Middle Eocene Climatic Optimum (MECO) impact on benthic and planktic foraminifera from some shallow water western Ligurian successions (Italy)

This PhD project was done to study the impact of the Middle Eocene Climatic Optimum (MECO) on foraminiferal assemblages in shallow-water setting of Western Liguria. In particular, the analysis focuses mainly on three shallow-water sections: Sealza, Capo Mortola and Olivetta San Michele, belonging to the Provençal Domain which underwent significant orogenetic events during the Late Cretaceous and Paleogene. This area yields a diverse micro- and macrofauna which permitted an integrated approach to understand paleoenvironmental variations and biotic responses related to climatic perturbations. The MECO is one of the most significant global warming events during the Eocene, characterized by a ~4–6°C temperature rise, and represents the best analogue to the ongoing climate change. Studying the responses of marine communities to the MECO is essential to predict potential future scenarios. The methodology used here includes field sampling techniques, sample preparation, biostratigraphy, sedimentological analysis, taxonomic and isotopic analyses. The MECO perturbation here provided a deep-time perspective on marine ecosystem resilience: while some taxa adapted to the new ecological conditions, others experienced lasting declines. The differential responses underscore the importance of biodiversity and ecological flexibility in mitigating the impacts of rapid climatic changes. The sedimentary records from the Ligurian region provided a detailed paleoenvironmental context for these biotic changes. In the Sealza section, changes in oxygenation and nutrient supply at the seafloor influenced biotic adaptation during the MECO. The marked decline in abundance of epifaunal benthic genera suggests a decrease in oxygenation which caused an increase in organic content and the consequent rise in infaunals genera that took advantage and proliferated. In addition, the planktic foraminiferal assemblages record the MECO warming in the water column as the warm-water index genera Acarinina and Morozovelloides increase in abundance and the cold-water index genus Subbotina marked decrease. In particular, the ecological changes induced by the MECO at Sealza led to a permanent restructuring of benthic and planktic communities, with no evidence of extinctions but with a transition to a new ecological regime. At Capo Mortola section, smaller benthic foraminifera showed only a little response to the perturbation, suggesting stability in oxygen and nutrient levels on the seafloor. In contrast, larger benthic foraminifera, such as Operculina and Discocyclina, thrived, showing remarkable adaptation to the new conditions while planktic foraminifera communities in the water column responded primarily to increased eutrophic conditions and hydrological changes, rather than temperature, underlining a differential impact of the MECO. Even in the Olivetta section, planktic foraminifera are more influenced by changes in the amount of nutrients rather that temperature with Subbotina that, despite being a cold-water index, rises up the water column, adapts to the increase in temperature and benefits from the increase in nutrients. In smaller benthic foraminifera assemblages, the epifaunal genus Heterolepa dominates and prevails over the others while the larger benthic ones are present only as reworked material. One of the key aspects that has been demonstrated in this work is that in shallowwaters the increase in temperature associated with the MECO event did not directly affect foraminiferal communities but affected the entire environment generated an intensification of the hydrological cycle and, consequently, increased precipitation in many areas. In this context, the impact on foraminifera varied depending on the local conditions of the section. It was not the high temperature that directly influenced their ecology, but rather the secondary effects of warming, like water depth, river influence, the reduction of light on the seafloor and the increase in the concentration of nutrients which created ecological stress for some taxa while others benefited from this increase. In conclusion, across all three successions, the MECO induced significant but varied ecological responses and the sedimentary records from the Ligurian region provide a detailed paleoenvironmental context for these biotic changes. The comparative study of these sections, using an integrated multi-proxy dataset, underscores the importance of local environmental conditions in mediating the biotic responses to global climatic events.