Non-seagrass meadow sedimentary facies of the Pontinian Islands, Tyrrhenian Sea: A modern example of mixed carbonate–siliciclastic sedimentation

The soft bottom of the Mediterranean continental shelf is characterized by a heterozoan skeletal assemblage ( sensu [James, N.P., 1997. The cool-water carbonate depositional realm. In: James, N.P., Clarke, J. (Eds), Cool-water Carbonates. Spec. Publ. Soc. Sediment. Geol., vol. 56, pp.1–20.]). Although the contemporary presence of terrigenous and skeletal carbonate sediments has been well established [Tortora, P., 1996. Depositional and erosional coastal processes during the last postglacial sea-level rise: an example from the Central Tyrrhenian continental shelf (Italy). J. Sed. Res. 66, 391–405.; Fornós, J.J., Ahr, W.M., 1997. Temperate carbonates on a modern, low-energy, isolated ramp: the Balearic Platform, Spain. Journal of Sedimentary Research , 67, 364–373.; Fornós, J.J., Ahr, W.M., 2006. Present-day temperate carbonate sedimentation on the Balearic Platform, western Mediterranean: compositional and textural variation along a low-energy isolated ramp. In: Pedley, H.M., Carannante, G. (Eds.) 2006, Cool-water Carbonates: Depositional Systems and Palaeoenvironmental Controls. Geological Society, London, Special Publications, 255, pp. 121–135], the interactions between carbonate and terrigenous–siliciclastic sedimentation has not been documented well enough. A total of 33 surface sediment samples from the Pontinian shelf (Tyrrhenian Sea, central Mediterranean) have been analysed. Sampling stations range from 15 to 250 mwd (meter water depth) and are located along five transects (PonzaW, PonzaNW, Ponza NE, Ponza E, Zannone), plus four samples collected around Palmarola Island. Sectors colonized by seagrass meadows have not been sampled. A total of 6 sedimentary facies (F) and 10 microfacies (mf) have been recognized by using component analyses, grain size percentage, sorting, carbonate content and authigenic mineralization rate. These facies and microfacies represent the Pontian Islands shelf sedimentation, in the interval between the upper infralittoral and the epibathyal zones that represent shelf-break and upper slope sedimentation. The Maerl facies (F4a,b; mf4a,b) and the skeletal sands (F2a,b; mf2a1, mf2a2, mf2b) fall within the circalittoral zone. The circalittoral zone in the water depth interval between 82 m and 112 m display relict facies (F6, mf6). Finally facies F5 (Siliciclastic sands) includes subfacies F5b (mf5b), located in the circalittoral zone at depths of 49 to 101 mwd and restricted to the western and eastern sectors of Ponza, and subf