The MIS 5 marine terraces on the Tyrrhenian Sea coast of central Italy between Civitavecchia and the Fiora River

Abstract

We reconstruct the marine terraces of the Marine Isotope Stage (MIS) 5 and the landscape evolution of the Tyrrhenian Sea coastal area between the Fiora River and Civitavecchia (central Italy), based on extensive fieldwork, biostratigraphical, palaeoecological, and geomorphological analyses, and ⁴⁰Ar/³⁹Ar dating. Our geomorphological mapping approach uses object-based image analysis, guided by field observations, to identify and map marine terraces using metrics calculated from a LiDAR-based digital terrain model. A suite of three marine terraces at elevations around 40 m, 20 m, and 6 m a.s.l. is recognized through this combined approach in the southwestern sector of the investigated area between Civitavecchia and Marina Velca. Geochronologic constraints based on ⁴⁰Ar/³⁹Ar dating of detrital sanidine extracted from the sedimentary deposits set a terminus post quem for the marine terraces, suggesting their correlation with MIS 5e, MIS 5c and MIS 5a.We have reconstructed an extensive paleosurface in this portion of the coastal area, marked by a CaCO₃-rich, cemented, Thetystrombus latus-bearing biodetrital conglomerate that gently dips seaward from ca. 20 m to the present sea level and represents a range of environments from coastal to shelf. Despite the occurrence of the mollusc species considered distinctive for the MIS 5e highstand, combined geochronologic constraints and paleoecological reconstructions support its attribution to MIS 5c. The lowest terrace forms a narrow strip along the coastline and comprises near shore deposits, including a second, distinct biodetrital platform, at 2–3 m a.s.l. which, assuming a staircase geometry for the suite of terraces, is correlated with MIS 5a. Such geomorphological setting coincides with that reconstructed in the adjacent coastal sector between Civitavecchia and the Tiber delta, pointing at a significant late Quaternary regional uplift.