The Versilian transgression in the Volturno river plain (Campania, southern Italy): palaeoenvironmental history and chronological data

Abstract

In order to reconstruct the Holocene evolution of the Volturno river coastal plain, a geomorphoiogical survey was carried out and three boreholes (A,B and C) were drilled in the southern sector of the area. Further stratigraphical data were available from pre-existing boreholes from scattered locations on the plain. For samples obtained from boreholes A,B and C, ostracod analysis, lithostratigraphical observations and AMS 14C dating were carried out. The Holocene deposits outcrop along the coastal beach-ridges of the strand plain, and in the flat back-barrier depression, the northern area of which is partially occupied by the composite and raised meander belt of the Volturno river. These deposits lie on the subaerial erosional landscape carved in the Campanian Ignimbrite formation (the latter being 42 to 27 ka BP in age) during the last glacio-eustatic low stand. The wedge-shaped sedimentary body (up to 30 m thick) is composed of sands and silts near the coast (penetrated by core A) and of clays, peats and silts (cores B and C) in the inner part of the plain. Both the sedimentary reconstructions carried out on the well-logs and the three dimensional arrangement of the Holocene sedimentary units allowed for both the reconstruction of the sediment geometry and the assessment of the major paleoenvironmental changes occurred in the area as a result of relative sea-level changes. The lower part of the Holocene succession is represented by a transgressive barrier-lagoon system, the onset of which is marked by beach sands, recognized in borehole A at a depth of 23-22 m b.s.l. The inferred age for this marine layer is about 10 ka BP. Due to the persistence of the sea-level rise, the barrier complex shifted inland, up to a maximum distance of 1.5 km from the modern position, and the lagoon depression also migrated inland. The subsequent late Holocene environmental history was characterized by a regression phase dominated by deposition, which resulted in the progradation of the palaeo-shoreline to its modern position. This progradation is identified by up to 10 m of Holocene deposits composed of dune sands (exposed across the area), which pass downwards to sands of shore-face and transition zone. Although no precise chronological constraints are available for the 14C dates obtained from peaty layers, it seems that the change from a transgressive to a regressive trend on this coastline occurred when the phase of the sea-level rise ended and gave way to minor fluctuations around its present position (i.e. between 6 and 4ka BP).