Segnalazione di nuove evidenze di antiche linee di riva in Penisola Sorrentina (Campania)

New evidence of ancient shorelines along the Sorrento Peninsula (Campania, Southern Italy) (Central Italy)

Abstract

A sector of the southern coastal slope of the Sorrento Peninsula, comprised between Capo Sottile and Punta Campanella, has been surveyed and numerous evidences of ancient shorelines recognized and studied. Among others the study has brought out for the first time the traces of marine episodes predating those of Eutyrrhenian age, which were previously supposed to be the most ancient ones in the area. The oldest of those pre-eutyrrhenian paleo-sea levels is represented in many localities by relatively broad platforms of marine abrasion cut onto the mesozoic carbonatic rocks and covered by beach conglomerates. These are in turn covered by well cemented continental detrital formations including talus breccias and fanglomerates. The variable altitude above sea level of said group of terraces can be attributed to a phase of tectonic fragmentation, uplift and tilting that occurred before the modelling of a second order of sea level marks. The latter is represented, in several places of the surveyed coast, by small abrasion platform, beach deposits, notches and coastal caves occurring between 8 and 10 a.s.l. Also this other order of sea level marks predates the one of Eutyrrhenian age (dated about 129 000 yr.B.P. through Th/U measurements on Cladocora coespitosa), which is often found in association with the other two orders at 7.4 a.s.l. The fact that the + 8/10 m. level (that we tentatively ascribe to a sea level rise of the oxigen isotopic Stage 7) maintains an almost constant elevation is a sign that since the time it was carved the study area stopped to be block-faulted and entered a period of uniform tectonic behaviour and, most likely, of very low rate of uplift. The latter deduction can be safely stated for post-Eutyrrhenian times, as sea level marks of that age are tectonically rised of not more than a couple of meters in our area. Other orders of paleo-sea level marks (mostly represented by notches) were recognized in many localities at about 5, 4.5, 3.5 and 1.5/2 m a.s.l. Based on geomorphological and stratigraphic evidence they can be considered younger than the Eutyrrhenian episode found at 7.4 meters a.s.l. and possibly traced to other minor sea level stands of the same stage 5. The notches at + 1.5/2 m of our study area and surroundings are currently ascribed to the highest peak of the Postglacial (Versilian) transgression. Such attribution could remain valid for same cases, but in the study area there are good evidence that a short stand of the sea level during the late Stage 5 worked out notches at the same elevation.