SEA URCHIN ASSEMBLAGES FROM THE MIOCENE OF SARDINIA AND THEIR RELEVANCE TO RECONSTRUCTING OCEANOGRAPHIC AND CLIMATE CONDITIONS OF THE MEDITERRANEAN TETHYS

Echinoids provide excellent possibilities for using skeletal features to reconstruct modes of life, biofacies as well as inferring past oceanographic conditions. Various depositional environments from different depths are present in Miocene sediments from Sardinia which contain a rich echinoid fauna. Ongoing studies on these faunas have shown how taxonomic richness and preservation potentials vary among different sedimentary environments along shelf gradients. The study includes detailed investigation of stratigraphy, sedimentology, palaeontology and taphonomy in both the field and in the laboratory. Emphasis is placed on composition, diversity and abundance of various fossils, reconstructing life habits using functional morphology and recording various taphonomic signatures.

These investigations have revealed: 1) mass accumulations of clypeasteroid echinoids including autochthonous assemblages to multiple in situ reworked accumulations in shore face environments, 2) specific studies on the distribution of morphotypes of the common genus Clypeaster, 3) echinoid assemblages dominated by various taxa of both irregular and regular echinoids in siliciclastic and carbonate shelf environments, and 4) the origin of well preserved monotypic shell beds of both regular echinoids and spatangoid from deeper water, siliciclastic environments.

Differences in the presence and diversity of the various echinoid taxa are related to biotic and abiotic ecological factors and preservation based on skeletal architectures and taphonomic bias. The distribution of faunal diversities and preservation potentials are shown along a gradient ranging from shoreface to deeper water. These are correlated to other echinoid biofacies occurring in the Miocene of the Mediterranean Tethys thus allowing the environmental, geographic and climate controls of these important benthic macrofaunal elements to be assessed and compared.