Facies Analyses, Chronostratigraphy and Paleo- Environmental Reconstructions of Jurassic to Cretaceous Sequences of the Congo Basin - Geology and Resource Potential of the Congo Basin - page 144

Dune migration

Backdune

D

Foredune

C

100 m

sub-section D

sub-section C

Depth Facies Grain-size

C S fS mS cS Gr P

Depth Facies Grain-size

C S fS mS cS Gr P

Large-scale
cross-bedded
coarse sands

-590 m

Aeolian Slt

Slt-b

Mixed
aeolian
and flood
deposits

Aeolian
dunes
deposits

Sm

Slt

-625 m

-595 m

Slt

Sm

Slt-b

Fl

-630 m

-600 m

Fig. 8.10 Aeolian facies successions from the middle part of the
Dekese core-section (Unit D4; Fig. 8.8b ). Sub-section C: massive
sandstones (Sm facies) with a thin cracked layer of carbonate. Sub-

section D: large-scale cross-bedded ferruginous sandstones with
inversely graded laminations (Slt facies), characteristic of aeolian
dunes (e.g. Kocurek 1996 )

• An upper sequence is 165 m thick and largely regressive,
comprising delta front bars of cross-laminated muddy red
sandstones (sub-Unit S5b), overlain by fluvial coarser
sandstones with ferricretes (sub-Unit S5c) that indicate
more frequent emersions. This thick upward-coarsening
sequence is terminated with an erosion surface at depth

which marks a short Kimmeridgian marine incursion
(Taverne 1975 ).

8.5.2 The Loia, Bokungu and Kwango Groups

845 m (Fig. 8.8b ), covered by thin carbonate-
conglomerates and thick green shales of the Loia Group.
These two main depositional sequences in the Samba
section, first shallow marine (e.g. Fig. 8.9 ), and then more
fluvial and arid, likely correspond to the lower and upper
Stanleyville subgroups defined in the Kisangani type-
section (see Fig. 8.2a ). In the lower part of the Samba
section, the marker bed (MFS) of black shales can possibly
be correlated with the horizon

In the Dekese section, diamictites with black shales and red
mudstones of the Carboniferous-Permian and Triassic
successions (the Lukuga and Haute Lueki Groups; Chap. 7 ,
this Topic) are truncated by a well-marked erosion surface at
depth 715 m (Fig. 8.8b ), overlain by a 10 m thick trans-

gressive sequence of fluvial green heterolithic sandstones
(Unit D5), and then 307 m thick almost exclusively large-
scale cross-bedded red sandstones (Unit D4). The latter

' Lime Fine ' at Kisangani,