Jökull - 01.12.1988, Page 13

CONCLUSIONS
The stratigraphy of the sections outlined above
spans the glacial history of the area, from before the
formation of the Búði moraine complex to the postg-
lacial marine regression. Four of the dated samples
were collected in immediate connection with the
Búði moraines proper (Table V). Two samples (Lu-
2404, Lu-2403) are shells collected in situ from a
stratigraphic position below the Búði moraines, at
Þjórsá (Minna-Hof/Búðaberg and Þrándarholt). One
sample was collected from disturbed glaciomarine
sediments constituting a morainic ridge at Hrepp-
hólar (Lu-2401). These sediments are from a strati-
graphic position below the moraines. One sample
was collected from laminated marine silts, strati-
graphically overlying the Búði moraines at Hrepp-
hólar (Lu-2402). The stratigraphical and chronologi-
cal evidence suggests that the glacial event, which
caused the fonnation of the Búði moraines at
Þrándarholt - Búðaberg by Þjórsá and at Hrepphólar,
occurred in the period 9.750 BP to 9.600 BP, i.e.
during the Preboreal Chronozone.
The structural evidence from Búðaberg and
Hrepphólar indicates that the glacier advanced
across glaciomarine sediments, and the moraine
ridges consist mainly of disturbed beds of glacioma-
rine diamicton.
Further to the southeast, in the general area
between Keldur and Gunnarsholt, the moraine
ridges are mainly of glaciofluvial sediments and of
littoral sand and gravel. This could indicate that
there the glacial event was rather characterized by a
grounded glacier and a substantial period of ice-
marginal sedimentation than of an ice advance. In
this area the moraine ridges are connected to the
huge sandur plain of Rangárvellir. Three datings
indicate the age of this plain, Lu- 2405, Lu-2406 and
Lu-2598; all from the westem part of the plain. The
age is between 10.015 - 9.500 BP, or Preboreal, and
in a good agreement with the age of the Búði
moraines.
Most of the radiocarbon dated samples come from
localities distally to the moraines. They indicate a
Preboreal glaciomarine sedimentation and subse-
quent marine regression and sediment reworking by
TABLE V. Radiocarbon age of samples from strati-
graphic positions below, within and above the Búði
end-moraine complex
TAFLA V. A/dursgreiningar á sýnum undir, í og
ofan á Búðagörðum.
Lab. no. Sýni Stratigraphic position Staðsetning Corrected 14C age Leiðréttur 14 C aldur
Lu-2403 Below the moraines 9.995±90
Lu-2404 Below the moraines 9.855190
Lu-2401 In the moraines 9.7451140
Lu-2402 Above the moraines 9.5951160
littoral and fluvial processes.
DISCUSSION
Evidence from several recent studies on the Late
Weichselian deglaciation of Iceland suggests that
ice extent and volume during the last stages of the
glaciation were greater than the deglaciation syn-
thesis of Einarsson (1968, 1978) concludes. Ingólfs-
son (1985, 1987) concludes that in the lower
Borgarfjörður area in westem Iceland, the Weich-
selian ice did more or less continuously extend
beyond the present coastline between about 12.000
BP and 10.300 BP. He found indications of two
advances corresponding roughly to the Older Dryas
and Younger Dryas stadials in northwest Europe. He
also suggests (Ingólfsson, in press) that ice marginal
formations in the Borgarfjörður tributary valleys,
inferred by Einarsson (1968, 1978) to be of Older
Dryas age, are of Preboreal age.
Hjartarson (1987) and Andersen et al. (1988)
dated shells from glaciomarine sediments in the
Reykjavík area, previously thought to be of intergla-
cial (Eemian) age. The dates suggest that these sedi-
ments are of Alleröd age, indicating that glaciers
reached beyond the present coast in the Reykjavík
area after 11.000 BP. They also suggest that the
Álftanes end-moraine, the traditional type site of the
Older Dryas Stage in Iceland, is of Younger Dryas
or Preboreal age.
JÖKULL, No. 38, 1988 11