Benthic foraminiferal proxies of environmental changes during the pre-Messinian salinity crisis of the Sinis Basin (W Sardinia, Mediterranean Sea)

The Messinian succession cropping out in a marginal basin of the Mediterranean Sea (Sinis Basin, W Sardinia) was studied in its benthic foraminiferal content in order to investigate the main palaeoenvironmental changes occurring. A shallowing upward depositional trend, from an upper bathyal-circalittoral environment to a coastal lagoon, was recognized during the pre-Messinian Salinity Crisis. In the lower part of the analyzed succession (Capo San Marco Formation), upper bathyal-circalittoral conditions are suggested by species with a wide depth-range, such as Cibicidoides pseudoungerianus, Melonis pompilioides, Oridorsalis umbonatus, bolivinids and buliminids. In the middle part of this formation, the progressively shallowing environment is indicated by the low abundance of planktonics coupled with the upward increase of shallow-water epiphytic species (Lobatula lobatula, Elphidium crispum, E. macellum, Ammonia beccarii, Hanzawaia boueana). The progressive marine restriction led to the development of hypohaline conditions typical of lagoonal environments as suggested by Ammonia tepida and oligotypic macrofaunas. The succession stops with the deposition of laminated limestones barren in fossils (Sinis Laminated Limestone Formation). A mixed siliciclastic‑carbonate platform (Torre del Sevo Formation), characterized by fluvial deposits intercalated in the marine succession, developed as suggested by benthic foraminifera, ostracods, very rare planktonic species and macrofaunas. Sinis Laminated Limestone Formation and Torre del Sevo Formation constituted part of the Terminal Carbonate Complex, strongly eroded by the Messinian Erosional Surface (MES) at its top. The palaeoecological conditions in the Sinis Basin were intermittently suitable for sustaining full-marine biota, indicating that this marginal basin was not constantly desiccated during the pre-Messinian salinity crisis.