Distefano S.*1, Gamberi F.2 & Di Stefano A.1
1 Dipartimento di Scienze Biologiche, Geologiche ed Ambientali, Università degli Studi di Catania 2 Istituto di Scienze Marine - Consiglio Nazionale delle Ricerche di Bologna
* Corresponding email: salvodist82@gmail.com
Keywords: seismic stratigraphy, structural characterization, stratigraphic setting.
Based on the seismo-stratigraphic interpretation of new seismic profiles (Sparker System) acquired along the southeastern offshore of Sicily, this work contributes to the improvement of our knowledge about the stratigraphic and structural context in the area connecting the Gela-Catania foredeep to the Hyblean plateau foreland. Three main aims have motivated the acquisition of new seismic profiles along the southeastern coastline of the Sicily, in the Marina di Ragusa offshore: i) a better comprehension of the Cenozoic stratigraphic and structural setting of the area and, in particular, the characterization of the Plio-Pleistocene sedimentary deposits and their areal distribution; ii) the identification of the eventual continuation, in the offshore area, of the main structural lineaments defined in the hinterland (Scicli-Ragusa-Irminio line); iii) the understanding of the meaning of these faults on the geodynamic evolution of the Sicily Channel. A simplified model of the stratigraphic-structural setting of the study area is proposed with a comparison with preexisting models derived from the literature. Our model shows that an extensional faults system, characterized by a main NE- SW orientation, affects exclusively the late Miocene formation originating a horsts and graben setting. These faults are probably the record of the early history of the Scicli Line and of the polyphase kinematic evolution of the N50 oriented regional fault systems, supporting recent interpretations that identify an offshore prolongation of the NE-SW oriented faults of the Marina di Ragusa Graben. The Gessoso-Solfifera formation (late Miocene) has been recognized in several parts of the study area. It displays large lateral variation in thickness and a typical vertical arrangement of seismic facies showing that variable depositional environment characterized the Messinian salinity crise. Furthermore, internal erosional surfaces reveal that the deposition was not continuous in time but was associated with erosional periods that resulted in channelized features. More in general, the Gessosa-Solfifera deposits of the study area have a wide regional implication, demonstrating that the evaporitic deposits are not, as widely recognized on land, a peculiarity of marginal sub-basins or of the thrust top mini-basins of the Appennine-Maghrebides belt, but they also formed in the extensional setting of the Hyblean foreland ramp. Moreover, the acoustic features of the Plio-Pleistocene deposits have permitted the identification of six seismic units that correlate with the depositional evolution of the nearby Gela foredeep and with three formations with regional distribution: Trubi, Ponte Dirillo and Argo Formations. The Plio- Pleistocene succession is not affected by any tectonic activity, and consists of laterally continuous seismic facies, interrupted only in a wide area, where gas rising from the deeper succession reaches, in some places, also the seafloor.
© Società Geologica Italiana, Roma 2018 CONGRESSO SGI-SIMP 2018
145
U-Pb detrital zircon ages from Gorgoglione Flysch sandstones (Southern Apennines, Italy):
inferences on source area
Fornelli A.*1, Gallicchio S.1, Langone A.2 & Micheletti F.1
1 Scienze della Terra e Geoambientali Department Bari University 2 IGG-CNR, Pavia Unit
* Corresponding email: annamaria.fornelli@uniba.it
Keywords: detrital zircon age, source area, sandstones.
LA-ICP-MS U-Pb ages were collected on detrital zircons from one sample of sandstone belonging to the Gorgoglione Flysch (GF) outcropping in Southern Apennines (Basilicata Region, Italy).
The Gorgoglione Flysch represents a sedimentary siliciclastic succession having ≈1500 m thickness consisting of coarse-medium grained turbidites with mudstone layers. The deposition age of detritus was Langhian-Serravallian in a wedge-top basin belonging to the Southern Apennine Foreland Basin System (e.g. Lentini et al., 2002). GF sandstones show immature mineralogical composition and textural features. The composition varies from arkoses to lithic arkoses with some abundance of micas; the texture shows widespread siliciclastic and calcareous matrix and scarce cementation.
The provenance studies on GF sandstones based on quantitative modal analysis, indicated a crystalline basement formed by continental crust rocks located in the eastern sectors of the Alpine Chain (Critelli & Loiacono, 1988). The prevalent granitoids and low grade metamorphic rocks occur in the crystalline basement as testified by nature of lithic fragments in GF sandstones.
The detrital zircon radiometric dating through U-Pb spot analyses, tend to establish the ages of the source rocks supplying the sedimentation basin in Langhian-Serravallian times.
The age data collected on nine detrital zircons selected by one sample of sandstone reveal twelve ages ranging from Neoproterozoic to Triassic ages and four Oligocene-Aquitanian ages. The oldest age (669±25 Ma) was measured on homogeneous luminescent zircon probably derived from metamorphites; a meaningful Carboniferous-Permian age cluster (n=10) ranging from 319±13 Ma to 262±4 Ma seem connected to zircons showing oscillatory magmatic zoning linked to granitoid and to recrystallized zircons in metamorphic conditions; one Triassic age (247±6 Ma) was measured on broken crystal whereas four sub-concordant ages (25±1 Ma to 23±9 Ma) are shown by two euhedral zircon crystals with regular oscillatory magmatic zoning.
The preliminary dating of detrital zircons from GF sandstones seem to indicate a provenance of detritus from Hercynian magmatic and metamorphic rocks forming the Alpine chain but the presence of a younger magmatic component suggested that even igneous rocks connected to Oligocene magmatic activity were present in the source area.
Critelli, S. & Loiacono, F. (1988): Provenienza e dispersione dei sedimenti nel flysch di Gorgoglione (Langhiano-Tortoniano, Appennino Lucano): Implicazioni sull’evoluzione delle mode detritiche arenacee nell’orogene sudappenninico. Mem. Soc. Geol. It. 41, 809-826.
Lentini, F., Carbone, S., Di Stefano, A. & Guarnieri, P. (2002): Stratigraphical and structural constraints in the Lucanian Apennines (southern Italy): tools for reconstructing the geological evolution. J. Geodynamics, 34, 141-158.