Carbon isotopes, rare-earth elements and mercury geochemistry across the K–T transition of the Paraíba Basin, northeastern Brazil
Published:January 01, 2013
Maria Valberlândia Nascimento Silva, Alcides Nóbrega Sial, José Antonio Barbosa, Valderez Pinto Ferreira, Virgínio Henrique Neumann, Luiz Drude De Lacerda, 2013. "Carbon isotopes, rare-earth elements and mercury geochemistry across the K–T transition of the Paraíba Basin, northeastern Brazil", Isotopic Studies in Cretaceous Research, A.-V. Bojar, M. C. Melinte-Dobrinescu, J. Smit
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The Paraíba Basin, northeastern Brazil, is divided into three sub-basins: Olinda, Alhandra and Miriri, which encompass the formations Beberibe (Coniacian–Santonian), Itamaracá (Campanian) and Gramame and Maria Farinha (Maastrichtian to Danian, respectively). In the Olinda sub-basin, the Cretaceous–Palaeogene transition (KTB) has been recorded by the carbonates of the Gramame and Maria Farinha formations. This study focus on the behaviour of C and O isotopes, major and rare-earth elements and mercury in carbonates from three drill holes in the Olinda sub-basin. The climate was fairly cold during the marine transgression in which carbonates of the Itamaracá Formation were deposited. A temperature and bioproductivity increase has been registered in the Early Maastrichtian (Gramame Formation), with a gradual fall during the rest of this period. A positive δ13C (+2‰) excursion near the KTB is followed by a drop to values around +1‰ immediately after this transition. In one drill hole, several negative δ13C anomalies predate the KTB, possibly related to either multiple impacts or volcanic activity that preceded this transition. In two of the three drill holes, the total mercury increases immediately after the KTB and, in two of them, mercury spikes (four of them in one case) precede this transition, which has been interpreted as an indication that volcanic activity predated the transition. Rare earth element patterns support a marine origin for the carbonates in the Campanian–Maastrichtian transition and KTB in the Olinda sub-basin. In carbonates from one of the drill holes, absent to weakly positive Ce anomalies (−0.1 and 0.002) in the KTB coincide with a fall in δ13C values, followed by an increase (from 2.3 to 1.8‰ and back to 2.3‰) and in increment in mercury values (from 0.4 to 2.7 ng g−1). The presence of pyrite nodules associated with a weakly negative Eu anomaly point to slightly reducing conditions around the KTB.
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Isotopic Studies in Cretaceous Research
The Cretaceous was a period characterized by very warm climate, oceanic anoxic and oxic events and enhanced volcanic activity. The end of the Cretaceous is punctuated by a well-documented asteroid impact and the extinction of, among other groups, the dinosaurs. This volume elucidates various aspects of Cretaceous marine and continental environmental conditions. The articles in this book present a broad range of interdisciplinary contributions, which are grouped into sections on marine environments(including anoxic and oxic events, volcanism and the Cretaceous–Palaeocene boundary); mixed marine–freshwater environments and continental records. The isotopic data are combined with further geochemical, palaeontological, lithological and mineralogical proxies. The interdisciplinary approach offered here gives a solid investigation base for this fascinating period. There are examples from Europe, Asia, South and North America, and from the Early Cretaceous to the Cretaceous–Paleogene boundary.