GNGTS 2016 - Atti del 35° Convegno Nazionale

222 GNGTS 2016 S essione 1.2 Edge Propagator (STEP) faults, characterized by a very specific time-space evolution in the upper plate deformation (Milia et al. , 2016). Data and methods. We constructe a 3-D model of the Plio-Quaternary basin’s key-surfaces of the ETM through the interpolation of close and regularly spaced 2D seismic reflection profiles, integrated and calibrated with borehole data. This study has been carried out using a seismic and borehole dataset and a Geographical Information System (GIS) software (Kingdom, IHS Inc.), which constructs a 3D representation of a geologic volume at depth. The study includes the following steps: a) collection of all the available seismic profiles and boreholes data; b) implementation of a GIS geological data base; c) interpretation of the seismic profiles and calibration of the seismic unit using well-log data; d) construction of 2D and 3D models of the subsurface. A total of 6000 km of seismic lines and data from 25 wells has been collected in the study area. We use seismic reflection profiles with different resolution and penetration: multichannel seismic profiles, CROP seismic profiles and Sparker data (MEAS). We interprete the seismic data-set using the seismic stratigraphy method: seismic units are groups of seismic reflections, whose parameters (configuration, amplitude, continuity, and frequency) differ from those of adjacent groups. Sedimentary units are delineated on the basis of contact relations and internal and external configurations. Results. The interpretation of seismic profiles calibrated by well data collected along the margin permit to identify the faults bounding the sedimentary basins and the stratigraphic infill. The stratigraphic analysis permit us to recognize three stratigraphic units in the studied sedimentary basins corresponding to Lower Pleistocene, early Middle Pleistocene and late Middle Pleistocene-Present sedimentary successions. We map the pre-Quaternary substrate and these three stratigraphic units (A, B, C) of the basin infills for 350 km along the ETM, to establish a coherent chronostratigraphic framework across the sedimentary basins and build a 3D model of the study area. The recognition of the syn-kinematic strata in the basin infill and analysis of the interplay between stratigraphic horizon and faulting enabled us to assign an age to fault activity in the eastern Tyrrhenian Sea Margin. We divide the fault structures into three groups according their age: Lower Pleistocene structures, Early Middle Pleistocene structures, Late Middle Pleistocene- Present structures. The interpretation of the seismic data reveals a complex fault pattern along the ETM due to a poliphased tectonic evolution. The 2-D and 3-D models of stratigraphic surfaces, faults and isochron maps of the stratigraphic units reveal that the major faults bounding the basins correspond to normal faults and strike-slip transfer faults. The process of lithospheric extension within the eastern Tyrrhenian Sea produced tilted blocks/halfgrabens (sensu Wernicke and Burchfiel, 1982). We also recognize in the ETM positive inversion structures, documented by the changes of structural relief from previous lows (indicated by thick deposits) to highs (indicated by flexural arching or uplift) . Quaternary evolution. The Quaternary evolution is illustrated in Fig. 2. During the Lower Pleistocene extensional tectonics affected the entire ETMand the western flank of theApennines, creating several basins: NW-SE normal fault formed along the ETM (offshore and onshore). NE-trending and E-W normal faults developed, in the Marsili and Paola basins, respectively. These three contemporaneous extension directions follow Martin’s double-saloon-door model (2006): the Campania margin and Marsili basin approximately match with the two arc- parallel rifts and the Paola basin with the rift orthogonal to the subduction zone. During this stage rapid counterclockwise rotations affected the hanging wall of the active thrust sheets along the outer front of the Apennines (Mattei et al. , 2004). In the late Lower Pleistocene (1.0-07 Ma) there was a change in the structural pattern: extensional faults continued their activity in the Campania Margin, Marsili basin, and western flank of the Apennines, while en echelon folds, linked to a NW-SE left-lateral transfer zone, formed in the Paola basin (the inset shows the 3D model of the 1.0 Myr surface). The activity of this transfer zone could be related to a higher speed of the Marsili basin opening compared to that of the ETM.