31 - Nontropical Carbonate Shelf Sedimentation. The Archipelago Pontino (Central Italy) Case History

Abstract

The Tyrrhenian Sea is in the central part of the Mediterranean Sea between the mainland of Italy and the islands of Corsica, Sardinia, and Sicily. The sea is located in a geodynamically active area, with extensive tectonics and a young volcanism related to the opening of a back arc basin that started during Late Miocene to Pliocene times. The Tyrrhenian Sea is characterized by a microtidal regime, which has only a secondary influence on the coastal dynamics. The Tyrrhenian Sea is a young back arc basin with a continental shelf characterized by siliciclastic sediments, delivered mainly by rivers. However, areas of carbonate sediments are also found on the shelf, as is characteristic of mid-high latitudes. The Archipelago Pontino in the eastern central Tyrrhenian Sea consists of five islands formed mainly of volcanic rocks of Plio-Pleistocene age. The low siliciclastic sediment input in this area can be attributed to the lack of significant river runoff, because there are no major rivers on the islands, which are located about 30 km away from the mainland. The relatively high-energy hydrodynamic regime around the islands also prevents the deposition of muddy sediments. The biogenic sediment fraction comprises mainly coralline algae, foraminifers, bryozoans, and undifferentiated bioclasts, and to a lesser extent bivalves, crinoids, echinids, gastropods, ostracods, pteropods, serpulids, and sponge spicules. A variety of depositional units that characterize particular marine habitats have been identified in the area. The most significant habitats include those of Posidonia oceanica, rhodoliths (unattached red algae), and “coralligène."