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Variability of depositional setting along the north-western Sicily continental shelf (Italy) ... 153
tary prism, although present, does not extend to the
edge).
Type 2 are depositional shelves (prevalent or ex-
clusive sedimentary origin), in which the pre-Calabrian
bedrock is buried by a considerable thickness of Qua-
ternary sediments and does not significantly influence
the sea floor morphology; seaward progradational out-
building contributes more than one half of the entire
shelf width. Also in this case it is possible to distinguish
two subtypes (Fig. 12): 2A are shelves in which the sub-
strate deepen regularly seaward; 2B are shelves in
which the structural setting determines a substrate uplift
in correspondence of the current position of the shelf
break (in this case the substrate is at shallow depths,
providing a support for sedimentary prism accumulate
and expand). The depositional shelves occur in the Cas-
tellammare, Palermo and Termini Imerese gulfs repre-
senting the 2A type, the type of continental shelf most
widespread in the area. In this type of shelf we can find,
in the inner platform, thick Holocene sedimentary wedg-
es that are absent in the shelves of the first type.
When we compare stratigraphic architecture and
depositional setting observed in the north-western Sicily
offshore with other Tyrrhenian margins, there is a striking
similarity mostly with the offshore Calabria and Cam-
pania. In these sectors we can observe depositional (type
2) shelves along the gulfs, e.g. Gulf of S. Eufemia (Chioc-
ci et al., 1989) and Gulf of Salerno (Aucelli et al., 2012);
otherwise, predominantly rocky shelves (type 1) are wide-
spread in front of morpho-structural salient, e.g. Punta
Licosa (Trincardi and Field, 1991; Ferraro et al., 1997)
and Capo Suvero (Mongardi et al., 2004). This type (1) of
continental shelf, characterized by prograding shelf mar-
gin deposits and absence of thick coastal prisms, is also
common along linear margin (without coastal embay-
ment) with scarce sedimentary supply, e.g. Marettimo
Channel, in the Egadi islands area (D’Angelo et al.,
2004), and Tuscan Islands (Roveri & Correggiari, 2004),
or along epicontinental shelf separated by the mainland,
e.g. Adventure Bank (Colantoni et al., 1985). A similar
variability of continental shelves, as that we illustrated re- around the main rocky headlands (Capo San Vito, Monte
spect to the NW Sicily offshore, has been detected by
Corradi et al., (1984), along the Ligurian Sea margin.
6.3. Geological evolution
The trend to tectonic uplift recorded along the
margin, documented by already described stratigraphic
relationships and in agreement with the outcrop alti-
tudes of paleo-shorelines along the coast, seems to
start with the Ionian (middle Pleistocene). Previously,
the sea recorded an episode of deepening that has al-
lowed transgression during the Calabrian in a large area
of the north-western Sicily, where now a neritic succes-
sion some tens of meters thick outcrops, discordant on
a pre Calabrian tightly deformed substrate (Ruggeri,
1978). The deposition of this succession marks the be-
ginning of the formation of the continental shelf in
northwestern Sicily margin, which, by the end of the Ca-
labrian, under the influence of glacioeustatic fluctuations
and slow uplift, produced a frontal accretion of the mar-
gin of some km (<10 km).
The recorded deepening of the margin at the be-
ginning of the Calabrian and the subsequent uplift,
which produced the emersion of the Calabrian portion of
the continental shelf, now outcropping up to about 100
m a.s.l., may be related to the succession of compres-
sional and extensional tectonic events recorded in the
margin during the Plio-Quaternary.
7. CONCLUSIONS
The integrated analysis of morphobathymetric and
high resolution seismic data collected on the continental
shelf to slope system was used to illustrate the present
stratigraphic and morphostructural setting of the North
Sicily continental margin and its Late Neogene-Quater-
nary geological evolution.
We recognized an upper Pleistocene-Holocene
sedimentary succession, deposited during the last eu-
static change (last 125 ky). This succession, interpreted
as a IV order depositional sequence (LQDS), shows
along the different sectors of the margin considerably
variable internal geometry and different stratigraphic
relationships with the underlying units. The lower
boundary of the LQDS is represented by a subaerial
erosional surface formed during the last eustatic sea
level fall, ended in the LGM (20-18 ka), and shaped
again during the Late Quaternary-Holocene sea level
rise. This unconformity lies at the top of a seaward dip-
ping Pleistocene succession whose depositional archi-
tecture is in turn controlled by Quaternary eustatic sea-
level fluctuations.
Even if depositional sequences in this margin are
the result of the interaction between sea level changes
and sedimentation, the tectonic activity has played a key
role, not only to determine the different characters of
each sequence in different areas, but also in the creation
of different types of continental shelves. As a conse-
quence we recognize different types of continental shelf
with different stratigraphic and morphostructural settings,
identified on the basis of the occurrence and thickness of
the LQDS deposits: a) type 1, predominantly rocky
shelves, both accompanied by a moderate frontal sedi-
mentary prism (1A) and with a structural edge (1B), in
the structural highs of the Monti di Palermo offshore and
Catalfano); b) type 2, depositional shelves, in the Castel-
lammare, Palermo and Termini Imerese gulfs, with a
regular seaward deepening of the substrate (2A) and
with a substrate uplift at the shelf break (2B).
A general tectonic uplift during the Pleistocene,
together with the episodic alternation of extensional and
compressional events, often with strike-slip component,
is responsible for the thickness and facies variation and
geomorphological features, both onland, where residual
Pleistocene marine deposits today outcrops, and in the
continental shelf, where most of the depositional se-
quences developed and are now recognized.
As well tectonic activity exerted a control on the
geomorphological features of the present day coastal
areas and shelf-slope system (e.g. pockmarks and
mounds) as well as for the submarine canyons and the
mass failure processes.
AKNOWLEDGMENTS
We wish to acknowledge the Italian National Re-
search Projects MaGIC (Marine Geological Hazard along