Diego Puglisi

Tectonic evolution of the Sicilian Maghrebian Chain inferred from stratigraphic and petrographic evidences of Lower Cretaceous and Oligocene flysch

Abstract The occurrence of a Lower Cretaceous flysch group, cropping out from the Gibraltar Arc to the Balkans with a very similar structural setting and sedimentary provenance always linked to the dismantling of internal areas, suggests the existence of only one sedimentary basin (Alpine Tethys s.s.), subdivided into many other minor oceanic areas. The Maghrebian Basin, mainly developed on thinned continental crust, was probably located in the westernmost sector of the Alpine Tethys. Cretaceous re-organization of the plates triggered one (or more) tectonic phases, well recorded in almost all the sectors of the Alpine Tethys. However, the Maghrebian Basin seems to have been deformed by Late- or post-Cretaceous tectonics, connected with a “meso-Alpine” phase (pre-Oligocene), already hypothesized since the beginning of the nineties. Field geological evidence and recent biostratigraphic data also support this important meso- Alpine tectonic phase in the Sicilian segment of the Maghrebian Chain, indicated by the deformations of a Lower Cretaceous flysch sealed by Lower Oligocene turbidite deposits. This tectonic development is emphasized here because it was probably connected with the onset of rifting in the southern paleomargin of the European plate, the detaching of the so-called AlKaPeCa block (Auct.; i.e. Alboran + Kabylian + Calabria and Peloritani terranes) and its fragmentation into several microplates. The subsequent early Oligocene drifting of these microplates led to the progressive closure of the Maghrebian Basin and the opening of new back-arc oceanic basins, strongly controlled by extensional processes, in the western Mediterranean (i.e. Gulf of Lion, Valencia Trough, Provençal Basin and Alboran Sea).

Geological map of the eastern sector of the Gorgoglione Basin (southern Italy)

In this paper we report new stratigraphic data related to a new geological map of the Miocene Gorgoglione Basin of southern Italy, traditionally considered as a piggy-back or wedge-top basin filled by a turbidite-like succession. Well exposed outcrops in the study area (eastern sector of the basin) show four unconformities in the Castelmezzano-Pietrapertosa area. Two of these unconformities pass to paraconformities southeastward, in the Cirigliano-Gorgoglione area. Based on new stratigraphic data the succession of the Gorgoglione Flysch can be divided into different informal units: Val Miletta formation and Gorgoglione supersynthem. The latter can be subdivided into the Cirigliano and Castelmezzano synthems. The previously established Cirigliano synthem is here divided into three subsynthems. The lowermost sediments of the Gorgoglione Flysch on the eastern sectors correspond to a complex unit (Val Miletta formation) including Numidian-like quartzarenites, Gorgoglionelike sandstones, and, at the top of the formation, an olistostrome of varicoloured clays, belonging to the Argille Variegate Group. The stratigraphic analyses and the biostratigraphic results based on calcareous plankton assemblage, improve the reconstruction of the geometries of the sedimentary bodies and the time-space facies evolution of the synthems. Sedimentologic and petrographic characters of the upper part of the Castelmezzano synthem show a clear fining and thinning upward trend. Medium- and fine-grained arenites, varying in composition from quartz sandstones to siltstones and shales, are locally marked by abundant planktonic foraminifera and are interpreted as contourites. Moreover, the relationships between tectonics and sedimentation are analyzed. The data are used to propose a scheme of the Burdigalian to Tortonian tectono-stratigrafiphic evolution of the eastern sector of the basin.

Mineralogy and Geochemistry of the Numidian Formation (Central-Northern Sicily): intra-formation variability and provenance evaluation

Mudrocks and sandstones of Numidian Formation in Sicily have been analysed for mineralogical, petrographic, major element and selected trace element compositions to constrain the intraformational variability and the sediment provenance. The mudrocks are characterized by a kaolinite-rich signature while the sandstones have a quartz-arenitic composition. The high Chemical Index of Alteration and Plagioclase Index of Alteration strongly suggest that recycling processes have been responsible for the present compositions. The mudrocks geochemical data suggested a compositional variability function of the paleogeographic depositional environments. In particular, the Numidian Formation of the more external Serra Del Bosco Unit is affected by the terrigenous contribution of epicontinental-type sediments. With regard to provenance, the geochemical data indicate a derivation from post-Archean sedimentary siliciclastic rocks. The contribution of African cratonic sediments was confirmed by the trace elements ratios and by the end-member modelling processed on mudrocks compositional data. In particular the suitability of the Nubian sediments as one of the sources of sediment supply is also attested.