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found in a gravel layer on top of clay in a ditch along the old
Oshwe-Bandundu road. On the shore of Lake Inongo, we
sampled lumps of solid bitumen on the surface of white
beach sands. We also sampled a fragment of the bitumen
that was used to waterproof our wooden boat.
The collected samples were analysed by GHGeochem
laboratories (Harriman
2012
), and their anthropogenic origin
confirmed for all of them. In summary, none of the hydro-
carbon seeps appear to be natural oil seeps. They contain
biomarkers that relate them to source rock which are too
young, too mature and of marine affinity, for which no
source rock are known in the CB.
Acknowledgements
This work benefitted from many informal
contacts and discussions that the first author had with individuals
interested on the CB. We thank also the editorial efforts of M. de Wit
and F. Guillocheau who motivated us to submit this paper.
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Conclusions
Based on the evidence presented, we do not share the
optimism of HRT Petroleum for large potential oil
reserves in the CB (e.g. Mello
2008
). Todate no petroleum
systems have yet been proven. The samples from the
Mamungi shales have negligible organic matter content
(C
org.
0.1 % on average), which do not allow any fur-
ther organic geochemistry or thermal maturation analysis.
Similarly, most of the Alolo shales analyzed also have
negligible organic matter content, except a few samples
from the Yambuya section, but which, when analyzed with
the Rock Eval, appear to have no oil potential. Further, the
Mamungi and Alolo shales are only known in outcrop and
have not been formally recognized in the 4 wells drilled in
the center of theCB.
The Lukuga Group that contains up to 2.4 %C
org
,is
largely a gas-prone peri-glacial or interglacial lacustrine
sequence of shales. Lacustrine sediments could have been
deposited in more temperate conditions, but OM would
be dominated by higher plants. The Stanleyville (Middle
or Upper Jurassic) and Loia Groups (Middle Cretaceous)
contain the best potential source rocks with some very
rich shales (up to 25 %C
org
). The kerogen is derived from
lacustrine algae, and is oil-prone type I (HI up to 950 mg
HC equivalent/g C
org
), but is too immature to have
generated significant quantities of oil where they have
been found. This Mesozoic petroleum system is, at the
present state of knowledge, the best potential target for oil
exploration.
In conclusion, there presently are no indications for any
active hydrocarbon systems, but as the current knowledge
of this large basin is still very limited, there is much room
for future exploration. There is a clear need for more, new
and modern geophysical and geological work to improve
the basic knowledge of this vast region. This should be the
backbone for future hydrocarbon exploration surveys.
There is currently not enough knowledge on the geological
evolution and architecture of the CB to predict the pres-
ence of viable hydrocarbon deposits.
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'
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