Geology Reference
In-Depth Information
SEDIMENTOLOGICAL LOGS
FACIES DESCRIPTIONS
MICRO-FACIES
Litho
Grain-size
C
S
fS mS cS Gr
P
a
7 m
CCi: Sandy carbonates with large intra-
clasts
- Carbonated, fine- to coarse-grained sands
with large intraclasts (1-5 cm).
- Beds 1 to 5 m thick, bioturbated,
with micro-karst infillings.
500
μ
m
0
b
Litho
Grain-size
C
S
fS mS cS Gr
P
CCg: Sandy carbonates with granules
- Carbonated fine- to coarse-grained sands
with small pebbles and granules (0.5-3 cm).
- Beds 1 to 10 m thick, root moulds and
micro-karst infillings.
7 m
500
μ
m
c
0
Litho
Grain-size
CCm: Muddy carbonates
- Carbonated muds with micrite agglomerates.
- Beds 1 to 10 m thick with cracks infillings and
recrystalizations.
C
S
fS mS cS Gr
P
4 m
500
μ
m
0
d
Litho
Grain-size
C
S
fS mS cS Gr
P
CCl: Laminar carbonates
- Carbonated muds with concentric and
laminar structures (stromatolith?).
- Beds 1 to 5 m thick with cracks infillings
and recrystalizations.
4 m
0
500
μ
m
DEPOSITIONAL ENVIRONMENT INTERPRETATION
Alternating
Pedogenesis
roots
<5 m
Microkarsts
Lime mud
Clastic-carbonates
Fig. 10.5
Facies descriptions of the Nxau-Nxau Calcrete Formation,
and shallow lake wetland depositional model. Microfacies: (
a
) Alveo-
lar structure filled with sparite (
white
); (
b
)
(
white
) coated with sparite; (
c
) circum-granular crack; and (
d
) laminar
micrite (
dark brown
)
'
floating
'
quartz grains
Sandstones
(c.f. Lepersonne
1945
; see Chap.
14
, this
Topic). These rocks are often cavernous, bioturbated and
fossiliferous with shells that display early silicification
(De Ploey
1968
). Ostracods (
Cypris farnhami
,
C. lerichei
,
'
Erpetocypris
sp.,
Gomphocythere?
sp.,
Oncocypria
sp.
and
Stenocypris bunzaensis
; Leriche
1927
; Polinard
1932
; Grekoff
1958
; Colin
1994
) and other lacustrine
fossils (charophytes and gastropods) suggest an Eocene
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