Page 20 - Carbonate Platforms Facies, Sequences, and Evolution

a
18
by
and
and
part
This
1987).
facies,
ripples,
Karstic
by
unit
transition
gradual
Paleokarst
Middle
mudstones.
(3) cavities
disappear
with
laminated
quartz-arenite
features
(Gandin, 1990a).
water diagenesis
(Gandin, 1990b).
change
consists
convolute
the
of
Dictyonerna
the platform (Fig. 5).
characterized
facies
Cambrian
upwards,
consist
.
with smooth
by
Post-depositional processes
towards
of
(Tremadocian Clonograptus
a
The
intercalations
at least
lamination
underlying
trilobite
(1)
as doc\Jmented
to
correspond
flabelliforrne
and
by
600 m
biozone;
rhythmical
deposits evolving from siltstones with
Cabitza
of
and
thinly
fibrous-radial and/or blocky calcite (Fig.
cavities
T.
walls and pipes
deeper-basin
to· more
blocky
Cabitza Shales (Middle Cambrian to Arenig)
slumps,
ing carbonate laminae and black shales (Fig.
assemblages
lOb);
filled
filled
docu­
shales of Cabitza lithologies or breccias and alternat­
Paradoxides rnediterranenus, followed by Jincella cf.
Barca et al.,
lOa).
and within it, breccias bodies are locally found (Fig.
lamination,
acritarchs
prantli assemblages (Rasetti, 1972) and in the upper
fine-grained
laminated
Limestone nodules occur locally at the
siliciclastic
located on top of unstable highs whereas the massive
stable
zones on the highs and in the troughs, respectively
Fossils are very rare, commonly concentrated in
small lenses. They are represented in the lower part
with
setting
Limestone
laminated mudstone
ments deposition by turbidity currents, and indicates
cements. Marine cement's are poorly developed and
locally show traces of dissolution. In the upper part
of the unit, palaeokarsts and neptunian dykes occur
calcite
of the Ceroide Limestone, support a meteoric origin
The Ceroide Limestone, underwent extensive fresh
the karstic cavities as well as of the blocky cements
whereas at the boundary with the Cabitza Limestone
and
by
breccias with hematitic niatrix; (2) fractures filled by
by
2). Contorted beds, interpreted as cohesive slumps
Stable isotope analysis of the fibrous radial calcite of
(Cocozza, 1969), occur along the eastern margin of
for the diagenetic waters from which the calcite was
1
2
of
of
at
Cocozza and A.
The
terial
the
the
western
deposits
Gandin,
Breccias
common
siltstones
diameter;
Slumping
Gandin
Limestone).
stone facies.
Ceroide
upper
included
along
Neptunian dykes
contact
these
margin
in
overlying
of
are
part
of Cabitza
the
Ceroide Limestone
platform
the
of
the
between
the Ceroide Limestone or
the eastern
precipitated (b 018 values =
was
that
the blocks (Gandin, 1990b).
Shale.
mainly
in
the
breccia
In
massive
platform
locally
margin
the
Gonnesa
affected
derived
of
matrix
platform,
bodies
by
have
and
latter
from
and
boundary sealed by the Cabitza Limestone.
platform and pelagic facies (Gandin, 1990b):
in
(Debrenne
the homogeneous facies of the Cabitza Limestone.
pressure­
rossa' is also documented by the red hematitic ma­
Turi, 1990). An extensive karstification of the plat­
grades upward to pink marls of the Cabitza Lime­
12.57 PDB; Gandin &
&
dissolved contacts. The matrix is a red hematitic silt
including
Two types of breccias occur at the boundary between
The clasts are derived from lithotypes
the
Karstic breccias of pebble-size, subrounded clasts
archaeocyathid-rich facies that only occur along the
form, with the resulting formation of residual 'terra
1985; Gandin, 1990b). The breccias occur
that also contains small calcite fragments and locally
(up to 1m wide) fractures filled by silicified marls
with echinoderm and trilobite debris, equivalent to
fracturing and most of the fractures were filled by
extensive
as lenticular bodies up to 10 m thick and 100 m long,
pockets exactly at its
in palaeokarstic sinkholes within the upper part of
fresh-water sparry calcite. However, there are small
(Cabitza
Cabitza
of Cabitza Limestone, the latter of black shales and
instance
Formations (Boni et al., 1981). Two different types
of matrix occur: the former consists of marly facies
clasts of Cabitza Limestone can also be found among
facies of the Ceroide Limestone although some of
various
Slope breccias of blocks up to several meters in
Deformation structures and associated breccias are
the Ceroide Limestone (Grey Dolomite). They occur
the Ceroide
them originated from the dolomitized equivalent of