The Pleistocene evolution of algal bioconstructions (reefs and rhodoliths) in the marine terraces of Crotone (Southern Italy)

The abundant and protracted record in the same area over multiple subsequent highstands outcrops of the Mid and Upper Pleistocene marine terraces of the Crotone peninsula represent an exceptional and strategic site for the study and interpretation of the crustose coralline algae (CCA) facies evolution, through their distribution, stratigraphic relationship, geomorphology, paleogeography, substrate and main bioengineers of the most important framework builders outside the intertropical belt. All these elements allow detailing the paleoenvironmental and paleoceanographic contexts related to the most important and recent climate oscillations of the past in the Mediterranean. This work aims to present a summary of the main features of fossil CCA facies by numerous studies carried out on these terraces (Cutro MIS7 or 9, Capo Colonnia MIS 5c or 5a, Le Castella MIS 3), and to provide new data on terraces so far not yet thoroughly investigated (Campolongo MIS 5e, Torre Brasolo MIS 5c). Algal reefs (= coralligenous) are widespread. They represent the most abundant facies, developing on mobile substrates like shell accumulations (Le Castella), rhodoliths, as fossil example of coralligène de plateau (Cutro, Capo Colonna), and basal conglomerate (all terraces). All substrates have a sub-horizontal geometry. From the geomorphological point of view, tabular reliefs characterize only the central portion of Capo Colonna, while in all other cases they are discrete reliefs. The maximum size of discrete reliefs, however, is variable, from a minimum of few decimeters (Le Castella, Capo Colonna, Campolongo) up to 2 m (Cutro, Torre Brasolo), the latter exceeding the present-day Mediterranean reports known so far. Algal reefs correspond to different geographic paleo-contexts. At Le Castella, they developed in a relatively protected area with low hydrodynamics and abundant mud (open framework). At Capo Colonna, dense algal frameworks occur both as proximal, relatively fast-growing reliefs, and distal, circalittoral outcrops. Titanoderma pustulatum, which is presently an uncommon report as primary bioengineer, dominates the bioconstructions of Cutro and is abundant in Le Castella. It is associated with an important fine sedimentation, resulting in abundant matrix in the studied deposits. At Capo Colonna, Mesophyllum alternans and Lithophyllum stictiformae are abundant, compared to presentday temperate Mediterranean algal reefs. The abundance ratio between the two has been used as an indicator of paleo-bathymetry, but this concept requires further investigation. Praline rhodoliths are reported both at Cutro, with spheroidal rhodoliths dominated by Sporolithon ptychoides (the most abraded, transported, warmer water) and T. pustulatum (the best preserved, mud tolerant), and at Capo Colonna, where Lithothamnion spp. dominate in an infralittoral paleoenvironment. Distal outcrops at Capo Colonna contain a maerl bed, multi-specific as the present Mediterranean maerl beds, and corresponding to the deepest circalittoral facies detected in the deposits. CCA facies showed a high variation in relative similar paleo-contexts, but the details of their specific features allow a more detailed depicting of the Pleistocene evolution of the area.