25th International Meeting on Organic Geochemistry IMOG 2011

P-326
Source rock investigations on Palaeozoic and Mesozoic
sediments of the Central Congo Basin, Democratic Republic of
Congo
Ralf Littke 1 , Victoria Sachse 1 , Damien Delvaux 2 , Jan Schwarzbauer 1
1 RWTH Aachen University, Institute of Geology and Geochemistry of Petroleum and Coal, Aachen,
Germany, 2 Royal Museum for Central Africa, Tervuren, Belgium (corresponding author:sachse@lek.rwthaachen.de)
The Congo Basin is one of the largest intracratonic
sedimentary rift basins in the world, but still poorly
investigated with respect to petroleum potential. Up to
now, the investigations by Daly et al. (1) contain the
most comprehensive source information on the
Congo Basin, including the basin structure and its
post- Paleozoic history. In addition, Giresse (2)
compiled the Mesozoic-Cenozoic history of the Congo
Basin. The approach of this work is to document
various types of source rocks of the Congo Basin,
their quantity, quality and maturity of OM as well as
the depositional environment in relation to tectonic
evolution. For this purpose, in total 147 samples
stored in the rock collection of the Royal Museum for
Central Africa, Belgium, covering various stratigraphic
units of the Congo Basin were investigated, including
samples of two wells (Samba and Dekese).
Palaeozoic and Mesozoic outcrop and core samples
covering various stratigraphic intervals from the
central Congo Basin were analyzed for total organic
carbon (Corg), total inorganic carbon (Cinorg) and total
sulfur content (TS). Rock-Eval analysis and vitrinite
reflectance measurements were performed on the
basis of the Corg content. Non-aromatic hydrocarbons
were analyzed by way of gas chromatography-flame
ionization detection (GC-FID) and GC-mass
spectrometry (GC-MS).
Our data revealed two highly potential source rocks in
the Congo Basin: sediments of the Loia and
Stanleyville Formation. All of the Pre-Mesozoic
sediments contain only a small amount of OM.
Samples of the Alolo shales, which belong to the Lindi
Supergroup (late Neoproterozoic / early Paleaozoic)
are in general very poor in Corg and contain a high
amount of degraded organic matter. All samples of
this formation revealed a Type III/IV kerogen and
cannot be considered as a potential source rock.
Sediments from the Lukuga Formation (Permo-
Carboniferous) contain moderate contents of organic
carbon, representing hydrogen-poor Type III/IV
kerogen having at best a very minor gas generation
potential. Tmax values indicate early mature organic
matter, and a slight higher level of maturity is
indicated by vitrinite reflectance and PI values. The
kind of OM as well as the biological markers led to the
conclusion of a terrestrial dominated depositional
environment.
Organic geochemical investigations on Late Jurassic
(Stanleyville Formation) to Early Cretaceous (Loia
Formation) samples from the Samba well and outcrop
localities, in the north-eastern part of the Congo
Basin, revealed moderate to high contents of organic
carbon (up to 25 %). The kerogen is characterized by
very high hydrogen index (HI) values reflecting Type I
kerogen of excellent quality in the Stanleyville
Formation and Type I/II kerogen in the overlying Loia
Formation. All of the samples studied here are too
immature for petroleum generation. Based on
biomarker analysis/n-alkane distribution a lacustrine,
anoxic depositional environment can be assumed for
these units. Stanleyville and Loia Formation can be
regarded as excellent petroleum source rocks and
could be part of a petroleum system if sufficient burial
and maturation has occurred.
Finally, vitrinite reflectance data was used to calibrate
1D models for wells Dekese and Samba, which give
an overview about burial-, thermal-, and maturity
history of the area.
Figure 1 Bulk geochemical data of various samples of
the Congo Basin: Rock-Eval HI and OI values.
(1) GIRESSE, P., 2005. Mesozoic-Cenozoic history of the Congo
Basin, Journal of African Earth Science, 43, 301-305.
(2) DALY, M. C., LAWRENCE, S.R., DIEMU-TSHIBAND, K. and
MATOUANA, B.,1992. Tectonic evolution of the Cuvette Centrale,
Zaire, Journal of Geological Society, 149, 539 – 546.
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