The paper focuses on the reservoir heterogeneity of a sandstone formation in which the main issue is the evaluation of diagenetic features. Integrated data from field observations as well as petrographic and geochemical analyses from surface and core sections from different structural settings were applied. In the shallow marine Pétervására Sandstone, eogenetic minerals are comprised of calcite, pyrite and siderite; mesogenetic minerals are albite, ankerite, calcite, quartz, mixed layer clays and kaolinite. Dissolution occurred during mesogenetic and telogenetic phases. Ankerite is only present in the core setting, where the sandstone is at ca. 900 m depth and diagenetic calcite predates quartz cementation. Based on stable isotopic values (δ¹³C_V-PDB −18.3 to −11.4 ‰ and δ¹⁸O_V-PDB −9.5 to −7.2 ‰), diagenetic calcite is of mesogenetic origin and was precipitated from fluids migrated along fault zones from the underlying, organic matter-rich formation. In outcrop setting, on the other hand, calcite is present in a larger quantity and postdates quartz cementation. Carbon isotope data (δ¹³C_V-PDB = −9.9 to −5.1 ‰) indicate less contribution of light isotope, whereas more negative oxygen isotopic values (O_V-PDB = −13.1 to −9.9 ‰) likely imply higher temperature of mesogenetic fluids. However, carbon–oxygen isotope covariation can indicate precipitation from meteoric fluid. In this case, further analyses are required to delineate the final model.