Mesozoic Sedimentary Cover Sequences of the Congo Basin in the Kasai Region, Democratic Republic of Congo - Geology and Resource Potential of the Congo Basin - page 182

South America (Gallego et al. 2010 ). Previously known
African species have been exclusively Late Jurassic, while
South American species of Congestheriella have ranged
from Late Jurassic to Early Cretaceous. The specimens
from the 173-X009 core are thought to be Late Cretaceous
based on zircon dates, making them the youngest represen-
tatives of the genus.
The presence of conchostracans is very suggestive about
the paleoenvironment. Living conchostracans are almost
exclusively ephemeral, freshwater animals (Webb 1979 ;
Frank 1988 ; Dumont and Negrea 2002 ). Some living
conchostracans can tolerate slightly elevated salinities
(Webb 1979 ), but there are no living marine representatives
(this may not have always been so, there are a very few fossil
conchostracan faunas that co-occur with marine fossils, see
Hegna 2012 ). In fact, they produce dormant resting cysts to
withstand dry periods (Dumont and Negrea 2002 ). In the
presence of predaceous fish, conchostracans are often preyed
upon to the point of local extinction (Frank 1988 ). Thus, the
occurrence of conchostracans suggests that the paleoenviron-
ments were likely small, ephemeral bodies of freshwater (i.e.
poorly drained) in a region with seasonal wet/dry periods.

region. It is possible, albeit unlikely, that marine deposits
exist within C3/C4 (Kwango) strata; however it seems more
likely that the specimen was either misidentified or collected
from the Lualaba Group, rather than the Kwango Group.

9.6.4 Vertebrates

Two cores, 157-X016 and 173-X050, contained vertebrate
fossil remains in the study area. In the upper part of this core
(157-X016), several fish bones were observed. The bones
appear to be mostly spines and isolated cranial bones. A
single, as yet unidentified, partially articulated actino-
pterygian fish skeleton (1.5 cm long) was also identified
from this core (157-X016; Fig. 9.16 ); however most of the
other material is too fragmentary and isolated to permit
detailed taxonomic assessment. The other core (173-X030)
also preserves rare fish scales. Several other fish have been
reported from the western margin of the Kasai area, includ-
ing fragments of teleosts and a specimen of Rhipis moorseli
(Cahen 1954 ).
Two other notable reports of vertebrates from the Kasai
region include large bones of sauropod dinosaurs in a
conglomerate facies below or at the base of the Kwango
Series near Luebo. Cahen ( 1954 ) reported the conchostracan
Bairdestheria at the same locality and through personal
communication with W.E. Swinton about the dinosaur
bones, suggested a Late Jurassic to Early Cretaceous age
for these basal conglomerates. Pterosaur bones, identified as
the Cretaceous taxon Ornithocheirus , were recovered from
the upper Lualaba Series along the Lubilash River (Cahen
1954 ).

9.6.3 Mollusks

Bivalve shell fragments were observed in a number of
localities. However, only a single invertebrate macrofossil
locality with identifiable material was found. This site
represents a bivalve shell accumulation in core 155-X040
near the base of the core, at ~115 m from surface. Multiple
partial specimens were found and several of these were
collected for further taxonomic identification. At least two
of the specimens appear to be articulated. Although the
shells are incomplete and of limited utility, L. Tapanila
(Personal Communication, 2008) was able to identify
enough characters, including the dentition, a thick, robust
shell and an oblate shape, to tentatively assign the bivalves
as members of the Unionoidea, a family of a freshwater
(rarely brackishwater) clams (mussels) that commonly live
in fluvial and lacustrine environments. Although they are of
little value for biostratigraphy, the identification of these
shells as Unionoids is significant because they are domi-
nantly a freshwater group and the thick shell morphotype
of these specimens is consistent with a higher-energy fluvial
mode of life (L. Tapanila, Personal Communication, 2008).
This is important because a marine bivalve identified as
Pteria sp. was reported from an outcrop in the Tshikapa/
Luebo region from the Kwango Series by Cahen ( 1954 ). The
taxonomic assignment of Pteria sp. in the Kwango Series is
questioned here based on the sedimentological investigation
of Cretaceous strata in this region and the overwhelmingly
continental character of the Kwango strata in the Kasai

9.7 Discussion

This study represents the first detailed investigation of the
Mesozoic cover sequences in the Kasai portion of the Congo
Basin since the seminal exploratory work of Cahen ( 1954 )
and early geologic mapping of the region. Over the last 50+
years, most inferences about the Kasai stratigraphy have
been drawn from the original work of Cahen ( 1954 ) and
various reports, primarily focused on diamond exploration
associated with the Mbuji-Mayi kimberlite fields. The exten-
sive De Beers Exploration drilling program in the Kasai
region has provided an important window and research
opportunity, which, for the first time, permits detailed obser-
vation and insight into the Mesozoic cover sequences of the
Kasai portion of the Congo Basin.
Klein ( 1995 ) highlighted the complicated and controver-
sial origin of intracratonic basins, particularly owing to
their long-lived histories that typically involve various
combinations and successions of basin forming processes.