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 122

New correlations of the Lukuga Group in the CB are also
proposed with the relatively thick sequences of red-brown
conglomeratic sandstones and dark brown siltstones that
directly overlie the Pan African carbonate rocks in both,
the Gilson (Units G7 to G9, in total 1,571 m thick;
Fig. 7.10 ) and the Mbandaka sections (Units M8 and M9,
in total 1,369 m thick). This

the experimental and analytical procedure see Biggin et al.
( 2011 ).
The ages reported in this study are not corrected for
common Pb, since correction by the 204 Pb method cannot
be applied due to the isobaric interference of 204 Hg, which is
a contaminant of the He gas carrying the ablated material
from the laser cell to the MC-ICP-MS. All analyses were
plotted on Concordia diagrams using Isoplot 3.0 (Ludwig
2003 ), and most concordant dates (

is only supported by

palynostratigraphy, however, in the Mbandaka section

between depths of 2,805 m and 2,825 m (Fig. 7.11 ). 110 %

conc.) are compared in frequency age-diagrams (Fig. 7.12 ).

80 % and

> <

7.3.3.2 Triassic Sequences of the Haute Lueki
Group
In the center of the CB, new lithostratigraphic correlations of
the Triassic Haute Lueki Group are proposed with the red
quartzitic sandstones and mudstones overlying the Carboni-
ferous-Permian black shales and dark brown siltstones in the
Dekese (Unit D6, 40 m thick; Fig. 7.10 ), the Gilson (Unit
G6, 538 m thick) and the Mbandaka sections (Units M5 to
M7, in total 1,778 m thick). No fossil, or spores and pollen
were found in any of these units (Fig. 7.11 ). However, in the
boreholes and seismic data, the top of this quartzitic succes-
sion marks a very distinct regional unconformity (U3;
Figs. 7.8 and 7.9 ). This enables correlation of the Haute
Lueki Group with the Unit S6 of the Samba section
(Fig. 7.10 ), previously attributed to the upper Neoprotero-
zoic Aruwimi Group by Cahen et al. ( 1959 ).

7.4.1 Samples D1400 and D1595 (The Lukuga
Group)

Two samples: D1400 and D1595 were taken from diamic-
tites of the Carboniferous-Permian Lukuga Group, at depths
of 1,595 m (Units D8 and D9), respectively,

in the lower part of the Dekese section (Fig. 7.10 ). The
zircons from these samples vary in size and shape. The
grains are sub-rounded to angular, transparent or smoky
grey, and frequently show magmatic zonings (e.g. Fig. 7.13 ).
74 analyses were performed on 69 grains in sample
D1400, and 83 analyses on 79 grains in sample D1595.
Results are summarized in Table 7.1 .

1,400 m and

7.4.2 Samples S1605 and S2035 (The Haute
Lueki Group)

7.4 U-Pb Detrital Zircons Geochronology

of the Samba and Dekese Cores

Two samples: S1605 and S2035 were taken from red quartz-
itic sandstones of the Triassic Haute Lueki Group at depths
of

U-Pb geochronology of detrital zircons collected from the
Samba and Dekese cores (Fig. 7.10 for sample locations) is
used to further constrain the stratigraphy and characterize
the source provenances of these Carboniferous-Permian and
Triassic sequences filling the CB, which in turn help to
reconstruct the basin

2,035 m (Unit S6), respectively, in the
lower part of the Samba section (Fig. 7.10 ). The zircons from
this unit are generally small (100-250 μ m), elongated, trans-
parent or reddish, and with crystal-shapes that indicate rela-
tively limited transport (e.g. Fig. 7.14 ). The grains show
magmatic zoning and some xenotime overgrows.
64 analyses were performed on 59 grains in sample
S1605, and 60 analyses on 48 grains in sample S2035.
Results are summarized in Table 7.2 .

1,605 m and

' s paleogeography (e.g. Fedo et al.

2003 ).
255 zircons were analyzed from the Lukuga and Haute
Lueki Groups (Tables 7.1 and 7.2 ; see Linol 2013 and Linol
et al. 2014 for details), with two samples from each group
(about 50-80 analyses per sample). U-Pb dating was done
using AEON s high resolution Multi-Collector Inductively

Coupled Plasma Mass Spectrometer (MC-ICP-MS), coupled
to a UP 193 solid-state laser system (New Wave Research)
and a desolvation nebulizer system (DSN-100, Nu
Instruments). The Nu Plasma MC-ICP-MS is equipped
with a special collector block allowing for simultaneous
detection of ion signals from masses 238 Uto 203 Tl. U and
Tl isotopes are measured on Faraday cups, while Pb isotopes
are measured on ion counters. For more information about

'

7.4.3 Synthesis and Sources Provenance
Analysis

In all samples of the Lukuga and Haute Lueki Groups, four
main age-populations were found: 1) early Paleoproterozoic
to Archean, 2) mid-Paleoproterozoic (Eburnian), 3) early
Neoproterozoic to Mesoproterozoic (Kibaran), and 4) Cam-
brian to late Neoproterozoic (Pan African), although there