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Variability of depositional setting along the north-western Sicily continental shelf (Italy) ... 151
acoustically transparent lenticular bodies, with an erosive depositional alternating with structural edge, present lack
base. These morphologies lie at 2-3 km seaward the of highstand-transgressive systems tracts in the oldest
mouths of the Freddo and the Jato Rivers, within a band depositional sequences recognized along the margin.
trending W-E in subsurface depths from 75 to 25 ms
(t.w.t.), where the thickness of the HST exceeds 25 m Furthermore, the occurrence of pockmarks and
close to the river mouths. Pockmarks in the subsurface mounds probably consisting of authigenic carbonates
occur up-dip the most significant wipe-out zones and they above faulted and folded strata suggests a local rela-
point out the existence of gas-charged fluid expulsion. tionship between structural control and fluid escape.
Some of the tectonic features could have represented a
The TST has four depocenters, aligned parallel to preferential escape route for fluids as evidenced by the
the shoreline off major river mouths, as in the central pockmarks. Pockmarks may in turn trigger mass failures
gulf, or at the base of the steep paleocliff in the eastern as evidenced by the headscarps observed below them
gulf off Capo Rama. Close to the western edge of the (Lo Iacono et al., 2011). The structural features are pos-
Castellammare Gulf the continental shelf is narrower sibly associated with the recent tectonics mapped on
and the seabed is a marine transgressive surface cut land (Catalano et al., 2011 a, b) as well as the wide-
above the pre-Quaternary rocky substrate, at places spread seismicity of the margin.
floored by a very thin, shallow sedimentary cover.
As a matter of fact tectonic activity persists today
5.4. Structural features with the occurrence of shallow (<25 km) seismic events
During the Pleistocene, faults, as well as folded of low to moderate magnitude along an E-W trending
belt located along the continental slope. The focal
structures, exerted a control on the morphology of the mechanisms related to the main seismic shocks are in
present day coastal areas and shelf-slope system, as agreement with a dominant NE-SW fault trend coupled
for the submarine canyons and the mass failure pro- with a NW-SE compressive offset direction. A minor
cesses. cluster in the Monti di Palermo offshore well match with
the extensional ENE-WSW trending extensional faults.
In the Termini Gulf E-W to NE-SW-trending normal
faults are prevailing. Very recent NW-SE vertical faults Uplift of the northern Sicily shelf and surrounding
displace the buried Quaternary succession in the west- areas during the Pleistocene is testified also by the
ern sector, being also seismically active. Pleistocene regressive coastal deposits in the western
sector of the margin (Mauz et al., 1997; Arces et al.,
In the Palermo Gulf NNW-SSE fault systems, with 2000), and the Pleistocene deposits, outcropping close
a downthrow ranging from some tens to 150 m, are to the study area, which are uplifted tens of metres (Hu-
prevalent off Monte Pellegrino and in the southeastern gonie, 1982). Moreover, uplift of the continental margin,
side (off the head of the Eleuterio canyon), whilst to the as a consequence of thermal perturbation due to the
north, between Capo Gallo and La Barra, faults appear thinning of the lithosphere which is not compensated by
to have a dominant NNE-SSW trend. Pockmarks and local isostasy, is predicted by forward modeling (Pepe et
mounds are often aligned with the fault systems trends. al., 2003), thus constraining the late Neogene to Recent
tectonic and stratigraphic evolution of the margin.
In the Monti di Palermo offshore main fault sys-
tems are and near vertical, oriented ENE-WSW (see La Therefore, it is evident that along the North Sicily
Barra structural high) or NNW-SSE, dipping NNEward. continental margin eustatic and tectonic processes
WNW-ESE trending fault systems were recognized par- combine to cause both relatively short- and long-term
allel to the coastline. In the Carini Bay, inner continental sea-level changes which control the space available for
shelf is characterized by N-S and NNE-SSW fault sys- sediments, forming a number of depositional sequences
tems with variable downthrow. from the early (?) Pleistocene to the Holocene.
In the Gulf of Castellammare the continental shelf 6.1. Effects of eustatic sea-level changes
develops in the southern part of a tectonic depression that Subsequent, rapid sea level changes impacted the
formed during the Quaternary (Fig. 11). It is bounded to
the East by N-S to NNW-SSE, with some hundreds of continental margins as consequence of astronomically
meters of downthrow, along which Meso-Cenozoic car- forced, worldwide climatic changes occurred during
bonate succession is juxtaposed to Plio-Quatermary de- Quaternary age. As documented by several studies on
posits; to the South pre-Pliocene deposits are intensely Oxigen isotopes (Chappel & Schackleton, 1986; Imbrie
folded and dissected by both reverse and extensional N-S et al., 1984; Williams et al., 1988), middle-late Quater-
to NNW-SSE faults, even very recent; to the West by nary sea-level changes have been asymmetrical fluctua-
NNE-SSW, NS and NNW-SSE faults. tions characterized by slow falling stages (1 mm/y) fol-
lowed by fast rising stage (1 cm/y); average amplitude of
6. DISCUSSION cycles was 100-150 m and the period was about 100-
200 ky. As we have illustrated, the internal geometry of
Several evidences highlight that the North Sicily the LQDS well documents the sedimentary response to
continental margin is tectonically immature. The Plio- specific segments of the last glacio-eustatic fluctuation.
Quaternary tectonic evolution of the NW Sicily margin
produced the development of a morphostructural setting The effects of eustatic changes appear less evi-
characterized by a series of depressions (intraslope ba- dent in the more ancient deposits where complete dep-
sins) separated by structural highs along the margin ositional sequences have not been detected. According
(Agate et al., 1993), as result of differential uplift and to us, the interpreted seismic profiles does not image
subsidence during Neogene to Recent times. past shelfal TST and/or HST deposits and subsequent
erosional surfaces are not clearly distinguishable. Oth-
Recent tectonic activity is testified by neotectonic el- erwise, beneath the LQDS, oblique seawards dipping
ements and seismic activity (Fig. 1), calculated uplift rates, layers only are preserved with small, interbedded, pro-