Identification and definition of primary and reworked tephra in Late Glacial and Holocene marine shelf sediments off North Iceland
Article first published online: 26 JUL 2011
Copyright © 2011 John Wiley & Sons, Ltd.
Journal of Quaternary Science
Volume 26, Issue 6, pages 589–602, August 2011
How to Cite
Gudmundsdóttir, E. R., Eiríksson, J. and Larsen, G. (2011), Identification and definition of primary and reworked tephra in Late Glacial and Holocene marine shelf sediments off North Iceland. J. Quaternary Sci., 26: 589–602. doi: 10.1002/jqs.1474
- Issue published online: 10 AUG 2011
- Article first published online: 26 JUL 2011
- Manuscript Accepted: 7 NOV 2010
- Manuscript Revised: 5 NOV 2010
- Manuscript Received: 5 OCT 2010
- time signal
Nine tephra layers in marine sediment cores (MD99-2271 and MD99-2275) from the North Icelandic shelf, spanning the Late Glacial and the Holocene, have been investigated to evaluate the effectiveness of methods to detect tephra layers in marine environments, to pinpoint the stratigraphic level of the time signal the tephra layers provide, and to discriminate between primary and reworked tephra layers in a marine environment. These nine tephra layers are the Borrobol-like tephra, Vedde Ash, Askja S tephra, Saksunarvatn ash, and Hekla 5, Hekla 4, Hekla 3, Hekla 1104 and V1477 tephras. The methods used were visual inspection, magnetic susceptibility, X-ray photography, mineralogical counts, grain size and morphological measurements, and microprobe analysis. The results demonstrate that grain size measurements and mineralogical counts are the most effective methods to detect tephra layers in this environment, revealing all nine tephra layers in question. Definition of the tephra layers revealed a 2–3 cm diffuse upper boundary in eight of the nine tephra layers and 2–3 cm diffuse lower boundary in two tephra layers. Using a multi-parameter approach the stratigraphic position of a tephra layer was determined where the rate of change of the parameters tested was the greatest compared with background values below the tephra. The first attempt to use grain morphology to distinguish between primary and reworked tephra in a marine environment suggests that this method can be effective in verifying whether a tephra layer is primary or reworked. Morphological measurements and microprobe analyses in combination with other methods can be used to identify primary tephra layers securely. The study shows that there is a need to apply a combination of methods to detect, define (the time signal) and discriminate between primary and reworked tephra in marine environments. Copyright © 2011 John Wiley & Sons, Ltd.