The Morphological and Optical Properties of Volcanic Glass: A Tool to Assess Density-induced Vertical Migration of Tephra in Sediment Cores |
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Authors: | Mihaela D Enache Brian F Cumming |
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Institution: | (1) Paleoecological Environmental Assessment and Research Lab (PEARL), Queen’s University, Kingston, ON, K7L 3N6, Canada |
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Abstract: | Volcanic ash layers in sediment cores are valuable geochronological markers in paleolimnological research. The composition
of volcanic glass is related to identifiable, chronologically distinctive volcanic eruptions. Consequently, tephra layers
provide time horizons allowing regional-scale correlations for lake sediments. Volcanic glass is often present in samples
routinely prepared by paleolimnologists such as diatom slides and thin sections. Knowledge of the morphological and optical
properties of volcanic glass allows for its identification. This is essential for the identification of ash layers that are
not macroscopically visible or to track their vertical migration in soft organic sediments. The purposes of this note are
to: (1) describe how the morphological (i.e., shape, vesicularity) and optical (i.e., refractive index and birefringence)
properties can be used to identify volcanic glass in preparations from lake sediments; and (2) show how the quantification
of volcanic glass from diatom slides is used to quantify the density-induced displacement of a 4.5 cm-thick Mazama ash-layer
through organic sediments and to approximate its timing of initial deposition. |
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Keywords: | Mazama Morphology Optical properties Sediment cores Tephra Vertical migration Volcanic glass |
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