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

Abstract

The Paraíba Basin in northeastern Brazil contains a complete carbonate sequence that recorded theCretaceousePaleogene transition, and is composed of the Itamaracá, Gramame and Maria Farinhaformations. In this study, the behavior of C and O isotopes, major and trace element chemistry have beenexamined 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 temper-ature and bioproductivity increase in the Early Maastrichtian.d18O values for this interval vary from 3&to 5&VPDB, andd13C, from 1.2&to 0.1&, reaching a maximum in the Late Maastrichtian, with valuesaroundþ2&. Early Danian carbonates have recorded a small positived13C excursion(þ2&), followed byvalues aroundþ1&right after the CretaceousePaleogene transition with increase of SiO2and Al2O3associated to terrigenous contribution. Upsection, carbonates recorded a period of marine regression,bioproductivity falls as recorded by thed13C curve (þ1&) and carbonate sediments with higher Mg/Caratios were possibly deposited in a shallow-marine environment. Carbon and oxygen isotope pathwaysin carbonates of the Paraíba Basin from the drill holes at Poty Quarry, Olinda and Itamaracá localities aresimilar to each other and to that observed in the El Kef type section, Tunisia, and in the Yacoraite Basin, inArgentina. In the Poty drill hole, remarkable negative spikes may have resulted from multiple meteoriteimpacts that predated the CretaceousePaleogene transition. Mercury stratigraphy in the same drill holedisplays a prominent positive anomaly in the K-T transition and suggests that important volcanismwitnessed the transition scenario