Structural controls on the formation of compartmentalized carbonate aquifers: the Kourenta anticline (Epirus, NW Greece)

The sustainable management of subsurface resources in tectonically complex regions requires the integrated understanding of geological and hydrogeological processes. In the Epirus region of northwestern Greece, fold-and-thrust belt related deformation, lithological variability, and long-standing hydrocarbon exploration provide an opportunity to examine such relationships. Hence, we combine surface structural mapping, recent 2D seismic reflection profile, and hydrogeological data to construct a three-dimensional structural and hydrogeological conceptual model. Results highlight the dominant control of Epirus regional structural framework on its groundwater flow system. A complex structure comprising a pop-up structure, controlled by ENE-dipping foreland-verging thrusts and WNW-dipping hinterland-verging backthrusts, developed in time into a broader box-type, asymmetric NNW-trending anticline structure. In its fold core, the impermeable Posidonia Shales control subsurface water flow, while the NW–SE thrusts and NE–SW oblique-slip faults, that are perpendicular to the anticline axis act as barriers. Two main hydrogeological systems are identified. The upper system is divided into western and eastern domains by fold asymmetry. Water recharge occurs through Eocene to Senonian limestones and is structurally controlled. In the fold core, the impermeable Posidonia Formation marks a lower structural system, bounded by thrust contacts and containing aquifers within the Pantokrator Limestone and associated dolomites. At depths greater than 1 km, an ultra-deep hydrogeological system is inferred, possibly brine-bearing, and extends to the flysch base. The potential hydraulic interaction between this deep system and overlying aquifers remains uncertain, depending largely on the sealing capacity of faults—an issue of critical importance for groundwater quality and sustainable use. This work is important as it proves the critical influence of structures on groundwater distribution, connectivity, and quality. The outcomes of this study have practical implications for groundwater resource management in regions with limited surface water and sensitive ecosystems.