The relict deposits of the Cilento offshore (Southern Italy): new seismo-stratigraphic data based on high resolution seismic profiles

The relict deposits of the Cilento offshore have been analyzed based on the geological interpretation of new seismo-stratigraphic data, consisting of the Sub-bottom Chirp profiles recorded in the oceanographic cruise GMS03_01 (R/V Urania, National Research Council of Italy) during the scientific and technical activities for the realization of the geological sheet n. 502 "Agropoli" (Cilento offshore, Southern Tyrrhenian Sea). In the Cilento offshore two kinds of relict deposits have been identified based on the geological interpretation of Sub-bottom Chirp profiles, including both the palimpsest deposits and the lowstand deposits. The sedimentary cover of the continental shelves basically comprises two types of sediments, i.e. those in equilibrium with the present-day environmental conditions and those that are not in equilibrium with the present-day environmental conditions, which are the relict sediments. Based on the classical definition of Emery (1968) the relict sediments have been deposited long ago, in equilibrium with the depositional environments therefore, while later, these depositional environments are no longer in equilibrium, even though they have not been covered by subsequent sediments. Thus, the unconsolidated sedimentary cover of the continental shelf basically comprises two types of sediments: those that are not in equilibrium with current environmental conditions (i.e., in a broad sense, relict sediments) and those in equilibrium with these conditions. Emery (1968) defined relict sediments as "sediments deposited long ago, in equilibrium with the environments therefore; later, the environments changed so that these sediments are no longer in equilibrium, even though they have not been covered by subsequent sediments". An important feature in recognizing the relict origin of a sediment is represented by the occurrence of coarse-grained sands, located at a greater distance from the coast and at greater depths than fine-grained sands, which are usually thinner than the fine-grained ones. Another important concept is that of the palimpsest sediments, having characteristics of two sedimentary environments, one older and one more modern. While the relict sediments represent remains of previous depositional environments, the palimpsest sediments correspond with relict sediments, which have been subsequently reworked. Intermediate phases are possible, starting from pure relict sediments, passing through palimpsest sediments, towards modern autochtonous sediments, not preserving the textural, sedimentological and petrographic characteristics of the previous depositional environments. The Cilento offshore (Southern Tyrrhenian Sea, Italy) represents a structural high, resulting from the seawards prolongation of the Licosa Cape structural high, bounded northwards and southwards by two half-graben, the Salerno Valley and the Policastro Gulf. The Salerno Valley is a half-graben basin, whose individuation has been controlled in the Early Pleistocene by the master fault Capri-Sorrento Peninsula, bounding southwards the margin of the Sorrento Peninsula with throws in the order of 1500 m, downthrowing the Meso-Cenozoic carbonate sequences through a step of normal faults. The structural high of Cilento has been the subject of geological and seismostratigraphic studies since the end of the 90s, when the interpretation of the AGIP multi-channel seismic showed extensive high structural zones, characterized by deaf acoustic facies with no acoustic base of internal reflections, alternating with sedimentary basins. Subsequently, the acquisition of deep multi-channel seismic along the Tyrrhenian edge, confirmed this structural set-up, highlighting how the upper Cilento structure is locally complicated by bending, reverse faults a