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 111

Early Carboniferous (e.g. Milani and de Wit 2008 ;
Monta˜ez and Poulsen 2013 ). The termination of the glacia-
tion is constrained by palynostratigraphy to the Early
Permian (e.g. Visser 1995 ; Modie and Le H ´ riss ´ 2009 ),
and with geochronology on zircons from tuff horizons
within the lowermost Ecca Group (the Prince Albert Forma-
tion), dated at 288 Ma (Bangert et al. 1999 ).

comprises mainly grey granites and migmatites (dated to
>

2.6 Ga; Cahen et al. 1984 ), strikes E-W, and dips
30-40 to the north to disappear in the CB beneath red
sandstones of the Kwango Group (see Chap. 8 , this Topic).
Within the bottom half of the Kwango nick-point, a lower-
most succession of well-bedded purplish-red conglomerates
and siltstones was mapped along a 5 km long section,
onlapping to the south and to the north across the crystalline
bedrock (Fig. 7.3 ). This succession, maximum 30 m in thick-
ness, comprises superimposed thick bars (1-3 m) of massive
and cross-bedded conglomerates that grade upward into red
siltstones with intercalations of micro-conglomerates (e.g.
Fig. 7.3A ). Pebble imbrications and cross-stratifications indi-
cate river bed-load deposition with a general paleocurrent to
the west (e.g. Fig. 7.3B ). These conglomerates also contain
boulder-size dropstones (e.g. Fig. 7.3C ) that suggest a proxi-
mal glacial environment (Eyles and Eyles 1992 ). Thus, this
lowermost fluvial-glacial succession can be correlated confi-
dently to the other glaciogenic deposits of the Lukuga Group
(Asselberghs 1947 ), and attests to the vast extent of ice-sheets
across a paleo-relief located in east and south-central Africa
during the Carboniferous (Dwyka) glaciation of Gondwana.
Field observations in the Kwango Valley show that this
succession is tilted 5-15 to the south and to the west, and is
unconformably overlain by tabular formations of white and
red sandstones of the Jurassic-Cretaceous Kwango Group
(Chap. 8 , this topic for details). This is consistent with the
other descriptions of the Lukuga Group along the eastern
margin of the CB (e.g. Jamotte 1932 ), but further field studies
are needed to precisely characterize this angular unconformity
regionally.

7.2.2 The Haute Lueki Group

The overlying Haute Lueki Group is between 50 m and
200-500 m thick in southeastern DRC, best preserved in
NNW-trending Cenozoic rift valleys (e.g. Luama), west of
Lake Tanganyika (Fig. 7.2 ). Outcrops are relatively poorly
described (Cahen 1954 ; Lombard 1961 ) and generally
divided into two:
1. A lower subgroup of grey-brown fine sandstones and
siltstones with red mudstones, up to 150 m in thickness.
2. An upper subgroup of cross-bedded red sandstones,
between 150 m and 300 m thick.
The Haute Lueki Group is dated locally in its lower part
by palynology as Lower Triassic (Bose and Kar 1976 ).
Ostracods and phyllopods collected from this group are
common in the Cassange Group of Angola (Cahen 1981 ),
which also yields Triassic fish fossils (e.g. Antunes et al.
1990 ). Thus, all these sequences of the CB are time-
equivalent to the Beaufort Group of southern Africa
(Catuneanu et al. 2005 ; Johnson et al. 2006 ).

7.3 New Stratigraphic Basin Analysis

7.3.2 Seismic- and Well-Data

Below, new field observations are described from the
Kwango region of the southwest CB, and the old seismic-
and well-data in the center of the basin are re-examined
to facilitate regional correlations of

The two different seismic and drilling methods completed in
the 1950s and in the 1970s represent the only subsurface
dataset available to study the structure of the central CB.

'
(Carboniferous-Permian and Triassic) sequences. This is
then complemented with U-Pb dates of detrital zircons
from core samples of two of the deep boreholes (Samba-1
and Dekese-1) to constrain the ages and the source
provenances of these sediments.

'

the Karoo-like

7.3.2.1 Borehole Locations and Depths
The four deep boreholes drilled in the center of the CB
(Figs. 7.1 and 7.2A for locations) were examined using the
original core and cutting descriptions, the well logs (Cahen
et al. 1959 , 1960 ;Esso-Zaire 1981a , b ), and by re-logging the
cores that are stored at the RMCA museum in Belgium (Linol
2013 ). Figure 7.4 presents the four new reconstructed litho-
stratigraphic sections: Samba, Dekese, Gilson and Mbandaka,
together with overlapping seismic refraction data.
The Samba-1 borehole (0 09 0 45 00 N; 21 15 0 10 00 E) is
located along the Maringa River, in the northeastern part of
the central CB. It cuts through 1,167 m thick subhorizontal,
red to green, bedded sandstones and mudstones (Units S1 to
S5; Fig. 7.4 ), and then 871 m thick red quartzitic sandstones

7.3.1 Field Observations

Fieldwork was conducted (in 2008) along the Kwango River
of the southwest DRC to document the structure and stratig-
raphy of exposed rocks and sediments in this remote region
(Figs. 7.1 and 7.2A for location; Linol 2013 ). Here, Archean
bedrock (the Dibaya Complex; Cahen et al. 1984 ) outcrops
locally within waterfalls and rapids near Tembo, forming a
major nick-point 150 m high (Fig. 7.3 ). This bedrock