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

• Published in: The Holocene
• Main Authors: Andrews, J. T., Eberl, D. D., Kristjansdottir, G. B.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Sage 2006
• Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems; Baffin Bay; Greenland; Saksunarvatn; Baffin; East Greenland; Hekla; Iceland
• Online Access: http://eprints.esc.cam.ac.uk/110/; http://eprints.esc.cam.ac.uk/110/1/The%20Holocene-2006-Andrews-1035-42.pdf; http://hol.sagepub.com/content/16/8/1035.abstract; https://doi.org/10.1177/0959683606069384

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.