Stable O and C isotope record for the lower Gelasian of Monte San Nicola (Gela, Sicily)

This thesis contributes to a broader ongoing project at the Department of Geoscience, aimed at reconstructing the long-term Early Pleistocene climate variability in the Central Mediterranean region, which is traditionally considered a key reference for this particular investigation area. In particular, the coastline of Southern Italy and Sicily hosts a well-exposed, expanded and richly fossiliferous stratigraphic record of the Plio-Pleistocene interval (ca. 5.3 to 0.1 Ma), which have been exploited in the last decades for establishing formal – i.e., globally validated – chronostratigraphic units. Among these, the base of the Gelasian Stage (ca. 2.6 to 1.8 Ma; Rio et al., 1998) marks the beginning of an intense cooling trend associated to the waxing and stabilization of vast glacial icecaps in the Northern Hemisphere. This episode is usually acknowledged as the “beginning of the ice ages". The climate changes associated to this event are documented in all 18O records globally by a triplet of severe glacial advancements (MIS 100, MIS 98 and MIS 96) that approximate the base of the Gelasian Stage. The Gelasian Stage marks the base of both the Pleistocene Epoch and the Quaternary Period (Rio et al., 1998). It was formally defined by a Global Stratotype Section and Point (GSSP) in the Monte San Nicola (MSN) section, close to the town of Gela (Southern Sicily). The MSN section satisfies all the requirements for a GSSP, being represented by an easily accessible, continuous, and expanded stratigraphy unaltered by tectonics and/or metamorphism, rich in fossils and yielding critical geochemical and geomagnetic markers of the boundary. Within the MSN section, dark, thin-laminated organic-rich layers known as “sapropels” provide extremely useful tools for intrabasinal and long-distance correlations, as well as accurate chronological constraints. Sapropels are usually barren of benthic faunas, being usually associated to mud settling in a deep-sea setting under anoxic conditions at the seafloor. Depositional models suggest that sapropels are the ultimate result of periods of massive freshwater input to the Mediterranean Sea during periods of increased precipitations, such as those promoted by the orbitally-driven intervals of maximum intensity of the African Monsoon. This would increase buoyancy at the surface and stratification of the water column, thus disrupting the deep-mixing and, eventually, ventilation at the bottom. Specifically, aim of this thesis is reconstructing a continuous and detailed benthic foraminiferal 18O record for the upper part of the MIS 100 – MIS 96 interval, which was so far investigated only partly and in low resolution.