Characterizing the Tinat Member: An Interdisciplinary Study Combining Sedimentology, Stratigraphy, and Petrophysics

Abstract Interacting fluvial, aeolian, and marine sedimentation processes typically yield complex, heterogeneous depositional sequences characterized by lateral and vertical variability. Consequently, precise stratigraphic correlations assume critical importance in predicting rock quality and connectivity, thus better characterization. However, correlating surfaces within deposits of terrestrial origin poses significant challenges. To address that, this study introduces a systematic approach on defining key stratigraphic bounding surfaces through integrating relationships among facies stacking patterns, correlative surfaces, and subsurface data. For the purpose of this study, more than 1000 ft. of core data were examined. Facies associations and major stratigraphic markers were defined, honoring regional sedimentology and stratigraphic understanding. Stratigraphic markers were then used as correlative surfaces to build frameworks across the field with the integration of wireline logs responses, facies stacking patterns, complemented by formation pressure data as validation tools for correlation and sub-unit divisions. Quality evaluation through the utilization of conventional core analysis and petrographic analysis also added to the study to have a comprehensive understanding about heterogeneity in relation with different stratigraphic sub-units and facies associations. Four surfaces were identified, including Major Surface 1, which corresponds to a 1st-order sequence, and three stratigraphic sub-unit surfaces, representing 4th-order sequences, derived from core. The remaining major surfaces were identified based on log characteristics, supplemented by regional geological understanding. The upper boundary of Tinat Member is marked by a pebbly conglomeratic unconformity (1st-order sequence), marking the transition between AP5 and AP6, as defined by Arabian Plate tectonostratigraphic nomenclature. Three additional surfaces were recognized from core data: Sub-Unit 1, distinguished by an abrupt textural shift coinciding with the presence of paleosols; Sub-Unit 2, identified as a regional wetting phase, characterized by the deposition of playa facies, likely linked to a rising water table; and Sub-Unit 3, representing a sudden transition from predominantly aeolian-marine setting to aeolian settings. The lower boundary of the Tinat Member is bounded by an unconformity recognized from high gamma-ray (GR) log responses corresponding to red siltstone deposits of interfluvial origins. The dominant depositional environment is continental, although evidence suggests intermittent aeolian-marginal marine interactions, manifesting as wetter aeolian system with increased muddy facies, bioturbation, and tidally influenced deposits. Pressure data verifies the subdivision of these three units, indicating variations in depositional processes which contribute to understand compartmentalization. The Tinat Member exhibits a distinct progradational stacking pattern, transitioning upwards from an aeolian-marginal marine system to a playa, and aeolian setting and finally terminating in interacted fluvial-aeolian system. Notably, the uppermost part of the Tinat Member is capped by a paleosol section, indicating a period of non-deposition preceding the deposition of the AP6 Megasequence. Three identifiable stratigraphic sub-units can be correlated, allowing for a more accurate assessment and subsurface modeling.