Neoproterozoic to Lower Paleozoic Sequences of the Congo Shield: Comparisons Between the Congo and Its Peripheral Basins - Geology and Resource Potential of the Congo Basin - page 94

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Neoproterozoic to Lower Paleozoic Sequences
of the Congo Shield: Comparisons Between
the Congo and Its Peripheral Basins

´ tienne Kadima Kabongo, Damien Delvaux, Michel Everaerts,
Mwene Ntabwoba Stanislas Sebagenzi, and Francis Lucazeau

6.1 Introduction basin subsurface structure. The CB appeared deeper than

previously thought, with the possible existence of several
thousand meters of sedimentary rocks beneath its upper
Paleozoic-Mesozoic sedimentary sequences.
Additional geophysical surveys were subsequently
conducted by various petroleum companies. Exxon-Texaco
shot 2,900 km of seismic reflection profiles in 1974-1976,
and Japan Oil National Corporation (JNOC) performed an
aeromagnetic survey and gravity measurements around
Kisangani in 1984; and two additional wells, more than
4,000 m deep, were drilled (Esso Zaire 1981a , b ). The
interpretation of this data was first presented in an ECL
( 1988 ) report by Petroza¨re, of which a short summary was
published by Lawrence and Makazu ( 1988 ). More detailed
interpretations of the seismic reflection profiles and wells
were presented as synthetic stratigraphic columns and a
tectonic model by Daly et al. ( 1992 ), in which early subsi-
dence of the basin was interpreted to reflect Neoproterozoic
processes of rifting and thermal relaxation, followed by two
regional contractional deformation phases that inverted the
subsiding basin during the early Paleozoic and the late
Paleozoic. The first inversion was attributed to late stages
of the Pan-African orogeny in Central Africa, and the second
inversion phase to far field intraplate stresses generated at
the southern margin of Gondwana during the formation of
the Cape Fold Belt. Daly et al. ( 1992 ) also speculated on the
possible role of evaporites in enhancing deformation process
at the deepest levels of the basin. Subsequently, Kadima
et al. ( 2011a ) further constrained the interpretation of some
of the seismic profiles using 2D gravity and magnetic
models, and delineated heterogeneous crust beneath the
sedimentary sequences of the basin consistent with the inter-
pretation that the central part of the basin is an intracratonic
rift inverted during compressional tectonics facilitated by
the presence of evaporites and salt tectonics.
Despite a renewed interest over the last decade, there are
still many unanswered questions regarding the nature of the
crystalline basement, the Neoproterozoic and Phanerozoic
stratigraphy, as well as the structure of

The Congo Basin (CB) is the largest and the least explored
African continental sedimentary basin. Outcrop scarcity,
intense weathering and dense forest constitute obstacles
to undertake direct geologically-based exploration
programmes, highlighting the importance of airborne and
ground-based geophysics. In the 1950s, the Syndicat pour

l' ´ tude g ´ ologique et mini ` re de la Cuvette congolaise

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conducted refraction and reflection seismic, gravimetric
and magnetic field surveys across the central parts of the
CB (Evrard 1957 ). During the seismic surveys, 117 refrac-
tion stations were employed in the basin interior, and 7
reflection lines were recorded along rivers (Evrard 1960 ).
In addition, about 6,000 gravity and magnetic measurements
were made with an average station spacing of 5 km along
rivers and dirt roads (Jones et al. 1960 ). Moreover, two fully-
cored stratigraphic wells down to ca. 2,000 m had been drilled
in the 1950s, reaching red sandstones at the bottom, that were
interpreted as pre-Carboniferous (Cahen et al. 1959 , 1960 ).
Using these geophysical and well data, Evrard ( 1957 ,
1960 ) and Jones et al. ( 1960 ) first imaged the structure and
extent of the CB and its subsurface geometry. The major
refractors mapped provided the first regional overview of the

the CB. The