• Coral bioconstruction. As a result of the extremely irregular and articulated substrate, the coral buildup appears as an organized lens-shaped structure, and its core is constituted by a relatively dense coral domestone with a moderate

•increase of platy corals in the upper part. A coral rubble associated with granitic cobbles and pebbles is locally present at the base. The inter-coral sediment consists of poorly sorted bioclastic wackestone to packstone. Results

•from this study clearly show evidence for the occurrence of a former submerged granitic substrate that, as very rarely documented in the geological record, is here interpreted as the subtidal substrate for growth of a small bioconstruction

•under relatively high energy and clear water conditions. The Cala di Labra bioconstruction is overlain by a finingupward quartzose conglomerate and sandstone succession interpreted as deposited in a coastal setting near fluvial

•point sources. The demise of coral growth was caused by a regressive event and by the consequent quite-sudden burial and related changes of trophic conditions. The inter-coral sediment consists of silt-size bioclastic debris dominated by benthic foraminifera, red algae and bryozoans.

•The terrigenous fraction generally does not exceed 30 % and is dominated by lithic fragments (granite) and by quartz and feldspar grains. The coral unit is overlain by a 10-m-thick unit of finingupward, dominantly quartzose to bioclastic sediment. The first 5 m are represented by a fine conglomeratecharacterized by 1 to 2-m-thick amalgamated beds with massive to crude stratification, and moderately sorted, subangular to subrounded pebbles. The conglomerate contains highly fragmented and abraded bivalves, echinoderms, barnacle fragments, and minor encrusting bryozoans and larger benthic foraminifera (Heterostegina). The upper portion of the unit (6 m thick) consists of coarse bioclastic quartz sandstone. The bioclastic sandstone is low-angle tabular–planar and trough cross-stratified, and contains fragmented and abraded oysters, pectinids and echinoids (clypeasteroids). Amalgamated hummocky cross-stratification, with both convex-up and convex-down internal beds up to 10 cm thick, is also locally present.