Geology Reference
In-Depth Information
Table 14.2
Relative chronology, characteristics, synonymy and age of the landforms of the Cameroon Highlands
RELATIONSHIPS WITH THE
OLDEST FORM
ELEVATION LANDFORM-WEATHERING (W.)
SYNONYMY
AGE
Upper
Planation
Surface 1a
(u1a)
1,500-1,800 m Complex geometry—several planation surfaces along the NE-SW basement faults:
pediments or faults scarps?
Highest relief: Mambilla High Plateau, part of the Bamil ´k ´ Plateau
w.
: bauxitic laterites on Proterozoic basement, «old» basalts or «recent» trachytes
(Mambilla Pl., Schwarz
1997
—Bamil
´
k
´
Pl., Fongo-Tongo, Hi
´
ronymus
1973
,
1977
,
1983
)
Cameroon
Minim—Martap—Bamil
´
k
´
Surface (S
´
galen
1967
)
Mont Bangou
: the top weathered surface of
the « old » basalts (
u1a
) is overlain by
basalts dated at
44.7 1Ma
(Fosso et al.
2005
—whole rock
39
K-
40
Ar)
Upper P.
Surface 1b
(
u1b
)
1,200-1,300 m Duricrusted planation surface - mantled etchplain?
Minim-Martap Plateau only
w.
: bauxitic laterite on «old» basalts (Belinga
1966
,
1972
,
1973a
,
b
)
Central African Republic
Lim - Bocaranga Surface
(Boulvert
1996
)
Bamoun Plateau
: pediment
u1p
cut through
Mount Nkogam «younger» granites dated at
67
7Ma
(Caen-Vachette et al.
1987
-
whole rock Rb/Sr age) and is overlain by
basalts at
51.8
2Ma
(Moundi et al.
2007
—whole rocks
39
K-
40
Ar—no data
provided) and the Mbepit ryolithic dome at
45.5
1.1 Ma
(Wandji et al.
2008
—whole
rocks
39
K-
40
Ar)
Upper P.
Surface 1p
(
u1p
)
1,100-1,500 m pediments downslope
u1a
w.
: no published descriptions
Scarps height: 100 to 200-300 m
Upper
Planatio
Surface 2
(
u2
)
900-1,200 m Pediplain
degraded
southern part of the Adamawa Plateau
w.
: no published descriptions
Transition to u1:
- Gradational (Tchabbal Ngou,
W Adamawa Plateau)
- Scarps (100 m—Minim-Martap
Plateau) (
Meiganga—Mandara—
Bamoun Surface (S´galen
1967
)
Bouar—Baboua Surface
(Boulvert
1996
)
400 m—Bamil´k´
Plateau)
Lower
Planation
Surface
(
l
)
600-800 m
Nearly flat, weathered duricrusted pediplain
most of the South Cameroon Plateau
w.
: laterite with iron cuirasses (Boy´ and
Fritsch
1973
; Yongue-Fouateu et al.
2006
)
Transition to u2:
- Gradational (south Pangar Plat.,
east Tibati Plain)
- Scarps (200 m—east Yoko
Escarpment)
Interior Surface («Surface
int´rieure») (S´galen
1967
)
Central-African Surface
(Boulvert
1996
)
Pediments
V-W
(
V
a
,V
c
,
W
a
,W
c
)
Scarps
10 m (low pediment
incision: 50-200 m)
detailed study in Yaound ´ area
(Embrechts and de Dapper
1990
)
Bamoun Plateau
: Pediment
V
a
cut through
basalts with a youngest age of
46.7 1.1 Ma
(Wandji et al.
2008
—whole
rocks
39
K-
40
Ar)
Two generations of large pedi-valleys/
pediplains (V ,W) two directions of drainage,
towards (1) the Atlantic Ocean (
Va, Wa
) and
(2) the Congo Cuvette (
Vc
0
,Wc
)
50 to 200 km large,
400 km long
Pediments
X-Y
(
X
a
,Y
a
)
Two generations of pedi-valleys (V, W) one
direction of drainage, towards the Atlantic
Ocean (
X
a
and
Y
a
)
Scarps
500 m (Cameroon
Highlands—Benue side) (more
deeply incised than V-W)
Rumpi Hills
: pediment
Ya
levels gabbros
dated (Walgenwitz
in
Nkoumbou
1990
)
between 10.8 and 5.6 Ma (whole rocks
39
K-
40
Ar) and
10.6
10 km large,
100-150 km long
0.5 and
0.4 Ma
(micas
39
K-
40
Ar)
9.9
Pediment
Z
(
Z
a
)
Large pedi-valleys to pediplains
Cameroon coastal plain—reentrant
of Benue Trough
merge with pediment
Ya
(south Benue Trough)
Scarps
200-300 m
Adamawa Plateau
:
Z-Y
erodes trachytes
(Tchabal Nganha, Nono et al.
1994
) with a
youngest age of
9.28 Ma
(Marzoli et al.
1999
—feldspars
39
Ar-
40
Ar)
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