Page 18 - Carbonate Platforms Facies, Sequences, and Evolution

2
3
1
1
4
at
16
in
(Fig.
(Fig.
ation
form,
the
lateral
the
lumps,
Shelf.
present.
Shoal.
tribution
calations.
7b);
12).
grainstone
semblages
end
have
boundstone
wackestone,
(Grey
and
This
of
central
peloids
and packstone.
These facies,
The
Three
Open lagoon.
(Fig.
with
variation
From
& Gandin, 1985).
with
are
Internal lagoon.
the
type (2)
part
fragments (Fig. 7h).
in the western area.
7d).
lagoonal facies occur.
occurs
grains and intraclasts,
west
of
grains
Dolomite).
in
represented by unsorted
local
different
to
a
Ceroide
the
In
facies have been recognized:
are
Mudstone,
In both
east
its
in thickness in
facies
and complex facies mosaic (Fig.
Archaeocyathus
4a), with rare trilobite fragments.
and rare trilobite
narrow
the
5).
facies,
platform,
upper
and
oncoids,
Limestone
belt
archaeocyathid
laterally discontinuous
T.
adjoining
altaicus,
is well-sorted ooid and
part
equivalent facies can be recognized (Fig. 1):
associations
following
trilobite
along
ments, commonly concentrated in small lenses.
a characteristic non-cyclic vertical
A.
(Fig.
tidal-flat
The archaeocyathids form as­
Ceroide Limestone is locally affected by dolomitiz­
Common fossils are echinoderm plates and trilo­
dis­
are represented by trilobite and echinoderm frag­
indicative of a shallow-water plat­
grandis, A. kusmini and Vologdinocyathus tener in­
laminated mudstone and marly inter­
bite fragments. Rare archaeocyathids and Epiphyton
deposition.
Tidal flat. Fenestral stromatolitic boundstone (Fig.
cf.
been found: type (1) consists of skeletal (Epiphyton)
5).
7f), and vadose pisolite (sensu Esteban, 1976) (Fig.
intraclast grainstone with
the
The Ceroide Limestone is noticeable for its great
There is no suggestion of a regressive trend through
have
The following
bedded marly limestone. of Cabitza Formation. The
The areal distribution of the facies indicates an
features, calcite veins as well as breccia bodies are
echinoderm fragments are common; and type (3) is
and
sections
echinoderm
that are probably reworked
micritized
Skeletal or poorly sorted granular
occur in the upper part of the limestone body, only
karstic
mounds
time
peloidal wackestone
this unit although there is clear evidence of exposure
dicating a Lower-Middle Toyonian age (Debrenne
However, at the base of the sequence, everywhere
oncoid
calcrete clasts, and minor quartz silt and clay. Fossils
or
isolated platform bounded by epicontinental basins
3
4
2
of
Cocozza and A.
the
type
This
silty
shale
pink,
3
the
different
channels.
unit
Cambrian
carbonate
Gandin
Platform
shales
fauna (Fig.
siliciclastics
is
facies
red or
shoal
the karstified
homogeneous
age
archaeocyathid
( Corynexochus
evenly bedded,
up
8b)
are
platform
well-stratified
made
to
lithotypes
facies
interior.
yellow.
up
density
production.
highly
(Rasetti,
platforms
80 m
mounds
can
of
sardous,
This
The
Ceroide
Three
be
Epiphyton
and silt-sized
Platform ramp-like margin.
1972),
thick.
interfingers
gradients,
variable
bedded,
interfered
It
and miscellaneous sponge spicules.
consists
in
intercalated with open-lagoon facies.
found:
quartz
interfinger
and residual 'terra rossa'
Cabitza Limestone (Middle Cambrian)
with
buildups
of
Limestone
irregularly
Pardailhania
(1)
including
genesis of the
intercalated red shales (Lecca et al., 1983).
triggered
with
has
grains,
with
thickness
by
with the in
alternating restricted-lagoon and tidal-flat facies.
compaction and dissolution of sediments with non­
1990a, b). The limestone facies are skeletal wacke­
(2) nodular marly limestone (Fig. Sa); and (3) alter­
tec­
open­
oolitic-oncolitic shoals (type 1 and 2 shoal facies).
In the eastern area,
coast of the Tyrrhenian sea (Buggerru area) where
in the platform interior where thin shale layers are
tonic instability of the shelf. This facies was therefore
fossiliferous limestone alternating with red or green
lagoon facies and in the upper part of a few sections
Platform rimmed margin. Along the western edge
nodular
unconformably
local
hispida),
massive,
intercalations, slump structures (Cocozza, 1969) and
overlies the Ceroide Limestone with a sharp contact
open-lagoon
facies. Here the limestone decreases in thickness, is
and contains thin marly and shaly
colour. The latter ranges from black to grey, green,
evenly-bedded limestone with wavy shaly partitions;
nating calcareous and shaly planar laminae (Gandin,
small
locally marked by a palaeokarstic surface and slope
locally nodular,
breccias. It contains rich assemblages of early Middle
irregularly
Limestone and
structure of the limestone can be mainly related to
trilobites
echinoderms, Chancelloria, brachiopods, hyolithids
The sedimentary features and fossil content of this
unit are ·on the whole indicative of a more or less
and hematite. The latter gives the red colour to the
pyrite
stones and packstones with a diverse open-marine
alternating
and
situ
restricted shallow-shelf environment, where pelagic
coming from