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 97

African orogen, between ca. 700 Ma and ca. 530 Ma
(Cailteux 1994 ; Hanson et al. 1994 ; Porada and Berhorst
2000 ; Key et al. 2001 ; De Waele et al. 2008 ). These
basins comprise the Roan, Mwashya, Nguba and
Kundelungu Groups. The Roan Group overlies the
877

For example, in the West-Congo basin, the Schisto-
Calcaire Subgroup overlies the Haut Shiloango Subgroup
and is overlain by the Mpioka Subgroup. The Haut
Shiloango Subgroup comprises predominantly carbonates,
with increasing siliciclastics upwards (Delpomdor et al.
2014 ; and Chap. 4 , this Topic). The Mpioka Subgroup
consists of up to 1,000 m of molasse-like sequences com-
prising conglomerates, sandstones and argillites (Alvarez
1995a , b ; Tack et al. 2001 ; Frimmel et al. 2006 ). Similarly,
in the Bangui basin, the basal Kembe sequence of
conglomerates is overlain by the Bimbo sandstones and the
Bangui carbonates. Here, no clastic sequence is observed
above this carbonate sequence (Poidevin 1976 ).
A similar succession is observed in the Fouroumbala-
Bakouma basin (Alvarez 1995a , b ; Tait et al. 2011 ). In the
Lindian basin, the Ituri Group consists of a basal clastic
sequence containing conglomerates and sandstones, overlain
by thick oolitic limestones and dolomites. Above it, the
Lokoma and Aruwimi Groups are predominantly clastic
(Verbeek 1970 ; Poidevin 2007 ). In both the Katangan and
Zambian basins, the Roan Group (880-750 Ma) consists of a
basal conglomerate, siliciclastics and carbonates (mainly
dolomites and dolomitic shales) that unconformably overly
Mesoproterozoic Kibaran formations (Cailteux et al. 2005 ;
Batumike et al. 2006 ; El Desouky et al. 2008 ). The Roan
Group is overlain by the predominantly clastic and volcano-
sedimentary rocks of the Mwashya the Nguba Groups
(750-620 Ma). The latter contain a basal tillite known as
the

11 Ma Nchanga granite (Armstrong et al. 2005 ),
and the Mwashya Group contains 765

5 Ma intrusions

(Key et al. 2001 ).
5. The Mbuji-Mayi basin is a SE-NW trending intracratonic
failed-rift basin. It contains a lower clastic sequence BI
and an upper carbonate sequence BII (Raucq 1957 , 1970 ;
Cahen et al. 1984 ; Delpomdor, et al. 2013a ). The pres-
ence of dolerite intrusions and pillow lavas were taken as
evidence of extensional magmatism during the deposition
of the Mbuji-Mayi sediments (Raucq 1957 , 1970 ; Cahen
et al. 1984 ). Isotopic data from the Mbuji-Mayi carbo-
nates and the presence of pseudomorphs of anhydrite and
gypsum filling veins and fractures reflect deposition and
early diagenesis in marine and evaporitic conditions
(Delpomdor, et al. 2013b ; see also Delpomdor et al.,
Chap. 4 , this Topic). The minimum age of sedimentation
for the Mbuji-Mayi Supergroup was first estimated by
amygdaloid basalts interpreted as capping the entire
sequence and dated at ca. 940 Ma (Cahen et al. 1984 ).
Delpomdor et al. ( 2013a ) further constrained the deposi-
tion of this Group between 1174 22 Ma and ca.

800 Ma; and the carbonate BII Group is now dated at
760-820 Ma by Carbon and Strontium chemical stratig-
raphy (Delpomdor et al., Chap. 4 , this Topic) and the
sliciclastic BI Group is either older than 880 Ma or aged
between 880 Ma and 850 Ma. Following this second
hypothesis, the Mbuji-Mayi Supergroup would be
coeval with the Roan Group in the Katanga and Zambian
basins, reflecting a similar early Neoproterozoic exten-
sion event.

(Lepersonne 1974 ), overlain by a
thick carbonate sequence including limestones, dolomites,
shales, dolomitic shales and interbbeded silts and sandstones
(Cailteux et al. 2005 ; Batumike et al. 2007 ). The overlying
Kundelungu molasses-like sequence (620-570 Ma) starts
with a second glacial horizon, known as

“ Grand Conglomerat ”

“ Petit Conglomerat ”

(Lepersonne 1974 ).

6.2.1 Neoproterozoic Siliciclastic
and Carbonate Sequences

6.2.2 RedBeds and the Transition Between
the Neoproterozoic and Paleozoic

The Neoproterozoic basins surrounding the CB have consis-
tent (similar) stratigraphic successions. In most of them, a
carbonate unit, of variable thickness, overlies a basal silici-
clastic sequence comprising silts, sandstones and conglo-
merates. The Neoproterozoic carbonates are in turn
overlain by relatively thick and persistent siliciclastic
sequences.

Throughout Central Africa, the transition between the upper
Neoproterozoic and the earliest Paleozoic sedimentary
sequences is poorly constrained because the transition
sequences are non-fossiliferous siliciclastic redbeds.
Throughout the CB and its surrounding basins, relatively
thick sequences of lithologically similar red sandstones
(known as the ' Redbeds ' ) have long been correlated and

Fig. 6.1 (Continued) ( a ) Geological setting of the Congo Shield with
the Congo Basin in its center, surrounded by Archean cratonic blocks
and Proterozoic mobile belts. Rectangle shows contour of ( b ). ( b )Geo-
logical map of

Neoproterozoic basins with location of the 2 stratigraphic wells
(Samba and Dekese) and the two exploration wells (Mbandaka-1 and
Dekese-1), indicated by their initials

the Congo basin and surrounding marginal