Late Cenozoic uplift of southern Italy deduced from fluvial and marine sediments: Coupling between surface processes and lower-crustal flow

摘要

We investigate the rates and magnitudes of Late Pliocene-Pleistocene uplift at key localities in the southern Italian regions of Basilicata and Calabria using fluvial and marine terraces. These rates show strong lateral variations, reaching maxima of ～1 mma~(-1) or more in the southern Apennines, which have uplifted by many hundreds of metres since the late Early Pleistocene and by well over 1 km since the Middle Pliocene. Integrated study has been facilitated by the realisation that altitudes of river terraces in this region require substantial correction for downstream channel lengthening, given the rapid coastal progradation that is occurring, before they can be compared with altitudes of marine terraces. These high rates of uplift, and the corresponding rates of subsidence of the sea-floor in adjacent offshore localities, are explained as consequences of coupling between erosion and sedimentation by induced flow in the lower continental crust, this coupling being particularly strong due to the narrowness of the southern part of the Italian peninsula. Numerical modelling indicates that time-averaged and spatially averaged erosion rates in this region have been ～0.5mma~(-1) since the early Middle Pleistocene, less than the regional uplift rates, indicating that the landscape is not in a steady state. Although southern Italy lies within a plate boundary zone, along which the African plate is subducting and within which the continental crust is extending, the observed vertical crustal motions are, nevertheless, controlled by surface processes; in particular, across much of this region, crustal extension is shown to be a much less important factor than onshore erosion in driving the observed rates of vertical crustal motion.