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Abstract

Syn-sedimentary deformation occurred during late Neogene time in the foreland and piggyback basins of Sicily, located between the South-Tyrrhenian belt and the North Africa foreland. The geometric relationships of the Plio-Pleistocene syntectonic strata (5.3–0.5 Ma) with structures like thrust-related folds are spectacularly preserved, together with the modifications in the stacking pattern of the parasequences. In some expanded successions, it is evident that significant pulses in the synsedimentary growth of structures occur on the time scale of Milankovitch cycles, producing stratal geometries that may become unpredictable by current models. Due to tectonic compressive stresses, the tectonic subsidence (or uplift) rate may exceeds the eustatic rate, generating stratal expansions or local unconformity surfaces, formed at the scale of systems tracts of the 4th order depositional cycles. High-resolution biochronostratigraphy and sequence stratigraphic interpretations allow precise evaluations of the vertical absolute growth and growth rates relative to very short time intervals. In the Caltanissetta area, central Sicily, structures having the amplitude of tens of meters are generated within the duration of Milankovitch cycles (5th order). In central and western Sicily, the available data indicate that the duration order of 0.4-1 my seems to be the necessary time interval to complete the growth of structures having the amplitude of some hundred meters; the resulting growth rates are between 0.5 and 2 m/ky. The total amount of uplift within the studied structures, calculated at the 3rd-, 4th- and 5th-order of duration, is not much greater than the thickness of the syntectonic strata that onlap the growth anticlines bordering the basins; this explains the evidence that the tectonic unconformities are only locally extended. Since individual growth events are unable to produce regional surfaces of erosion during the considered time intervals, the sequence stratigraphic analysis has been profitably applied in this setting of active compression. Regionally-extended unconformities with constant age on wide areas related to glacio-eustasy can be recognized, dated and used for large scale correlations.

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