Pre to syn orogenic evolution of the European margin: clues from the Flysch units of the Ligurian Alps (CARG Project – Ormea sheet 244).

Our research is part of the ongoing geological fieldwork aimed at creating the 1:50,000 scale "Ormea Sheet" (n. 244) within the framework of the CARG Project (Italian National Geological Cartography). The goal is to integrate existing data and observations to reconstruct the structure and evolution of the European (Alpine) margin. The study area is located in the Ligurian Alps, the southeastern end of the Western Alps. This region is crucial for understanding its geodynamic evolution, as the contact between lithological units from different domains is preserved (e.g., the Briançonnais domain representing the European passive margin and the Piedmont-Ligurian sedimentary covers corresponding to the oceanic domain). The structural framework is characterized by thrust sheets, superimposed non-cylindrical folds, and local deformations, which provide evidence of a complex polyphase tectonic evolution. These units underwent low-grade Alpine metamorphism, partially overprinting and reworking the original sedimentary structures and features.        
Our work focuses on the Flysch Units outcropping within the Ormea Sheet, particularly the formations that constitute the Colla Domenica-Leverone unit, as referred to in the literature. Previous authors have hypothesized that these turbidite systems were deposited in an abyssal plain, resulting from the rifting and spreading of the Piedmont-Ligurian Ocean. These systems are characterized by basal complexes made up of thinly bedded turbidites, often containing olistostromes, followed by sand- or carbonate-rich turbidite systems (Decarlis et al., 2014), which are interpreted as trench environment deposits (Di Giulio, 1992). 
During the advancement of the accretionary wedge towards the European foreland, these sedimentary units underwent a migration and stacking process, resulting in an inverted stratigraphy, with the oldest unit at the topmost part of the nappe pile. Our intense fieldwork revealed an erosional boundary between the Arnasco-Castelbianco and Borghetto units and the overlying Colla Domenica and Leverone formations, differently from previous assumptions of a tectonic surface, essentially revisiting the idea of classifying the Colla Domenica-Leverone as a tectonic unit.            
Moreover, we are investigating the origin of the sediment supply through various analyses. Different basalt samples collected from the chaotic event in the Colla Domenica Shale, analyzed using ICP-MS and XRF instruments, show compositional similarities with the results proposed by Saccani et al. (2008) for the basalts from the Balagne region (Northern Corsica). This preliminary evidence suggests that these formations filled the closing oceanic basin (as proposed by the model of Pandolfi et al., 2016) through mass transport events originating from different areas, likely from the European margin and the front of the accretionary wedge.          
Additionally, petrographic analyses of sandstone samples are in progress to identify the source areas, and biostratigraphic analyses have been performed to provide additional time constraints to complement the limited existing data. We are currently working on stratigraphic logs to describe in detail the facies and boundaries of these formations.