Holocene evolution of the Sibari Plain (Southern Italy) in a tectonics controlled setting

The Sibari Plain is located close to the boundary between the Calabrian Arc and the Southern Apennines. During the Holocene, the plain was characterized by the Crati delta building and by the re-activation of the transverse Sybaris Fault Zone (SFZ), a northward dip fault interpreted as an oblique normal-dextral fault zone, 45°N-55°N striking, recognized by archaeoseismic data recorded in the Sybaris ruins. We carried out a muldisciplinary approach combining boreholes stratigraphy and ancient cartography analysis and acquisition of 2D Electrical Resistivity Tomography (ERT). We identified four main units: (1) the Late Pleistocene sandygravelly alluvial and coastal plain deposits, (2) early-middle Holocene clayey sediments of marine-marshy-lagoon origin, (3) a middle-late Holocene sandy beach ridge system and (4) late Holocene deltaic sediments. The elevation contours of the top for the Pleistocene basement reveal a Holocene SFZ activity or reactivation that has probably created space for a different arrangement of late Pleistocene and Holocene units in the surrounding Crati River area. Furthermore, an ERT allows to observe evidences of the SFZ close to Sybaris. Considering the different stratigraphic units thickness and association, we suggest that the SFZ Holocene activity drove the plain evolution influencing the development of different depositional environmental conditions between hanging wall and footwall. In detail, major delta-building events reconstruction suggests that at the end of last-glacial transgression (around 6 kyr B.P.) a wide wetland and a shallow water bay environment took place on the hanging wall. On the foot wall, the Crati River built its terminal plain and its delta. Up to Sybaris time (2.7-2.5 kyr B.P.), the high subsidence on the hanging wall favoured the deposition of thick wetland deposits passing seaward to the shallow water sediment of the coastal embayment. At the same time, on the foot wall the Crati Delta progradation went on reaching the area southward from the Sybaris settlement. Up to the present day, the tectonics has been influenced the plain topography, producing a depressed area on the hanging wall, marked by widespread presence of humid zones. The present confluence between Crati and Coscile Rivers happens in correspondence to the SFZ. We suggest that the the ground-tilting drives the Coscile River channel to avulse periodically toward the SFZ (the down-tilt side with minimum elevation), with the consequent confluence in the Crati River, during the active tectonic period and to move away from the SFZ during quiescent one producing the two rivers separation. The latter can be favored by sediments accumulation close to the SFZ, which re-establish the pre-tilting equilibrium. In conclusion, our approach aims to identify the SFZ as a major agent controlling deposition and landform development by creating accommodation space for the deposition of coastal sediments along Sibari Plain during the Holocene.