Jökull - 01.01.2009, Side 57

Holocene sediment- and paleo-magnetic characteristics from the Iceland and E-Greenland margins
sulting plot (not shown) shows little variability. The
data fit an exponential expression (r2=0.992) ARM
ratio=1.32*e("0.0411mT ), median reduction in the ra-
tio occurs at 25 mT. This result indicates that we are
dealing with the demagnetization of pseudo single do-
mainmagnetite; the data from the two regions are very
similar indicating the dominance of the basalt in con-
trolling the magnetic mineralogy.
For thirteen cores we have physical grain-
size data (Andrews et al., 2002a) (Appendix 2).
Mean grain-size for the sediment matrix <2 mm
is poorly correlated with median ratios of kARM/k
(not shown) but has a significant association with
ARM(J0)/ARM(J20) (r2 = 0.5), indicating that larger
phi means (= finer grain-size in µm) are more resis-
tant to AF demagnetization (Figure 3B). However, an
inspection of Figure 3B shows two contrasting asso-
ciations; there is a group of Icelandic samples that
have high ARM ratios and a tendency for the ratio
to increase as grain-size decreases (larger phi medi-
ans), whereas the remaining data from Iceland and
East Greenland show an opposite trend. The four Ice-
land sites all come from the inner margin of Vestfirðir
(Figure 1) indicating that there are regional variations
in some of the magnetic properties. The East Green-
land sediments are generally in the medium to finer-
grained category, whereas the Iceland sediments are
somewhat coarser. This may be related to the input
of significant amounts of volcanic glass on the Ice-
land shelf (Andrews et al., 2006; Kristjánsdóttir et al.,
2007) (Appendix 2) and to more extensive reworking
of shelf sediments by storms. Icelandic tephras are not
a dominant element in East Greenland shelf sediments
(Jennings et al., 2002).
Figure 3. The sites from East
Greenland or Iceland are distin-
guished in the following scatter
plots by different symbols. A)
Correlation between massMS and
kARM; B) Median phi grain-size of
the sediment <2mm and ARM(J0)/-
ARM(J20) – notice that the coarser
sediments have the smaller phi
units; C) ARM(J0)/ARM(J20) and
NRM(J0)/NRM(J60); D) Median
ARM(J0)/ARM(J20) and Median
NRM destructive field. – Stað-
ir frá Austur-Grænlandi og Ís-
landi eru aðgreindir í eftirfarandi
dreifiritum með mismunandi tákn-
um. A) Fylgni massasegulvið-
taks og segulmögnunarstuðuls fyrir
hliðrað riðstraumssvið ; B) Mið-
gildi phi-kornastærðar sets <2 mm
og ARM(J0)/ARM(J20) – gildi phi-
kornastærðar er í öfugu hlutfalli
við grófleika setsins; C) ARM(J0)/-
ARM(J20) og NRM(J0)/NRM(J60);
D) Miðgildi ARM(J0)/ARM(J20) og
miðgildi helmings-afseglunarsviða.
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