Paleogeography and Tectono-Stratigraphy of Carboniferous-Permian and Triassic ‘Karoo-Like’ Sequences of the Congo Basin - Geology and Resource Potential of the Congo Basin - page 127

African mobile belts and their overlying sedimentary cover
surrounding the CB, thus could have constituted important
secondary sources for the sediments in the center of the basin
(Fig. 7.15 ).

of Gondwana during the opening of the Indian Ocean (see
Chap. 13 , this Topic).
U-Pb detrital zircons geochronology from these
sequences characterizes the evolution of source prove-
nances for the CB during the late Paleozoic and early
Mesozoic. In the lower diamictites of the Lukuga Group
in the Dekese section, abundant detrital zircons of
1.85 - 2.05 Ga and subordinates of 1.37 - 1.42 Ga indicate
largely dominant contributions from Eburnian and
Kibaran sources in east Africa, as supported by the
west-facing paleo-glacial valleys along the margins of
the basin (Fig. 7.16 ). An elevated paleo-topography in
east Africa during the Carboniferous-Permian is also
consistent with recent thermochronology in Tanzania
(Kasanzu 2014 ) that shows ca. ~7 km of exhumation of
the Tanzanian Craton from 460 Ma to 220 Ma. In the
overlying Haute Lueki Group in the Samba section, more
dominant detrital zircons of 950 - 1100 Ma and
500 - 800 Ma derived from north-central Africa, as
shown by the crystal shapes of the zircons that indicate
limited transport (Fig. 7.14 ). In contrast, input from the
Kibaran Belt of eastern DRC is almost absent in all these
samples, suggesting that this vast region stopped acting as
a main source for the CB, possibly being covered by
sediments or subsided below sea level during the
Mesozoic.

7.4.3.4 Cambrian to Late Neoproterozoic
(500-850 Ma)
Cambrian to late Neoproterozoic dates are relatively abun-
dant in all the samples (Figs. 7.12b, d ). This large peak
between 500 and 850 Ma indicates important Pan African
contributions to the CB. However, because Pan African fold-
and-thrust belts and associated molassic sequences with this
age-range completely surround the basin, at this stage it is
not possible to differentiate between these widely different
source terrains (Fig. 7.15 ). Sediment dispersal directions
favor Pan African sources located to the east (e.g. the
Lufilian and Mozambique Belts) and to the north (e.g. the
Oubanguides Belt). Also, the increase in abundance of this
500 - 850 Ma zircon age-population in the samples from the
Lukuga Group (22 grains) to the Haute Lueki Group (36
grains) suggests progressive concentration by sediment
recycling during the early Mesozoic.

Conclusion
The four new stratigraphic sections reconstructed from the
deep boreholes drilled in the center of the CB in the 1950s
and 1970s, all show at their lower part great thicknesses
of conglomerates, quartzitic sandstones and red siltstones
(e.g. 3 km at Mbandaka) overlying deformed Pan African
carbonate rocks (Fig. 7.10 ). The lowermost sequences
locally include dark siltstones and black shales dated by
palynostratigraphy to the Carboniferous-Permian in the
Dekese and Mbandaka sections (Boulouard and Calandra
1963 ; Colin and Jan du Chˆne 1981 ), and attributed to the
glacial-periglacial Lukuga Group. In the center of the
basin, this first supersequence is between 900 and
1,600 m thick, truncated at the top by a regional erosion
surface (U2), and is in turn overlain by 900 - 1,800 m thick
red quartzitic sandstones and siltstones of the Triassic
Haute-Lueki Group. The angular unconformity separating
these two groups is equivalent to the main erosion surface
that separates the lower and upper Karoo successions in
southern Africa, and thus may be linked to large-scale
deformation across the entire interior of Gondwana
during the late Paleozoic Mauritanian-Variscan (ca.
275 - 325 Ma; Dabo et al. 2008 ) and Cape-de la Ventana
(ca. 245 - 278 Ma; Newton et al. 2006 ) orogens along its
northwestern and southern margins, respectively
(Fig. 7.16 ; Scotese 2014 ). The overlying major unconfor-
mity (U3) across these Carboniferous to Triassic
sequences of the CB is now re-assigned to the Jurassic,
and believed to be related to the initial period of break-up

Acknowledgments We acknowledge funding through the Inkaba
yeAfrica and !Khure Africa programs, supported by the DST/NRF of
South Africa. We thank Anthony Tankard and an anonymous referee
for critical reviews that improved the chapter. This is AEON contri-
bution number 127 and Inkaba yeAfrica contribution number 97.

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