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

Andrews, J. T. and Eberl, D. D. and Kristjansdottir, G. B. (2006) An exploratory method to detect tephras from quantitative XRD scans: examples from Iceland and east Greenland marine sediments. Holocene, 16 (8). pp. 1035-1042. ISSN 0959-6836 DOI 10.1177/0959683606069384

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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 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.

Item Type:	Article
Uncontrolled Keywords:	2007 AREP IA53 2006 P
Subjects:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title:	Holocene
Volume:	16
Page Range:	pp. 1035-1042
Identification Number:	10.1177/0959683606069384
Depositing User:	Sarah Humbert
Date Deposited:	16 Feb 2009 13:01
Last Modified:	11 Apr 2014 09:29
URI:	http://eprints.esc.cam.ac.uk/id/eprint/110

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