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GEOMORPHOLOGICAL EVOLUTION OF WESTERN SICILY, ITALY 89

Fig. 7. Morphoevolutionary model of western Sicily. See text for discussion.

slab involves uplift (Doglioni 1991), and processes of gradual and lows located on previously lowered and uplifted, faulted
land emersion. On the other hand, if the low rates of uplift blocks, respectively. Rounded hills were formed again, where
(0.032 m/ky) have ensured that the sea returns to the same erosion totally removed the Miocene layers of hard rocks.
level several times, creating well developed polycyclic plat- Therefore, data analysis shows that the strong denudation
forms, and that the slow emersion of the latter produces the involves novel and continuously changing landforms, although
present-day existence of broad and well preserved flat sur- relief modelling affects these areas for a long time.
faces in the south-western coastal areas, the higher uplift rates In north-western Sicily and the Sicani Mountains, the ever
we achieve in the south-eastern coastal areas (0.4 m/ky) better deeper progress of the erosion led to the exhumation of the
explain the numerous orders of marine terraces present here, oldest rock successions in Sicily (Mesozoic–lower Oligocene
consisting of smaller wave-cut platforms strongly dissected by carbonates). The result is a geomorphological setting charac-
river valleys (Chappell 1983; Schumann et al. 2012 and refe- terized by large landforms due to differential erosion. Gene-
rences therein). rally, the down-cutting processes considerably slowed down
The geomorphological setting of central-, and north-western along the resistant carbonate rocks, located on structural highs,
Sicily is the result of the interaction between the tectonic uplift producing an elevated and large mountain relief (pop-up or
acting to elevate the relief and the following processes of river anticline-type mountains); whereas they acted with greater
incision and denudation in general, which tend to lower it, strength and depth along the easily erodible rocks (upper
removing great volumes of rock (e.g., Summerfield 1991; Oligocene–Miocene clays and marls) still preserved in struc-
Kooi & Beaumont 1996; Burbank & Anderson 2012). These tural lows, creating deep and wide river valleys (synclinal or
regions represent areas that became dry land long ago, and triangle zone-type valleys). The cause which led to a general
where erosion has already removed younger upper clastic matching between topography and tectonic structure is the
deposits, destroyed ancient marine terraces, and progressively geological setting marked by weak rocks above hard rocks
exhumed older underlying rock. (Agnesi et al. 2000; Di Maggio 2000); unlike central-western
In central-western Sicily, river incision and denudation pro- Sicily, where the occurrence of weak rocks beneath hard rocks
cesses over time dismantled more resistant Quaternary cover permitted the development of relief inversion processes. How-
rocks and unearthed easily erodible Neogene rocks below. ever, the large distribution of resistant carbonate rocks in
Isolated, rounded hills originated on the latter. Anticlinal north-western Sicily is responsible for the preservation of the
ridges and synclinal valleys developed where the progressive oldest landforms of Sicily, such as the not fully developed pla-
down-cutting has resulted in the exhumation of deeper folded nation surfaces with their hanging, small ridges and hills, and
layers of hard rock (middle–upper Miocene evaporite lime- abandoned valleys. Within the geomorphological literature,
stones and gypsum, and conglomeratic and sandstone a similar landform set is known as palaeolandscape
benches). In the innermost areas, where a major incision par- (Widdowson 1997 and references therein), gentle erosional
tially brought to light masses of weak rock again (Oligocene– landscape (Amato & Cinque 1999) or relict landscape (Clark
middle Miocene clayey component deposits) relief inversion et al. 2006). Though the best potential for their preservation
processes (Summerfield 1991; Pain & Ollier 1995) produced exists in the cratonic cores and in the tectonically stable inte-
synclinal ridges and anticlinal valleys, or topographic highs riors of continents, planation surfaces and low-relief surfaces

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