Abstract The Paraíba Basin has a well-defined carbonate depositional sequence from the Upper Cretaceous (Campanian) to the Eocene. The carbonate sequence consists of the Itamaracá, Gramame, Maria Farinha and Tambaba formations, which mainly contain calcareous sandstones and carbonates with siliciclastics, limestone–marl alternations, limestones and marls, and limestones, respectively. The Tambaba Formation is composed of reef limestones, ranging from fossil- and ichnofossil-rich calcilutite to calcarenite. We investigated rocks of this unit located in a representative geological section at the Tambaba Beach, northeastern Brazil, in order to elucidate the environmental responses recorded in geochemical proxies (C and O isotopic composition, and distribution of major and trace elements). The δ 13 C and δ 18 O values ranged from 1.0 to 2.7‰ VPDB and from −1.3 to 1.1‰ VPDB, respectively. The interpretation of this response suggests environmental changes, such as an increase or decrease in bioproductivity of the organisms that make up these reef limestones. These changes are also recorded in the behaviour of the major and trace elements – for example, the relationship between SiO 2 , Al 2 O 3 , MgO and CaO, characterizing two different cycles during the deposition of these limestones: the first one characterized by a predominantly carbonate deposition, and the second one presenting a pulse of siliciclastic content. In addition, palaeotemperature values (9–15°C, from δ 18 O data) obtained, together with chemostratigraphic profiles of previous studies (e.g. δ 13 C, CaO, MgO, SiO 2 , Al 2 O 3 ), indicate that the reef limestones of the Tambaba Formation were probably deposited about 5 myr after the Paleocene–Eocene Thermal Maximum event.

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.

Abstract The Neoproterozoic successions of the São Francisco Craton are primarily represented by the Bambuí and Una groups, deposited in cratonic epicontinental basins, and by the Vazante and Vaza Barris/Miaba groups, which accumulated on passive margins on the edges of the craton. The epicontinental basins comprise three megasequences: glaciogenic, carbonate platform (marine) and dominantly continental siliciclastics. Possible correlative sequences are observed in the passive margin deposits. At least two major transgressive–regressive sea-level cycles occurred during the evolution of the carbonate megasequence, which lies above glaciomarine diamictites of probable early Cryogenian (i.e. Sturtian) age. C, O, Sr and S isotope trends from analyses of well-preserved samples, together with lithostratigraphic observations, provide reasonable correlations for most of the Neoproterozoic successions of the São Francisco Craton. The 87 Sr/ 86 Sr record of these successions, ranging from 0.70769 to 0.70780, supports the proposed correlation with the Bambuí, Una and Vaza/Barris successions, and with the basal units of the Vazante Group. In addition, C-isotope positive excursions ranging from +8.7 to +14‰ and negative excursions from –5.7 to –7‰ VPDB in the Bambuí, Una and Vaza-Barris successions provide key markers for correlations. The precise ages of the sedimentation in these successions remains a matter of debate, but organic shales of two units of the Vazante Group have been dated by Re–Os techniques in two different laboratories, both yielding Mesoproterozoic ages. The Neoproterozoic and Mesoproterozoic successions preserve significant glaciogenic deposits.