High-resolution biostratigraphy of pliocene-pleistocene deposits in the Dahra Massif (NW Algeria): paleoenvironmental dynamics and mediterranean correlations

The Pliocene-Pleistocene succession exposed at Ouled Lakhdar (Lower Chelif Basin, NW Algeria) records cyclic alternations between marine and continental sedimentation driven by the combined effects of tectonics, eustatic sea-level fluctuations, and climate variability. An integrated high-resolution biostratigraphic framework based on planktonic foraminifera and calcareous nannoplankton constrains the chronostratigraphy of the Zanclean–Gelasian interval (∼5.33–∼1.93 Ma) and the overlying late Villafranchian continental deposits. This framework allows detailed reconstruction of palaeoenvironmental changes linked to orbital forcing and to regional geodynamic evolution during the Pliocene–Pleistocene. The succession documents alternating phases of subsidence (phases 1, 2 and 4) and uplift (phases 3, 5 and 6), which controlled accommodation space, sediment stacking patterns, and the development of key stratigraphic surfaces. Deep marine marl sedimentation during the Zanclean culminated in a condensed section close to the Zanclean/Piacenzian boundary (∼3.6 Ma). This was followed by shelf sedimentation characterized by tectonically induced high-energy deposits in the latest early Piacenzian (3.36–∼3.31 Ma). Prograding shallow marine carbonate-siliciclastic and siliciclastic-dominated systems developed during the mid-Piacenzian Warm Period (3.3–∼3.0 Ma). Brackish ostracods recorded near the end of this interval suggest an episode of Mediterranean–Paratethys connectivity, followed by the establishment of lacustrine carbonate deposition. The Piacenzian/Gelasian boundary is marked by an angular unconformity, overlain by fluvio-glacial valley fills indicative of a major glacial expansion at ∼2.5 Ma. A further condensed section separating shelf sandy marls from marly sands and carbonates marks the lower/upper Gelasian transition at ∼2.09 Ma. The overlying late Villafranchian succession consists of cyclic continental deposits driven by high-frequency glacial–interglacial oscillations. Regionally, the identified sequence boundaries correlate with Pliocene-Pleistocene oxygen isotope stages, associated sea-level changes, and unconformities recognized in other peri-Mediterranean basins. Overall, this study highlights the dominant allocyclic control of eustatic, climatic, and tectonic forcing on sedimentary processes and provides insights into Pliocene-Pleistocene palaeoenvironmental evolution and regional geodynamics in the western Mediterranean.