Potential Offshore Groundwater Reserves from the Late Quaternary Succession of the Western Central Adriatic System (Italy): A New Frontier for Integrated Sequence-Stratigraphy and Source-To-Sink Analysis?

The research for unconventional groundwater reserves stored in the continental shelf may represent one of the future challenges for geoscientists. Despite genetic differences and multifaceted approaches, source-to-sink (S2S) and sequence stratigraphic analysis can be helpful, when used in synergy.

Coastal plain-to-shelf stratigraphic correlation of Last Glacial Maximum deposits from the western Central Adriatic sector (Italy) allowed testing a source-to-sink approach for the exploration of offshore groundwater reserves contained in buried lowstand fluvial deposits (LST). The LST reservoir, up to 25 m thick, can be tracked continuously from the coastal-plain paleovalleys to about 30 km away from the modern shoreline. In offshore position, the LST is sealed by a mud-dominated wedge (TST + HST) composed of estuarine and delta plain deposits in lateral transition to thick shallow-marine and prodelta clays.

The LST deposits (total volume of 57.2 km3) spread across a 5600 km2 wide area, with average thickness of 10 m, and are continuously overlain by a thicker (up to 80 m) succession of TST + HST fine-grained strata (total volume of 130 km3). Sediment provenance analysis fingerprints two distinct detrital sources (Apennine rivers vs. Po River), leading to quantification of sediment fluxes (about 52 km3 from the Apennines catchments and 5 km3 from the Po system). The S2S approach allowed the identification of a potential offshore aquifer much extensive, thought laterally continuous, of the onshore counterpart. This lowstand reservoir, vertically confined by the thick low-permeability barrier (TST + HST) unit, is likely to contain about 16 km3 of groundwater with salinity lower than seawater.