Microfacies Distribution and Depositional Environments of the Lower Cretaceous Gadvan Formation (Barremian–Aptian) in the Persian Gulf

The Gadvan Formation (Barremian–Aptian) in the Persian Gulf represents a heterogeneous mixed carbonate–siliciclastic succession with important implications for depositional architecture and reservoir characterization. In this study, fourteen distinct microfacies (MF-1 to MF-14) were identified based on detailed core descriptions and petrographic analysis of thin sections from five wells across several oil fields.

Outer-ramp facies (MF-1 to MF-4) are dominated by mud-supported argillaceous bioclastic mudstones and wackestones, radiolarian- and sponge spicule–rich wackestones, and planktonic foraminiferal wackestones, reflecting low-energy open-marine deposition below the storm wave base. Middle-ramp facies (MF-5 to MF-8) comprise echinoderm-rich wackestones, orbitolinid wackestones, benthic foraminifera–echinoderm wackestones, and sandy bioclastic facies, indicating moderate-energy open-marine conditions with episodic siliciclastic input. Inner-ramp facies (MF-9 to MF-13) include peloidal packstones to grainstones, Lithocodium floatstones to boundstones, and green algae–benthic foraminiferal wackestones, representing shoal, back-shoal, and semi-restricted lagoonal environments. Coastal to proximal depositional settings (MF-14) are characterized by argillaceous sandstones and scattered quartz grains, reflecting sporadic terrigenous supply from nearby continental sources.

The vertical and lateral distribution of these microfacies documents deposition on a homoclinal carbonate ramp that locally evolved into a distally steepened geometry, particularly in the northwestern part of the Persian Gulf. Shoal complexes acted as barriers separating open-marine conditions from restricted lagoonal settings. This microfacies-based framework improves the depositional model of the Barremian–Lower Aptian Gadvan Formation on the northeastern Arabian Plate and provides a robust basis for regional correlation and reservoir-scale interpretation.