Facies analysis of four superimposed transgressive-regressive sequences formed during the two last interglacial-glacial cycles (Central Tuscany, Italy)

G. Sarti, D. Bertoni, M. Capitani, A. Ciampalini, L. Ciulli, A. C. Feroni, S. Andreucc i, G. Zanchetta, I. Zemb o, Facies analysis of four superimposed Transgressive-Regressive sequences formed during the two last interglacial-glacial cycles (central Tuscany, Italy). In this paper we present the results of a detailed facies analysis carried out on a set of 115 late Quaternary-Holocene stratigraphic sections from the northern Tyrrhenian coast (central Tuscany, Italy). The stratigraphic leitmotif is the cyclic alternation of coastal-marine and continental deposits grouped in four transgressive/regressive sequences (T-R1-4). The marine-coastal deposits constitute the transgressive base of each T-R sequence; to the top they are replaced by continental deposits that characterize the top of each T-R sequence. Three OSL dates provide the chronological constraints of the T-Rs. Marine deposits related to the last interglacial period (Marine Isotope Stage 5) constitute T-R1, which represents the base of T-R2. T-R2 consists of coastal dune deposits related to the last MIS 5 phase (MIS 5a). T-R3 consists of coastal dunes and marine deposits related to MIS 3. T-R4 (Holocene age) is occasionally preserved within the transgressive tract. The present-day altitude of MIS 5e (T-R1) sea-level markers suggests the occurrence of uplifting tectonic movements within the study area. Conversely, the evidence of the stratigraphic overlap of MIS 3 coastal dune deposits above the MIS 5 beachface sediments implies the activation of subsidence processes that are necessary to compensate the post-MIS 5 eustatic fall rate. As a consequence, the uplift processes responsible of the present-day outcrop elevations of MIS 5 sea-level markers occurred after MIS 3, pointing out a far more complex local tectonic history. This approach, based on facies analysis of the whole sedimentary succession, emphasizes the need of a consistent number of dates in order to better constrain the framework of the spatial-Temporal evolution. In the study area, this would enable to improve and/ or validate the temporal evolution of the local tectonics. As the context seems to be more complex than the one derived from the sole use of MIS 5e sea-level markers, we encourage the application of this methodological approach to different study areas.