Fróðskaparrit - 01.01.1991, Blaðsíða 66

70
A NOTE ON THE OCCURENCE OF LAND PLANARIANS
Fig. 1. Sites of pre-settlement Plantago lanceolata men-
tioned in the text.
on the northern shore of Bitrufjordur, a 3m
deep stream section cut into marine silts of
at least 8m thickness is truncated at its land-
ward and upper surface by an erosional
scarp which is itself draped by a sand and
gravel deposit (Fig 2). This deposit contains
a lOcm thick layer of peat which slopes sea-
wards from 8.5m asl to about 6.5m asl.
Statigraphically above the peat layer is a dis-
tinct beach ridge composed of course marine
sands and gravels. Contained within this
ridge is a lOcm thick layer of peat whose up-
per surface gives way to gravel and cobbles
capped by soil. Incremental samples were
taken through the entire section for sedi-
ment, pollen and microfaunal analysis. Sam-
ples 3-10 were taken from the main section
whereas samples 1-2 came from the beach
ridge which lies stratigraphically above, but
seaward of, the main section (Fig 2). The
pollen diagram from these samples suggests
a sedge-grass tundra, with some dwarf wil-
low and birch, juniper, heaths and heathers
(Fig 3). The diagram can be divided into
two: a basal assemblage with grasses around
20% of total pollen and sedges thereby
reduced, and an upper assemblage heavily
dominated by sedges and a considerable inci-
dence of spores. Of significance here is the
early occurrence of P. lanceolata (2% of to-
tal pollen) at 3.5m depth at the base of the
diagram. It also occurs at two points above
this at values of 1% and less than 1% total
pollen. Examination of the samples for
microplankton revealed a rich, decidedly
boreal, fauna of which the basal section,
corresponding to the marine silts, yielded a
predominantly marine taxa deriveđ almost
exclusively from a shallow lagoonal or estua-
rine environment (Hansom and Briggs,
1991). The pollen and microplankton suggest
a boreal aspect throughout with a shallow
lagoonal marine environment up to 8m asl.
Radiocarbon dating of both the upper and
lower peats indicates that freshwater condi-
tions at 8830 BP (Grn-15844) were temporar-
ily halted at about 6910BP (Grn-15843) by a
high energy marine event which deposited a
beach ridge replete with marine taxa on top
and in front of the eroded surface of the
silts. It follows that the P. lanceolata pollen
in the lower part of the curve pre-dates 8830
BP and therefore that the species was present
in this part of Iceland considerably before
the arrival of humans.
Exactly how long the species has been