The 'Camporeale wedge-top Basin' (NW Sicily; Italy) in the frame of the Late Miocene Sicilian Foreland Basin System; Inferences from the Upper Tortonian-Lower Messinian Terravecchia Formation

摘要

Since the latest Oligocene-earliest Miocene the building of the Sicilian fold and thrust belt has been accompanied by development of a "peripheral" foreland basin system which migrated toward the foreland. In north-western Sicily, the sedimentary record of the foreland basin system migration is represented by a stratigraphic succession made up of several lithostratigraphic units, bounded by regional unconformity surfaces, deposited recording at least four main sedimentary phases, each characterized by the development of different types of syntectonic basins. In particular, during the Late Miocene (Late Tortonian to Early Messinian) a wide wedge-top depozone developed in the innermost sectors of the Sicilian foreland basin system, above the moving thrust sheets. There, wide to quite narrow "syn-kinematic" sedimentary basins developed in response to the tectonic deformation of the deeper carbonate units (Cu). These basins were filled by a thick wedge of silico- and carbonate-clastic deposits pertaining to the Terravecchia Formation (Upper Tortonian-Lower Messinian) which unconformably overlaid the already deformed substrate. Among these basins, the "Camporeale wedge-top Basin" (NW Sicily) was located between an uplifting subaerial chain (northward) acting as source area for coarse elastics and a major depositional area (foredeep depozone) mainly characterized by fine-grained marine sedimentation. Integrated stratigraphic and sedimentologic analyses performed on the Terravecchia Fm. in the Camporeale Basin allowed us to identify a coarsening to fining upward "outer wedge-top sequence" characterized by three main facies associations (i) sandy-to-gravelly unconfined braidplain, (ii) sandy-wave and storm-dominated delta front, (iii) clayey offshore, settled in several adjacent sedimentary environments. Sedimentation has been driven by several interplaying control factors among which the tectonics played a predominant role. Moreover, the structural analysis performed on the Camporeale Basin fill allows us to recognize major E-W, NE-SW, N-S-, NW-SE-trending structures (faults and folds) interpreted as the superficial expression of deep-seated thrusts with both S-ward and predominantly N-ward vergence, developed under a roughly Nl 70' -oriented stress field. The comparison of the Camporeale Basin with other coeval basins of Sicily allows us to image the Late Miocene Sicilian foreland basin system, as being characterized by a wide continental to shallow-marine wedge-top depozone characterized, in turn, by an inner and outer sector passing basinward, through a foredeep transition zone, into a foredeep depozone characterized by open marine deposition.