During the Early Cretaceous, several extensive carbonate shelves were developed in the sedimentary basins located on the Central Segment of the South Atlantic Ocean. These marine successions are ...characterized by mixed carbonate and siliciclastic sediments with a diverse fossil content, deposited during the late Aptian–Albian interval. The microbiofacies content of two continuous cores (SER-01 and SER-03), each approximately 200 m deep, drilled in the onshore region of the Sergipe–Alagoas Basin, north-eastern Brazil consists of mudstones, wackestones, packstones, grainstones, rudstones, marls, claystone, shales and sandstones in Core SER-01, whereas those from Core SER-03 are essentially fine-grained lithologies such as mudstones, wackestones, claystone and shales. Two low-frequency sedimentation cycles are identified, with SER-01 being characterized by restricted and shallow-marine facies that grade up in a transgressive trend, which is also present throughout Core SER-03. Six microfacies are recognized, indicating deposition in a high-energy shallow-marine environment with a sand-bar system, which later evolved into a low-energy deeper-marine environment (outer shelf). The microfossil content includes planktic and benthic foraminifera, which are dominant in both cores, as well as macrofossils such as echinoderms and molluscs. Cadosinids, green algae, microcrinoids and inoceramids occur locally in both cores. In addition, Core SER-01 is characterized by abundant microbial units. The fossil content shows palaeogeographic affinities with the Tethyan Realm. These records suggest water connections between the South Atlantic and the North Atlantic/West Tethys Sea since the late Aptian interval.
This study reports a set of primeval marine incursions identified in two drill cores, 1PS-06-CE, and 1PS-10-CE, which recovered the Barbalha Formation, Araripe Basin, Brazil. Based on a multi-proxy ...approach involving stratigraphy, microbiofacies, ichnofossils, and microfossils, three short-lived marine incursions were identified, designated Araripe Marine Incursions (AMI) 1-3. AMI-1 and AMI-2, which occur within the shales of the Batateira Beds (lower part of the Barbalha Formation), were identified by the occurrence of benthonic foraminifera, calcareous nannofossils, dinocysts, and a mass mortality event of non-marine ostracods. AMI-3 was recognized in the upper part of the Barbalha Formation, based on the occurrence of ichnofossils and planktonic foraminifera. The observation of the planktonic foraminifera genus Leupoldina for the first time in the basin indicates early Aptian/early late Aptian age for these deposits, and the first opportunity of correlation with global foraminifera biozonation. Our findings have implications for the breakup of the Gondwana Supercontinent, as these incursions represent the earliest marine-derived flooding events in the inland basins of northeastern Brazil.
The Southern Ocean paleoceanography provides key insights into how iron fertilization and oceanic productivity developed through Pleistocene ice-ages and their role in influencing the carbon cycle. ...We report a high-resolution record of dust deposition and ocean productivity for the Antarctic Zone, close to the main dust source, Patagonia. Our deep-ocean records cover the last 1.5 Ma, thus doubling that from Antarctic ice-cores. We find a 5 to 15-fold increase in dust deposition during glacials and a 2 to 5-fold increase in biogenic silica deposition, reflecting higher ocean productivity during interglacials. This antiphasing persisted throughout the last 25 glacial cycles. Dust deposition became more pronounced across the Mid-Pleistocene Transition (MPT) in the Southern Hemisphere, with an abrupt shift suggesting more severe glaciations since ~0.9 Ma. Productivity was intermediate pre-MPT, lowest during the MPT and highest since 0.4 Ma. Generally, glacials experienced extended sea-ice cover, reduced bottom-water export and Weddell Gyre dynamics, which helped lower atmospheric CO
levels.
Multi‐scale transgressive–regressive cycles from the mid‐Jurassic were recognised in the Central Lusitanian Basin, Portugal. These cycles allow the depositional evolution of the basin to be better ...understood and aid in the construction of stratigraphic sequences composed of three hierarchies. The stacking pattern of high‐frequency transgressive–regressive sequences forms larger clusters that define medium‐frequency transgressive–regressive sequences. Likewise, the stacking pattern of medium‐frequency transgressive–regressive sequences generates two Bathonian–early Callovian low‐frequency transgressive–regressive sequences. Integration of several methods supported the interpretation of facies associations representing clastic deposition in offshore to shoreface environments and carbonate sediments in outer to inner ramp settings. New data from calcareous nannofossils and dinoflagellate assemblages constrained the interval's Bathonian–early Callovian age, thus unveiling the Middle–Upper Jurassic disconformity and filling the Middle Jurassic stratigraphic record gap in the Central Lusitanian Basin. This study may be helpful for similar successions in Tethyan domains and comparable depositional settings elsewhere.
Middle Jurassic multi‐scale transgressive–regressive cycles were recognised in the Central Lusitanian Basin, Portugal. New data from calcareous nannofossils and dinoflagellate assemblages constrained the Bathonian–early Callovian age for the studied interval, thus filling the gap of the Middle Jurassic in the Central Lusitanian Basin. Using descriptive criteria to identify sequences based on the T–R cycle anatomy, recurrence, and trends, cyclic stratigraphy has enabled the definition of a conceptual model for the deposition of the studied section that is more robust than conventional interpretations.
Non-marine Oligocene ostracods from Tremembé Formation (Taubaté Basin, Southeast Brazil) are studied for the first time. The study reveals rich assemblages which are probably composed of many new ...taxa, two of which are described here. The sixteen ostracod species registered are classified in the generaCypretta Vávra, Strandesia Stuhlmann,Potamocypris Brady, Heterocypris Claus,Eucypris Vávra, Herpetocypris Brady and Norman, Cytheridella Daday and LimnocythereBrady. Two new species of the latter are herein proposed: L. mandubi sp. nov. and L. katu sp. nov. The succession of ostracod assemblages along the studied core changes conspicuously in composition, abundance and preservation, and are characterized by the following associations: Herpetocypris-Cytheridella (lower), Limnocythere-Cypretta (middle) andPotamocypris-Heterocypris (upper). It is assumed that these associations represent different ecological phases of the paleolake Taubaté which is in accordance to previous stratigraphic and paleontological studies in the basin. The results from this pioneering taxonomic and paleoecological study on ostracods from Tremembé Formation reinforce the potential of these fossils for paleolimnological researches in Brazilian Cenozoic deposits.
International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea’s Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean ...near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well‐resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ18O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ18O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ18O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ18O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession‐paced variations not captured in benthic δ18O during the 41‐kyr world.
Key Points
Extended composite and correlated equivalent depth scales are presented for Antarctic proximal International Ocean Discovery Program Sites U1536 and U1537
U1536 and U1537 have excellent magnetostratigraphy and clear imprint of orbital variations in their lithology
Changes in terrigenous versus diatomaceous Dove Basin facies are out of phase with benthic δ18O during intervals between 3.3 and 1 Ma
Ostracodes são microfósseis carbonáticos que têm se destacado na pesquisa de isótopos estáveis devido à rápida calcificação da carapaça, sua elevada sensibilidade aos parâmetros ambientais e à sua ...ocorrência em diferentes ambientes aquáticos. Os isótopos de carbono proporcionam informações sobre paleoprodutividade e disponibilidade de nutrientes dos oceanos e lagos. Os isótopos de oxigênio são utilizados para estimar a paleotemperatura e a paleosalinidade vigentes em determinada bacia sedimentar ao longo do tempo geológico. Até o momento, as análises isotópicas em carapaças de ostracodes são realizadas principalmente em material do Cenozoico, com poucas pesquisas realizadas para o Mesozoico. Esta técnica é amplamente utilizada em ostracodes de ambientes não-marinhos, sendo realizada com cautela em ambientes transicionais e marinhos, onde a composição da carapaça será semelhante à da rocha carbonática que o contém. Este texto compreende conceitos de isótopos estáveis, da técnica analítica utilizada, da realização das análises em ostracodes e da interpretação dos resultados nos estudos paleoambientais, e propõe um protocolo de pesquisa considerando as dificuldades de amostragem e de aplicação em carapaças do Cretáceo.
PDF
