Cenozoic biostratigraphy of larger foraminifera from equatorial carbonate platform of northwestern Brazil

The off-shore Cenozoic succession of the Pará-Maranhão Basin of the Brazilian equatorial margin is studied to investigate skeletal and foraminiferal assemblages during the Oligocene-Miocene interval, one of the fundamental moments in the environmental evolution of our planet. The material from core 1-MAS-16-MA is analyzed using a combination of conventional paleontological analyses, and innovative approaches like micro-CT scan and U/Pb dating on carbonates. The results allowed to clearly constrain the Oligocene – Miocene interval and divide it into four foraminiferal assemblages and seven biofacies useful for both paleoenvironmental reconstructions and stratigraphic correlations. The paleoenvironmental analysis indicates a common pattern of relative sea-level oscillations with the nearby Foz do Amazonas Basin, highlighting a common behavior of this part of the equatorial passive margin during the Oligocene – Miocene interval. The comparison between the succession of skeletal and foraminiferal assemblages of the investigated core and other successions of the Southern and Central American area indicated the presence of stratigraphically relevant foraminiferal assemblages that could be useful for improving the correlation between the various Cenozoic successions of the area (assemblages dominated by nummulitids and lepidocyclinids in the Rupelian; assemblages dominated by Heterostegina (Vlerkina) antillea, lepidocyclinids, and primitive miogypsinids in the Chattian; assemblages dominated by Heterostegina (Vlerkina) antillea, lepidocyclinids, and miogypsinids other than Miogypsinoides and Miogypsinella, in the Aquitanian; assemblages dominated by advanced miogypsinids in the Burdigalian; post Early Miocene assemblages characterized by the lack of abundant lepidocyclinids and miogypsinids). Finally, the overall resilience of most of the large benthic foraminifera taxa to the Oligocene – Miocene transition testifies once more to the adaptability of this group of carbonate producers.