What Factors Determine the Geometries of Fault-Associated Dolomitization Geometries in Shallow-Marine Carbonates?

The present study investigates the controls on fault-associated dolostone geometries based on the Benicàssim outcrop analogue (Maestrat Basin, E Spain). It is also aimed to provide new insights into the prediction of fault-associated dolomitized hydrocarbon reservoirs. To this end, mapping, logging and log correlation were carried out in the Benicàssim area, where a >1600 m-thick succession of Aptian-Albian carbonate ramp sediments of the Benassal Fm are partly replaced by fault-associated dolostones. The results reveal that km-wide massive dolostone patches form near large-scale faults, indicating that they acted as entry points for dolomitizing fluids. These dolostones laterally pass to large stratabound bodies extending for at least 7 km away from feeding faults. The presence of a siliciclastic low-permeability unit (Escucha Fm) on top of the Benassal Fm constrained the dolomitizing fluids to a window whose top and bottom boundaries are about 100 m and 550 m below the base of the sealing unit, respectively. Thus, only the limestones comprised within this interval were dolomitized, indicating a clear relationship between the stratigraphic framework and the preferred replaced beds. Dolomitization mostly affected mid-ramp sediments (wackestones and packstones). Such facies are mostly abundant in the eastern part of the study area around the maximum flooding zone of the top sequence, which is preferentially dolomitized.