<p>Geopetal fabrics are important sedimentary indicators of horizontality and the original upward orientation of strata, and can provide valuable insights into depositional environments and early diagenetic pathways. This study examines the occurrence, morphology, and diagenetic evolution of geopetal fabrics within the Pennsylvanian Atoka bank carbonates on the northwestern shelf margin of the Delaware Basin, based on detailed core and thin-section analyses. The Atoka carbonates, dominated by phylloid algal biostromes and associated shallow-marine facies, were deposited in a normal-marine, open-shelf setting with limited siliciclastic input. Geopetal fabrics occur mainly in fossil chambers (brachiopods and gastropods), phylloid algal molds, and borings, and exhibit a characteristic two-phase infill: (i) an initial marine phase, dominated by peloidal sediment—the principal internal fill—which displays clear evidence of marine cementation by former Mg-calcite and aragonite and commonly incorporates small intraclasts, fragmented algal debris, and localized accumulations of ostracod shells, and (ii) a subsequent meteoric phase consisting of vadose calcite silt overlain by scalenohedral and blocky equant low-Mg calcite cements. Petrographic evidence indicates that the marine phase developed along high-energy bank margins under marine–phreatic conditions. In contrast, the meteoric phase formed during subaerial exposure associated with relative sea-level falls. The alternation of these phases records repeated marine–meteoric transitions driven by sea-level oscillations. The preservation of basal geopetal horizontality and upward orientation further demonstrates the tectonic stability of the Atoka Bank complex during burial. Overall, these results emphasize the combined influence of depositional energy, facies architecture, and sea-level changes on the diagenetic evolution of shallow-marine carbonate banks.</p>