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 131

8

Facies Analyses, Chronostratigraphy and Paleo-
Environmental Reconstructions of Jurassic to
Cretaceous Sequences of the Congo Basin

Bastien Linol, Maarten J. de Wit, Erika Barton, Francois Guillocheau,
Michiel C.J. de Wit, and Jean-Paul Colin

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8.1 Introduction

representing unique stratigraphic sections through the center
of the basin. The complete core-collections are archived at the
Royal Museum for Central Africa (RMCA) in Tervuren,
Belgium. The two younger exploration wells, Gilson-1 and
Mbandaka-1, were logged by geophysics (Gamma Ray,
Resistivity, Sonic) and cored occasionally to check significant
lithological changes (Esso-Zaire 1981a , b ), but most of these
core-samples are now lost.
In this study, we present new facies analysis and regional
correlations of the Jurassic-Cretaceous (J-K) sequences,
based on field mapping in the Kwango Valley along the
southwestern margin of the CB, and by re-logging the four
wells/cores in the center of the basin (Fig. 8.1 for locations).
This sequence-stratigraphic basin analysis enables more
detailed paleogeographic interpretations of the CB during the
period between the initial break-up between East and West
Gondwana (ca. 160-180Ma) and the final separation of Africa
from South America (ca. 80-130 Ma). In addition, U-Pb
geochronology of detrital zircons from these J-K sequences,
collected both from the cores and in outcrops, characterizes
the maximum ages and source provenances for the sediments.

The Congo Basin (CB) covers about 1.8 million km 2
(Fig. 8.1 ), centered on the Democratic Republic of Congo
(DRC, formerly Zaire), and extends to the west into Angola,
Republic of Congo and Gabon, and to the north into the
Central African Republic (CAR). The structure and strati-
graphy of this vast continental basin was essentially described
from two exploration programs in the 1950s and 1970s,
including extensive field mapping, geophysical surveys (e.g.
Evrard 1960 ) and drilling of four deep boreholes, each
between 2 km and 4.5 km deep. The first two, Samba-1 and
Dekese-1, were cored with excellent core recovery of ca.
78 % and 84 %, respectively (Cahen et al. 1959 , 1960 ),

8.2 Current Litho- and Bio-Stratigraphy

(the Congo Supergroup)

The complete J-K succession is about 1,000 m thick in the
center of the CB, and includes: the Stanleyville, Loia,
Bokungu and Kwango Groups (Cahen 1954 ; Lepersonne
1974 ; Cahen 1983a , b ). It overlies a major unconformity
that truncates Precambrian basement and Carboniferous to
Triassic sequences (Chap. 7 , this Topic). Along the margins
of the basin, the lateral equivalents of these J-K sequences
correlate with the Calonda Formation in Angola (de
Carvalho 1981 ) and the Carnot and Moukka-Oudda
Formations in the CAR (sourced from the southeast; Censier
and Lang 1999 ), and all of which contain alluvial diamond
paleo-placers suggesting concurrent kimberlite intrusions