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

Abstract

Abstract The Paraiba Basin in northeastern Brazil contains a complete carbonate sequence that recorded the Cretaceous–Paleogene transition, and is composed of the Itamaraca, 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 Itamaraca). The deposition of carbonates in this basin was initiated during a marine transgression with temperature and bioproductivity increase in the Early Maastrichtian. δ 18 O values for this interval vary from −3‰ to −5‰ VPDB, and δ 13 C, 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 δ 13 C excursion(+2‰), followed by values around +1‰ right after the Cretaceous–Paleogene transition with increase of SiO 2 and Al 2 O 3 associated to terrigenous contribution. Upsection, carbonates recorded a period of marine regression, bioproductivity falls as recorded by the δ 13 C 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 Paraiba Basin from the drill holes at Poty Quarry, Olinda and Itamaraca 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.