Impact of the global Annulata Events (upper Famennian) on benthic foraminifer assemblages at Ziar (Moroccan Meseta)

This study examines benthic agglutinated foraminifera from the cyclic nodular limestones of the Ziar Member in the Moroccan Meseta, where the first such assemblages were documented for the region. The investigated interval spans the global Annulata Event Interval around the proposed middle–upper Famennian boundary, including the Lower and Upper Annulata Blackshales, the intervening Annulata Intralimestones, and the overlying Wagnerbank Equivalent. Using bed-by-bed diversity analysis, cluster analysis, and taxonomic grouping, the study distinguishes clear pre-event, syn-event, and post-event foraminiferal assemblages. The results show that both hypoxic and transgressive Annulata events had strong short- and long-term effects on benthic communities. Shallow-water globular and hemispherical morphogroups disappeared with the onset of the Lower Annulata Event, while biodiversity and abundance had already begun to decline slightly before black shale deposition. This indicates a gradual deterioration of seafloor conditions prior to fully developed eutrophic, anoxic, and low-energy event facies. A brief recovery occurred during deposition of the Annulata Intralimestones, but shallow-water forms became extinct during the anoxic peak at the base of the Upper Annulata Blackshale. Recovery was delayed until after the Wagnerbank Equivalent and is marked by the appearance of a deeper-ramp Hyperammina–Tolypammina Biofacies. A further marked decline in foraminiferal assemblages occurred near the top of the studied interval, below the global Dasberg Crisis Interval. Taxonomically, 22 species belonging to eight genera are described as new records for the Moroccan Meseta, showing that although agglutinated foraminifera are weak biostratigraphic markers, their distribution was strongly controlled by anoxic events.