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

Andrews, J. T.; Eberl, D. D.; Kristjansdottir, G. B.

Abstract:

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 (r2 = 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 um 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. ?? 2006 SAGE Publications.

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Article

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70028812

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Andrews, J. T.; Eberl, D. D.; Kristjansdottir, G. B.

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1042

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English

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Holocene

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An exploratory method to detect tephras from quantitative XRD scans: Examples from Iceland and east Greenland marine sediments; 2006; Article; Journal; Holocene; Andrews, J. T.; Eberl, D. D.; Kristjansdottir, G. B.