Allala River Sandstone (Miocene) gravel beaches and rocky shoreline (Tenes area, Lower Chelif basin, Algeria): Interplay of geological context and sedimentary processes

ABSTRACT The classification and spatial delineation of shoreline zones in gravel‐beach settings remain debated, despite numerous studies of both modern and ancient analogues. Here, we refine the sedimentological framework for ancient gravel beaches by proposing a standardised terminology, a new zonation scheme and a detailed facies characterisation applicable to microtidal, wave‐dominated coastal systems developed at the base of palaeo‐seacliffs. Exceptionally preserved Miocene deposits in the Tenes area (Lower Chelif Basin, Algeria) record the development of gravel beaches and rocky shorelines during a marine transgression over a structurally and lithologically heterogeneous basement. Detailed facies analysis of well‐preserved pocket‐beach successions allows reconstruction of a complete vertical facies architecture for cliff‐bound gravel beaches. The successions display a characteristic two‐stage stacking pattern within an overall transgressive context. An initial progradational phase records the transformation of immature, cliff‐derived gravel accumulations into mature, berm‐bearing gravel beaches. This phase reflects localised autogenic progradation driven by high coarse‐clast supply and strong geomorphologic confinement during the earliest stages of relative sea‐level rise. This is followed by a retrogradational trend marked by systematic backshore‐to‐offshore facies shifts, indicating a dominance of allogenic controls. These results demonstrate that basement lithology and inherited coastal geomorphology exert first‐order control on shoreline zonation and facies stacking patterns. The facies model and zonation proposed here provide a practical tool for interpreting ancient gravel‐beach systems and for distinguishing local autogenic responses from basin‐scale transgressive signals in gravel beach and rocky shoreline successions.