Sedimentology and Sequence Stratigraphy of the Late Precambrian Carbonates of the Mbuji-Mayi Supergroup in the Sankuru-Mbuji-Mayi-Lomami- Lovoy Basin (Democratic Republic of the Congo) - Geology and Resource Potential of the Congo Basin - page 68

Table 4.2 (continued)
Lithofacies/
microfacies Occurence and thickness Sedimentary structures Components and microfacies Environment

(ii) hypidiotopic texture; possible
mudcracks; fenestral cavities;
between the laminations, replacive
evaporites and evaporite cements

MF8:
stratiform
stromatolite

Centimeter- to decimeter-scale
beds associated with MF7-MF9;
microfacies in an inner ramp and
lacustrine closed-lake (salt lake);
sharp contact with MF9

Stratiform, LLH-S stromatolites,
millimeter to decimeter-sized
domes and massive beds of mats;
gradual transition with MF7, as
well as sharp to MF9; fenestral and
thomboidal texture; often syn-
sedimentary or early diagenetic
brecciation; desiccation cracks;
often silicification

Alternation of submillimetric
laminations of (i) dark micrite and
(ii) light dolomicrospar; (i) smooth
to crinckly laminae of
equigranular xenotopic to
hypidiotopic texture (5-10 μ m);
(ii) hypidiotopic dolomite crystals
(10-15

Restricted shallow
intertidal zone

m); dolomicritic films,
clots and grumeaux;
interlaminated 'pallisadic'
dolomite crusts; replacive
evaporites and evaporite cements

μ

MF9: oolitic
grainstone

Thickness: centimetric beds;
interbeds of MF7; association with
MF8

Massive; planar cross-lamination,
low angle through cross-
lamination; graded; rare erosion
surface

sand-sized oolites and oncoids
with micritic rim; ovoid with
microcrystalline dolomite
(5-10

Restricted high-
energy shallow
intertidal zone
including sandy
carbonate shoal

m) anc concentric
tangential cortex; rare aggregate
grains; microfacies associated
with bioclasts; evaporite crystals
and cements; often silicified

μ

Lacustrine
environment

Lacustrine
pond (closed-
lake)

MF10:
lacustrine
dolomite

Metric-thick beds compiled to
MF6, MF7, MF8; centimeter-scale
interbeds of MF9

Clean structureless dolomudstone,
laminated dolomustone, stratiform
stromatolite; abundant fenestral
and thromboidal texture;
brecciation; desiccation cracks;
recrystallized microfacies;
silicification

Microfacies similar to MF6-MF7
and MF8; peloidal texture filled by
dolomitic vadose cements; rare
rendant beard-like cements

Closed-lake with
probable perennial
pond submitted
semi-arid and warm
conditions

Early diagenesis

MF11:
evaporite

Millimeter- and centimeter-thick
interbeds associated to MF6 untill
MF10; abundant in MF10

Isolated evaporite casts, nodular,
bedded or massive skeletal halite
casts; slumping; deformation;
brecciation

Prismatic and hemipyramidal
crystals with dolomicritic rim;
laminar chevron-like texture; rare
halite crystals; replacive
evaporites by dolomite or silica

Evaporative
environment

sea level change magnitude. The first half part of the unit
records greater relative sea-level fluctuations from deeper
subtidal outer-ramp to shallower subtidal middle-ramp
settings (parasequences 68-80) than second half part from
restricted environments to intertidal and supratidal domains
(parasequences 81-104). This change is also recorded in
average thickness cycle ranging from

The parasequences 115-117 indicate that aggradational
processes are superimposed to progradational ones. Relative
deepening, if at all, was limited since most of these
parasequences are capped by supratidal facies with thin
calcretes and evaporites. Subsequent parasequences in the
BIIe subgroup display shallowing from deep subtidal to
shallow subtidal. Previously overfilled accomodation space
of the BIIc-BIId Subgroups is now replaced by underfilled
accomodation space, since no intertidal or supratidal caps
are present. This leads to recognition of early highstand
systems tracts, which probably followed a transgressive
systems tract between BIId and BIIe subgroups. No cores
or material across this transitional stratigraphic interval
are available for

< 5 m in first half

and 5 m in second one. This model distinguishes an early

highstand systems tract (first half) and a late highstand
systems tract (second half). Their Fischer plots are also
similar and suggest that the studied BIId subgroup is the
continuation of the previous late highstand systems tract.
One has to note the second appearance of numerous levels
of oolites.

>

study. Reported biohermal buildups