Page 38 - Carbonate Platforms Facies, Sequences, and Evolution

of
The
from
sition
basins
which
1982).
where
during
forms,
further
uplifted
indicate
cratonic
resulted
opening
platform
forms
tensional
Massiccio
arid
behaviour
the
deposition
carbonates
in
fresh-water
of
Bernoulli &
from
some
early
to
physiographic
compressional
dolomitization.
rifting
the
of
along
have
Tuscan-Ligurian
evolution
the
exposure
Iapetus
deposits
(D'Argenio,
indicating
Mediterranean
humid
Sardic
settings
movements
been
are
within
which
humid-tropical
were
Tethyan
Palaeozoic
cementation,
1970;
Ocean
intertidal-supratidal
Mesozoic
towards
Jenkins, 1974).
normal
phase
the
in
the formation of
has been ascribed
Triassic
laid
underlying
although
an
conditions
Ocean
would
persisted
to a
facies
interpreted
and
controlling
conditions
which
TECTONO-SEDIMENTARY
the
down
salinity.
eastern
documented
continental margins
Bernoulli,
to
are
sequences
Sardinia
of
later
karstification
in
by
Triassic
oceanic
early
side
water
(Ciarapica
These
the
and
(Bernoulli,
result
and
Bahamian-type
1972).
open.
of
deformed
throughout
et
record
subjected
SETTING
been considered as the record of an oblique intra­
the Cambro-Ordovician basin was the re­
represented and never affected by early dolomitiz­
plat­
Early extensional tec­
depo­
platform is marked by the gradual but rapid tran­
a/.,
Ocean in the Middle Jurassic (Bernoulli et at., 1979).
(Grezzoni Dolomite or Rhaetavicula contorta beds).
tonics along embryonic passive continental margins,
local
The lower boundary of the Massiccio Limestone
extensive
ation processes. Organisms were scarce but consist
abundantly
sitional setting. Persistent humid conditions during
points
deposits
normal marine in the Jurassic. Such a depositional
was different: metahaline-hypersaline in the Triassic,
Jurassic
climatic change
The uppermost Triassic sed!ments and the lowermost
from
salinity
equivalent
The
the
and
branch of the Tethys into the opening of the Ligurian
Jurassic and Cretaceous, surrounded by deep-water
Gondwana craton, at some distance from the zone
sponse to transpressioaal movements that prevented
the
opening
The Sardinian Lower Palaeozoic sequences have
The
the
sedimentation
to
evolution of an intracratonic rift in a N -S trending
extensional tectonic regimes in connection with the
early
1972;
(Carannante et a/., 1984; Vai & Cocozza, 1986). The
not
the
the
The
stage
1985).
facies.
basins.
similar
sidence
Jurassic
Mesozoic
early
migration
(Barron et
to
non-cyclic
did
Bahamian
Palaeozoic
pericratonic
pelagic
directly
The
is
of
complication
the
northern
and/or
of
some
The depositional
the
relief.
(Read,
sequences
of
tectonic movements.
Middle
Carbonate deposition during early rifting, Italy
Palaeozoic
present
platforms
relative
drifting
Jurassic (Frakes, 1979).
depositional
comparable
magnetic data (Scotese et
is
the
documented
1985).
of
evolution
to
evaporitic
by
Jurassic.
sedimentological
documents
Persistence
fringed
The
the
pattern
syndepositional
situation
sea-level
belt
TECTONO-SEDIMENTARY
a
uplifted
of
of
in
by
Europe
lack
documented
from
of
the
the
analysis
similar
blocks
by
Siliciclastic
tectonics
by the distribution of trilobite faunas (Jell,
during
of
palaeomagnetic
fluctuations.
of the Cambrian
Triassic
Cambrian-Lower Ordovician and Upper Triassic­
lands, during early Palaeozoic, can explain this dif-
tinuous balance between carbonate production, sub­
upbuilding and differential subsidence. One differ­
Synsedimentary extensional tectonics is also docu­
palaeo­
deposition throughout their growth document a con­
1973).
Bahamas.
EVOLUTION
tectonic
the
However, during their growth they were surrounded
(Read,
been established for carbonate systems without the
by shallow-water basins and only in the late sinking
achieve
The southward drifting of southern Europe during
sediments produced during the humid stage in the
Their growth started under an arid climate
and ended in a humid regime. The features of the
Mesozoic in Tuscany were a response to major plate
of the two platforms. Both units represent isolated
control in the segregation and depositional behaviour
two platforms reflect facies distribution and climate
epicontinental
The
and
drowning trend of the platforms is reflected by the
a/., 1981) and suggested by the southerly
data
early Mesozoic platforms in Sardinia and Tuscany is
shallow-water
early
33
planckton in the seas and lack of vegetation on the
of the pelagic Middle Cambrian-Lower Ordovician
compared with the prevailing carbonate character of
ence can be found in the pure siliciclastic deposition
basinal
calcareous
deposits are reported to be a common feature in the
models that have
a/., 1979), and suggested
mented by high rates of sedimentation resulting in
to
calcareous