Stratigraphic Evolution of the Middle to Upper Jurassic Gotnia Platform Margin, Saudi Arabia

Platform-to-basin correlations require an integrated approach due to the rapid lateral changes in facies, stratal geometries, environments, and biota. The Gotnia Basin is characterized by the presence of world-class source-rocks, while reservoir-seal pairs are found across the depositional profile in the platform, slope, and basin (Yousif and Nouman, 1997; Sharland et al. 2001; Ziegler, 2001). Developing a genetic understanding of platform-margin evolution is crucial for predicting elements of the petroleum system including reservoir-seal distribution. In this study, a stratigraphic cross-section is constructed from platform to basin for the Middle to Upper Jurassic Gotnia Basin margin in Saudi Arabia. Sequence boundaries and maximum flooding surfaces are defined from well logs, core, and observed seismic geometries. A robust biostratigraphic framework exists on the platform, whereas reliable age-control in the basin is limited, primarily due to the highly restricted, hypersaline nature of the basin sediments. By combining these multiple data-types, a stratigraphic cross-section is constructed, capturing depositional facies, stratal geometries, and chronostratigraphic relationships. From the Bajocian to Callovian, the marine shelf undergoes a transition from a low-angle mud-dominated ramp to a high-rise platform with distinct margin and slope geometries, characterized by an estimated vertical relief of over 200 metres. Multiple cycles of basin restriction and desiccation occur during the Kimmeridgian, most likely initiated by small eustatic sea-level drops, but with the majority of the sea-level fall attributed to evaporitic drawdown due to restricted seaway connections, resulting in the deposition of thick intervals of halite. Sylvite stringers within the halite provide evidence for complete evaporation. These evaporite packages correlate with exposed sequence boundaries on the platform top. During the Tithonian, the deposition of peritidal and evaporite-dominated sabkha on the platform and correlative carbonate muds and sub-aqueous evaporites in the basin infill the high-rise platform topography, modifying the depositional profile from platform back to ramp. The Middle Jurassic to Lower Cretaceous thickness map exhibits near-isopachous characteristics across the platform margin, suggesting that the high-rise margin architecture that occurs in the Callovian to Oxfordian is the result of spontaneous, self-organizing carbonate growth rather than a response to fault-related subsidence. Core in the basin reveals that autochthonous biostromal stromatolite and sabkha deposits develop between halite accumulations in a lowstand position, potentially forming effective reservoirs.