Geologos, 2009, 15, 2
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Item Polish palaeontological research in the Arctic(Bogucki Wydawnictwo Naukowe, 2009) Chwieduk, EdwardItem Reflections on subglacial megafloods: their possible cause, occurrence, and consequence for the global climate(Bogucki Wydawnictwo Naukowe, 2009) van Loon, A.J. (Tom)Huge water reservoirs exist subglacially, for instance in the form of lakes. Failure of a wall around such a lake underneath the central part of a large ice mass may result in huge water outbursts. The resulting megafloods will rarely be traceable along the ice front, because much power is lost by friction and because the flood spreads subglacially over a large area. Truly giant meltwater outbursts might, however, still have an enormous power when reaching the marginal area of an ice cap. Such a megaflood may both affect the integrity of the ice mass, and help create a sliding layer over which huge ice masses can be easily transported towards the ocean, thus triggering a Heinrich-like event. This would have great impact on the global climate. Some of the Heinrich events that occurred during the past hundreds of thousands of years may well have been due to giant subglacial water outbursts, and such a situation may equally well occur in the time to come.Item The survival of megafauna after the end-Pleistocene impact: a lesson from the Cretaceous/Tertiary boundary(Bogucki Wydawnictwo Naukowe, 2009) Ruban, Dmitry A.Survival of Pleistocene megafauna after the hypothesized impact of a bolide during the latest Pleistocene seems to be partly island-centered, whereas that the survival of dinosaurs and ammonites after the comparable catastrophe at the Cretaceous/Tertiary boundary seems to have occurred in a fairly haphazard way within the areas affected by the impact. This poses some new questions about the possible mechanism behind the end-Pleistocene extinction, although it does not disprove an impact as a plausible cause.Item Sedimentary development and isotope analysis of deposits at the Cretaceous/Palaeogene transition in the Paraíba Basin, NE Brazil(Bogucki Wydawnictwo Naukowe, 2009) Neumann, Virgínio Henrique; Barbosa, José Antônio; Silva, Maria Valberlândia Nascimento; Filho, Mário de LimaNew data are presented for three formations (Itamaracá, Gramame and Maria Farinha) and two boundaries (Campanian/Maastrichtian and Maastrichtian/Danian) in the Olinda Sub-basin of the Paraíba Basin. Currently accepted facies models, sequence stratigraphy characterizations, and stable-isotope data of carbon and oxygen are reviewed. The carbonate cement of the Itamaracá Formation sandstones shows carbon- and oxygen-isotope ratios consistent with a shallow-marine depositional environment: δ18O ranges from -0.8 to -2.7‰ PDB, and δ13C ranges from +1 to +2‰ PDB. Within the Itamaracá Formation, a maximum flooding surface at the Campanian/Maastrichtian transition has been identified. During the Maastrichtian, a Highstand System Tract was deposited, which shows an increase in temperature and marine bioproductivity as recorded by stable-isotope values (δ18O from -3 to -5‰ PDB, and δ13C values of -1.2, -0.3, 0.1 and +2.3‰ PDB). Just below the K/Pg boundary, the O-isotope signal indicates three warming phases, alternating with four cooling phases.Item Probability mapping of petroleum occurrence with a multivariate-Bayesian approach for risk reduction in exploration, Nanpu Sag of Bohay Bay Basin, China(Bogucki Wydawnictwo Naukowe, 2009) Suyun, Hu; Qiulin, Guo; Zhuoheng, Chen; Shiyun, Mi; Hongbin, XieA multivariate-Bayesian approach has been applied to the Nanpu Sag of the Bohai Bay Basin, eastern China, to evaluate probability of oil occurrence. The geological data from 343 exploratory wells and seismic interpretations that were available at the end of 2004 were used for the purpose. Seventeen wells were drilled after the evaluation in 2005, sixteen of which reached their target horizon. Eight of the nine wells drilled in areas with a predicted high probability of hydrocarbon occurrence (>50%) encountered commercial oil, indeed; post-drilling analysis indicated that seven of these eight wells yielded high flow rates from thick net pay, and that one of these wells yielded a low flow rate. Seven wells were drilled in areas with a predicted relatively low probability (<50%) of oil occurrence; three of them were dry and four recovered oil with relatively low flow rates. Comparison of the post-drilling results with the pre-drilling prediction suggests that the multivariate-Bayesian approach can help visualize geological risk, thus improving exploration success by optimizing the drilling strategy.