Cretaceous-Paleogene transition at the Paraíba Basin, Northeastern, Brazil: Carbon-isotope and mercury subsurface stratigraphies

The Paraíba Basin in northeastern Brazil contains a complete carbonate sequence that recorded the Cretaceous–Paleogene transition, and is composed of the Itamaracá, Gramame and Maria Farinha formations. In this study, the behavior of C and O isotopes, major and trace element chemistry have been examined in core drill carbonate samples from three drill holes (Poty Quarry, Olinda and Itamaracá).The deposition of carbonates in this basin was initiated during a marine transgression with temperature and bioproductivity increase in the Early Maastrichtian. δ18O values for this interval vary from −3‰ to −5‰ VPDB, and δ13C, from −1.2‰ to 0.1‰, reaching a maximum in the Late Maastrichtian, with values around +2‰. Early Danian carbonates have recorded a small positive δ13C excursion(+2‰), followed by values around +1‰ right after the Cretaceous–Paleogene transition with increase of SiO2 and Al2O3 associated to terrigenous contribution. Upsection, carbonates recorded a period of marine regression, bioproductivity falls as recorded by the δ13C curve (+1‰) and carbonate sediments with higher Mg/Ca ratios were possibly deposited in a shallow-marine environment. Carbon and oxygen isotope pathways in carbonates of the Paraíba Basin from the drill holes at Poty Quarry, Olinda and Itamaracá localities are similar to each other and to that observed in the El Kef type section, Tunisia, and in the Yacoraite Basin, in Argentina. In the Poty drill hole, remarkable negative spikes may have resulted from multiple meteorite impacts that predated the Cretaceous–Paleogene transition. Mercury stratigraphy in the same drill hole displays a prominent positive anomaly in the K-T transition and suggests that important volcanism witnessed the transition scenario.

► K-T boundary recorded in northeastern in Brazil.
► C and O-isotope stratigraphy using drill holes.
► Mercury is used as tracer for coeval volcanic activity during the KTB.
► Mercury anomalies suggest multiple volcanic activities predated the KTB.