Publication: Registro evolutivo de meteorización en rocas graníticas a partir de pilancones
desarrollados tras la última glaciación en Serra da Estrela, (Portugal)
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Publication Date
2008
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Sociedad Geológica de España.
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Abstract
El estudio de pilancones o gnammas mediante análisis morfométrico puede ser de gran utilidad para obtener información paleoambiental. En este trabajo se pretende avanzar en el conocimiento del significado evolutivo del índice morfométrico basado en el ratio de profundidad, y en la fiabilidad de los registros obtenidos mediante este método. Para ello se han seleccionado dos localidades próximas entre sí, pertenecientes a Serra da Estrela (Portugal), localizadas dentro y fuera de los límites del glaciar desarrollado en estas montañas durante la última glaciación. Los resultados muestran que la estación que comenzó la formación de pilancones tras la retirada del glaciar, presenta menor número de fases de meteorización en función del ratio de profundidad y valores absolutos más bajos de ése índice. Ambas estaciones presentan un registro de fases de meteorización muy semejante para sus últimas seis subpoblaciones, lo que permite su inequívoca correlación. Esto sugiere que el método de análisis empleado es válido para la caracterización evolutiva de pilancones, y que estas morfologías son sensibles al registro de variaciones paleoambientales relacionadas con sus procesos de meteorización. La mayoría de pilancones activos que se reconocieron tienen una edad inferior a 16 ka, lo que sugiere la rápida formación de estas cavidades.
Gnamma (weathering pits) morphometric analysis seems to be a powerful tool in order to obtain paleoenvironmental signs. This study aims to clarify the relationship between a morphometric index (depth ratio) and the evolution of gnammas with time, as well as the reliability of the records obtained with this method. Two locations were selected in Serra da Estrela (Portugal) for such propose, in and out of the limits affected by the glacier developed in these mountains during past glacial stage. Results show that the location inside the glaciated area has less phases of gnamma development based on depth ratios, and absolute values achieved are lower. Characteristics of recorded weathering phases in both measurement stations are quite similar for last six sub-populations, providing a precise correlation. This suggests that the method used for analysis is valid, and that gnammas are able to record paleoenviromental information in relation with weathering processes. Most of the gnammas studied were developed during last 16 ka, which suggest a quick evolution for such morphologies.
Gnamma (weathering pits) morphometric analysis seems to be a powerful tool in order to obtain paleoenvironmental signs. This study aims to clarify the relationship between a morphometric index (depth ratio) and the evolution of gnammas with time, as well as the reliability of the records obtained with this method. Two locations were selected in Serra da Estrela (Portugal) for such propose, in and out of the limits affected by the glacier developed in these mountains during past glacial stage. Results show that the location inside the glaciated area has less phases of gnamma development based on depth ratios, and absolute values achieved are lower. Characteristics of recorded weathering phases in both measurement stations are quite similar for last six sub-populations, providing a precise correlation. This suggests that the method used for analysis is valid, and that gnammas are able to record paleoenviromental information in relation with weathering processes. Most of the gnammas studied were developed during last 16 ka, which suggest a quick evolution for such morphologies.