The Upper Mantle Seismic Velocity Structure of South-Central Africa and the Seismic Architecture of Precambrian Lithosphere Beneath the Congo Basin - Geology and Resource Potential of the Congo Basin - page 3

Fig. 1.1 Topographic map of
central and southern Africa
showing the major Archean
cratons (Kaapvaal, Zimbabwe,
Tanzania, Kasai, Bomu, Ntem;
solid black lines ), the greater
Congo Shield ( dashed black line ),
the zero thickness contour for the
Mesozoic and Cenozoic
sediments of the Congo Basin
( blue line ), the inferred location
of Neoproterozoic rifts within the
Congo Basin ( red dashed lines ),
and the outline of the Bouguer
gravity map in Kadima et al.
( 2011a )( rectangle outlined with
red dashed lines ). K-A Belt is the
Karagwe-Ankole Belt. The
location of the Samba (S), Dekese
(D), Mbandaka (M), and Gilson
(G) wells are shown with black
circles

0˚ 10˚ 20˚ 30˚ 40˚ 50˚

10˚

10˚

Bomu
Craton

Ntem
Craton

M S

0˚ 0˚

G

K-A
Belt D

Tanzania
Craton

Kasai
Craton

Bangw-
eulu
Block

-10˚ -10˚

S.

Irumide

Belt

Zimbabwe
Craton

(km )

-20˚ -20˚

4

3

Kaapvaal
Craton

2

-30˚

-30˚

1

0

0˚ 10˚ 20˚ 30˚ 40˚ 50˚

based on Rayleigh wave group velocities. By comparing
similarities and differences between this model and previ-
ously published models, we gain additional insights into the
architecture of lithospheric structure under the basin, which
in turn we use to evaluate the proposal of a northwest-
southeast trending mobile belt beneath the northern portion
of the basin. Whether or not a mobile belt extends under the
basin has implications not only for geodynamic models of
basin formation invoking uniformly thick lithosphere
beneath the basin, but also for understanding Neoproterozoic
tectonism that may have initiated basin subsidence.

et al. 1992 ; Kadima et al. 2011a , b ; see Chaps. 2 - 4 for more
details) to show that the basin contains 4 to 9 km of
sediments ranging in age from Neoproterozoic to Neogene.
The pre-Cretaceous sediments are thought to have been
deposited during a post-rift subsidence phase (Lawrence
and Makazu 1988 ; Daly et al. 1992 ; Crosby et al. 2010 ;
Kadima et al. 2011a , b ). Neoproterozoic, Late Cambrian
and Permian-Triassic unconformities have been identified
in seismic profiles, and the latter two have been linked to
NE-SW compression that resulted in reverse faulting and
the development of basement highs near the center of the
basin (Daly et al. 1992 ). However, the validity of the ages of
these unconformities has been questioned elsewhere (e.g.
Linol 2013 ; and see Chap. 6 ) .
A detailed description of the basin stratigraphy can be
found in Kadima et al. ( 2011a ). The four wells penetrated
mostly formations of sandstones and clays and none of them
reached crystalline basement. At the top of the basin is 1 km
of undeformed Lower Cretaceous to Quaternary sediments
deposited in fluvial, lacustrine and aeolian environments.
Paleozoic and Neoproterozoic sediments outcrop along the
margin of the basin, and tectonic subsidence curves from
back-stripping the four wells show very slow subsidence

1.2 Geological Setting

The Congo Basin has a mean elevation of ~300-400 m
above sea level and is surrounded by uplifted regions on all
sides (Fig. 1.1 ; and see Chap. 8 for greater detail). Details of
the basin fill come from four, 2-4 km deep wells (Samba,
Dekese, Mbandaka, Gilson), field studies, and a number of
seismic reflection profiles. Data from the wells (cores and
drill logs) and the reflection profiles have been used in a
number of studies (e.g. Lawrence and Makazu 1988 ; Daly