Post-Greek Coastline Shifts Interpreted by Biostratigraphic Analysis on Hipponion's Seismotectonically Active Margin, Calabria, Italy

Abstract

Coastline migrations since the Greek period are identified on the seismotectonically active Tyrrhenian margin near ancient Greek Hipponion (Vibo Valentia), in SW Calabria, Italy. The study area is characterized by the Trainiti River mouth area, with its small delta-shaped protuberance and two large, submerged, coast-abutting breakwaters that once delineated a harbor for late Greek, Roman, and subsequent settlements. Biogenic facies and ecological analyses define the depositional settings of late Holocene sediment sections in cores recovered on shore just landward of the harbor's eastern breakwater. Radiocarbon-dated biogenic facies in the cores show sediments accumulated in inner-shelf settings to depths of about 10 m, indicating the coastline had retreated about 200 to 300 m landward of its present position from about the late Greek and Roman periods to the 13th century AD. This phase was followed by seaward advance of the shore, resulting in shallower, current-formed, offshore bar to forebeach settings during and following the medieval time that originated the delta-shaped body. The latter, positioned behind the eastern breakwater, is anomalous in that it formed on an otherwise straight coastline subject to active structural displacement and erosion. A thin upper veneer of deltaic sediment indicates that the Trainiti mouth reached the study area within the past 300 years, its channel having migrated from the west. Post-Greek tectonic displacement of this coastal margin resulted in the seaward-tilted configuration of the eastern breakwater, originally constructed as a coast-detached structure with a horizontal surface on the inner shelf. As the shoreline advanced seaward during the past approximately 800 years, the gap between land and offshore breakwater narrowed, altering coastal sedimentation processes and topography. It is proposed that vestiges of major Greek and Roman port facilities and settlements on land are likely buried by a thick alluvial cover on the coastal plain, probably south and west, rather than just landward, of the eastern breakwater study area.