Fault Zone Permeability and Fluid Flow in Carbonate Aquifers: Insights from Marl Smear Zones in Malta

Summary Fault zones in carbonate aquifers exert a primary control on groundwater flow, acting as barriers, conduits, or hybrid systems. While clay smears are widely recognised as effective permeability barriers in siliciclastic lithologies, their occurrence and behaviour in carbonate fault zones remains poorly understood. This study examines marl smearing in normal faults across the Maltese Islands, where Neogene extensional tectonics have dissected a sequence of Oligo – Miocene carbonates. Detailed field mapping and logging reveal that marl smears, formed by the offset of the Blue Clay Formation, are common across a range of displacements. A positive correlation is observed between fault displacement and smear thickness. Low offset fault zones (<5m) exhibit narrow, continuous smears which may locally reduce permeability. In contrast, high offset faults (>100m) display wide, mixed zones of disaggregated marl where original bedding is obliterated, likely significantly impeding cross fault flow.