ASSESSING SPECIES-ENVIRONMENT RELATIONSHIPS AND PALAEOENVIRONMENTAL GRADIENTS BY MEANS OF SEDIMENTOLOGICAL AND BIOLOGICAL (MOLLUSCS-OSTRACODS-FORAMINIFERS) SIGNALS

Integration of facies analysis, sequence stratigraphy and multivariate ordination techniques represents a powerful synergy able to provide an improved understanding of the ecological factors governing species-environment relationships and their evolution through time. Through application of detrended correspondence analysis (DCA) to a composite fossil (ostracods, foraminifers and molluscs) dataset from the post-glacial succession of Core M3, in the Arno coastal plain (Tuscany), we offer a refined picture of stratigraphic variations in faunal content from a paralic depositional setting, and reconstruct the palaeoenvironmental gradients that account for such variations. Despite distinct ecological behaviours and taphonomic and sedimentological constraints, a strong ecologic control on meio- and macro-based biofacies and taxa turnover is documented across the study succession. Among all possible mechanisms that may play a role in ‘shaping’ fossil distribution, the ecological signal driven by salinity represents the most fundamental parameter controlling composition of fossil associations in the cored succession. DCA performed on mollusc associations can even provide outstanding quantitative estimates of palaeosalinity along the sampled core. When plotted stratigraphically, the three fossil sub-datasets show consistent patterns of vertical evolution that enable prompt identification of the key surfaces for sequence stratigraphic interpretation in otherwise lithologically indistinguishable deposits.