Shallow-water sedimentary environments across the MECO as recorded in NW Italy: palaeodiversity and palaeoecological constraints.

During this work we have sampled and analysed over 150 meters of sedimentary succession outcropping in three localities in NW Italy near Ventimiglia (Olivetta San Michele, Capo Mortola and Sealza) as they were deposited during the Bartonian and therefore possibly containing signals for the Middle Eocene Climatic Optimum (MECO) event.

The MECO has been identified in all three sections by means of both isotopic shifts and biostratigraphic markers (larger benthic foraminifera, planktonic foraminifera and nannofossils). The three sections have been studied for gamma ray emissions variations, microfacies analyses, Rockeval and lithostratigraphic variations. Even if the three sections are all deposited in a relatively similar environment and are separated by few kilometers today, they display three different sedimentary successions both before, during and after the MECO. We observed that each succession has its peculiar lithological variations that do not seem to correlate with the other sections. The only similarity is that they record a transgressive trend from very shallow deposits to deeper settings as testified by the nummulite rich calcarenites covered by planktonic foraminifera marls. In spite of this similarity, some successions have heterolithic conglomerates at their base, whereas others have thick Microcodium-rich successions almost barren of any body fossils. The successions develop very different taxonomic richness, from extremely rich in nummulites, to much more diverse with abundant corals, mollusks, echinoids and a highly diversified foraminiferal association. The MECO in two sections is characterized by a drastic change in faunal composition, whilst in the other does not seem to be characterized by any faunal variation. From a lithological perspective, we observed that a sharp increase in the marly component seems to be present exactly during the MECO; but again this is only true for two out of three sections. Data also cannot completely rule out whether the finer material can be either caused by enhanced runoff due to instable climatic conditions, or if tectonic activity has increased its stress on the sedimentary conditions, or, alternatively, both factors combined.