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152 Sulli A. et al.

grading wedges. We hypothesize these deposits rec- shelves, where seabed corresponds to polygenic ero-
orded falling and lowstand depositional stages respec- sional surfaces modeled on a pre-Calabrian bedrock, in
tively (Caruso et al., 2011). places covered by thin layers of Holocene deposits. This
type is found in the structurally high areas in the Monti di
A possible explanation for this could be the tecton- Palermo offshore and around the main rocky headlands
ic evolution of the margin. According to Mougenot et al., (Capo San Vito, Monte Catalfano). They can be divided
(1983), in a prograding type shelf margin, the sedimen- into two subtypes (Fig. 12): 1A are rocky shelves ac-
tary response to sea-level fluctuations is better pre- companied by a moderate frontal sedimentary prism; 1B
served for the influence of important subsidence. It does are rocky shelves with a structural edge (the sedimen-
not seems the case of the NW Sicily offshore where
high frequency sea-level changes punctu-
ated a slow, long-lasting tectonic uplift.

Even if the effects of sea-level
changes are ubiquitarious, thickness and
internal geometry of LQDS are also con-
trolled by margin physiography, sedimen-
tary input and local hydrodynamic condi-
tions. TST and HST deposits are thicker
and extensive in the central sectors of
gulfs where a major number of sedimen-
tary entry points are present. This aspect
contributes to differentiate the morpho-
stratigraphic pattern of depositional
shelves, where TST and HST deposits
are extensive and well developed, from
structural-erosive ones where TST and
HST deposits are absent or very con-
densed (Fig. 12).

6.2. Different types of continental shelf Fig. 12 - Cartoons image the stratigraphic setting of the middle (?)-late Quaternary
In physiographic setting as that bor- depositional units detected by means of seismostratigraphic analysis in different sec-
tors of north-western Sicily continental shelf: 1A) Bay of Carini; 1B) La Barra salient;
dering majority of the Tyrrhenian Sea, 2A) Gulf of Palermo and Gulf of Castellammare; 2B) Gulf of Termini Imerese. Qua-
mainly characterized by a well-defined ternary deposits. The illustrated different settings are controlled by geological pro-
continental shelf-slope system associated cesses discussed in the text.
to a pronounced shelf break, during the
Late Quaternary sea level changes type 1
depositional sequences (Vail, 1987) devel-
oped, characterized by enhanced lower
sequence boundary. However, even if
glacio-eustacy is an ubiquitarious pro-
cess, different types of depositional set-
tings are distinguished in the shelfal sec-
tors, mainly depending on subsidence,
local climatic conditions and total sediment
supply; moreover, localized features occur
due to continental shelf palaeo-topogra-
phy and distribution of entry points along
the migrating shoreline. In fact, all these
factors determine both location and depth
of sedimentary deposits generated during
the eustatic cycle.

In the investigated area the analysis
of stratal pattern, lithological assemblag-
es and architecture of depositional se-
quences, the identification of different
stratigraphic and morphostructural set-
tings along the margin, led to the recogni-
tion of two main types of continental shelf
(Fig. 12), structural-erosive and deposi-
tional shelves respectively. For each of
these types, interaction of tectonics, sea-
level change and different types of sedi-
mentary inputs developed different types
of prograding shelf margin and different
internal geometry of LQDS.

Type 1 are predominantly rocky