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Abstract

Cool to periglacial conditions, accompanied by a sea-level drop, are thought to result in an unchanged composition and ecological meaning of the rhodalgal carbonates, which occur frequently in the present-day, current-swept areas of the Mediterranean upper shelf. Form, internal structure and species composition of rhodoliths are believed to reflect the environmental conditions present in their biotope. To test these hypotheses, the relationship between rhodolith facies and sea-level rise was investigated in four cores recovered at the Pontian Islands (Tyrrhenian Sea) shelf break. The core basal intervals have been AMS radiocarbon dated providing uncalibrated ages ranging from 10 040 ± 50 years bp to 10 380 ± 50 years bp. All four cores show a transition from basal rhodolith-rich, biodetritic, muddy-gravelly sand to rhodolith-barren, silty sand or sandy mud, along a deepening-upward succession. A facies of coralline-coated fragments of bryozoan colonies has been identified above the rhodolith facies as the deepest coralline growth form in all cores, before the final burial. Molluscan associations and rhodolith abundance, morphology and composition are ecologically compatible with the embedding sediment and testify the transition from the late Pleistocene circalittoral coastal detritic or shelf-edge detritic assemblages at the base of cores, up to the present-day bathyal muds. In the late Pleistocene and Holocene, as at present, the Pantine shelf was characterized by a low sedimentary input under moderate current action, fostering deep coralline growth.

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