Weathering phases recorded by gnammas developed since last glaciation at Serra da Estrela, Portugal |
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| Authors: | David Domínguez-Villar Laura Razola Rosa M Carrasco Carrie E Jennings Javier Pedraza |
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| Institution: | aSchool of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston B15 2TT Birmingham, UK;bDepartamento de Ingeniería Geológica y Minera, Universidad de Castilla-La Mancha, 45071 Toledo, Spain;cMinnesota Geolcogical Survey, 2642 University Ave. St. Paul, MN 55114, USA;dDepartamento de Geodinámica, Facultad de Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain |
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| Abstract: | The morphometrical analysis of gnammas (weathering pits) in granite landscapes has been used to establish the relative chronology of recent erosive surfaces and to provide the weathering history in a region. To test the validity of gnammas as relative chronometer indicators, and the reliability of the obtained weathering record, two sites have been studied in Serra da Estrela, Portugal. The first site is within the limits of the glacier that existed in these mountains during the last glaciation, whereas the second site is located in an unglaciated sector of the mountains, which preserves a longer record of weathering in the bedrock surface. The number of gnamma weathering phases recorded in the latter site (8) is larger than those from the former (6). Correlation between both measurement stations based on morphometrical criteria is excellent for the younger six weathering phases (1 to 6). Consequently, the parameter used for relative chronology (δ-value) has been verified to be age dependent, although absolute values are modulated by microclimate due to altitude variations. The weathering record was essentially duplicated once the surfaces at both sites were exposed, demonstrating the reliability of gnamma evolution as a post-glacial environmental indicator for the region. |
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| Keywords: | Gnamma Weathering pit Granite geomorphology Morphometry Relative chronology Weathering Paleoenvironmental proxy |
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