Late Cretaceous Foraminiferal Biostratigraphy and Paleoenvironmental Reconstruction of the Sergipe Basin, Brazil, based on Integrated Micropaleontological and Stable Isotope Data

The Sergipe Basin in northeastern Brazil provides an exceptional stratigraphic archive for deciphering the paleoceanographic evolution of the equatorial South Atlantic during the Late Cretaceous greenhouse climate. In this study, we present a high-resolution integrated analysis of planktonic and benthic foraminiferal biostratigraphy coupled with bulk carbonate stable carbon and oxygen isotope systematics (δ¹³C and δ¹⁸O) across the Cenomanian to lower Campanian succession of the Cotinguiba Formation. Biostratigraphic calibration resolves five distinct planktonic foraminiferal biozones spanning from the Rotalipora cushmani Zone to the Dicarinella asymetrica Zone. A pronounced positive carbon isotope excursion of +3.8‰ captures the global Cenomanian–Turonian Oceanic Anoxic Event 2 (OAE 2), coinciding with the proliferation of low-oxygen tolerant opportunists such as Heterohelix reussi and unkeeled hedbergellids, alongside an epifaunal benthic turnover. Paleobathymetric reconstructions based on planktonic/benthic ratios and benthic morphogroup analysis indicate a progressive deepening from outer neritic to upper bathyal conditions disrupted by episodic bottom-water dysoxia. Concurrently, δ¹⁸O trends record a phase of climatic optimum followed by gradual thermal deterioration during the Coniacian–Santonian. These findings highlight the interplay between regional tectonic subsidence associated with South Atlantic rifting and global eustatic and paleoceanographic drivers controlling carbon cycling and marine ecosystem stability.