Page 14 - Carbonate Platforms Facies, Sequences, and Evolution

12
the
for
1980;
As
coast.
bonate
present
Tuscan
Graben
a
Tuscany
internal
Gandin,
Tuscany
Ligurian
Sardinia)
tensional
Miocene)
intrusions
major
is
Cretaceous
Nappe
and
(Carmignani et
1986).
poorly-exposed
Nappe
part
Tuscan
platform
exposed
Nappe
Carannante
Zone
beyond
in the
of
oceanic
that
et
in
consequence
movements
palinspastic
(Carmignani
the
of
and
has
a!.,
Domain
the
the
basement
et
fracture
developed
deposits
their
comprises
been
resulting
1984;
a!.,
built during the Alpine orogeny.
northern
in
and
Nappe
(Apuan
with
along
corrections,
(Gandin
a!., 1986b; Gandin et
on Palaeozoic basement (Decandia et
surrounded
in
locally
the
et
tectonic
Upper
Alps
Campidano
1986a,
Zone
a!.,
T.
by
the
except
a!.,
Apennine
b).
ophiolites.
Zone
extensional tectonics produced NW
a!., 1987).
history,
for
sheared
Courjault-Rade
by a NE-SW trending transcurrent-fault system.
Caledonian and Hercynian structures were later re­
Cambrian this collapsed, to be replaced by an intra­
During Lower Cambrian times a shallow-water car­
Jurassic­
1987).
The
&
continental basin lasting until Tremadocian (Gandin,
poorly exposed. However, they maintain their orig­
(Bithia Formation), transgressive on a metamorphic,
deposited on a proximal segment of the Gondwana
Graben
(eastern
Iglesiente-Sulcis is a dome and basin structure. To
The deeper part of this basin is at
the north and southeast this structure is overlain by
Campidano
granite
activated during the Alpine orogeny by exclusively
chain
overthrust Cambrian (?) Lower Ordovician rocks of
Triassic-Jurassic
The Lower Palaeozoic sequences of Sardinia were
continental shelf. The Cambrian-Lower Ordovician
Middle
the Tyrrhenian
cycle starts with an Atdabanian (?) deltaic sequence
Massa Zone) of a metamorphosed Mesozoic cover
1980). At
the
Livorno-Sillaro dextral transcurrent fault that puts
trending graben-and-horst structures, later dissected
the
-SE
inal palaeogeographic relationships without the need
Lower Mesozoic deposits of the Tuscan Nappe are
the end of the compressive orogenic phases (Lower
off
along Upper Triassic evaporites, consists of: (1) an
external Tuscan Domain of Palaeozoic metamorphic
sediments occur in different tectonic units that have
each other in an eastern direction. The more internal
been detached from their basement and thrust over
The
basement and Mesozoic-Tertiary cover and (2) an
and
et
Cocozza and A.
the
the
was
aN
ively
these
facies
1979).
The
The
quence
basinal
bonates
of
members:
are
Gandin
finally
marginal
the
(Figs
Lower
Alpine
2
deepened
(Nebida
&
buried
endemic
biostratigraphic
facies
siliciclastics
3)
CAMBRIAN
in
(Decandia et at., 1980).
by
intrusions (Carmignani et
underwent fragmentation,
'abortive' rifting (Gandin et
towards
was
depositional
OF
species
a!., 1984; Gandin, 1990a).
Formation).
zonation
Triassic-Jurassic
(Cabitza
the
contact
further
and
cycle
The
Cambrian to Lower
a!., 1986a).
with
cannot
erates and megabreccias ('Puddinga').
deposited
shelf
with lateral variations, especially in the
starts
platform
be
the
genera
SARDINIA
Ligurian
on
to Hettangian a carbonate platform existed,
so
an
-S trending segment of Tethys (Bernoulli et
exclusively
with
(Fig.
Shales-Scisti
Ordovician
unit. Its base (Bithia Formation, Lower Cambrian­
Middle-Upper Triassic Verrucano arid-climate red­
epicontinental basin was established, which progress­
car­
(Bithia Formation) were gradually replaced by car­
epi­
se­
with angular unconformity by post-Arenig conglom­
ably been removed during the emergence and depo­
Cabitza). The upper part of the sequence has prob­
1).
Palinspastic reconstructions of the Triassic-Jurassic
sequences place the Tuscan Units on the European
a!., 1982). From Norian
the
beds sedimented on a continental basement already
affected by extensional tectonics and Middle Triassic
a!.,
?Atdabanian) is exposed only in the southernmost
Ocean
continental margin of the Ligurian Ocean that was
internal
carbonate
but at
The Cambrian sequence is up to 3500-4000m thick,
the beginning of the Sinemurian it collapsed and an
based on trilobites and archaeocyathids and most of
that
precisely
Biostratigraphy in Sardinian Cambrian is mainly
continental shelf where deltaic terrigenous sediments
bonate Gonnesa Formation consists of two informal
Laminated Dolomite (Dolomia rigata) at
part of Sulcis region because of the structural setting
of the area and the occurrence of Hercynian granite
It is overlain
the base, and Ceroide Limestone (Calcare ceroide)
carbonates
uplift and drowning and
at the top (Cocozza, 1979). The carbonate platform
di
sition of the Puddinga (Cocozza, 1969; Carannante
(Cabitza Limestone-Calcare nodulare) and then by