The role of Middle-Late Pleistocene climatic cycles on the presence of offshore freshened groundwaters in the Adriatic Sea

The Adriatic Sea is developed in a foreland basin extending for several hundreds of kilometers along a predominantly NW–SE axis. The evolution of the Mid-Late Pleistocene Adriatic shelf margin is characterized by repeated climate-driven shoreline progradations and retrogradations, fed from Alpine and Apennine catchments. This cyclic behaviour is well recorded in the shelf margin topset stratigraphic architecture as stacked cyclothems, which reflect the alternation of shallow-marine, coastal and continental depositional environments in response to Quaternary climate oscillations. In recent years, several studies have linked sea level fall and lowstand conditions to the emplacement of offshore freshened groundwater (OFG) in continental shelf sediments.

In this study, we examine the relation between climate-driven cycles and the presence of offshore freshened groundwater in the north-central sector of the Adriatic Sea, stored in the overall progradational shelf margin of the paleo-Po fluvio-deltaic complex, through publicly available seismic and well-log data. The main goal of this work is to recognize the stratigraphic architecture of the low-salinity aquifer-bearing succession. The Mid-Late Pleistocene climate-driven cycles have been tied to the continuously-cored CNR well Venezia 1, allowing a precise dating of each cycle. Until ca. 600ky the shelf margin was still located within the present day Po Plain (filling the Pliocene marine gulf between the Alps and the Apennines) and reaching the present Po Delta around MIS 14. Later, several regressive pulses can be recognized, so that the shelf break gradually prograded up to 300 km in a southeastward direction.

Our preliminary results show that low-salinity water reserves are contained in the topsets of all these cycles, sometimes including shelf-edge deltas associated with falling-stage and lowstand systems tracts. The freshened waters fill reservoirs that are strongly diachronous, so that aquifers occur in progressively younger topsets in a seaward direction.