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Carbon isotopes, rare-earth elements and mercury geochemistry across the K–T transition of the Paraíba Basin, northeastern Brazil

2013; Geological Society of London; Volume: 382; Issue: 1 Linguagem: Inglês

10.1144/sp382.2

2041-4927

Maria Valberlândia Nascimento Silva, Alcídes N. Sial, José Antônio Barbosa, Valderez P. Ferreira, Virgínio Henrique de Miranda Lopes Neumann, Luiz Drude de Lacerda,

Geological and Geochemical Analysis

Abstract 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 δ 13 C (+2‰) excursion near the KTB is followed by a drop to values around +1‰ immediately after this transition. In one drill hole, several negative δ 13 C 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 δ 13 C 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.