Insights into the Eocene stratigraphic succession of the Lessini Mountains volcanic district by integrating field geology and geomorphological interpretation of Red Relief Image Maps from high resolution DTM (CARG Project, Sheet 124, Verona Est, Italy)

The Lessini Mountains volcanic district (Venetian Prealps, Italy), belonging to the Veneto Volcanic Province, is mainly composed of Paleogene basaltic volcanics in complex stratigraphic and tectonic relationships with a Meso-Cenozoic sedimentary succession of a shallow-marine environment. The geological framework was shaped by extensional tectonics, with N–S-trending faults such as the Castelvero Fault, which separates the mafic rocks to the east from the carbonate lithologies to the west. The volcanic succession is characterized by a relative lithological homogeneity of basic volcanic products and by discontinuous outcrops due to dense vegetation and agricultural cover. Consequently, detailed reconstruction of the internal stratigraphy based on field data alone is challenging and requires further investigation to identify stratigraphic reference horizons. Overall, the succession records a transition from submarine to subaerial volcanism (Barbieri et al., 1991; Brombin et al., 2019). The lower portion is characterized by basaltic deposits emplaced in a marine environment (i.e., hyaloclastites to lava flows of fissural eruptions), frequently intercalated with Nummulitic Limestones which testify to phases of quiescence of the volcanic activity. The upper portion reflects the establishment of predominantly subaerial conditions, with the growth of shield volcanoes. Above the last nummulitic level (the Roncà Horizon), marking the base of the upper part of the volcanic sequence, the internal stratigraphy remains poorly constrained, as no laterally continuous stratigraphic markers have been recognized so far. This study focuses on this part of the volcanic succession, exposed along the ridges between Alpone Valley and Agno Valley, through the integration of remote-sensing analyses and detailed field observations. In recent years, the increasing availability, quality, and spatial resolution of remote-sensing data have made geomorphological analyses based on Digital Terrain Models (DTMs) an increasingly important complement to traditional geological investigations. Among the available visualization techniques, the Red Relief Image Map (RRIM) method has proven particularly effective in highlighting subtle morphological variations in volcanic terrains (Chiba et al., 2008; Favalli & Fornaciai, 2017). Within the framework of the CARG Project (Sheet 124 – Verona Est), RRIM-based geomorphological analysis integrated with detailed fieldwork provides new constraints on the stratigraphic reconstruction of the upper volcanic succession of the Lessini Mountains. A key result is the recognition of a decametre-thick volcaniclastic sedimentary level, mapped as the Cortivo Unit, clearly detectable in RRIM by its association wiht areas of lower slope gradients. This unit records a significant phase of volcanic quiescence, during which erosion, transport, and deposition processes led to the reworking of previously emplaced basaltic rocks. It therefore represents a stratigraphic hiatus and a marker horizon that subdivides the succession into a lower unit predating and an upper unit postdating the Cortivo Unit. Future geochemical and petrographic analyses and radiometric dating will allow calibration and refinement of the reconstructed stratigraphic framework.