Facies Analyses, Chronostratigraphy and Paleo- Environmental Reconstructions of Jurassic to Cretaceous Sequences of the Congo Basin - Geology and Resource Potential of the Congo Basin - page 137

KALAHARI GROUP

C S fS mS cS Gr P

a

NNW

Gravels and boulders of calcrete

diamonds

100 m

KWANGO GROUP (max: 190 Ma)

Poorly consolidated
cross-bedded red sandstones

SW

Sample
W P 19

50 m

KIONGO FORMATION

Cross-bedded white sandstones
with ventifacts

5 cm

Ventifacts and
detrital garnets

S

b

KAROO SUPERGROUP (300-350 Ma)

Conglomerates with dropstones
and red siltstones

W

0

DIBAYA BASEMENT (>2.6 Ga)

0.5 mm

Fig. 8.5 Stratigraphic section across the Kwango nick-point. ( a )
Ventifacts and ( b ) heavy mineral assemblage dominated by sub-
rounded pink garnets with frosted-glass appearance indicate aeolian

deflations (hiatuses) near the base of the Kwango Group (e.g. the
Kiongo Formation; Linol 2013 )

sandstone (intraclasts 10-20 cm in diameter), disseminated
wind-faceted pebbles and cobbles of quartz and black silica,
and relatively abundant detrital garnets (Fig. 8.5 ). These
observations suggest that there are major aeolian deflations
(hiatuses) near the base of the Kwango Group.
Overlying red sandstones, exposed at several cliffs
downstream along the Kwango River (e.g. Swamasangu,
Kisengamu and Menzelele; Fig. 8.6 ), and inland, at the
stream water-heads (e.g. Vunza; Fig. 8.7 ), all show large-
scale trough and planar cross-stratifications, with cross-bed sets
of up to 10 m in thickness that are characteristic of aeolian dune
deposits (Kocurek 1996 ). These outcrops of red sandstones are
often truncated by flat erosion surfaces, and covered by blocks
and boulders of silcrete and calcrete, and river terraces that are
exploited for alluvial diamonds (see Chap. 16 , this Topic).
Paleocurrents directions measurements from the Kwango
Group indicate predominant paleo-winds blowing toward
the south and the southwest (see Fig. 8.3 ). Also, the vast
extent of this aeolian succession suggests a paleo-desert
environment (Kocurek 1996 ). This is very similar to time-
equivalent J-K aeolian sequences in Namibia (the Etjo and
Twyfelfontein Formations; Jerram et al. 1999 ; Miller 2008 )
and eastern Brazil (the Sergi and Botucatu Formations;
Scherer and Goldberg 2007 , 2010 ), and suggest a vast
expansion of arid conditions across central West Gondwana
before the opening of the South Atlantic Ocean (Sellwood
and Valdes 2008 ; Myers et al. 2011 ; see also Chap. 13 , this
Topic).

8.3 Mapping in the Kwango Valley Area,

Southwest Congo Basin

During fieldwork in the Kwango Valley (Fig. 8.3 ), an exten-
sive succession of red sandstones of the Kwango Group was
mapped, unconformably overlying Precambrian basement
and Carboniferous-Permian (

' '

) fluvial-glacial
deposits (Linol 2013 ; Chap. 7 , this Topic). Field observations
show this succession to be monotonous, comprising almost
exclusively large-scale cross-bedded, red or white, fine to
medium sandstones (e.g. Fig. 8.4a ). Neither the Inzia and
Nsele Formations (Lepersonne 1951 ), nor the basal dia-
mondiferous conglomerates as identified at Tshikapa
(Cahen 1951 ) were recognized in the studied area, implying
there are regional facies changes from south to north, and
from west to east within the Kwango Group.
The best sections of the (Lower) Kwango Group in the
Kwango Valley are exposed along the banks of the Kwango
River (e.g. Fig. 8.4b ) downstream from a major, 150 m high,
nick-point of Archean granites and migmatites (the Dibaya
Complex; Cahen et al. 1984 ), and within large dongas (ero-
sional gullies) away from the river (e.g. Fig. 8.4c ).
The base of the succession is marked by a distinct (indu-
rate), 5-10 m thick unit of coarser white cross-bedded
sandstones, at the confluence between the Kwango and
Kiongo Rivers (Fig. 8.3 for location). This formation (e.g.
the Kiongo Formation) contains large reworked pebbles of

Karoo-like