Page 39 - Carbonate Platforms Facies, Sequences, and Evolution

a
34
be
the
the
The
since
At
stage
The
Ceroide
of
first
evidence
tensional
the
sabkha
behaviour
the
siliciclastic
Botomian)
of
eastern
cold regimes.
Carannante et
of
sign
platform
second
rimmed margin.
to humid zones.
of
began
the
collapse,
system.
Lower
sloping to the east.
movements
occurrence
stage
divergent
platforms are
carbonate
with
ramp-like
rifting
of
developed
of
Lower Cambrian platform
Lower
an
on
in a tidal-fiat/lagoonal system.
differential
the
a
regarded
Conversely,
controlled
margin,
possible
abrupt
western edge a pulsing subsidence
(Bernoulli
on
a
Cambrian
both
form was isolated from the mainland.
Cambrian-Middle
et
the
tillites
T.
platform
delta-plain-coastal
the
and
climatic
movements
Botomian,
al. ,
resulted
regular
and
of
With the cessation of the siliciclastic influx the plat­
detach-
towards humid conditions and mild extensional tec­
the platform into blocks. As a consequence, differ­
indicative of the very beginning of continental rifting.
1979;
taken into account for the Sardinian sequences
The fracturing and drowning of the Massiccio and
Upper
Moreover, the sharp transition from early dolomite
by the authors as
inherited and controlled by the underlying basement.
al. , 1984}. However, the depositional
ment of the platforms and their internal stratigraphy
during growth. Therefore they can be interpreted as
ential subsidence and high rates of sedimentation,
shortly before their collapse, could be interpreted as
development of a more subsident basin seaward of a
This morphology was probably
to pure limestone, occurring within the two platforms
(Upper
mixed
led to the drowning of the platform. During the first
the
system
boundary a stronger pulse of extensional tectonics
movements that caused the
fringed by an oolitic shoal to the west, and gently
ference. Nonetheless a climatic variation should also
drifting of the continental plates from tropical arid
During the
under an arid climate; in the platform interior and in
caused the up-building of a complex facies mosaic
moderate subsidence controlled the development of
change
Cambrian
and
bryozoan-dominated littoral faunas in the overlying
first stage of growth, the isolated platform developed
platform
tonic movements that resulted in the dissection of
in the
Caradocian deposits suggest a climatic trend towards
the
Triassic-Jurassic sequences suggests that earlier ex­ '
a
Cocozza and A.
on
the
the
with
lapse
blocks.
the
growth
eastern
towards
gression
structure
processes
platform.
further
is
deposited.
Gandin
eastern
west
zone
platform
resulted
by
humid
of
flooded
Breccias
side,
and
in
During
marked
During
the carbonate
dissection
the
produced
developed.
the
did
material and breccias.
transpressional phase.
on
the
by
the
early
lagoonal system resulted.
and
an
the
The
conditions.
region
in
caves,
accumulated
platform,
climate and regular subsidence,
muds giving
and
Carnian
the
drowning
at
abrupt
exposed
residual
a
on
of
the
Sinemurian
the
Upper Triassic-Lower Jurassic plat form
a
red
the
hematitic
Extensional
controlled
most
climatic
blocks
drowning
fault
position of a wide evaporitic sabkha system.
highs pure carbonate deposition developed.
marine
first
of
the
of
trans­
During Middle Cambrian the second stage of col­
carbonate production balanced subsidence, the up­
de­
sub­
to the final drowning of the platform and the instal­
blocks, probably related to isostatic compensation,
along the more active western and eastern edge p of
resulted in tilting, uplifting or sinking of the different
karstic
sediments underwent differential compaction so that
on top of the more unstable blocks a typical nodular
characteristic
lation of pelagic and turbiditic deposition that was
red colour. The third and stronger tectonic pulse led
basin (La Spezia basin) and only in late Rhaetian on
subsident zone evaporites and carbonates were laid
material derived from the exposed blocks was mixed
hematitic
In the
down. Since Norian time, the platform was bordered
interrupted during Lower Ordovician by the Sardic
tectonic
residual
The platform developed on the Palaeozoic basement,
during the Middle Triassic continental red beds were
already fragmented into horsts and grabens, where
previously emergent blocks and the establishment of
a marginal plateau structure. The onlapping neritic
structural
the
change
sca_y(s
mergence stage led to the onlap of neritic sediments
movements of low intensity caused the dissection of
The beginning of the second stage of the platform
the platform in blocks and consequently high rates
building of a complex facies mosaic in a tidal-fiat/
of sedimentation and differential subsidence. Since
A stronger pulse of tectonic subsidence resulted in
a low-energy marginal shoal
a margin facing an epicontinental
form. During this stage of the platform growth, arid
the
more rapid in the