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88 DI MAGGIO, MADONIA, VATTANO, AGNESI and MONTELEONE

Palermo) or 300 m a.s.l. (plains of Partinico, Buonfornello and For the whole of western Sicily, geomorphological survey
Sant’Agata di Militello). These terraces are carved on points out both numerous forms produced by river down-
Emilian–Sicilian deposits or pre-Quaternary rocks (Figs. 4h, cutting, such as V-valleys and canyons; and a number of forms
5h, 6f,g). The first postdate the age of the terraces to marine due to a downward migration of erosion, namely staircases of
highstand phases of the Middle–Upper Pleistocene stages, as planation surfaces, erosion glacis on soft rocks, and river or
supported by palaeontological records (Di Maggio et al. 1999 marine terraces. River down-cutting and development of
and references therein; Antonioli et al. 2006 and references “terraced surfaces” indicate a gradual lowering trend in the
therein) and numerous isotopic datings performed on terrace general base level of erosion. This trend is typical of areas
deposits by previous Researchers (Hearty et al. 1986; Bada et affected by a widespread uplift trend (Ahnert 1970; Chappell
al. 1991; Mauz et al. 1997; Antonioli et al. 1999; Scicchitano 1974; Iwata 1987; Merritts & Hesterberg 1994; Burbank et al.
et al. 2011; Giunta et al. 2012). These terraces are also charac- 1996; Abbott et al. 1997; Whipple & Tucker 1999; Hovius
terized by few orders and large and well-preserved polycyclic 2000; Jamieson et al. 2004; Ascione et al. 2008; Walker et al.
wave-cut surfaces in north-western Sicily (e.g., plains of 2011; Gioia et al. 2014).
Castelluzzo and Trapani), and by several orders and narrow Along the northern side of western Sicily, geological, and
and dissected coastal platforms as they proceed eastward geomorphological analyses underline the occurrence of
(plains of Buonfornello and Sant’Agata di Militello). The inner lowered faulted blocks (half-graben) sealed by the Calabrian
edge of the MIS 5.5 terraces is from 10 m (Trapani and San deposits of the Marsala synthem; these latter lie on Mesozoic
Vito lo Capo areas), 15 m (plain of Castelluzzo and Partinico), or Cenozoic rocks with strong angular unconformities.
20 m (Palermo area), 25 m (plain of Buonfornello) to about The acquired information indicates an extensional tectonic
50 m a.s.l. (Sant’Agata di Militello area). Geological and geo- event producing subsidence, block drowning, and deposition
morphological analysis further show that the wide and tall of the Marsala synthem, which occurred in northern Sicily
scarps surrounding the coastal plains are abandoned coastal during the Calabrian stage. At the same time, a similar tectonic
cliffs derived from original fault scarps (Figs. 4f,h, 5f,h, 6f,g). event producing horst-and-graben structures also involved the
Some large tectonically-controlled cliffs are still active, falling Tyrrhenian margin of the southern Apennines (Amato &
in a sheer drop into the sea; whereas broad fault scarps or Cinque 1999; Caiazzo et al. 2006).
slopes affect the innermost areas, along the mountain flanks The overall analysis of data allows the proposition of the
facing the sea, where they cut off and displace the ancient morphoevolutionary model described below (Fig. 7).
low-relief surfaces (Figs. 4h, 5h, 6g). The presence of great During the Quaternary period, coastal morphogenesis and
fault scarps and “lowered blocks” at their foot allows the tectonic uplift have dominated the more recently surfaced
coastal depressions to be interpreted as half-grabens. Finally, southern areas. After the deposition of the clastic sediments
a number of forms produced by DSGSD phenomena are present belonging to the Agrigento fm. (after the Santernian regional
along the mountains of the Tyrrhenian coast and inland stage) coastal processes over time produced wave-cut plat-
characterized by high relief. forms and slightly later deposition of coastal sediments.
Owing to uplift movements, the coastal platforms developing
during marine highstand phases, in warm climate events,
Discussion progressively emerged and migrated to higher altitudes, pro-
ducing the present-day stair-step flight of marine terraces.
The collected data from western Sicily show four distin- Given the altitude of the inner edge of the MIS 5.5 marine
guished regions (Figs. 1, 3), marked by peculiar geological, terrace, the average rate of post-Tyrrhenian uplift is between
geomorphological, and topographical settings with rocks, 0.032 (SW coast) and 0.4 m/ky (SE coast). Unlike our inter-
landforms, and landscapes progressively older from south pretations, Antonioli et al. (2006) suppose that the Tyrrhenian
to north. We find flat coastal areas characterized by terrace is drowned beneath the Sicilian Channel, suggesting
upper Miocene–Quaternary evaporite/clastic rocks in a post-Tyrrhenian tectonic subsidence in southern Sicily
southern Sicily, where successions of uplifted marine terraces linked to the development of the Quaternary Gela foredeep.
are present; hilly areas characterized by Oligocene–Pliocene However, as previously discussed, all our data from south to
clayey, marly and evaporite deposits in central Sicily, where north Sicily show a geomorphological evolution characterized
rounded valleys and isolated rolling hills occur; mountain by prevailing vertical erosion and downward migration of the
areas characterized by mainly Mesozoic carbonate rocks general base level of erosion, indicating a tectonic uplift trend.
in northern Sicily, where exhumed structural mountains As demonstrated by the facies and distribution of the Neogene
and deep V-valleys develop; topographically-depressed to Santernian marine units present here, this area of “old”
coastal areas characterized by Quaternary clastic deposits foredeep/wedge-top basins was submerged during the con-
lying with strong unconformity on Meso–Cenozoic rocks struction of the accretionary wedge. After the end of the accre-
on the northern side of Sicily, where stair-step flights of tion, and the south-westward constant migration of the Gela
uplifted marine terraces occur along tectonic lows (half- Thrust System and its foredeep (the present-day Gela Fore-
graben) bounded inwards by large tectonically-controlled deep is further south-west of the southern coasts of Sicily), it
coastal cliffs. is fair to assume that the elastic rebound of the Iblean-Pelagian

GEOLOGICA CARPATHICA, 2017, 68, 1, 80 – 93