Page 24 - Carbonate Platforms Facies, Sequences, and Evolution

the
and
with
A
Most
basin
sisted
karstic
1990b)
breccia
12 IV).
duction
uplifted.
the
platform
material.
of
emergent
first
Positive
developed
Limestone
Limestone
Limestone
Limestone.
only
and
pelagic
was
units
the
on
are
more
dolomitization.
marginal zones.
was
posed platform,
zones
a
Platform collapse
were
topography
clays
Their
During
Ceroide
and discontinuous.
or karstic breccias,
solidated sediment.
drowning
of
regressive
rather
distal
rhythmically
lithofacies
occur
were
and
The
breccias
the
number
laminated facies including
covered
blocks.
event
also
characterized
dissolution producing
of
by
carbonate
characterized
subrounded
suddenly
marginal
in
occur
sequences
fractured
by
alternating
seafloor
by
the
at
marginal-plateau structure (Fig. 12).
within
indicate local
blocks.
cavities
thin shaly
drowning of
and
areas
deposition of Cabitza Limestone.
clasts
autochthonous
Cabitza
Deposition
attests
with
flooded
intervals
the
the
the
of
and
of
The
early
resulted
to
layers
were
lime
a
to a
carbonate
in
in
clasts
subjected
persistence
the upper early-lithified sediments. The lack of well­
hematitic material, previously produced on the ex­
depth. Exposure and shallow-water deposition per­
fresh-water cementation of sediments not yet com­
uplift of the blocks that was responsible for circu­
were filled with marine uncon­
well­
diversified benthic fauna developed. The block-and­
different facies of the Cabitza Limestone. The mass­
pro­
muds.
carbonates.
Negative zones at the top of the Ceroide
uplifted platform began to collapse and drown (Fig.
to
of
never
the
rapid
restricted-lagoon,
siliciclastic
Slope breccias accumulated at
Most of the
the fault scarps, mostly along the western and eastern
margins of the platform (Boni et al., 1981; Gandin,
Cambrian (Pardailhania hispida horizon) resulted in
Middle
Cabitza
Ceroide
of
pletely lithified in the marine environment, and local
lation of meteoric waters and consequent extensive
Limestone-Cabitza Limestone contact, but smaller
Cabitza
evidence indicate that the drowning was differential
platform
was achieved through two main stages leading to a
At the beginning of Middle Cambrian the previously
Biostratigraphic data and sedimentological
Ceroide
Fissures and karstic cavities, not yet filled by calcite
residual
ive calcareous facies was formed on structural highs
was in part swept out and mixed
neritic
two
The
they
ively
along
dance
The
preted
humid
Middle
Cabitza
few
of
proposed
the
as
were
to
deeper-water
lower
Megabreccias
the sequence.
tropical
Climatic control
only locally and
siliciclastic
both
blocky
(Gandin, 1990b).
Cambrian
which no traces of
Limestone
structural
western
made
Carbonate deposition during early rifting, Italy
explain
laid
settings.
indicative
distal
up
regime persisted when,
boundary
also
calcite
highs
of
why
of
conditions (Gandin, 1980).
conditions
The
down
margin
in
that
and
(Paradoxides
limestone isotopic values (o 018 =
turbidites
cements
drowned
normal
Ceroide
during
the
nodular
the
were
blocks and their differential drowning.
and
and
were
the Ceroide
different early diagenetic processes (Fig.
left
same
the
the
facies
carbonates underwent early dolomitization.
same
marine
4),
Limestone
deposition
mediterraneus
in the Cabitza Shale basin in which only later exclus­
with the uplift of the plat­
-8.9 PDB) indi­
(Debrenne & Gandin, 1985). Moreover, the abun­
The Epiphyton-dominated buildups have been inter­
the early diagenetic processes of the Ceroide Lime­
deposited.
cavities were filled by black or grey Cabitza Shales.
occurs
at different stratigraphic levels of
Its genesis records instability of the
whereas the laminated marly facies was deposited in
found in the widespread intertidal-supratidal facies.
of Ceroide Limestone and
Jincella horizons). It led to the final foundering of
fault scarps mostly along the western margin of the
locally Cabitza Limestone clasts accumulated at the
the platform and to resumption of connections with
21
of
the mainland. Quartz sands were at first transported
karstic
average
cementation, karstification and local dolomitization.
A second drowning event took place later in the
The Ceroide Limestone is a pure calcareous unit in
platform and were embedded in black muds and silt
exposed
to
stone (Gandin & Turi, 1990). These features imply
cate a consistent supply of meteoric waters during
and
platform is marked by a rather sharp transition from
Limestone
the underlying Laminated Dolomite. The latter was
deposited in an arid, evaporitic tidal fiat where the
A climatic change from arid to humid has been
Laminated Dolomite sediments went through such
water
humid
early dolomitization have been
form, the sediments underwent extensive fresh-water
since
tidal-fiat