The shoreline in the Po Plain-Northern Adriatic basin during the Latest Messinian sea-level drop: 3D modeling and backstripping analysis

The Po Plain-Northern Adriatic basin (PPAF) offers a unique example of the Messinian Salinity Crisis (MSC) sedimentary evolution, happened between 5.96 and 5.33 Ma, in a high complex geologic setting. Recent papers published by the Eni E&P group after decades of study on the PPAF subsurface (Ghielmi et al., 2013, Rossi et al., 2015) added new fundamental constrains on the MSC evolution, moving the interest towards the Po Plain region. In detail, it is now possible to describe the 3D geometry and the facies distribution in the basin: a moderate deformed foreland slope/ramp ca.W-E elongated is extended from Veneto to the Northern Adriatic region; a southward prograding coastal wedge evolved during the MSC, recording relative sea-level changes. Seismic sections along the Western-Central Southern Alps margin and the Southern Alpine lakes show several deep V-shaped N-S oriented canyons; to the east in the Northern Adriatic-Venetian foreland, a strong evident intricate drainage network converges toward the foredeep axis in the south. Incisions are interpreted as the result of fluvial regressive erosion all around the marginal regions, close to the coast line due to latest Messinian sea level drawdown. Stratigraphic relationships on the decompacted S-prograding coastal wedge suggest the total lowering of the relative base-level did not exceed 900m (Ghielmi et al., 2013), which is less severe than ca.1500m sea level drop estimated by previous studies on the eastern and western Mediterranean margin. Facing this new scenario, derived from the availability of recent publications and new data analysis, In this study we propose the unraveled Latest Messinian coast line, modeling the 3D backstripping and the relative sea level fall on the Top Messinian/Base Pliocene surface, using TISC program (Garcia-Castellanos, 2002). The Latest Messinian topography is calculated as the result of a vertical surface restoration, in addition a the first attempt to remove the post-Messinian vertical tectonic component is performed. The main outcome defines the coast line position during the Messinian maximum lowstand, which strongly agrees with the fluvial network and the continental lithofacies distribution of the PPAF margin, visible by seismic and well log analysis. The modeled paleobathymetry of the depocenters implies a deep-water condition during the entire MSC period, confirmed by the absence of an erosive unconformity and the constant turbiditic sedimentation. According with 800-900m relative seal level drop, we argue a compartmentalization of the Po basin itself and the isolation of Adriatic sea from the rest of the Mediterranean basin. In the Po Plain the active thrust fronts acted as sills, dividing the Northern Apennine migrating foredeep in smaller sub-basins; the southern Italian Adriatic foreland is made by the Apulia carbonate platform, partially emerged during Messinian time. The Apulian western sector was involved exactly into the Late Messinian tectonic phase, growing thrust top basins filled by continental sediments (Matano et al., 2005). During the MSC lowstand, we suppose that the Apulia platform worked as a regional sill, protecting the Northern Adriatic basin from a complete desiccation or stronger erosive event.