The Pleistocene coralligenous build-ups of Le Castella and Capo Colonna terraces (Calabria, Southern Italy)

Autochthonous coralligenous build-ups are mainly formed by encrusting coralline algae, currently develop on Mediterranean hard and soft bottoms with a patch distribution along the coast. However, few fossil examples have been described in the literature and their evolution in the context of a stratigraphic cycle has seldom been modelled in detail (Basso et al., 2007; Titschack et al., 2008). Wide marine terraces are preserved in the area of the Crotone peninsula, Ionian Calabria, southern Italy (Zecchin et al., 2004; Nalin et al., 2006; Nalin et al., 2009). They are related to the interplay between Pleistocene sea-level changes and the progressive uplift of the Calabrian arc from the middle Pleistocene onwards (Massari et al., 2002). The deposits are up to 10 m thick and consist of mixed carbonate and siliciclastic sediments, in which coralligenous build-ups and other red algal facies are dominant. Usually the terraces are characterized by 3 layers: 1) a blocked basal conglomerate, forming by the erosion of ancient terrace deposits; 2) the algal reefs; 3) the biogenic sandstone-grainstone bodies, which occupy the cavities between the coralligenous bodies and/or cover them at the top. These 3 layers are the result of the shallow deposition during an entire sea-level cycle. The two youngest marine terraces are related to Marine Isotopic Stage (MIS) 3 and 5.1 (Gliozzi, 1987; Belluomini et al., 1988; Palmentola et al., 1990; Zecchin et al., 2004; Nalin, 2006). The MIS 3 terrace outcrops in the area of Le Castella, S of Isola di Capo Rizzuto village whereas the MIS 5.1 is placed along the Capo Colonna cape, placed in the NE part of the peninsula. Their major stratigraphic features and facies have been already described but very few details exist on their paleontological content. Stratigraphic sections in both terraces have been measured and sampled. Thin sections have been prepared for red algae identification and to measure the diagnostic anatomical microfeatures of the algal thalli in order to conduct statistical analysis. Sandstone and grainstone associated to build-ups have been disgregated in order to separate particles in a conservative way and conduct paleontological analysis of the algal fragments forming the sediment. The coralligenous build-ups are dominated by the coralline algae Mesophyllum alternans (Foslie) Cabioch & Mendoza and Titanoderma pustulatum (Lamouroux) Nägeli usually alternated with bryozoan crusts. Other red algae species like Lithophyllum stictaeforme (Areschoug) Hauck, Phymatolithon calcareum (Pallas) W.H. Adey & D.L. McKibbin and Neogoniolithon sp. rarely occur. A quantification of the dominant coralline species involved in the bioconstruction and forming the sediment is provided, in order to define the coralline assemblage variation in a shallowing-upward paleoenvironment. The relative abundance of each coralline species provides more details on the behaviour of the identified species and allows a better correlation with the sea-level cycle. The paleontological results have been framed in the context of a geneticstratigraphic interpretation of the marine terraces.