north-east of the basin with trellis and dendritic drainage
lying on the downstream side to the west and north, while
rectangular angulate and contorted drainage occurs upstream
in the southern and eastern sections. The Lindi systems thus
appears to be influenced both by the structural influence of
the EARS to the west and the trellis network of the down-
stream mid-Congo. It is possible that the Lindi System was
part of the Cuvette Centrale and Luvua (sub) dendritic
system and has been subsequently isolated by downstream
capture and modified by the EARS in its headwater zones.

15.3.2 Sub-dendritic

15.3.2.1 Cuvette Central (D-Sd3 in Fig. 15.3 )
There are several of zones of sub-dendritic drainage that
occur within the overall dendritic pattern of the Cuvette
Central . This sub-dendritic drainage dominantly occurs in
the western, eastern and southern zones of the Cuvette

15.3.2.4 Luvua System (Sd6 in Fig. 15.3 )
The Luvua system occurs in the south-western areas of the
Congo Basin and extends northward along the CR. The