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In-Depth Information
10°E
15°E
20°E
25°E
30°E
10°N
10°N
S
?
Marshes
to shallow lake?
Bakouma
lignite
Equator at 40 Ma
5°N
5°N
Fluvio-deltaic
Eo
lian
LAKE
Samba
Mbandaka
1
Yangambi
0°
0°
deepest
Koukouya
Gilson1
Dekese
5°S
5°S
AEOLIAN
«Grès polymorphes» Fm
Central Cuvette Cenozoic sediments
and overlying planation surface
DESERT
10°S
10°S
Mean lithology
on wells and sections
Eolian deposits
Paleocurrents
Shoreline
10°E
15°E
20°E
25°E
30°E
Fig. 14.7
Palaeogeographic map of the CB and surrounding highs
during the progradational trend of the
“
Gr`s polymorphes
”
—Yangambi
Fms cycle of Paleogene pre- to syn- Middle Eocene age, according to
the proposed age model (5.2.7). Paleocurrents data from de Heinzelin
(
1952
)—Yangambi area—Le Mar
´
chal (
1966
)—Bat
´
k
´
Plateau and
field studies north of Brazzaville. Centrafrican data (Bakouma) from
Bigotte and Bonifas
1968
and Miauton
1980
environments are characterized: a hot arid desert with aeo-
lian dunes and a lake with marshes. The lake paleoshoreline
is traced using facies distribution. The lake is located in the
northwestern part of the present-day CB. This implies that
during the Paleogene (Eocene?) time interval a depression
filled by a lake predefined the present-day CB. The facies
distribution is consistent with the position of the equator
during Paleocene-Eocene (Fig.
14.7
): the humid
environments (marshes, perennial lake) are closest to the
equator and the hot arid desert environment occupied a
transition between the lower and middle latitudes. The west-
ward migration of aeolian dunes in Congo-Brazzaville is in
good agreement with the direction of the winds operating at
these latitudes, e.g. the westward trade winds.
The U-Pb single grain dating of
Gr
`
s polymorphes
”
zircons in Gabon (S´ranne et al.
2008
) suggests that these
sands were reworked from older sediments across a flat
topography at the scale of the Sub-saharan African Shields.
“
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