Mesozoic Sedimentary Cover Sequences of the Congo Basin in the Kasai Region, Democratic Republic of Congo - Geology and Resource Potential of the Congo Basin - page 158

9

Mesozoic Sedimentary Cover Sequences of the
Congo Basin in the Kasai Region, Democratic
Republic of Congo

Eric Roberts, Hielke A. Jelsma, and Thomas Hegna

9.1 Introduction The Congo Basin has traditionally been described as a

classic, saucer-shaped intracratonic basin, thick in the center
and thinning uniformly towards the margins (e.g., see Cahen
et al. 1960 ; Daly et al. 1992 ; Giresse 2005 ), and interpreted
as a passive downwarp, likely cored by a failed Proterozoic
rift (Daly et al. 1992 ; Kadima et al. 2011a , b ) and rimmed by
topographic highs including Proterozoic orogenic belts
(Kibaran and Ubangi belts), the uplifted Atlantic margin
and East African Rift shoulder, and basement highs of the
Central African Shield (Fig. 9.2 ). Although much of the
basin (i.e., Cuvette Centrale; Figs. 9.1 , and 9.2 ) is indeed
within a fully intracratonic setting, the sedimentary cover
sequences extend well beyond this region.
The Congo Basin has been summarized as one of relative
complexity during the Late Proterozoic-Early Paleozoic
(Daly et al. 1992 ), whereas the Late Paleozoic-Cenozoic
basin history has typically been interpreted as a period of
extended regional tectonic stability, without noticeable sub-
sidence and with passive sediment infilling (Sahagian 1993 ;
Giresse 2005 ). Recent geophysical investigations by
Downey and Gurnis ( 2009 ) indicate that a large negative
free-air gravity anomaly is centered over the Congo Basin
and they interpreted the basin as currently active and being
depressed due to generation of dynamic subsidence by
downward flow of an anomalously dense region in the man-
tle lithosphere (or asthenosphere, Moucha 2011 ). Although
Downey and Gurnis ( 2009 ) cannot constrain how or when
this density anomaly developed, they hypothesize that it is
most likely coincident with deposition of Mesozoic-
Quaternary cover sequences across the basin. In contrast,
Kadima et al. ( 2011b ) interpret a residual gravity anomaly as
the remaining crustal thinning associated with a Neoprotero-
zoic failed rift proposed by Daly et al. ( 1992 ). These studies
indicate a more complex basin model than previously
envisioned, which emphasizes the need for improved, field-
based structural and stratigraphic investigations to validate
geophysics-based basin models.
A synthesis of the major published investigations in the
basin was presented by Giresse ( 2005 ), and can be briefly

The Congo Basin of Central Africa is one of the largest
continental sedimentary basins in the world (Daly et al.
1992 ), with a surface area of over 1,200,000 km 2
(Fig. 9.1 ). Despite its size, its gold, tin and copper resources,
the potential for hydrocarbons (Clifford 1986 ), and its exten-
sive alluvial and primary diamond deposits along the south-
ern margin (Fieremans 1955 , 1961 , 1996 ; Bluck et al. 2005 ),
it is remarkable that so little is actually known about the
Congo Basin.
The term Congo Basin (also known as the Zaire Basin and
Cuvette Congolaise) is widely used by geologists and
geographers alike to define the area drained by the modern
Congo River and the sedimentary cover sequences preserved
within this enormous circular depression (Fig. 9.1 ) (e.g.,
Cahen 1954 , 1983 ; Gouldie 2004 ; Giresse 2005 ). Intra-
basinal correlation of cover sequences is problematic due
to inconsistent nomenclature between countries and between
portions of the basin, general inaccessibility with decades of
conflict, minimal outcrop exposure across vast areas, limited
seismic, core and well data (often of proprietary nature), a
general lack of datable volcanics (with the exception of
kimberlites), and the sporadic distribution of age and
paleoenvironmentally diagnostic fossils (see Giresse 2005 ).