Fossil-diagenesis of a fossil coral reef from the Pleistocene of Fauglia (Tuscany, Italy)

A new palaeontological geosite has been discovered in the vicinities of Fauglia (Tuscany, Italy), in the Neogene Tora-Fine Basin. Here, an entire coral reef has remained “frozen in time” from Pleistocene times, exhibiting a peculiar fossil preservation. The studied outcrop extends over a 65 m-long artificial cliff where a 4-m-thick stratigraphic section is exposed. The section features an alternation of mudstones, clayey sandstones, and massive sandstones that host a reef of colonies of the Mediterranean scleractinian coral Cladocora caespitosa. The entire reef is covered by a thick layer of sand. The sedimentological features and the macrofossil assemblage suggest positioning of the outcrop in the Morrona Formation, which is locally referred to the early Pleistocene (Calabrian stage). The faunal association of the reef includes several species of echinoids, bivalves, gastropods, scaphopods, crustaceans, and cnidarians. Complex interactions between animals have also been recognized (e.g., corals growing around bivalves and Oichnus traces). Body fossils display a peculiar preservation style. Corals, mollusks and echinoids are mainly comprised of composite molds, inner and outer molds, and pseudomorphs; pristine shells are rare . Bivalves exhibit a geopetal structure that testifies for three stages of mineral precipitation, namely: the cementation of the terrigenous infill; the precipitation of large crystals filling the voids; the re-precipitation of the shell carbonate to form pseudomorphs. Microscope analyses revealed a calcite composition of all these phases. Subsequent stages of dissolution and re-precipitation of calcite are here hypothesized, revealing a complex and unusual diagenetic history for this Pleistocene coral reef.