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[en] When a spill of radioactive waste occurs, one of the main concerns is the flow pattern of ground water in the area of the spill. Ground probing radar is a relatively new geophysical technique which can provide high resolution data on the surficial geology and water distribution. The results of some preliminary radar experiments conducted at Chalk River Nuclear Laboratories (CRNL) of the Atomic Energy of Canada Limited (AECL), Chalk River, Ontario are presented. (auth)
[en] The Palo Duro Basin, Permian Basin, Texas is an asymmetric, relatively shallow, intracratonic basin in the southern Texas Panhandle filled mostly by Mississippian, Pennsylvanian, and Permian sedimentary rocks. Although deeper and prolific prolific petroleum-producing basins adjoin it on the north (Anadarko Basin), south (Midland Basin), and east (Hardeman Basin), the Palo Duro Basin has produced remarkably small amounts of oil and gas to date. This is all the more noteworthy because the sedimentary sequence and rock types of the basin are similar to those of the adjacent basins. Analyses of the stratigraphic succession and structural configuration of the Palo Duro Basin suggest that adequate reservoir rocks, top-seals, and geologic structures are present. Most of the structures formed early enough to have trapped hydrocarbons if they were migrating in the rock column. Although additional work is under way to properly address the question of the petroleum source rocks, generation, and migration, the general absence of production in the basin may relate to an overall deficiency in hydrocarbon generation within the basin. Geologic information in this report will form part of the basis for further analysis and conclusions on hydrocarbon potential in the Palo Duro Basin
[en] A diverse and abundant organic-walled microphytoplankton assemblage, consisting of 49 species of acritarchs, prasinophyte phycomata and chitinozoans, was recovered from a 13.3 m-section of the Middle Devonian (Givetian) Arkona, Hungry Hollow andWidder formations at Hungry Hollow, Ontario, Canada. Close similarity exists between this assemblage and others described previously from the Givetian of North America. Marine palynofloras of comparable age from elsewhere in North America share between 59–96% of the species identified in the present assemblage, thus testifying to its stratigraphic-correlative applicability in a regional context. Species widely occurring in North America and typically Givetian (although not restricted therein) include: Arkonites bilixus, Cymatiosphaera canadense, Diexallophasis simplex, Duvernaysphaera angelae, D. tenuicingulata, Estiastra rhytidoa, Exochoderma arca, Gorgonisphaeridium inflatum, Hapsidopalla chela, Leiofusa pyrena, Muraticavea munifica, Oppilatala sparsa, Palacanthus ledanoisii, Polyedryxium ambitum, Staplinium cuboides, Tyligmasoma alargada, Uncinisphaera acantha, Veryhachium pastoris, Villosacapsula compta and V. rosendae. Palaeogeographically, Middle Devonian organic-walled microphytoplankton taxa display a conspicuous degree of cosmopolitanism, with many species shared with Laurasia (Laurentia, Avalonia, Baltica), Gondwana (principally Argentina, Ghana, Libya, Algerian Sahara, Western Australia) and Kazakhstan (northwestern China).
[es]Una asociación diversa de micropláncton de pared orgánica con gran abundancia de ejemplares, que está integrada por 49 especies de acritarcos, ficomas de prasinofitos y quitinozoos, fue obtenida en los materiales de la sección de 13,3 m de potencia del Devónico Medio (Givetiense) de Arkona, formaciones Hungry, Hollow y Widder, Ontario, Canadá. Esta asociación es muy parecida a otras que previamente se describieron en el Givetiense de Norte América. Algunas palinofloras marinas de otras partes de Norte América presentan asociaciones compuestas por un 59-96% de las especies que se estudian en este trabajo. De este modo, se pone de manifiesto su aplicación estratigráfica y de correlación en un contexto regional. Entre el conjunto de especies norteamericanas y típicamente givetienses (aunque no se encuentran restringidas a esta edad) identificadas están: Arkonites bilixus, Cymatiosphaera canadense, Diexallophasis simplex, Duvernaysphaera angelae, D. tenuicingulata, Estiastra rhytidoa, Exochoderma arca, Gorgonisphaeridium inflatum, Hapsidopalla chela, Leiofusa pyrena, Muraticavea munifica, Oppilatala sparsa, Palacanthus ledanoisii, Polyedryxium ambitum, Staplinium cuboides, Tyligmasoma alargada, Uncinisphaera acantha, Veryhachium pastoris, Villosacapsula compta y V. rosendae. Paleogeográficamente, los taxones microplanctónicos de pared orgánica del Devónico Medio que hemos identificados, son cosmopolitas en un alto grado, con muchas especies distribuidas por Laurasia (Laurentia, Avalonia, Báltica), Gondwana (principalmente Argentina, Ghana, Libia, el Sahara argelino, el Oeste de Australia) y Kazakhstan (noroeste de China
[en] The structure of Africa became established at the end of the Precambrian era (500-600 million years ago). It is the result of a series of relatively brief paroxysmal events, which constitute good chronological markers, and of long periods of relative stability. A complete succession of events - erosion, transport, sedimentation and folding - constitutes an orogeny or cycle; the final, paroxysmal phase is called an ''orogenesis''. As regards Africa, authors distinguish between four major orogeneses: Precambrian A (500-600 to 900-1200 million years ago), Precambrian B (900-1200 to 1800-2000 million years ago), Precambrian C (1800-2000 to 2500 million years ago), Precambrian D (before 2500 million years ago). Africa is conventionally considered to be made up of four consolidated and granitized cratons: the West African (or guineo-eburnean), Congolese, Kalahari and nilotic cratons. With these cratons are associated internal, ''intracratonic'' basins with relatively shallow detritic sedimentation and intercratonic zones with their own deep sedimentation; the latter, located at the periphery of the cratons, on the fold axes, are called ''mobile belts''. Gabon lies in the north-west part of the Congolese craton. The Franceville basin is one of the intracratonic basins of the Congolese craton. The age of its sediments has been estimated at 1740+-20 million years. The Franceville basin can thus be assigned to the Precambrian B orogenesis
[en] Rb-Sr isochrone analyses of granitoid rocks from the southern part of the Veporic zone - the so-called Kohut zone - are presented. In this region, the Sinec (Rimavica) type of granitoids formerly considered to be Late Palaeozoic to Neoide, is found. The present isochrone research determines them as equivalents of granitoids of the Sihla type (387±27 m.y.). The Sinec (Rimavica) granite reaches an age of 392±5 m.y. This extended age must partly be attributed to additional processes which took place in the stage of retrograde alterations. The conclusions are of considerable importance in clarifying the metamorphic age and stratigraphy of the crystalline complex in the region of the southern Veporic zone. (author). 9 figs., 4 tabs., 38 refs
[en] The research conducted under DOE grant DE-FG26-98FT40385 provides a detailed assessment of size scaling issues in natural fracture and active fault networks that extend over scales from several tens of kilometers to less than a tenth of a meter. This study incorporates analysis of data obtained from several sources, including: natural fracture patterns photographed in the Appalachian field area, natural fracture patterns presented by other workers in the published literature, patterns of active faulting in Japan mapping at a scale of 1:100,000, and lineament patterns interpreted from satellite-based radar imagery obtained over the Appalachian field area. The complexity of these patterns is always found to vary with scale. In general,but not always, patterns become less complex with scale. This tendency may reverse as can be inferred from the complexity of high-resolution radar images (8 meter pixel size) which are characterized by patterns that are less complex than those observed over smaller areas on the ground surface. Model studies reveal that changes in the complexity of a fracture pattern can be associated with dominant spacings between the fractures comprising the pattern or roughly to the rock areas bounded by fractures of a certain scale. While the results do not offer a magic number (the fractal dimension) to characterize fracture networks at all scales, the modeling and analysis provide results that can be interpreted directly in terms of the physical properties of the natural fracture or active fault complex. These breaks roughly define the size of fracture bounded regions at different scales. The larger more extensive sets of fractures will intersect and enclose regions of a certain size, whereas smaller less extensive sets will do the same--i.e. subdivide the rock into even smaller regions. The interpretation varies depending on the number of sets that are present, but the scale breaks in the logN/logr plots serve as a guide to interpreting the intensity of rock fragmentation as a function of scale
[en] The sudden appearance of biomineralized metazoans in limestone facies of the Pockenbank Member (Namibia) appears to reflect a rapid change of redox state, calcium concentration and alkalinity of the ocean. The coupling of a major biological innovation with the end of a profound carbon isotope excursion supports the view that the Shuram was a tectonic and oceanographic phenomenon, as opposed to a global diagenetic conspiracy. The temporal concordance of these profound events as preserved in strata from southern Namibia may thus be considered as exceptional geological markers for the base of the terminal Ediacaran.
[es]La repentina aparición de metazoos biomineralizados en las facies calcáreas del Miembro de Pockenbank (Namibia) parece reflejar un rápido cambio en el estado redox, la concentración de calcio y la alcalinidad del océano. La combinación de una importante innovación biológica con el final de una profunda excursión de isótopos de carbono respalda la idea de que la anomalía Shuram fue un fenómeno tectónico y oceanográfico, en contraposición a una “conspiración” diagenética mundial. La concordancia temporal de estos profundos acontecimientos, tal como se conservan en los estratos de Namibia meridional puede considerarse, por tanto, como marcadores geológicos excepcionales para la base del Ediacárico terminal.