An exploratory method to detect tephras from quantitative XRD scans: examples from Iceland and east Greenland marine sediments

Tephras, mainly from Iceland, are becoming increasingly important in interpreting leads and lags in the Holocene climate system across NW Europe. Here we demonstrate that Quantitative Phase Analysis of x-ray diffractograms of the <2 mm of marine sediment fraction (ie, sand, silt and clay) from Ic...

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Bibliographic Details
Published in:The Holocene
Main Authors: Andrews, John T., Eberl, D. D., Kristjansdottir, Greta B.
Format: Article in Journal/Newspaper
Language:English
Published: SAGE Publications 2006
Subjects:
Paleontology
Earth-Surface Processes
Ecology
Archeology
Global and Planetary Change
Baffin Bay
Greenland
Saksunarvatn
Baffin
East Greenland
Hekla
Iceland
Online Access:http://dx.doi.org/10.1177/0959683606069384
http://journals.sagepub.com/doi/pdf/10.1177/0959683606069384
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Summary:Tephras, mainly from Iceland, are becoming increasingly important in interpreting leads and lags in the Holocene climate system across NW Europe. Here we demonstrate that Quantitative Phase Analysis of x-ray diffractograms of the <2 mm of marine sediment fraction (ie, sand, silt and clay) from Iceland and East Greenland can detect peaks in volcanic glass concentrations (weight%) even though discrete tephra layers are not visible; thus it provides a rapid overview of the probable location of volcanic glass within sediment sequences. Experiments in spiking samples from Baffin Bay and an artificial mixture of minerals with known weight% fractions of an Icelandic tephra (Hekla 4) demonstrate a significant correlation (r 2 =0.92 and 0.97) between known and estimated weight percentages, although the slope of the measured to observed weight% is around 0.65 and not 1.0 as expected. In core B997-321PC off North Iceland we identify tephras from point counting in the > 150 μm fraction and identify these same peaks in XRD scans two of these correlate geochemically and chronologically with Hekla 1104 and 3. At a distal site to the WNW of Iceland, on the East Greenland margin (core MD99-2317), the weight% of volcanic glass reaches values of 11% at about the time of the Saksunarvatn tephra. The XRD method identifies the presence of volcanic glass but not its elemental composition; hence it will assist in focusing attention on specific sections of sediment cores for subsequent geochemical fingerprinting of tephras.

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