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86 DI MAGGIO, MADONIA, VATTANO, AGNESI and MONTELEONE

The terms “fault slope” and “fault-line slope” are used to (Mio–Pliocene gypsum, calcarenites, and conglomerates
indicate a gentle hillslope with an origin related to the evolu- intercalated in the foredeep and wedge-top marly/clayey
tion of a fault scarp or a fault-line scarp, and as a result of deposits). Along the areas closest to the coastal regions, the
processes of slope replacement or slope decline; structurally structural reliefs are anticline ridges, and syncline depressions
controlled complex slope indicates a hillslope made up of an (e.g., Siculiana area; Fig. 6a). In the inland areas, they are syn-
alternation of hard and weak rocks, on which an alternation of clinal ridges (e.g., Ciminna area), and anticline valleys (e.g.,
steep and gentle slopes is respectively produced. upper valley of San Leonardo river; Fig. 6a), both delimited by
In addition, we worked out some geological cross-sections structurally-controlled complex slopes (Fig. 6e); or isolated
(Fig. 6) to better recognize landforms and generally the rela- mountains bounded by obsequent fault-line scarps and
tionships between topography and geological features. founded on blocks lowered by faults (e.g., Rocca Entella).
Successions of river terraces and erosion glacis on soft rocks
are also present along the hillslopes (e.g., middle-upper valley
Data and results of Belice river).
Large structural mountains coincident with tectonic highs
We present here the data from the morphotectonic studies and set on Mesozoic carbonate rocks occur in the northern
performed in western Sicily from its southernmost zones. areas of western Sicily and in the Sicani Mountains (Figs. 3,
A stair-step flight of uplifted marine terraces develops from 4d,f–h, 5d,f–h, 6d–g); they are pop-up or anticline-type moun-
sea level up to about 450 m a.s.l. in the southern areas of tains (e.g., Kumeta and Busambra ridges; Figs. 4d, 5d, 6d).
western Sicily (Figs. 3, 4a–c, 5a–c, 6a–c). The oldest and River canyons and narrow V-valleys down-cut these moun-
highest marine terraces are carved in Calabrian clastic rocks tains. Broad and deep valleys coincident with tectonic lows
(Agrigento fm.; Figs. 4c, 5c, 6b) of the Santernian regional and founded on Mio–Pliocene mainly clayey rocks separate
stage (sensu Ruggieri et al. 1984), that postdate the genesis of the main mountain groups; they are synclinal or triangle zone-
the terraces to marine highstand phases of the late Calabrian– type valleys (Figs. 4d, 5d). Along the valley slopes, flights of
Late Pleistocene. In these areas, the better-preserved terraces river terraces or erosion glacis on soft rocks are also present
are in the westernmost southern region (Marsala – Castel- (e.g., valley of Imera Settentrionale river). Mountains and val-
vetrano – Sciacca area; Figs. 4a,c, 5a,c), where less orders leys are the result of strong processes of river down-cutting
and very large polycyclic coastal platforms are recognized and generally intense denudation, which are selectively per-
(Fig. 6b, c); and near the coasts, where only the most recent formed; the boundaries between mountains and valleys are in
terraces occur. Towards the south-eastern coast and towards fact marked by wide resequent fault-line scarps and slopes or
the interior (Realmonte – Palma di Montechiaro area; Figs. 4b, large inclined structural surfaces (e.g., M. San Calogero;
5b), marine terraces are dissected by river valleys and become Figs. 4d,f, 5d,f, 6d,e). Relicts of hanging planation surfaces,
fragmented (Fig. 6a); some cycles of river terraces or erosion located from a few hundred metres to over 1900 m a.s.l., are
glacis on soft rocks are present in the valley slopes (Figs. 4e, present along the slopes and at the top of the mountains. These
5e, 6a). Along the coast of the south-western end, fossils of planation surfaces are not entirely flat or very gently rolling
Strombus bubonius and assemblages of “Senegalese fauna” of but also include small ridges, hills, and abandoned valleys
the Tyrrhenian regional stage (Antonioli et al. 2006 and refe- (low-relief surfaces) due to partial relief reduction (e.g., area
rences therein), contained in coastal deposits lying on wave- of M. Ferro – Carbonara; Figs. 4g, 5g). In the head areas of the
cut platforms, allow us to recognize the marine terrace of the river basins that flow into the Tyrrhenian Sea, a number of
Marine Isotope Stage (MIS) 5.5. On the south-eastern coast, streams show an inverted drainage produced by river capture
the terrace deposits contain insignificant fossils (Strombus processes at the expense of the southern catchments (e.g.,
bubonius is missing), and the terrace of the last interglacial is upper area of the basins of the Iato and San Leonardo
inferred from altitude and “preservation” (we think that it is rivers; Fig. 3).
the better-preserved, broader, and quite continuous terrace Large and discontinuous topographical depressions occur
occurring at the lower heights). The inner edge of the MIS 5.5 on the northern side of western Sicily (Tyrrhenian coast).
terrace is from 10 m (SW coast) to 55 m a.s.l. (SE coast). On A flat bottom (coastal plain), opened to sea and surrounded by
the south-eastern coast, at lower altitudes we also recognize wide scarps hundreds of metres tall to the inland, characterizes
occasional and smaller marine terraces post-MIS 5.5 with these depressions (e.g., Castelluzzo and Conca d’Oro plains;
wave-cut platforms developed between 0 and 15 m a.s.l. (e.g., Figs. 3, 4h, 5h, 6f,g). Wedges of Calabrian coastal and neritic
Eraclea area) clastic deposits from few to tens of metres thick crop out in the
In the inland areas of central-western Sicily, the marine ter- coastal plains. These deposits belong to the Marsala synthem
races disappear and are gradually replaced with a dense net- (Di Maggio et al. 2008, 2009) and date to the Emilian–Sicilian
work of river valleys (Figs. 3, 4e, 5e, 6a,c– e). River valleys regional stages (sensu Ruggieri et al. 1984); in addition, they
isolate small rounded hills (e.g., Caltanissetta area; Figs. 4e, show a very slight dip to the sea and lie on the Meso–Cenozoic
5e) in weak rocks (Mio–Pliocene clays and marls of foredeep rocks with strong angular unconformities. Along the coastal
and wedge-top deposits) or steep structural reliefs (e.g., plains, successions of marine terraces develop from 0 m up to
M. Capodarso; M. Gibil Gabel; Figs. 4e, 5e) in hard rocks 100 m (plain of Castelluzzo; Figs. 4h, 5h), 200 m (plain of

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