Sedimentology and ichnology of the early Tortonian marine transgression onto the Beni Chougrane Massif, Lower Chelif Basin, northwestern Algeria

The Oued Feraguig Detrital Formation, exposed along the southern margin of the Lower Chelif Basin in northwestern Algeria, records the earliest marine deposits associated with the late Miocene transgression onto the Cretaceous substrate of the Beni Chougrane Massif. This study integrates sedimentological, ichnological and planktonic foraminiferal data to constrain the age, depositional environments and palaeogeographic significance of this transgressive succession. The formation is 80–90 m thick and unconformably overlies a weathered Upper Cretaceous substrate. Ten sedimentary facies were identified and grouped into two facies associations that record deposition from lower-shoreface to middle- and upper-shoreface environments. The basal conglomeratic deposits represent transgressive lags formed by erosion and reworking of the Cretaceous substrate during the initial phase of marine inundation. Up-section, the succession is dominated by well-sorted sandstones displaying planar lamination, planar and trough cross-stratification, hummocky and swaley cross-stratification, and local soft-sediment deformation structures. These features indicate deposition in a high-energy shoreface system influenced by waves and storms. The trace-fossil assemblage comprises 14 ichnotaxa and is dominated by vertically oriented dwelling burrows, including Ophiomorpha , Skolithos and Diplocraterion ; this composition is consistent with the Skolithos ichnofacies. Subordinate horizontal traces record brief colonization during fair-weather intervals. Asteriacites stelliformis and Diplopodichnus biformis are reported from Algeria for the first time. Local development of oyster banks composed of Crassostrea gryphoides indicates short-lived phases of substrate stabilization within the shoreface system. Planktonic foraminiferal assemblages constrain the age of the formation to the early Tortonian, corresponding to planktonic foraminiferal subzones MMi9–MMi10 (ca. 11.54–10.55 Ma). These results refine the timing and sedimentary record of marine flooding along the southern margin of the Lower Chelif Basin and provide new insights into Miocene transgressive systems along structurally controlled basin margins in the western Mediterranean.