Foraminifera from the Campanian–Maastrichtian of the Miriri Sub-Basin, Paraíba Basin, Brazil: implications for biostratigraphy and paleoenvironmental reconstruction

This study investigates the core RT-01-PB from the Miriri Sub-Basin, Paraíba Basin, analyzing planktic and benthic foraminifera from the upper Campanian to lower Maastrichtian. The strata belong to the Itamaracá and Gramame formations. Lithostratigraphic, biostratigraphic, and paleoenvironmental interpretations were developed using microbiofacies and benthic foraminiferal morphogroups. Fifty samples were processed for foraminiferal recovery, and thirty-five petrographic thin sections were analyzed to identify bioclastic constituents and diagenetic features, aiming to describe and classify the microbiofacies. Two planktic foraminiferal zones were identified: Gansserina gansseri Zone (upper Campanian–lower Maastrichtian) and Contusotruncana contusa Zone (lower Maastrichtian). Benthic foraminifera were classified into morphogroups by morphology and habitat, associating strata with depositional environments. Petrographic analysis revealed five microbiofacies types, including the first occurrence of larger benthic foraminifera in Brazil during the Upper Cretaceous. During the upper Campanian–lower Maastrichtian, the Miriri Sub-Basin was a platform environment, ranging from inner to mid-ramp (0–100 m depth) under oligotrophic conditions, with predominance of epifaunal forms. In the lower Maastrichtian, a middle–outer ramp (100–200 m) shifted to mesotrophic conditions, marked by increased infaunal foraminifera and authigenic phosphate, coincident with a gamma-ray peak. These data offer perspectives on climatic and palaeoenvironmental variations across the northern South American Platform during the Campanian–Maastrichtian.

Key words
Environmental change; larger benthic foraminifera; morphogroup analysis; phosphatic level; Upper Cretaceous