MINERALOGY AND OXYGEN ISOTOPE PROFILE OF PELECYORA GIGAS (VENERIDAE, BIVALVIA) FROM TUSCAN PLIOCENE

a specimen with joined valves of Pelecyora gigas, an extinct species, was collected in a sandy layer of Early Pliocene age in the northern part of the Siena Basin (Tuscany, Italy). XRD data demonstrated that the original mineralogical composition of the specimen was aragonitic and it maintained substantially the original structure and composition. Neglecting possible changes in sea salinity during different seasons, we can estimate, using oxygen isotope composition a maximum seasonal temperature differences of ca. 9 °C experienced during the life of the individual. An approximate estimation of past sea water composition allows to calculate an average temperature of 23.0±2.7 °C for the water where the shell lived, whereas calculated temperature extremes are 18.5 °C for the colder season and 27.6 °C for the warmer. These data are in a good agreement with those proposed on the basis of the Pliocene Mediterranean taxa nowadays living along the western African shores.