Eustatic and tectonic control on Late Quaternary alluvial fans along the Thyrrenian Sea coast of Calabria (South Italy)

The Late Quaternary evolution of the western Coastal Range (northern Calabria) has been reconstructed by means of a multidisciplinary approach. We have focused on the role of allocyclic mechanisms, tectonics and base-level change considered as factors influencing alluvial fan development. In particular we identify no clear evidence for a major influence of climate. Age constraints were provided by a tephra layer and a paleosol, coupled with geomorphological correlations. Middle Pleistocene perched terraces and fan relicts hanging above fault scarps, indicate that tectonics caused switches in fan dynamics between aggradational and erosional phases. As tectonic activity declined during late Middle Pleistocene, eustatically driven changes in base-level, possibly plus low rates of tectonic subsidence, represent the main factor which controlled Late Pleistocene fan development. The two major fan aggradation phases occurred during periods of climate amelioration prior to highstands, whereas high sea levels (OIS 5 and 1) promoted channel incision into the fan surfaces; this continued during periods of climate deterioration with a seaward progradation of alluvial deposition. Sea-level rise is seen as creating accommodation space, producing very open fans, locally within mountain embayments. The fans are characterised by a mushroom shape in plan-view and by a retrograde stacking pattern of alluvial fan facies.