Page 3 - valerio agnesi - geographical-phisical aspect Sicily

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ous-arenaceous rocks, isolated and generally hilly, where the selective erosion processes,
has generated tabular (mesas) and monoclinal (cuestas) reliefs.

Such sectors are crossed by Sicily’s major streams as the Platani River and the Imera
Meridionale (or Salso) River.

This last one flows into the great Gulf of Gela forming a vast alluvial coastal plain
edged by wide dune–like fields that, in some places, have originated humid coastal zones
(Biviere di Gela), but there are now upset by agriculture.

The widespread evaporitic rocks are connected to most of the small and ephemeral
Sicilian lakes. In fact, except for few summit lakes on the Nebrodi Mountains (Biviere di
Cesarò, Quattrocchi, etc.), for small Naftia lake near Palagonia (whose origin is due to
hydrocarbon emissions), and for coastal ponds, most lacustrine basins occupy karstic
depressions as Preola and Gorghi Tondi lakes, near Mazara del Vallo, small Gorgo lake,
south of Cattolica Eraclea, “Lo Sfondato”, near S. Cataldo, and Pergusa Lake that, being
1,83 km² wide, is Sicily’s largest lake, today threatened by man’s heavy presence.

The south–east part of the island is occupied by the Altopiano Ibleo, made up of cal-
careous and calcareous-arenaceous rocks, characterised by its generally tabular morphol-
ogy due to the subhorizontal bedding, crossed by deep fluvial incisions. The eastern sec-
tor between Peloritani and Hyblaean area is dominated by the Etna that, with its 3,340 m,
is the highest active volcano in Europe. The volcanic building starts in the wide Piana di
Catania, originated during the Quaternary by the alluvial contribution of the Simeto River,
river with the widest drainage basin of Sicily, and of its present tributaries. Piana di Catania
has recently (1950) undergone a deep anthropic change due to the drainage of the Biviere
di Lentini (the largest humid area in Sicily) dried up by means of water canalization of
Dittaino and Gornalunga Rivers and their deviation into the Simeto River.

Moving towards north, along the Ionic cost, there is the Alcantara River that originates
from the southern slope of the Peloritani and that, fed by waters flowing from the northern
side of Etna, represents the stream characterised by the greatest average flow in Sicily. The
growth of the Etna Volcano, due to north migration of emission centers that had previous-
ly realized the most ancient Hyblaean volcanism, has caused progressive deviation of
Simeto and Alcantara River and has created lakes of volcanic obstruction (Gurrida lake)
and humid areas characterised by uncertain pattern directions.

2. The environment in Sicily from Middle Pleistocene to Holocene

At present there are no specific studies as regards climate and environment conditions
of Sicily during Middle Pleistocene-Holocene, yet it is reasonable to say that the paleocli-
matic situation of the island must have been similar to the one of the Italian peninsula, tak-
ing into account that the closeness of the African coast probably used to stress aridity dur-
ing temperate-warm climatic phases and used to mitigate climatic harshness during glacial
phases. Probably, the climate of the northern mountain sector was quite different from the
hilly one or, coming down south, from the plains; perhaps the island was an environment
mosaic, with microclimatic differences strongly influenced by physiographic features.

Paleoenvironmental reconstructions, limited by the almost complete absence of pollinic
data, are mostly based on paleontologic information (observation of continental mammal