Serpulid build-up from Miocene last tropical ecosystems in SE Sicily

A small carbonate bioconstruction, consisting of serpulids (Annelida, Polychaeta) of the genus Spirobranchus and micrite, is described from the Upper Miocene of the Monte Carrubba Formation at Faro Santa Croce, Augusta (southeastern Sicily). The build-up is lens-shaped and consists of serpulids forming roughly alternating layers of tubes with erect distal ends subparallel to one another, and layers with irregularly coiled tubes. Fine micrite sediment partly detrital (i.e., likely derived from physical processes) and partly autochthonous (i.e., putatively induced by in situ heterotrophic microbial activity) fills the inter-tube spaces. The build-up presumably formed in a shallow-water intertidal/subtidal palaeoenvironment, where scattered hard substrates within predominantly soft bottoms were colonised by serpulids. The tubes were subsequently encrusted by conspecifics and other epibionts, including coralline algae and bryozoans. Rapid micritic infilling stabilized the 3D skeletal structure of the serpulid tubes, preventing total collapse despite significant fragmentation. Post-depositional processes locally caused tube dissolution and pervasive diagenetic recrystallization. The occurrence of this serpulid build-up highlights local habitat heterogeneity in the Mediterranean during the Late Miocene, a critical interval of environmental change that remains poorly understood. It also represents the first documented Upper Miocene serpulid-dominated build-up from the Mediterranean and other open-marine settings, complementing the Middle Miocene record of serpulids-microbialite bioherms known from the Paratethys.