Paleoecology and dynamics of coralline dominated facies during a Pleistocene transgressive–regressive cycle (Capo Colonna marine terrace, Southern Italy)

摘要

The Upper Pleistocene deposits of Capo Colonnamarine terrace (Calabria, southern Italy) contain a volumetrically important record of red algal facies developed during a transgressive–regressive cycle, well-expressed along a nearshore–offshore transect. This setting presents an ideal opportunity for the acquisition and interpretation of paleoecological information on coralline-dominated deposits and their response to relative sea level changes. The Capo Colonna deposits include rigid build-ups, rhodolith accumulations, and a maerl bed. The build-ups, identified as a fossil example of the present day Mediterranean coralligenous, are primarily formed by Mesophyllum alternans and, subordinately, by Lithophyllum stictaeformae, Titanoderma pustulatum and Lithothamnion sp., rarely alternatingwith encrusting bryozoans. Fruticose praline rhodoliths occur in a packstone bed, up to 160 cm thick, 2 to 5 cm in size and composed of Lithothamnion sp., Mesophyllum sp., and rare T. pustulatum. The maerl bed is about 60 cmthick and laterally continuous for several tens of meters, and consists of interlocked unattached red algal branches of the species Lithothamnion corallioides, Phymatolithon sp., Lithophyllum sp., and Lithothamnion sp. The lateral distribution along the shelf profile of different red algal facies was influenced by transgressive–regressive trends. While praline rhodoliths and the maerl bed developed on mobile substrates mostly during the early highstand, respectively at intermediate and distal shelf sectors, the Mesophyllum-dominated coralligenous build-ups continued to grow for most of the regressive phase, progressively occupying all the preserved paleoshelf profile during sea level fall and resulting in a characteristic ecological vertical succession of crustose algae facies in the distal segment of the transect.Differences in substrate types determined variability in the coralligenous morphologies, with dome to mushroom shapes starting from discontinuous blocks of a basal conglomerate, and WE elongated platforms developing from a hardground and from rhodolith beds. Eventually, the development of red algal deposits became in itself the dominant control on substrate type. The red algae rich deposits of Capo Colonna marine terrace not only suggest a relationship between available substrate and geomorphological expression of the coralligenous build-ups, but also provide a framework for the paleoecological interpretation of other Neogene and Quaternary rhodalgal deposits from the Mediterranean region.