Page 4 - valerio agnesi - geographical-phisical aspect Sicily

26 Agnesi: Sicily in the last one million years

associations and of sea deposits) and on geomorphologic data. Climatic variations, and the
consequent eustatic oscillations, have left traces in morphology and in sedimentary fea-
tures of the talus, in paleosoils and in fluvial deposits. Along the coasts, wing furrows mark
the different sea level.

The geodynamic evolution of Sicily, characterized by particularly active neotectonics that
has caused the raising and emerging of large areas, has interacted with the significant climatic
fluctuations and the eustatic oscillations, aiding remarkably in the landscape evolution.

2.1 The environment during Middle Pleistocene and Early-Upper Pleistocene (1,000,000-
75,000 years B.P.)

Data belonging to environment conditions in the first part of Middle Pleistocene are
poor and fragmentary. Most likely, at the end of the Lower Pleistocene, the Sicilian-
Maltese insular complex had a rather different paleogeography than today’s. The islands
basically consisted of a partially emerged chain, continuously raising, that was the bone
structure of the present Sicilian Apennine; such structure was built up during Middle
Pliocene and towards south-east, in a large sublevel emerged area corresponding to the
structure of the Hyblaean foreland. Between these areas was the wide foredeep sedimen-
tation basin divided into two sub-basins (Caltanissetta and Castelvetrano Basins) separat-
ed by a structure.

The first part of the Middle Pleistocene is characterised by an important widespread
phase of sea withdrawal ( Regressione Romana, Ruggieri & al. 1984) happened ca.
between 0.9 and 0.8 millions of years before present (Ma B.P.). During this phase there is
a further elevation of the northern chain and, more to the South, the emersion of large areas
(northern portion of the Caltanissetta Basin and most of the Castelvetrano Basin) which
still show their emerging tendency, already manifest in the previous period.

Moreover, raising too were narrow sectors as Mt. Pellegrino, Mt. Gallo and the promon-
tory of Capo Milazzo. In the south-east sector, the raising determines the widening of the
Hyblaean area, that at those times extended from Capo Passero, SE, to Licodia-
Grammichele-Mineo sector, NW, and the widening of Siracusa’s coastal areas (Magnisi
and Maddalena peninsulas). Along the north and west coasts, the areas near the chain were
characterized by variable direction movements, nevertheless tending to ultimate emersion.
Exceptions of this general picture, showing a strong lowering tendency, are certain sectors
of Sicily’s south-west coast (areas of Capo Bianco, Selinunte, Mazara del Vallo and
Marsala) and the Piana di Catania (Ghisetti & Vezzani 1982).

The north zone and most of the central sector of the island seem still, while the coastal
areas reported oscillations of the sea level and transgressions that, in some cases, reached
also inner areas, causing the formation of wide terraces whose most representative exam-
ples are in the coastal area of Trapani, Agrigento and the Hyblaean zone (Bonomo & al.
1996; Carbone & al. 1982).

This long period is characterized by climatic oscillations that, especially during the ini-
tial phase, seems to have met hot-arid fluctuations significant enough for the shaping of
wide planation surfaces ( like pediment located in some areas of Southwestern Sicily
(Ruggieri & Unti 1977).