Studio dei terrazzi marini dell'alto Ionio cosentino: considerazioni su sollevamento regionale e deformazione tettonica locale

Abstract

The paper reports the results of a study of a sequence of marine terraces in a tract of -70 km of the Ionian coast of the northern Calabria region. Seven orders of marine terraces have been recognized; the good preservation of the inner edge of these terraces allowed the reconstruction of the corresponding strandlines at elevations ranging from -12 m to ~420 m. Amino acid geochronological datings in the literature indicate that the 85 m-high terrace at Piano S. Nicola corresponds to the Oxigen Isotope Time scale (OIT) substage 5c. By taking into account also the correction for the terrace formation height and for the continental deposits overlying the platform, we calculated an uplift rate of 0.73 mm/yr during the past 102 ka for the northern extremity of the study area. The whole sequence of terraces was compared with the highstands of the paleosea-level curve, and the correlation of the terraces to the OIT stages 1, 5a, 5c, 5e, 7, 9, and 17 (or 15) was obtained. The uplift cumulative curve indicates that uplift might have not been constant in time because uplift rate at Piano S. Nicola varies from an average value of -0.4 mm/yr during the period of formation of the two oldest terraces to ~0.7 mm/yr from 215 ka to the present. The lack of terraces older than 700 ka indirectly confirms that the regional uplift started in this period, as indicated in the literature. Moreover, the uplift is not homogeneous in the area, but the rate progressively increases southward, where the sequence of terraces is closer to the axis of the Apennines belt, i.e. the axis of maximum uplift. Within the regional deformation field, the marine terraces record further local sharp vertical variations that can be originated by the activity of tectonic structures. In a first case, we recognized the coseismic nature of the deformation observed in the terraces of the Sibari plain by comparing their setting to the pattern of surface deformations induced by the Castroviilari fault, which is a seismogenic structure of the area. The comparison between deformation profile and the 102-ka strandline setting permitted to evaluate an average return time of ~1300 years for a great earthquake along this fault and a minimum slip-rate of ~0,2 mm/yr. These values are comparable to those in literature. In the second case, the lack of significant vertical deformation in correspondence of the Pollino fault, suggests to exclude that the activity of the eastern sector of this structure has been prevalently exten-sional since upper Pleistocene time.