A thousand-year journey of lithification: CT-analysis and radiocarbon dating of algal reef from Central Mediterranean

Calcareous algal reefs are Mediterranean carbonate structures, formed by coralline red algae, that display early lithification and preserve key geobiological records. These structures exhibit complex three-dimensional frameworks influenced by environmental conditions and biological interactions, but their lithification processes, porosity evolution, and long-term growth patterns remain poorly understood. In this study, we use Computed Tomography (CT) scanning and radiocarbon dating on four coralligenous build-ups collected along a depth gradient offshore Marzamemi, SE Sicily, to investigate internal skeletal density, porosity distribution, and age profiles. Our findings reveal that lithification progresses gradually from High-Density (HD) to Ultra-High-Density (UHD) material, correlating inversely with porosity. Radiocarbon dating indicates a lithification timeline of roughly 1000 years, with the oldest, densest material dating back over 5000 years. The structures demonstrate a depth-density and age-depth gradient: deeper and older build-ups exhibited higher quantity of UHD material, whereas younger, shallower build-ups contain a higher proportion of HD material. Additionally, evidence suggests that specific build-ups may have been fragmented and relocated due to environmental or anthropogenic factors, further influencing growth patterns. The CT-analysis contributes to improving knowledge on coralligenous reef formation and evolution, underscoring the role of lithification in maintaining structural stability over millennia and providing insights applicable to the study of fossil reef systems.