Internal structure of a trough blowout, determined from migrated ground-penetrating radar profiles

Ground‐penetrating radar (GPR) was used to investigate the relationship between the geomorphological development of a large aeolian trough blowout and the stratigraphy and internal sedimentary structure of its associated deposits. Although analogous, many of the data‐processing techniques routinely applied in seismic reflection are very rarely applied in GPR studies. In this study, a simple migration program was used that significantly enhanced the quality of GPR images from a large trough blowout at Raven Meols on the Sefton coast, northwest England. These improvements aided subsequent data interpretation, which was achieved through application of the principles of radar stratigraphy. GPR shows the pre‐blowout dunes to have a complex internal structure that suggests they were formed in the presence of at least a partial vegetation cover. Subsequent to stabilization of these dunes a thin soil developed. This dune soil forms an important radar sequence boundary and delineates a complex topography beneath the depositional lobe of the blowout. The internal structure of the depositional lobe of the blowout does not conform to a model of simple radial foreset deposition, as derived from contemporary process studies reported in the literature. Instead, the pattern of deposition has been extensively modified by the antecedent dune topography and by varying spatial and temporal exposure to important sand‐transporting winds that is partly controlled by interactions between the regional wind pattern and local dune morphology. Trough blowout deposits in coastal aeolian sedimentary sequences are likely to be recognized by the presence of laterally continuous packets of relatively high‐angle cross‐strata, which often display a spatially‐variable radial dip pattern that is only very poorly or partially developed. In addition, a soil, or other surface representing a significant hiatus in dune deposition, is likely to underlie the blowout deposits, the topography of which will show a clear relationship to the dip and orientation of the overlying cross‐strata.     

Strukturelle Verhältnisse in den Südlichen Patagonischen Anden und Deren Beziehung zur Antarktis: Eine Diskussion

Zusammenfassung Das zum pazifischen Rückland konvexe Umbiegen der patagonischen Kordillere im Raum von Magellanstraße und Feuerland ist sehr uneinheitlich. In den subandinen Elementen hat sich um die Dawsoninsel eine eigentliche Knickstelle gebildet, mit beidseitig stärkerer Faltenscharung und Verschuppungstendenz. Der Zusammenschub des Gebirges auf Feuerland ist viel stärker als im N—S-streichenden Abschnitt nördlich der Magellanstraße. Dabei haben sich Blattverschiebungen entlang hauptsächlich NNW-, z. T. auch NE-streichender Bruchsysteme herausgebildet. Die Dawsoninsel selbst ist als ein zwischen solchen Bruchflächen südwärts zurückgebliebener Keil zu verstehen.Die mehr gebirgeeinwärts liegenden, zentralandinen Elemente machen das konvexe Umbiegen nur undeutlich mit, indem mehrere voneinander abgetrennte, an sich konkav stehende Segmente rotiert sind und mehr oder weniger stark nach NE vorgestoßen sind. Das Strukturbild der zentralandinen Zone ist denn auch unvergleichlich viel komplexer und gestörter als dasjenige des Subandins. Dabei macht sich am äußersten Südostzipfel Südamerikas eine starke Virgation der Gebirgselemente bemerkbar, die mit Richtungen zwischen ENE und SE ins Meer ausstreichen.Als weiteres, wichtiges Strukturelement wird die WNW-streichende Magellan-Bruchzone erwähnt, die auf 600 km Länge das Gebirge diagonal durchschneidet und gewissermaßen Südamerika nach S begrenzt; ihre Bedeutung wird diskutiert.Anhand fazieller und tektonischer Vergleiche, vor allem zwischen den zentralandinen Elementen auf Navarino und Südgeorgien, und basiert auf mehr spekulativen Betrachtungen der physiographischen Verhältnisse des Meeresbodens wird gezeigt, daß der Raum des Südantillenmeeres möglicherweise von einem System NE-streichender Blattverschiebungen beherrscht wird; diese wären im Gefolge des Ostdruckes eines starren Südpazifikblockes entstanden. Der Südantillenbogen würde sich damit aus verschiedenen, abgescherten Fragmenten zusammensetzen, die sich ungefähr bogenförmig um diesen Raum gruppieren. Das stärkere Zusammenpressen der feuerländischen Kordillere mit all ihren Komplikationen und Sekundärstörungen, wie auch die Bildung der Magellan-Bruchzone könnten ebenfalls durch diesen Vorstoß eines südlich davon liegenden, pazifischen Krustenteils erklärt werden.Das Zerreißen einer vorher direkten, tektonischen Verbindung zwischen Südamerika und der antarktischen Halbinsel hat erst im Anschluß an die andine Orogenese stattgefunden. Es wird vermutet, daß als Folge davon das Südantillenmeer wohl hauptsächlich von sialischem Krustentyp ist.

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The convex bending, with respect to the Pacific back-land, of the Patagonian Cordillera around Straits of Magellan and Tierra del Fuego is not at all uniform. Near Dawson Island, the subandean fold belt changes direction abruptly, showing simultaneously a tendency to develop narrow fold bundles and dislodged slices. Compression of the mountain belt in Tierra del Fuego is more pronounced than north of the Straits of Magellan, where the strike is roughly N-S. Consequently, wrench faulting occurred along NNW-, partly also NE-striking fracture systems. Dawson Island itself is considered a wedge which is left behind south, with respect to near-by segments that have advanced further along such fault planes.Elements of a more central position in the mountain belt do not show the convex bending to the same degree: individual segments, each in itself concavely bent, have rotated differently and been pushed to the NE by differential moving. Thus the structural picture of the central-andean part is much more complicated, as compared to the subandean belt. Between both areas, a pronounced virgation of the fold axes, which fan out in directions between ENE and SE, is evident toward the extreme southeastern tip of South America.Another, very important structural feature is the WNW-striking Magallanes Fault Zone, which over a distance of 600 km cuts obliquely across the area; in a way it delimits the continental block towards the south.Tectonic and facies relations, particularly between the central-andean elements of Navarino Island and South Georgia, as well as more speculative considerations of the physiographic ocean-bottom features suggest the Scotia Sea area being controlled by a system of NE-trending wrench faults; they are supposed to have developed in response to an easterly-directed pressure of a stable block in the South Pacific. The Scotia Arc would thus by composed of a number of differentially detached segments, their above-sea portions being located in an arc-like manner around the area. By such an advance of the Pacific crust south of Tierra del Fuego, both the pronounced compression of the Cordillera in the latter area with all its further implications, and the development of the Magallanes Fault Zone could equally well be explained.The rupture of an originally more direct, tectonic connection between South America and the Antarctic Peninsula occurred as a consequence of Andean orogeny. It is supposed that the Scotia Sea crust therefore is mainly of a sialic type.

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Resumen En base de nuevos antecedentes, se presenta un análisis tectonico-estructural de la Cordillera patagonica austral, discutiendo en adición su posible relación, através del Arco escosés, con la Peninsula antárctica. Un extracto mas extenso del tema fue publicado, en lengua castellana, por la Sociedad Gelógica de Chile («Resúmenes» no. 7/16, Santiago 1964 — ver Bibliografía al final).

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Résumé Dans la région du Détroit de Magellan et de la Terre de Feu, l'arc convexe, vu de l'arrière-pays, de la Cordillère patagonique est construit d'une mannière très irrégulière. Autour de l'île de Dawson, une véritable déflexion s'est formée dans les éléments subandins, exposant une tendance à la formation de faisceaux de plis et de lames charriées. La compression de la chaîne est beaucoup plus forte en Terre de Feu, qu'au nord du Détroit de Magellan où elle maintient une direction presque nord-sud. Des failles transversales se sont ainsi développées qui ont une direction surtout NNO, ou aussi NE. L'île de Dawson elle-même serait un coin resté en arrière au sud, par rapport aux segments voisins qui sont plus avancés le long de ces zones de faille.Les éléments qui se trouvent plus au centre de la cordillère suivent la forme de l'arc d'une manière peu prononcée. De différents segments qui eux-mêmes sont concaves, sont avancés différentiellement vers le NE à cause d'un mouvement rotatoire. C'est ainsi que la structure de la zone centrale-andine est beaucoup plus complexe que celle de la zone subandine. En outre, on note une forte virgation de tous les éléments vers l'extrême bout du continent, prenant une direction qui va entre l'ENE et le SE.De plus, on trouve une zone de faille régionale très importante qui a une direction ONO, traversant toute la région d'une longueur de 600 kms; elle est appelée «Zone de Faille de Magellan».Des comparaisons de la faciès et tectonique, surtout entre les éléments central-andins de l'île de Navarino et Géorgie du Sud, et des considérations plus spéculatives de la physiographie du fond de la mer, font présumer que la région de la mer écossaise soit controlée par un système de failles transversales de décrochement, ayant une direction nord-est. L'arc écossais serait composé ainsi par des éléments décollés le long de ces failles, groupés autour de la mer écossaise. Ce décollement, ainsi que la compression de la cordillère en Terre de Feu avec toutes ces complications secondaires seraient le résultat d'un avancement vers l'est de l'écorce du Pacifique sud.La rupture d'une connection tectonique originairement plus directe entre l'Amérique du Sud et l'Antarctique s'est produite en conséquence des mouvements orogénétiques andins. On suppose que pour cette raison la région de la mer écossaise soit occupée par une écorce sialique.

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Broken Hill — A Precambrian hot spot?

Studies on the variations of metamorphism in the Precambrian granulite facies terrain of Broken Hill has revealed that these high-grade rocks are most frequently found in an elliptical zone known as the Broken Hill Basin. The density distribution of these granulite facies rocks, together with their lithological—structural—geophysical—mineralization relationships suggest local conditions of high-grade metamorphism. Several models to account for these observations are possible including lithological, structural-stratigraphic and mineralization controls. However in the light of current views of plate tectonics, a crustal-spreading hot spot model should also be seriously considered. The association of high-grade metamorphism and Broken Hill type mineralization is thought to be significant and this relationship could be applied in the search for ore deposits.     

Chemical studies of L-chondrites—I. A study of possible chemical sub-groups

Radiochemical neutron activation analysis of Ag, As, Au, Bi, Co, Cs, Ga, In, Rb, Sb, Te, Tl and Zn and major element data in 14 L4-6 and 3 LL5 chondrites indicates that the L-group is unusually variable and may represent at least 2 sub-groups differing in formation history. Chemical trends in the S/Fe-rich sub-group support textural evidence indicating late loss of a shock-formed Fe-Ni-S melt; the S/Fe-poor sub-group seemingly reflects nebular fractionation only. Highly mobile In and Zn apparently reflect shock-induced loss from L-chondrites. Data for L5 chondrites suggest higher formation temperatures and/or degrees of shock than for LL5 chondrites.     

Assessing the impact of climatic change on food production

Attempts to assess the impact of a hypothetical climatic change on food production have relied on the use of statistical models which predict crop yields using various climatic variables. It is emphasized that the coefficients of these models are not universal constants, but rather statistical estimates subject to several sources of error. Thus, any statement regarding the estimated impact of climatic change on food production must be qualified appropriately.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The geochemical evolution of the Pleistocene Lake Lisan-Dead Sea system

The geochemical history of Lake Lisan, the Pleistocene precursor of the Dead Sea, has been studied by geological, chemical and isotopic methods.Aragonite laminae from the Lisan Formation yielded (equivalent) Sr/Ca ratios in the range 0.5 × 10^?2?1 × 10^?2, Na/Ca ratios from 3.6 × 10^?3 to 9.2 × 10^?3, $\text{δ}{}^{18}\text{O}{}_{\mathrm{PDB}}$ values between 1.5 and 7%. and $\text{δ}{}^{13}\text{C}{}_{\mathrm{PDB}}$ from ?7.7 to 3.4%..The distribution coefficient of Na⁺ between aragonite and aqueous solutions, $\text{λ}{}^{\mathrm{A}}{}_{\mathrm{Na}}$, is experimentally shown to be very sensitive to salinity and nearly temperature independent. Thus, Na/Ca in aragonite serves as a paleosalinity indicator.Sr/Ca ratios and $\text{δ}{}^{18}\text{O}$ values in aragonite provide good long-term monitors of a lake's evolution. They show Lake Lisan to be well mixed, highly evaporated and saline. Except for a diluted surface layer, the salinity of the lake was half that of the present Dead Sea (15 vs 31%).Lake Lisan evolved from a small, yet deep, hypersaline Dead Sea-like, water body. This initial lake was rapidly filled-up to its highest stand by fresh waters and existed for about 40,000 yr before shrinking back to the present Dead Sea. The chemistry of Lake Lisan at its stable stand represented a material balance between a Jordan-like input, an original large mass of salts and a chemical removal of aragonite. The weighted average depth of Lake Lisan is calculated, on a geochemical basis, to have been at least 400, preferably 600 m.The oxygen isotopic composition of Lake Lisan water, which was higher by at least 3%. than that of the Dead Sea, was probably dictated by a higher rate of evaporation.Na/Ca ratios in aragonite, which correlate well with $\text{δ}{}^{13}\text{C}$ values, but change frequently in time, reflect the existence of a short lived upper water layer of varying salinity in Lake Lisan.     

The incorporation of uranium into diagenetic phosphorite

The behavior of U during the diagenetic formation of marine phosphorite has been modelled. The model examines a dissolution-reprecipitation replacement of skeletal hydroxyapatite, calcium carbonate and earlier generated francolite by francolite. The amount of organic matter consumed relative to the mass of francolite formed, the replacement reaction progress, and the concentration of U in the replaced phases are the important parameters which dictate the concentration of U in the phosphate rock.A partition coefficient between apatite and interstitial solution was calculated, and is $\text{λ}{}_{\mathrm{U}}{}^{\mathrm{F}}\text{= 0.57}$.Natural phosphorites have been examined and are discussed in the light of the proposed model. The U mass-balance in a Recent phosphorite is in good accord with theoretical predictions. Differences in U concentrations between sea-floor phosphorites are explained either by the (original) variation in the organic matter distribution in the corresponding sediments and/or by mineralogical differences (CaCO₃vs. hydroxyapatite) therein.Senonian phosphate rocks which were formed via the francolite → francolite transformation, demonstrate that during that process the organic matter content in the sediment was approximately 50%.The model supports the idea that phosphorite rock formation is a multistage process.     

The vortex tube and the tornado

Summary When votex flow is induced in a stream of gas, as in the Ranque-Hilsch tube, the temperature of the axial portion of the vortex is lowered while the temperature of the peripheral portion is raised. The principle of conservation of angular momentum appears to control the conversion of hat to mechanical energy. A similar mechanism may account for some characteristics of tornadoes.