Pleistocene Coralligenous Build-Ups and Associated Bioclastic Deposits of Le Castella and Capo Colonna

Autochthonous carbonate build-ups are mainly formed by encrusting coralline algae, which are one of the most important carbonate sediment contributors in the benthic communities of the Mediterranean area. They represent one of the most productive ecosystems in temperate regions and currently develop on Mediterranean hard and soft bottoms with a patch distribution along the coast. Light, salinity and temperature seem to be the main environmental factors influencing their distribution. Several types of assemblages have been described so far, due to the high heterogeneity of coralline growth-forms, distributed from the intertidal down to 160 m water depth, from rhodolith-beds to coralligenous build-ups. In particular, coralligenous build-ups are frameworks with three-dimensional structure that serve as shelter and provide storm protection by buffering wave action along coastlines. Coralline red-algae build-ups have high potentiality to be conserved in the fossil record. However, few fossil examples have been described in the literature and their evolution in the context of a stratigraphic cycle has seldom been modeled in detail. Wide marine terraces are preserved in the area of the Crotone peninsula, Ionian Calabria, southern Italy. They are related to the interplay between Pleistocene sea-level changes and the progressive uplift of the Calabrian arc from the middle Pleistocene onwards. These terraces overlie a Plio-Pleistocene slope succession (Cutro Marly Clay Fm). The two youngest marine terraces have been correlated with Marine Isotopic Stage (MIS) 3 and 5.1. Many authors have already studied the deposits of these terraces, defining their major stratigraphic features and facies, but very few details exist on their paleontological content. The deposits up to 10 m thick consist of mixed carbonate and siliciclastic sediments, in which red-algal reefs (= coralligenous build-ups) and other red algal facies are dominant. Stratigraphic sections in both terraces have been measured and sampled in order to obtain a complete spatial description of the terrace deposits. Samples have been collected both in the red algae facies and in the grainstone and sandstone that occupy the cavities within the main algal bodies. Thin sections have been prepared for red algae identification. A statistical analysis has been performed on the diagnostic anatomical microfeatures of the algal thalli. Bio-calcarenite have been disgregated in order to separate particles in a conservative way and conduct the quantitative paleontological analysis of the molluskan shell assemblages along with grain-size and chemical analyses. Species identification of bryozoans has been provided for facies dominated by this taxon. The coralligenous build-ups are dominated by Mesophyllum alternans (Foslie) Cabioch & Mendoza and Titanoderma pustulatum (Lamouroux) Nägeli usually alternated with bryozoans crusts. Other red algae species like Lithophyllum stictaeforme (• • Areschoug) Hauck, Phymatolithon calcareum (Pallas) W.H.Adey & D.L.McKibbin and Neogoniolithon sp. rarely occur. The molluskan assemblages in the grainstone associated to algal build-ups vary from typical coralligenous (C) to coastal detritic (DC), whereas they record an infralittoral environment in the uppermost unit. The paleontological results have been framed in the context of a genetic-stratigraphic interpretation of the marine terraces.