The effect of annealing on the luminescence decay-time of synthetic calcite:Mn

Calcite was synthesized by four methods, and the luminescence decay-time was measured for nine samples before and after heating hydrothermally in the temperature range 200–400°C. Decay-time data were collected between room temperature and approximately 15 K. The decay time at room temperature is approximately 50 ms, with little difference between a given calcite before and after hydrothermal treatment. The decay time at 15 K is always greater than at room temperature as the effect of thermal quenching diminishes. Differences in decay time before and after heating are more apparent at low temperature owing to this reduction in thermal quenching. The decay time decreased significantly in two samples, and an increase in decay time was observed in the remaining seven samples following heating. Among the latter group, the change in decay time was insignificant in three samples. The results are compared with previous data in which it was shown that the effect of heating is to increase the intensity of luminescence.     

Meeting the Challenge of Systemic Change in Geography Education: Lucy Sprague Mitchell’s Young Geographers

The history of K–12 geography education has been characterized by recurrent high hopes and dashed expectations. There have, however, been moments when the trajectory of geography education might have changed to offer students the opportunity to develop a thorough working knowledge of geography. Lucy Sprague Mitchell’s geography program developed in the 1920s and 1930s was brilliant in its conception and execution but it did not lead to large-scale systemic change. Analyzing the origins, development, and outcome of her program suggests the conditions that facilitate and inhibit systemic change, and therefore perhaps we can learn to capitalize on comparable moments in the future.     

Use of Recycled Polyethylene Terephthalate Strips in Soil Improvement

Geotechnical and Geological Engineering - Many studies have investigated polyethylene terephthalate (PET) and polypropylene fibers in soil improvement. However, there is a lack of research using...     

Cretaceous and Paleogene geologic history of coastal Ecuador

Following a general review of the Cretaceous and Paleogene geology of Ecuador, we propose a geologic history from early Cretaceous through Oligocene time with emphasis on the coastal part of the country that is based on the interpretive interaction of three oceanic plates (the Bolívar, proto-Nazca, and Nazca) and the continental South American plate. The proposed history invokes large lateral displacements, the intervention of the previously unrecognized Bolívar plate, the development of three successive subduction zones, the formation of a distant oceanic island arc and its subsequent collision with the South American plate, the emplacement of a major olistostrome complex, and an intricate record of displacement on a currently inactive transform fault. The proposed history offers a viable solution to four major problems of the geology of coastal Ecuador.

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Zusammenfassung Aus der Kreide- und Paläogen-Geschichte Ecuadors läßt sich die Entwicklung der Küstenregion ableiten. Sie wird vom Zusammenwirken von drei ozeanischen Platten (Bolivar, Proto-Nazca und Nazca) und der kontinentalen Platte Südamerikas bestimmt. Die Entwicklung umfaßt ausgedehnte Seitenverschiebungen, das Auftreten einer bisher nicht erkannten Bolivar-Platte, die Anlage von drei aufeinanderfolgenden Subduktionszonen, die Bildung eines Inselbogens und die folgende Kollision mit der Südamerikanischen Platte, die Ablagerung eines großen Olisthostrom-Komplexes und die Verschiebungen entlang einer heute inaktiven Transform-Verwerfung. Damit sind eine Reihe von Problemen der Geologie des Küstenabschnittes Ecuadors gelöst.

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Résumé Passant en revue la géologie de l'Equateur au Crétacique et Paléogène, les auteurs proposent une histoire géologique allant depuis le Crétacique inférieur à l'Oligocène en mettant l'accent sur la région cÔtière, et en se basant sur l'interaction de trois plaques océaniques (bolivienne, proto-Nasca et Nasca) et de la plaque continentale de l'Amérique du Sud. L'histoire proposée fait appel à de grands déplacements, à l'intervention de la plaque bolivienne non reconnue antérieurement, au développement de trois zones de subduction successives, à la formation d'une guirlande d'Îles océaniques distante et sa collision subséquente avec la plaque de l'Amérique du Sud, à la mise en place d'un grand complexe olistostromique et à un déplacement sur une faille transformante inactive. L'histoire proposée apporte une solution viable à quatre problèmes de la géologie de la Région cÔtière de l'Equateur.

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. (, protoNazca Nazca) . : , , , , , Olistostrome . .

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Contribution No. 6 A, Departamento de Geología, Escuela Politécnica Nacional, Quito, Ecuador.