Facies associations map of the Pliocene marine deposits of the central-southern Siena Basin (Tuscany, Italy)

The Siena Basin is a post-collisional basin of the inner Northern Apennines (Tuscany, Italy) characterized by a thick siliciclastic Neogene infill, mainly composed of marine sediments with subordinate alluvial deposits close to basin margins. The central-southern sector of the basin shows a more complex stratigraphy with the occurrence of sandy deposits also in distal areas, far from the basin margin. The aim of this paper is to provide a new 1:10,000-scale geological map of this key sector (about 45 km2) of the Siena Basin, helpful for a better reconstruction of its sedimentary evolution. The new fieldwork was based on the identification and mapping of different facies associations (expression of different sedimentary environments), whose shifts in time and space provide elements to understand the basin-fill history. The recognition of two main intra-Pliocene erosional surfaces allowed the subdivision of the succession into three alloformations. Therefore, a more complex depositional history, with respect to the previous knowledge for this key-sector of the Siena Basin, has been reconstructed, thus highlighting the importance of this kind of approach with respect to the classical lithostratigraphic criteria.