AN EXPLORATORY METHOD TO DETECT TEPHRAS FROM QUANTITATIVE XRD SCANS: EXAMPLES FROM ICELAND AND EAST GREENLAND MARINE SEDIMENTS

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=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 ?m 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.