Sea level variations, deposits and Pleistocene morphogenesis in the Pontine Islands (Tyrrhenian Sea)

Abstract

The Pontine Islands consist of remnants of deeply eroded volcanoes, located on a structural high of the Latium continental shelf, which were active during the Pliocene up to the Early Pleistocene. Continental deposits, marine abrasional surfaces, raised beaches and aeolian sands, occurring at different places in the islands, indicate that the sea level fluctuated several times during the Quaternary, because of the combined effect of climatic changes and tectonics. The oldest beach deposits in the Archipelago are located at Monte Quardia (Ponza Island); it is Early Pleistocene in age and it is buried below pyroclastic deposits of the last volcanic activity in the area. Marine erosional surfaces at the elevations comprised of between 200 and 270 m a.s.l., still preserving beach gravel, occur both in the Ponza (Monte Guardia) and in the Palmarola (Monte Guarniere) Islands; they are referred to the late Early Pleistocene, mainly on the base of the geomorphological evidence. In the Ponza Island a system of abrasional surfaces, located at the elevation of 100-120 m a.s.l., is well preserved and covered by a thick and strongly weathered paleosol, which indicates an Early Middle Pleistocene age for the mentioned surfaces. A further abrasional. surface, at 45-50 m a.s.l., occurs both in the Ponza bay and in the Zannone Island, where it is covered by gravel beach deposits. In the Ventotene Island, the local corresponding erosional surface is located at the elevation of 25 m a.s.l., and it is coverd by littoral sediments, which are dated to the isotopic Substage 5e. Aeolian sand deposits occur everywhere in the Archipelago; in the Ponza and Ventotene Islands they are represented by thick layers of weackly cemented aeolianites. On the ground of isoleucine epimerization analyses on mollusk shells and of radiocarbon datings, the aeolian deposits are dated to the Upper Pleistocene.They were originated by strong deflation of the wide continental platform surrounding the islands, which was exposed in consequence of the sea level drop during the glacial periods of the Upper Pleistocene. The Holocene sea rise toghether with tectonic uplift are documented by remnants of marine notches at 3 m a.s.l. in the Ponza Island and by raised beach deposits up to more than 10 m in the Palmarola Island.