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8 F. NIGRO
Fig. 9. A. High-resolution seismic profile showing the low-an- Fig. IO. A. Map view of the top of Late Pliocene-Early Pleistu-
gle norma! fault system cutting the Pleistocene sequences. Attempt cene sequences cxposed in Centrai Sicily. Thin lines indicate the
of sequence stratigraphy distinguishes some depositional se- altitude above sea leve!. l - Plio-Pleistocene sequences; 2- pre-
quences in the sedimentary successions. Sequence boundaries per- Middle Pliocene sequences; 3- axes offolds involving the overall
mi t to date deformation events. B. Seismic section shows outcropping sequences; 4- axes of folds involving only the Late
evidences of inversion (or transpression) tectonics affecting the Pliocene and the pre-Pliocene sequences. B. Simplified structural
Plio-Pleistocene sequences in the Eastern Sicily offshore From section across Centrai Sicily. Dashed !ines indicate the supposed
Nigra & Sulli (1995) buried right-lateral transcurrent fault system that may have at:.
fected the region. l- Plio-Pleistocene sequences; 2- Gela Nappe;
3- Sicanian units; 4- Hyblean foreland
Montagnareale) we can reconstruct the tectonic history of polyphase folded, creating dome and basin geometries. In
the last 1-1.5 Myr. The outcropping Pleistocene shallow- the Butera area, arenaceous Pleistocene sequences (Gephy-
water sequences (G. inflata-G. cariacoensis biozones in the rocapsa biozone) are affected by the second of these two
Patti Marina area) are gently folded and covered by very fold systems, the NE-SW trending one (Fig. l 0). Neotec-
shallow sequences of Sicilian age (G. truncatulinoides ex- tonic structures also characterise the most stable geologica]
ce/sa biozone). The entire sequence was subsequently area outcropping in Sicily (Hyblean region, SE Sicily). This
faulted and tilted northwards In the Patti area, an asymmet- part of Sicily represents the gently deformed foreland of the
ric graben was produced, while the Jistric geometries of the Neogene to Pleistocene collisional belt. Severa! thick car-
fault system are revealed by block tilting. This system was bonate sequences of a Mesozoic-Tertiary age outcrop in this
subsequently cut by a N-S trending, right-lateral strike-slip area. Carbonate bodies are locally very gently folded and
fault determining the en-echelon folding of the more recent bounded by very recent fàult systems revealing a preva-
outcropping sequences (G. cariacoensis-G. truncatuli- lently distensive-transtensive displacement (Ghisetti & Vez-
noides excelsa biozone). zani, 1981a; Ben-Avraham et al., 1987; Grasso & Reuther,
1988, 1990, 1992; Grasso, 1993).
The predominance of tàults decreases towards the
south, where Cretaceous to Miocene plastic covers (t1ysch- The Hyblean element is overthrust by the frontal part of
like sequences) and Pliocene-Pleistocene marine deposits the Sicily Chain (Gela Thrust System), its emplacement
crop out. Also, in this part ofthe region, the NE-SW trend- having started during the Plio-Pleistocene.
ing large scale gentie en-echelon fold systems, interpreted as
field evidence of a buried E-W trending right-lateral deep The tectonic setting of this part of Sicily is al so charac-
transcurrent fault system, can be observed (Figs. 8D and terised by some neotectonic "lineaments'' which are a clear
SE). expression of the emergent and buried strike-slip fault sys-
tems regionally trending E-W to N-S, with some different
En-echelon fold systems are also present in centrai Sic- displacements.
ily. In this area, unpublished geophysical data from geoelec-
trical sounding surveys with quadripolar Schlumberger con- Towards the NW, the Hyblean element is also bordered
figuration, make it possible to reconstruct the top geometry by an extensional (probably transtensional) NE-SW,
of the Late Pliocene-Early Pleistocene sequences. As illus- NNE-SSW and WNW-ESE trending fault systems
trateci in Fig. l OA, the Plio-Pleistocene sequences are (Ghisetti & Vezzani, 1981 a), separating the foreland from
the frontal part of the Sicily Chain and the recent "Gela-
