Unraveling the coast line in the Po Plain-Northern Adriatic region during the late Messinian sea level drop

The Po Plain-Northern Adriatic foreland basin (PPAF) offers an unique record of the late Messinian Salinity Crisis (MSC) in the Mediterranean region in various geological settings consisting of deep-water turbiditic basins and a series of marginal and intra-slope basins, including the foreland. Most studies on the MSC have focused on the western and eastern offshore Mediterranean Sea whereas few studies have focused on the onshore areas; the marginal position and the syn- to post-Messinian tectonic activity shaped a more complex context to study. A majority of these studies interpret a progressive evaporation of the basin during the acme of the MSC, estimating a sea level drop of 1000 to 1500m, based mainly on erosion surfaces identified in seismic imaging. In the PPAF the stratigraphic relationships into a decompacted Messinian coastal wedge, suggest that the total lowering of the relative base-level did not exceed 900m (Ghielmi et al., 2013). The aim of this study is to apply the 3D backstripping technique to restore the vertical position of the Base Pliocene regional surface at the PPAF. The results are compared with the coast line position at that time derived from seismic and lithofacies studies (Eni data). The new topography and bathymetry are calculated as the result of flexural isostatic compensation of Plio-Quaternary sediment removing and water column changes during the maximum MSC lowstand. To perform the backstripping we make use of TISC software (Garcia-Castellanos, 2002) to calculate the vertical flexural isostatic motions with an elastic thin plate approach and laterally-constant lithospheric elastic thickness. The surfaces used as inputs are: DEM by TOPO30 project, latest Messinian unconformity (after interpretation of Eni seismic lines for the local framework) and top of the Mesozoic carbonate succession. The required parameters into the decompaction algorithm are calculated from lithological log analysis on the deepest hydrocarbon wells (Eni data), reaching the complete pre-Messinian sedimentary succession. Our restored surface and the resulted coast line position after the considered 850m relative sea level drop, agrees and supports previous studies on facies associations distribution of the entire PPAF. In addition in the northern sector of the PPAF, a network of valleys can be observed, extending several tens of km and linked to the foredeep where turbidite systems persisted in the deeper zones throughout the whole MSC.