Paleoenvironmental and paleoceanographic dynamics of Tethyan phosphogenesis on the Brazilian Margin: Insights from Campanian–Maastrichtian foraminiferal assemblages

Late Cretaceous phosphogenic systems are widely documented along the Tethyan and Atlantic margins. However, the paleoenvironmental conditions controlling phosphorite formation along the Brazilian Equatorial Margin remain poorly understood. This study reconstructs the paleoenvironmental, depositional, and phosphogenic evolution of the Itamaracá, Gramame, and Jandaíra formations along the equatorial South Atlantic margin during the late Campanian–early Maastrichtian, integrating microfacies, foraminiferal assemblages, and quantitative paleoenvironmental proxies. The results reveal distinct but interconnected depositional systems governed by variations in nutrient flux, water-mass stratification, and bottom-water oxygenation. The upper Campanian stratigraphic sequence limit KCa7 records intensified upwelling, enhanced productivity, and the onset of dysoxic conditions, triggering the initial stages of phosphogenesis in both basins. The early Maastrichtian stratigraphic sequence limit KMa1 interval corresponds to maximum flooding, extreme sedimentary condensation, expansion of the oxygen minimum zone, leading to pervasive phosphatization in the basal Gramame Formation analogous to the classical Tethyan and North African phosphorite systems. In contrast, the early Maastrichtian stratigraphic sequence limit KMa2 reflects improved ventilation, oscillatory nutrient supply, and reduced phosphogenic intensity. These findings support regional and intercontinental correlations between the Late Cretaceous phosphatic deposits of northeastern Brazil and phosphogenic systems developed in the Neo-Tethyan domain. They further refine the role of upwelling-driven productivity and redox instability in controlling the development of Campanian–Maastrichtian carbonate–phosphate systems.