The pleistocene marine terraces of Le Castella and Capo Colonna (Calabria, Southern Italy): a paleoecological study of the coralligenous build-ups and associated bioclastic facies

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. 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. Coralline red-algae build-ups are frameworks with 3-D structure that serve as shelter and provide storm protection by buffering wave action along coastlines. For this reason coralline build-ups have high potential of preservation. However, few fossil examples have been described in the literature and their evolution in the context of an eustatic 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 present paleoecological study aims at describing biogenic marine terrace deposits from Capo Colonna, correlated to Marine Isotopic Stage5.1 and 3. Stratigraphic sections have been measured and sampled at each visible facies change. Thin sections have been prepared for red algae identification. The deposits up to 10 m thick consist of a Plio-Pleistocene slope clay unit overlain unconformable by a transgressive erosional surface and a shallow-marine succession, in which well-developed Pleistocene temperate red-algal reefs and their associated deposits are dominant. Stratigraphic sections have been measured and sampled at each visible facies change. Thin sections have been prepared for red algae identification. Bioclastic calcarenite units have been disaggregated in a conservative way to conduct paleontological, sedimentological, chemical and statistical analyses. Species identification of bryozoans has been provided for facies dominated by this taxon. The coralligenous build-ups are the most common facies, formed metrical structures, and developed as coralligenous de plateau, or alternatively, as coralligenous on hard substrate. The coralligenous build-ups of Capo Colonna form algal reefs dominated by 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. occur. Moreover crustose coralline algae (CCA) are the dominant biogenic-carbonate producers, and form other facies in the deposits, like prâline rhodoliths or maërl bed. The occurrence of other CCA facies led to a high detailed interpretation of the temporal evolution of marine terrace deposits, in the framework of the Mediterranean benthic bionomy. The coralligenous build-ups of Le Castella 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 dominance of M. alternans in both marine terrace coralligenous build-ups suggests infralittoral paleoenvironmental conditions. The molluskan assemblages in the packstone occupies the base of the deposits represent a Posidonia meadows paleoenvironment, whereas the grainstone associated to algal build-ups vary from typical coralligenous (C) to coastal detritic (DC), to an infralittoral environment in the uppermost unit, with species linked to AP/HP biocoenoses. The paleontological results have been framed in the context of a genetic-stratigraphic interpretation of the marine terraces to reconstruct a temporal evolution of both marine terrace deposits.