Fróðskaparrit - 01.01.1998, Síða 266

272
MACROFOSSIL STUDIES OF LACUSTRINE SEDIMENTS FROM SKÁLAFJØRÐUR,
THE FAROEISLANDS, PRELIMINARY RESULTS
custrine sediments below, in which the
Saksunarvatn ash layer shows only slightly
elevated values. In the marine part, an in-
terval with high MS values corresponds to
coarser-grained sediments contaning,
amongst others, gravel-sized basaltic mate-
rial.
Considering the extremely small sample
size, the diversity of macrofossils is sur-
prisingly high, and the concentration of re-
mains of lacustrine animals is high.Some of
the taxa recorded undoubtedly represent
several different species. The preservation
is usually good to excellent, although the
Salix leaves were fragmented, and only a
few leaf fragments retained the dentate leaf
margin and could be safely identified as be-
longing to Salix herbacea. A few small,
worn twig fragments were present at 140
cm, these were avoided for dating.
The lowest sample, from 170 cm, only
contained two head capsules of midge lar-
vae, and these sediments were probably de-
posited in a glaciolacustrine environment.
The sediments between c. 167 cm and 87
cm are characterised by a diverse and rich
flora and fauna of obligate freshwater taxa
that clearly indicate that these sediments
were deposited in a former lake basin. At
87 cm the first marine fossils occur, and at
the same time lacustrine fossils become
rare. This shows that the threshold was
transgressed by the sea. The rare lacustrine
fossils present at this level and above could
represent redeposition or inwash from
freshwater basins in the drainage area.
Salix herbacea leaves were also recorded
fronr early Holocene lake sediments by
Jóhansen (1985), and this species was also
an early immigrant to Iceland and East
Greenland (M. Rundgren, personal com-
munication, 1997; Bennike et al. in press).
S. herbacea is an indicator of snow-patch
vegetation, and the species is common on
high elevation sites in the Faroe Islands at
present. Jóhansen did not separate pollen
grains of Oxyria digyna and Rumex aceto-
sa, but he suggested that most pollen came
from Oxyria digyna. The presence of a few
nutlets and perianths of Rumex acetosa
shows that this species that often grows as
a weed, is native to the Faroes, and that it
arrived early. Microspores of Selaginella
selaginoides were reported from the early
Holocene by Jóhansen (1985), and the
presence of macrospores in the Skálafjørð-
ur sediments shows that it grew locally.
Coleoptera remains include three elytra,
of which one could be identifíed as Nebria
rufescens. This is a medium sized ground
beetle that is common in Faroe Islands at
the present (West, 1937: Nebria gyllen-
hali). It is most frequent in damp biotopes,
but is geographically and ecologically
widespread on the archipelago. Its geo-
gráphical range is circumpolar, including
Iceland and southwest Greenland, and it
lives in northern temperate and low arctic
climates (Bocher, 1988).
It appears that Potamogeton fúiformis
and Nitella sp. are new to the fossil flora of
the Faroe Islands, but this merely reflects
that few macrofossil studies of lake sedi-
ments have been carried out. It is not sur-
prising that these taxa arrived early, since
the fruits or oospores are effetively spread
by migrating birds. Along the same line,
most of the lacustrine animals recovered