Preliminary taphofacies analysis of a palaeoecologically diverse marine succession of the Mediterranean lower Pleistocene

In the Montalto quarry, in the vicinities of Fauglia (Tuscany, Italy), a lower Pleistocene (Calabrian) stratigraphic succession crops out. This succession is characterised by an alternation of sandstones, clayey sandstones and mudstones, featuring abundant fossils of invertebrates and plants. Throughout a 6-m-thick measured stratigraphic section, several different preservation styles can be observed (hence the recognition of different taphofacies) and a complex taphonomic history can be reconstructed. At the base of the section, in massive sandstones, accumulations of disarticulated bivalve shells and bivalve internal moulds are preserved in discontinuous lenses. In the overlying stratum, infaunal molluscs such as Panopea are preserved in life position, as calcite-cemented internal moulds and rare external moulds. Isolated blocks of external moulds of Cladocora caespitosa frames are found in the clayey sandstone above, together with pectinids preserved as original shells. Overlying this unit, a sandy mudstone interval hosts several well-preserved vegetal remains, including a horizon that is rich in exceptionally preserved specimen of Posidonia oceanica with both rhizomes and leaves. In the overlying strata, Cladocora caespitosa occurs as forming a conspicuous coral reef, primarily appearing as isolated blocks consisting of compound moulds and recrystallised corallites developing upwards into a fully developed bioconstruction that is mainly preserved as external moulds. In this unit, bivalves are partially or completely recrystallised, and they also exhibit geopetal structures that testify to at least three stages of mineral precipitation, namely: the cementation of the terrigenous infill; the recrystallization of the aragonitic shell material; and the precipitation of large crystals filling the remaining voids. Microscopic analyses revealed a calcite composition for all these phases. All the materials that were sampled from this unit become luminescent under UV light excitation, suggesting a high content of elements that comprise luminescent centres such as manganese (Mn). At the top of succession, pectinids, oysters and barnacles, which are predominantly composed by calcite, are preserved as original shells. Subsequent stages of dissolution of aragonite and calcite and re-precipitation of calcite are here hypothesised, with different diagenetic paths for each taphofacies revealing a complex and much peculiar diagenetic history for this Pleistocene fossiliferous succession.