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5°E
10°E
15°E
5°E
10°E
15°E
Cretaceous sediments accumulation
Cenozoic sediments accumulation
0°
0°
0°
0°
C
C
A
A
B
5°S
5°S
5°S
B
5°S
D
D
Thickness (m)
4000
Congo
canyon
Congo
canyon
Thickness (m)
3000
2600
1800
1000
2000
a
b
1000
200
5°E
10°E
15°E
5°E
10°E
15°E
SW
NE
850 km
D
C
B
A
0
R
: Miocene - Pliocene boundary
bMM
: base mid-Miocene
1
BO
: base Oligocene
2
3
4
5
6
7
8
9
10
TC
: top Turonian
Syn-rift
R
bMM
Oligo-Miocene fan
Aptian salt
BO
TC
Cretaceous fan
Aptian oceanic crust
c
50km
km
Fig. 10.13
Off-shore isopach maps of (
a
) Cretaceous and (
b
) Cenozoic sediment accumulations of the Congo Fan, and (
c
) interpreted reflection
seismic profiles (from Anka and S´ranne
2004
). Note the relative thickness between the Cretaceous and the Oligo-Miocene deep-sea fans
following the Early Cretaceous rifting of the South Atlantic
(e.g. Moulin et al.
2010
; Heine et al.
2013
). It is currently
sourced by the Congo River (the world
These Cretaceous deposits, together with their proximal
age-equivalent sequences on the shelf, contain a minimum
of 0.2 x10
6
km
3
sediments, representing almost one-third of
the volume of the Cenozoic fan (Anka and S´ranne
2004
;
Anka et al.
2009
). These observations suggest that the Congo
River has been one of the major off-shore sediment suppliers
since the opening of the South Atlantic, and that the location
of its outlet has remained relatively stable ever since. Thus,
the observed variations in the off-shore sedimentation his-
tory of the Congo Fan (Fig.
10.14
) are most likely primarily
controlled by changes in the on-shore CB.
The two episodes of high-sediment supply, represented
by the deposition of both (Cretaceous and Oligo-Miocene)
submarine fan systems, are separated by a long period
(Coniacian-Eocene; 89-34 Ma) of condensed sedimentation
and basin starvation (Fig.
10.14
). On-shore, however, apatite
fission track results generally suggest accelerated erosion
and denudation at that time (e.g. Brown et al.
1990
; Spiegel
et al.
2007
; Tinker et al
2008
; Turner et al.
2008
). We
propose that off-shore resumption of high sedimentation
following this event was driven by enhanced continental
erosion of the CB due to onset of karst topography beneath
s second largest river
by drainage area; Runge
2007
), and extends over 1,000 km
offshore from the shelf as far as to the abyssal plain (Savoye
et al.
2000
; Droz et al.
2003
). The existence of a direct
connection between the Congo River outlet and the subma-
rine fan through an impressive submarine canyon is one of
the most important characteristics of this system
(Barbonneau et al.
2002
), linking directly the marine strati-
graphic record of the Congo Fan to the on-shore erosion and
sediment transport dynamics of the Congo River (Anka et al.
2009
).
Detailed analysis of deep-offshore seismic reflection data
(Anka and S´ranne
2004
) has revealed that the volume of the
Cenozoic fan (Oligocene-Recent) is at least 0.7
'
10
6
km
3
.
In addition, an Albian-Turonian (mid-Cretaceous) wedge
that extends across the Continent-Ocean boundary beneath
the Cenozoic fan (Fig.
10.13c
), and whose depocenter is
centered near the present-day Congo canyon, indicates that
an older Cretaceous fan was also sourced by a paleo-Congo
located nearby the present-day river (Anka et al.
2010
).
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