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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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