Formation and Collapse of the Kalahari Duricrust [‘African Surface’] Across the Congo Basin, with Implications for Changes in Rates of Cenozoic Off-Shore Sedimentation - Geology and Resource Potential of the Congo Basin - page 199

Samba Section

C

C SfSmS cS Gr P

0 m

10 m

20 m

30 m

40 m

Unconsolidated
sands

50 m

S1

60 m

70 m

80 m

90 m

Kaolinite

100 m

Silcrete pebbles

110 m

120 m

130 m

140 m

bioturbation (roots)

S2

150 m

Kaolinite

160 m

170 m

180 m

190 m

Cretaceous
(ostracods and
phyllopods)

200 m

S3

Fig. 10.11 ( a ) 3-D seismic block diagram showing a relatively flat
uppermost main reflector at 2,400 m/s (surface in yellow ), and ( b ) bore-
hole stratigraphic correlations of the Kalahari Group across the central CB
(see also Chaps. 7 and 8 , this Topic). ( c ) New Kalahari stratigraphic

column of Samba cores (photos on the right ) archived at the RMCA
museum in Tervuren, Belgium. The Kalahari succession comprises two
sequences separated by a horizon with pebbles of silcrete, similar to those
observed in the Kwango Valley along the southwest margin of the CB

Cretaceous (83 Ma) kimberlites that corresponds to the
'

(Fig. 10.8 ), where it merges with the characteristic calcrete
and silcrete deposits of the

(e.g. du Toit 1954 ;King 1963 ;
Summerfield 1983 ; Partridge and Maud 2000 ; Decker et al.
2013 ; Linol 2013 ). This basal sequence of the Kalahari
Group extends continuously to the northern flank of the
KP, overlapping the southwestern margin of

African Surface ' (Cahen

and Lepersonne 1952 ). Below the KP, in the Kwango Valley
and across the central CB, abundant boulders and pebbles of
calcrete and silcrete appear to be derived from the disinte-
gration of this polymorph unit of duricrusts. We thus

' Polymorph Sandstones '

the CB