Page 40 - Carbonate Platforms Facies, Sequences, and Evolution

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2
1
so
early
phase.
typical
lapsed,
regions
Ocean.
that
graphic
of
developed.
extensional
on
dissection
epicontinental
levels.
the
top
of
nodular
From
of
intra-cratonic
The
Conversely,
ferential subsidence
basement structures;
the
On the more active,
tectonics
basins.
the
the
final
structure
and uplift of a number of
rifting
Gondwana
The
form collapse never evolved
isolated
of
more
Sinemurian
produced
a basin was formed and
phase.
collapse
to
into the Ligurian branch of Tethys.
CONCLUSIONS
control
evolution
of
landmass,
In
horst
of
unstable
of
platforms
this
Upper
and
Ammonitico
the
and
blocks
western margins breccias ac­
from the mainland in relation to extensional move­
Pleins­
dif­
events in Tethys. After the carbonate platform col­
The epicontinental basin established after the plat­
leading to the beginning of pelagic turbiditic depo­
ments induced by thinning of the continental crust;
the nodular facies wer � produced at different strati­
platforms is documented by the following features:
regime,
with the early phase of opening of the Iapetus Ocean.
The general setting of both Lower Palaeozoic and
gradually evolved
blocks tilted or uplifted and .consequently emerged.
Mesozoic platforms is directly related to the Alpine
of open fissures (neptunian dykes). Afterwards, as a
pelagic sediments underwent differential compaction
and breccias. Others blocks sunk and the onlapping
The events controlling the evolution of the Cambrian
platform are related to intracratonic rifting in distal
on the shallow-water platform deposits and the filling
concomitant
sition coincided with the first opening of the Ligurian
cumulated at the fault scarps and karstic processes
on the exposed blocks produced caves, vadose fillings
Rosso
consequence of isostatic compensation, a number of
the platform
owing to the transpressional movements of the Sardic
early
the
bachian the blocks readjusted several times so that
into an oceanic basin
graben
drowning of the platforms with associated tilting
structures that gradually evolved into platforms and
of the resulting blocks during
their growth as a consequence of the reactivation of
Lower Mesozoic carbonate sequences represents an
tectonics on the depositional evolution of the two
detachment and tilting of the carbonate platforms
extensional
blocks as a response to
4
26th
their
The
BARCA,
PIITAU
platform
mentary
87-90.
July
persistent,
subsidence.
piattaforma
1109-1113.
be interpreted
but
assistance
1989.
geodynamiques.
results of
DEMELIA,
during
response
S., CocozzA,
BALASSONE, G., BoNI,
has been supported
P.
Carbonate deposition during early rifting, Italy
Education (MPI 40%
to
Compt.
He did
carbonatica.
inferieur par Dictyonema
intensified
in drafting
(1987)
this study
T., DEL
not
anonymous reviewer for the
Rend.
acceleration
Rend.
and
Rio,
REFERENCES
have
ful suggestions and documentation.
of
Datation
coupled with isostatic compensation;
indicate
Soc.
Acad.
M. ,
seeing this, his ,Jast paper, published.
flabelliforme
extensional
the
typing.
de
et
ACKNOWLEDGEMENTS
Sardinia did not reach a spreading stage.
Sci.
the
Research Program).
constructive
Geol.
extensional tectonics
ments of the continental plates during rifting.
PILLOLA,
Paris
!tal.
pleasure
L.
establishment of a marginal plateau and progress­
The authors are grateful to Milvio Fazzuoli for help­
Further evidence of the tectonic control on sedi­
as the response to divergent move­
that the sedi­
ive onlapping of pelagic sediments onto the drowned
tectonic
Tuscany was analogous despite the different age and
movements
Sadly, Tommaso Cocozza died suddenly on the
the different further evolution of the intra-cratonic
Formazione di Gonnesa nell'Iglesiente nord orientale e
of
SAVIANO, N. (1985) Alcune particolarita nei litotipi della
rifting that evolved in a passive continental margin
in Mesozoic Tuscany whereas in the early Palaeozoic
by the Italian Department of
nel Fluminese: ulteriori possibili evidenze di margine di
35
Also to James
for the improvement of its clarity. The authors are
305,
which occurred during the platform growth. It can
This study
remarks
indebted to Anna Bellini and Giancarlo Pagani for
dans Ia partie superieure de Ia formation "Cambrienne"
M. , D1 MAio, G., SAVIANO, G. &
Lee Wilson, Fred Read and Paul Crevello, and an
Lower Palaeozoic in Sardinia and Lower Jurassic in
&
during
mentation can be recognized in the climate change
following their critical reading of the manuscript and
Acritarches
!'Ordovician
8,
BARRON, E.J., HARRISON , C.G.A., SLOAN , II, J.L. & HAY,
de Cabitza (SW de Ia Sardaigne, Italie): consequences