Tracking paleoenvironmental changes in coralline algal-dominated carbonates of the Lower Oligocene Calcareniti di Castelgomberto formation (Monti Berici, Italy)

Lower Oligocene, shallow-water carbonates of the Calcareniti di Castelgomberto formation (Monti Berici, Italy, Southern Alps) are studied in detail with respect to fabric and component distributions in order to trace paleoecological changes along a monotonous sedimentary stacking pattern. The carbonates are dominated by coralline algal rudstones with a packstone to wackestone matrix. Non-geniculate coralline algae include six genera: Lithoporella melobesioides, Mesophyllum, Neogoniolithon, Spongites, Sporolithon, and Subterraniphyllum. The algae are found in the form of encrusting thalli, rhodoliths, and coralline debris. Non-algal components include larger, small benthic, and planktonic foraminifera associated with bryozoans, zooxanthellate corals, and echinoderms. Four carbonate facies are distinguished: (1) coralline algal facies, (2) coralline algal-coral facies, (3) coralline algal-larger foraminiferal facies, and (4) coralline algal debris facies. Marly horizons also occur in the section. The facies and coralline algal content are interpreted with respect to light intensity, hydrodynamic energy, biotic interactions, and substrate stability. Facies development along the studied section shows systematic variations, suggesting asymmetric sea-level changes with rapid regressions and gradual transgressions.