Outcrop and subsurface characterisation of a mixed tidal and wave‐influenced coastline (Triassic Red Beds, SE Spain)

Paralic depositional systems are complex and heterogeneous sedimentary environments, presenting challenges for predicting reservoir architecture and connectivity. Their stratigraphic and facies variability arises from the dynamic interplay between fluvial, tidal and wave processes, and their sensitivity to sea‐level fluctuations, sediment supply and accommodation space. However, the predictive potential of facies models based on process proportions remains poorly constrained in ancient systems. To address this problem, a multi‐scale, multidisciplinary study was conducted on the Heterolithic Unit (H Unit) of the Triassic Red Beds of the Iberian Meseta (TIBEM, SE Spain). The studied succession is approximately 40 m thick and is exposed across laterally continuous outcrops covering ca 0.68 km 2 . By integrating outcrop observations, Digital Outcrop Models, core data and wireline log, this study provides a high‐resolution characterisation of the depositional style and architecture of the H Unit, improving the understanding of heterolithic systems in the fluvio‐marine transition zone. Fifteen lithofacies were grouped into five facies associations, reflecting a range of depositional environments from storm‐dominated shoreface to fluvio‐tidal channels: Storm‐dominated shoreface (HFA 1), Subtidal complex (HFA 2), Intertidal complex (HFA 3.1 and HFA 3.2), Supratidal flat (HFA 4) and Fluvio‐tidal channel (HFA 5.1 and HFA 5.2) deposits. These are organised into two subunits separated by a major incised valley surface, and four depositional sequences comprising up to four transgressive‐regressive cycles were identified. The resulting conceptual model describes a mixed‐energy coastal system in which tidal processes dominated during transgressive phases, whereas wave processes became more significant during high relative sea‐level stages and subsequent regressions, promoting storm‐dominated shoreface deposition within the confined incised‐valley setting. This stratigraphic organisation highlights the role of relative base‐level changes, valley incision and transgressive reworking in controlling the distribution and connectivity of heterolithic sedimentary bodies, providing a predictive framework for analogue reservoirs in paralic mixed‐energy settings.