From the Messinian Salinity Crisis to the Quaternary Ice Age: Geological Evolution of the Western Mediterranean Sea. Evidences from the West Sardinian margin and the Valencia Trough

This thesis investigates the different settings of sediment deposition and consequent seismic facies in the western Mediterranean Sea during the Plio-Quaternary (PQ) age, focusing on the West Sardinian margin and the Valencia Trough. The study spans from the end of the Messinian Salinity Crisis (MSC) to the present day, examining how post-MSC sea-level changes and subsequent climatic shifts shaped sedimentary processes, particularly during the Pliocene epoch and Quaternary period. The MSC, which isolated the Mediterranean from the Atlantic Ocean, led to significant evaporite deposition which also affected the PQ sequence. Subsequent climatic fluctuations, including the onset (ca. 3.8 Ma) and later intensification of Northern Hemisphere Glaciations (iNHG) around 2.6 Ma, significantly affected sediment deposition patterns in the Mediterranean. The primary aim of this project was to analyze the Plio-Quaternary sedimentary sequence using seismic reflection data to better understand the mechanisms driving the facies transitions observed in the PQ sequence across multiple Mediterranean basins. Additionally, this study addressed the effects of tectonics, halokinesis and volcanism shaping the West Sardinian margin and influencing depositional patterns during the PQ. Active halokinesis, initiated during the deposition of the Messinian Upper Unit (UU), is shown to be an ongoing process, peaking during the Pliocene. Seismic analysis revealed offshore volcanism that correlates with known Oligo-Miocene and Pliocene magmatic events. Fault reactivation and margin tilting appear to be closely linked to thermal subsidence, isostatic adjustments and sea-level oscillations, highlighting complex interactions between tectonics and sedimentary processes. These factors influenced sedimentation patterns, driving the formation of clinoforms and canyons. The canyons of the West and South Sardinian margins are not inherited from the MSC but are linked to glacio-eustatic sea-level changes. Conversely, in the Valencia Trough, the PQ sequence records the evolution of the Valencia Channel and its surrounding margins, showing that this mid-ocean channel was first shaped during the MSC and reactivated in the Quaternary after a period of inactivity during the Pliocene. The channel’s reactivation during the Quaternary reflects the influence of sea-level fluctuations and increased sediment supply from the Iberian margin, while its inactivity during the Pliocene represents the globally stable climate of that period. A key result of the study is the identification of the horizon coinciding with the transition from the Pliocene to the Quaternary, called A0 in the West Sardinian margin and BQD in the Valencia Trough. This horizon separates two distinct seismic facies within the PQ sequence, a more transparent lower unit (Pliocene) and a more reflective upper unit (Quaternary). This diferrent seismic signature is observed in several Mediterranean basins and aligns with the Pliocene-Quaternary boundary, leading to the correlation with the intensification of the Northern Hemisphere Glaciations, well documented in sedimentological and oxygen isotope records. Given the widespread presence of the two distinct facies in multiple Mediterranean basin, in fact, their differences appear to not be related to local geological events, but rather reflect global climatic shifts. By correlating seismic facies with climatic variations, this study provides a new framework for interpreting seismic data in relation to global climate cycles. This approach not only enhances our understanding of past climate changes but also offers a valuable tool for predicting future sedimentary responses to ongoing climatic shifts.