Magnetic characterisation and correlation of a Younger Dryas tephra in North Atlantic marine sediments

A technique for identifying non-visible basaltic tephra-rich horizons of Younger Dryas (YD)/Greenland Stadial (GS) 1 age in northeast Atlantic sediments using rapid, non-destructive magnetic measurements is presented. Three high-resolution marine sediment cores have been studied in an E–W transect across the Hebridean margin: St Kilda Basin (MD95-2007), Barra Fan (MD95-2006) and Rockall Trough (MD04-2822). Magnetic susceptibilities and remanent magnetisations were measured at contiguous 1 cm resolution on bulk sediments. In all three cores, an interval with higher proportions of hard magnetic minerals coincides with a clearly defined peak in basaltic tephra shard (250 µm) counts, which can be constrained to the early part of the YD/GS1 based on faunal climate proxies. Electron microprobe analyses of the magnetically distinct basaltic tephra interval, in all three cores, displays the same major element geochemistry as published for the Vedde basaltic (I Tab. 1), i.e. sourced from the Icelandic volcano Katla. The identification of transitional alkalic basaltic tephras within marine sediments could potentially be facilitated by magnetic analysis as a useful chronostratigraphic screening tool.