Cenozoic Landscape Evolution in and Around the Congo Basin: Constraints from Sediments and Planation Surfaces - Geology and Resource Potential of the Congo Basin - page 283

Table 14.4 Relative chronology, characteristics and age of the landforms of the western flank of the East African Dome

RELATIONSHIPS WITH
THE OLDEST FORM ELEVATION LANDFORM-WEATHERING (W.) AGE

Upper
Planation
Surface 1
( u1u )

1,400-2,700 m Complex geometry - several planation surfaces along the rift: pediments or faults scarps? not
studied in details
Highest relief: Blue Mountains, Mitumba Mounts, Itombwe Plateau - with doubt: Masseba and
Marungu Plateaus
at regional-scale draw a half dome: maximum elevation in the Mitumba Mounts, minimum in the
Blue Moutains (north) and the Masseba Plateau (south)
w. : no published descriptions

Named by analogy with Cameroon Highlands (same stepping in
reference to the Lower Planation Surface)

Upper
Planation
Surface 2
( u2, u2d )

900-1,800 m Pediplain ( u2 ) degraded (u2d) by incised rivers connected to

younger pediments
Blue Mountains (Kibali-Ituri Plateau)—900 m—to Itombwe
Plateau—1,800 m merge to the west (Central Cuvette) with the
Congolese Surface ( Cd )
w. : only studied in the Blue Moutains (Mbuluyo 1991 )
- No preserved weathering on u2 (stripped etchplain?)
- Iron-duricrusts on pediments degrading u2

scarps:

500 m—Itombwe Plateau
0-50 m—Kibali-Ituri Plateau

Lower
Planation
Surface
( l, lp, ld)

600-800 m Lateral extension of the duricrusted pediplain of the Ubangian

Rise—three types:
- Duricrusted pediplain ( l )
- Upstream pediments of the pediplain with few duricrusts ( lp )
- Degraded pediments ( ld ) dissected by valleys connected to
pediment X difficult to map south of the Bukavu Volcanic
Province: (1) highly degraded and (2) several stepped pediments
(equivalent Pediments V and W ?)
w. : no published descriptions

Scarps 100-300 m (maximum
height in the Mitumba
Mounts)

Pediment X
( Xc , Xf )

N-S trending EW asymmetrical pediment systems (connected
incised rivers: X f )
- West: pediplain (200-500 m below the Congolese surface
( Cd )
- East: deeply incised pedi-valleys (E-W to NW-SE trending)
Transition between the Central Cuvette and the East African
Dome from Upemba Lake (south) to Itimbiri Pedi-valley (north)
Present-day Congo River outlet toward the local base level of
the Likuala Swamps
w. : no published descriptions

Scarps (pedi-valleys)
200-500 m

Lugulu basaltic flow (W Kahuzi-Biega) : - incised by the river
network of the Lubimbi Rivers that fit with the local base level of
pediment X c
- Lugulu basalts (undated) belongs to the initial episode of the
Bukavu volcanic province
- oldest age : debated, between 17.6 0.5 Ma (Baubron, in

Kampunzu et al. 1998 ) et 10.0 2.2 Ma (Pasteels et al. 1989 )

0.3 Ma (whole rock 39 K- 40 Ar
Kampunzu et al. 1998 —Kahuzi-Biega)

- Youngest age : 5.9

Pediment Y
( Yc )

Pediplain
Southern Lualuba (¼Congo) at the confluence with the Lukuga
Merge northward with pediplain X c

Elevation between X c and Y c
< 100 m

Incised
channels

Cut across pediplains Xc and Y c
Lualuba (¼Congo) River and tributaries (Luvua, Lukuga and
Luama Rivers)

Greater incision 100-200 m, in
the south (Lukuga and Luama
Rivers)