Geology Reference
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Fig. 14.5
Samba boreholes:
Scanning Electron Microprobe
pictures of the cuttings (samples
location in Fig.
14.3
). 1: RG35-
145, stacked kaolinite sheets
(
arrow
) on quartz grains. 2:
RG35-145, dissolution structures
(
arrow
) on quartz grain surface.
3: RG35-166, subangular very
coarse quartz grain with
dissolution structures (
rectangle
).
4: RG35-170, subangular coarse
quartz grain. 5: RG35-176, blunt
irregular (subangular) coarse
quartz grain. 6: RG35-183,
dissolved rounded aeolian fine
quartz grain. 7: RG35-183, detail
of the previous one showing the
dissolution structures. 8: RG35-
183, highly dissolved quartz grain
leading to an angular shape
1
2
1
µ
m
1
µ
m
3
4
1 mm
100
µ
m
5
6
100
µ
m
10
µ
m
7
8
10
µ
m
10
µ
m
14.4.2 Boreholes and Wells: Dekese, Samba,
Gilson 1, Mbandaka 1
A
basal truncated weathering profile
, superimposed on
Late Albian sediments (Linol et al., this volume), alterna-
tion of calcareous claystones and fine-grained (rounded
aeolian grains—reworked?) sands (Fig.
14.5
.6). These
aeolian quartz sands are highly dissolved (Fig.
14.5
.7)
and its rounded grains can become angular (Fig.
14.5
.8).
The claystones transformation is low (no kaolinite,
14.4.2.1 Samba and Dekese Boreholes (See Plate
2 for Location)
The
Samba
borehole (190 m of Cenozoic deposits,
Fig.
14.3
), consists of three units:
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