Late Quaternary sequence stratigraphy as a tool for groundwater exploration: Lessons from the Po River Basin (northern Italy)

Sequence stratigraphy, typically used for hydrocarbon exploration in ancient strata, can be applied to late Quaternary successions to decipher complex spatial relations among their aquifers. Late Pleistocene-Holocene strata of the Po Basin were investigated using a sequence stratigraphic approach to produce a highresolution model for guiding groundwater exploitation. Because facies tend to be diachronous across depositional basins, facies analysis was done within the conformable intervals of strata revealed by sequence stratigraphy to accurately interpret and map coeval lateral facies relations. Volumetric assessments, sand-distribution mapping, hydraulic characterization of facies, and spatial variations of hydraulic parameters revealed two aquifer systems: The lowstand systems tract (LST) and the highstand systems tract (HST) vertically separated by an aquitard, the transgressive systems tract (TST). The LST aquifer consists of amalgamated fluvial sands (average transmissivity: 3.5 E-3 m2/s [37.7 E-3 ft2/s]) with considerable width (>25 km [>16 mi]) preferentially elongated downstream. The widespread TST aquitard is dominated volumetrically (~57%) by low-permeability estuarine deposits. The HST aquifer (average transmissivity: 5.4 E-5 m2/s [58.1 E-5 ft2/s]) is 5-10 km (~3-6 mi) wide, elongated parallel to the modern shoreline. Sequence stratigraphic analysis at the parasequence scale revealed an almost unprecedented level of detailed insight into aquifer (or aquiclude) dimensions and the complex distribution of hydraulic parameters in the subsurface, showing that similar facies have different permeabilities depending on systems tract. In contrast, lithostratigraphic mapping obscures subsurface connectivity and directional trends and hasminimal predictive power away from control. These insights should be useful for guiding correlation and mapping of the deep subsurface and for hydrocarbon reservoir modelers.