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 166

moderate to good sorting. Beds show weak normal grading
and are thin, a few cm to a few meters thick at most. Well-
preserved trough to planar cross-bedding is diagnostic of this
lithofacies and basal erosional scouring into underlying beds
is common. This lithofacies represents high-energy, traction
dominated depositional environments.
LF4A and 4B comprise ungraded to normally graded,
massive granulestones to coarse-grained sandstones (LF4A
and 4B, respectively) that are identical in character to LF3A
and 3B, but are completely massive and lack evidence of
cross-bedding (Fig. 9.5e —LF4A).
LF5A and 5B are two of the most common lithofacies
observed in the study. They comprise fine- to medium-
grained sandstones with well-defined small- to large-scale
trough or tabular cross-bedding. Plane bedding is commonly
observed between cross-bedded intervals. Color ranges from
dominantly orange in LF5A, to dominantly red and purple
colors with common heavy mineral laminations in LF5B.
LF5A is diagnosed by having larger scale cross-bedding
with higher angle foresets, and in some cases, slight inverse
grading (i.e., pinstripe bedding) along foresets. In other
locations, smaller-scale current ripple cross-lamination is com-
mon. LF5A is typified by clean, extremely well-sorted sand-
stone with no mud content, and well-rounded quartz grains.
Another important feature is the presence of frosted grains.
LF5B differs in having a modest to high mud content and
poorer sorting (Fig. 9.6 ), with sub-rounded to rounded grains
with isolated granule to pebble sized clasts, and is less compo-
sitionally mature. In addition, LF5B lacks the large, high
angle cross-bedding and pinstripe bedding. Burrows or root
traces are moderately common, particularly in LF5B,
although no macro- or micro-fossils have been observed in
this facies.
LF6A and 6B are similar to LF5A and 5B, except that
they are completely massive with no indication of bedding.
Lithofacies 6A has no mud matrix, whereas LF6B has minor
to abundant mud matrix. In places, bleaching and small iron-
oxide concretions are present. Isolated pebbles are rare to
common, particularly in LF6B. Burrow or root structures are
also common in some samples, particularly in LF6B. In one
core (155-X040), well preserved, robust bivalves were
identified in LF6B. Their massive character is most likely
due to bioturbation, bleaching or other post-depositional
process that has obfuscated whatever original bedding may
have existed.
LF7 comprises massive mudstones and siltstones
(Fig. 9.7 ). Rare examples of remnant planar laminations
are present. Moderate to intense bioturbation is commonly
present, along with less common desiccation cracks. Small
to quite large, and sometimes amalgamated, carbonate
nodules are locally present (Fig. 9.7 ). Color is typically red

9.4 Sedimentology and Depositional

Environments of the Kasai Cover
Sequences

9.4.1 Lithofacies

LF1A and 1B comprise pebble to cobble breccias and sub-
ordinate conglomerates, with clasts typically ranging in size
from 2-7 cm. Lithofacies 1A and 1B are identical, except
that 1A is clast-supported (Fig. 9.5a ), whereas 1B is matrix-
supported (Fig. 9.5b ). Matrix is typically characterized by
brick red sandy mudstone to poorly-sorted muddy sandstone
(Fig. 9.5b ). This facies tends to be oligomictic, but may be
polymictic. Four primary basement-derived clast types are
typically observed across the Kasai region, which include
Proterozoic stromatolitic limestones and basalts (east:
Mbuji-Mayi and Kabinda) and, less common, granitic and
metamorphic clasts (west: Tshikapa). A diagnostic feature
common with many examples of this lithofacies, are calcrete
coatings around the clasts (Fig. 9.5c ). Calcrete rims range
from 3-8 mm in thickness and may coat the entire clast, or in
many cases, the coatings are thicker on the upper surfaces of
the clasts, and commonly absent on the basal surfaces. Most
clasts associated with this LF are locally derived from
nearby basement blocks; in particular Proterozoic limestone
and basalt clasts.
LF2A and 2B comprise small- to medium pebble conglo-
merates, with most clasts falling within the 0.5 to 2.5 cm
range, with isolated clasts reaching up to 15 cm in diameter.
LF2A is clast-supported, well-sorted and generally upward-
fining, whereas LF2B is matrix-supported, poorly-sorted and
lacks obvious grading (Fig. 9.5d —LF2B). Clasts are gener-
ally moderately to well-rounded and represent a much
broader spectrum of lithologies than LF1A and 1B clasts,
containing metamorphics, vein quartz, agate, chalcedony,
black chert, limestone, basalt, granitic pebbles, and rare to
abundant intraformational mudstone rip-up clasts. Matrix is
dominantly sand-sized, although there are examples of mud-
stone matrix. This lithofacies is typically brick red colored.
LF3A and 3B comprise g ranulestones to coarse-grained
sandstones. As with the previous two lithofacies, LF3A and
3B are distinguished by clast versus matrix support, respec-
tively. In the case of matrix-supported LF3B, the matrix is
typically deep red claystone/mudstone. The color of this
facies ranges from almost white, in the case of quartzose
clast-supported granulestones (LF3A), to deep red, as in
the case of mud-supported granulestones (LF3B). Granule
lithology is most typically dominated by quartz, meta-
morphic lithics, and intraformational mudstone rip-ups.
Clasts are typically subangular to subrounded and show