Petroleum Potential of the Congo Basin - Geology and Resource Potential of the Congo Basin - page 375

Fig. 18.6 Field photographs of
hydrocarbon seep sites, taken
during the 2011 MRAC-
COMICO field campaign
(location on Fig. 18.1 ). ( a ) Frontal
view of the Tolo seep site. ( b ) Pit
drilled in the Tolo site trough a
layer of soil mixed with rubbish.
( c ) Ilanga-Kolo seep site in a
ditch along an old road, near a
bridge. ( d ) Ilanga-Kole site:
Impregnated gravel layer at base
of superficial and above a
compact clay layer. ( e ) Typical
shore of Lake Inongo/Mai-
Ndombe with lateritic
promontories and sandy bays. ( f )
Mpunzuiboko beach with
bitumen pellets covering the sand
in the upper part of the beach

a b Tolo, pit

Tolo

c Ilanga-Kole

d Ilanga-Kole, pit

e

f

Inongo lake shore

Mpunzuigoko beach

River and along the beaches of Lake Inongo (Mai-Ndombe).
They reported that the biomarkers of the Ilanga-Kole and Tolo
seeps suggest derivation of black oil from a marine source rock
in the Late Cretaceous, mixed with an older, deeper marine
source. The seeps contain a high concentration in Oleanane, a
component present in the angiosperms, which appeared in
Early Cretaceous and became dominant in the Late Creta-
ceous-Tertiary. Mello ( 2008 ) attribute them to some input
from Neogene sediments, but source rocks are not known
from the Neogene sequences. Mello ( 2008 ) thus predicted the
presence of two or three active petroleum systems in the CB,
and speculated that it could hold

By contrast, Harriman ( 2011 ), disregarded the bitumens
found on the beaches of Lake Inongo, and suggested they
may be residues from the sealing of local fishing boats, and
therefore likely of anthropic origin.
In 2011, we re-visited and re-sampled the Tolo and
Ilanga-Kole seeps along the Lukenie River and the bitumen
from the Mpunzuiboko beach along Lake Inongo (Figs. 18.1
and 18.6 ). The Tolo seep site was found along the river bank
at the foot of a ~15 m high scarp that separates it from
an inhabited plateau occupied by traditional houses.
Beige-color clay with a slight odour of light hydrocarbons
was found in a 1-m deep pit dug through a superficial layer
of soil mixed with rubbish. At Ilanga-Kole, also along the
Lukenie River and upstream Tolo, light hydrocarbons were

(size not
specified) accumulations of light oil, condensates and gas
hydrocarbons, suggesting a promising petroleum province.

' giant to supergiant '