Geology Reference
In-Depth Information
Table 14.6 Relative chronology, characteristics, synonymy and age of the landforms of the Central African Atlantic Swell—Angola Swell
RELATIONSHIPS
WITH THE
OLDEST FORM SYNONYMY
LANDFORM-
WEATHERING (W.)
ELEVATION
AGE
Upper
Planation
Surface 1
( u1u )
2,500 m
Highly degraded planation surface—stripped etchplain
? isolated mounts and hills along the Atlantic side of
the Bi ´ Plateau
w. : bauxites mentioned by by Carvalho ( 1961 )—
unknown exact location
Surface V (Jessen
1936 )
Named by analogy with
Cameroon Highlands
Upper P.
Surface 2
Lower P.
Surface
( u2lu )
2,200-2,400 m Weathered pediments at time of
u1u stripping?
most of the Bi ´ Plateau and
Serra Canguejo
w. : similar than u1u
Difference of
elevation with u1u
100 m
Surface IV (Jessen
1936 )
Pediments V
( V kc )
large pedi-valleys to pediplains
- asymmetrical: narrower on the
Bi ` Plateau flank (lithologic
effect?)
well preserved east of Bi ´
Plateau - remnants upstream of
Cassange Escarpment (Serra
Biringa to S. Cambala)
w. : 10 to 15 m-thick iron
duricrusted conglomerate
(well-rounded quartz pebbles,
<
Greater incision
500 m (north of
Serra Canguenjo)
6 cm) upstream Cassange
Esc. (Cabatuquila duricrust,
Marques 1992 )
Pediments
W
( W kc )
large pedi-valleys to pediplains
- two drainages:
- to the west (Atlantic
Ocean), Cuenza
- to the north (Central
Cuvette), Kwango
Greater incision150
m decrease
northward
Surface II-III (Jessen
1936 ) with different
contours
Cassange Trough: pediment
Ykc cut across pediment Xkc
capped by silicified lacustrine
deposits with gastropods,
ostracods, characeans of
(middle?) Pleistocene age
(based on gastropods, Mouta
and Dartevelle 1954 )
Bangalas (Bango Mount) and
Cassanza River, close from the
Cassange Escarpment (Serra
Bango Cassala) related to the
Gr ` s polymorphes Fm
comment: similar facies but
different age than the «Gr ` s
polym.» of the Kasai and
Kwango Plateaus as indicated
by their geomorphological
setting
Pediments X
( X kc )
large pedi-valleys to
pediplains—asymmetrical with
a sharp SW scarp (Cassange
Escarpment)
Kwango pedi-valley only:
southeast of Cassange Trough
Incision 200-300 m
decrease northward
Pediment Y
( Y kc )
Large pedi-valleys to
pediplains Kwango pedi-valley
only: Cassange Trough
connection to its local base
level (Congo River) trough a
dense network of incised rivers
Re-incision of the
Cassange
Escarpment
￿ The Kwango present-day catchment is a stepping of four
large pedi-valleys to pediplains ( V kc , W kc , Xk c , Yk c ), the
youngest one being nested and smaller than the older ones.
￿ Downstream the pediment system is intermediate
between pediplains and large pedi-valleys bounded on
both sides by scarps (e.g. Cassange) or steepest slopes
(width between
(only recorded in the Kwango), the Cuanza large pedi-valley
is inactive, fossilized; erosion is localized along the Atlantic
Escarpment.
The only available date is of low resolution (Table 14.6 ).
Pediment Y kc is young, Plio-Pleistocene but possibly older,
because the gastropods fossils used by Mouta and Dartevelle
1954 have poor stratigraphic resolution.
10 km to 100 km).
￿ Upstream the system corresponds to highly dissected
slopes by a dense drainage of incised rivers connected
to the pediplain/pedi-valley.
Pediments W kc record the initiation of a new drainage of
large pedi-valleys, the Cuanza on the west side, flowing
toward the Atlantic Ocean and the Cuango (
14.5.2.6 West: Central African Atlantic Swell,
North of the Congo River (R of Congo—
DRC, Gabon, Equatorial Guinea, South
Cameroon)
This domain (Plate 1) is subdivided into two parts, separated
by the Ogoou´ River (Gabon): the Chaillu Massif in the
Kwango) to
the north, flowing toward the CB. At time of pediments X kc
¼
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