Geology Reference
In-Depth Information
Fig. 7.1
Simplified geological map of the CB with location of the
studied four deep boreholes and the field area in the Kwango Valley
(
red box
). Precambrian geology is from de Wit et al. (
1988
), and
Phanerozoic sedimentary cover compiled from various national geo-
logical maps (e.g. Lepersonne
1974
; de Carvalho
1981
; Desthieux
1995
; Rolin
1995
)
these Pan African mobile belts are overlapped by wide-
spread upper Neoproterozoic to lower Paleozoic
Oubanguides and Lufilian fold-and-thrust belts (Fig.
7.1
).
These sequences, mainly of quartzitic and conglomeratic
red sandstones and siltstones, were deposited with regional
paleocurrents to the south (Alvarez et al.
1995
; Master et al.
2005
), and all are considered to post-date the Pan African
orogens (ca. 530-650 Ma; de Wit et al.
2008
). Their stratig-
raphy, however, is poorly constrained by field observations
and to date there are no reliable age constraints (Tait et al.
2011
).
The overlying Carboniferous to Triassic sequences in the
CB correspond to the Lukuga and Haute Lueki Groups that
outcrop mostly in eastern DRC (Figs.
7.1
and
7.2
). Along the
southwestern margin of the basin, in northern Angola, their
stratigraphic equivalents correspond to the Lutoe and
Cassange Groups (de Carvalho
1981
). These sequences
'
(e.g. Lepersonne
1978
; Poidevin
1985
), and Carboniferous
to Triassic sequences that contain a rich Gondwanan flora,
similar to those from southern Africa, Madagascar and India
(Bose and Kar
1978
; Cahen and Lepersonne
1978
). In the
CB, these successions are peneplained and in turn covered
by Jurassic-Cretaceous
'
red-beds
and Cenozoic
sediments
(see
The lowermost, upper Neoproterozoic to lower Paleozoic
succession of red-beds comprises the Inkisi, Aruwimi and
Biano (formerly Upper Kundelungu) Groups, each about
1,000-1,500 m thick (Lepersonne
1974
; see also Chap.
6
,
this Topic), unconformably overlying the West Congo,
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