Late Quaternary palaeoenvironmental evolution of the Central Adriatic coast in the Trigno river mouth area (Molise region)

Three cores (MBS1, MBS2 and MBS3), 15-12 m thick, were drilled offshore near the Trigno river mouth area, 150-300 m from the present coastline. Palaeoecological analyses by means of benthic foraminifera, molluscs and ostracods, supported by stratigraphic and chronological data, have been performed to reconstruct the Late Quaternary palaeoenvironmental evolution of the northern sector of the Molise Adriatic coast. Five main lithofacies, arranged in four lithostratigraphic units, were recognized. At the bottom of the cores MBS1 and MBS3, barren gravels (lithofacies G, unit A), 2.25 m and 1.8 m thick respectively, are present. In the core MBS2 the succession starts with grey clays (lithofacies Cg, unit B), 0.9 m thick, containing marine infralittoral foraminifera, hygrophilous terrestrial molluscs and freshwater ostracods. Sediments of lithofacies Cg, 1.5 m thick, were also recognized above lithofacies G in the core MBS3; here the fossil record consists of marine infralittoral foraminifera, freshwater and hygrophilous terrestrial molluscs, freshwater and marine infralittoral ostracods. Two AMS C dates constrain the deposition of lithofacies Cg (MBS3) between 19945 ± 345 and 19165 ± 195 yr BP. In the cores MBS2 and MBS3, lithofacies Cg is overlaid by brown silty clays (lithofacies Csb, unit C), 1.6 m and 2.7 m thick respectively, containing marine infralittoral foraminifera, molluscs and ostracods, and freshwater ostracods. In the core MBS1, both lithofacies Cg and Csb lack, and lithofacies G is overlaid by grey silty clays (lithofacies Csg, unit C), 0.75 m thick, containing hygrophilous terrestrial molluscs and freshwater ostracods. The three cores are closed up by brown, fine to medium sands (lithofacies S, unit D), 9-10 m thick, recording the dominance of marine infralittoral fauna. One AMS C date carried out on benthic foraminifera (Ammonia sp.) collected from the lower portion of lithofacies S (core MBS3) gave an age of 8120.5 ± 108.5 yr BP. The results of this study point out that, in the Trigno river mouth area, during the Last Glacial, as the eustatic sea-level dropped and the coastline was located several km seaward with respect to its present position (Vai & Cantelli, 2004), fluvial gravels (unit A) deposited and successively were incised. Incisions were filled by clays (unit B) of marshes developed on the alluvial plain. As the eustatic sea-level rised, a shallow marine bay developed and sediments of lithofacies Csb (unit C) deposited. Lithofacies Csg (unit C), overlaying lithofacies G (unit A) in the core MBS1, is very likely heteropic with lithofacies Csb (unit C) of the cores MBS2 and MBS3; therefore marshes on the higher, not incised glacial fluvial deposits, developed contemporaneously to the shallow marine bay. Finally, both the lithology and the faunal content of unit D suggest the development in the study area of a shoreface under marine infralittoral conditions.