Jökull - 01.12.1987, Blaðsíða 80

gionally extensive marine terraces at 60-70 m a.s.l. re-
late to the relative sea level during stage H. The Mela-
bakkar glaciomarine facies was deposited primarily
from suspension during this stage. The isostatic rebound
is registered in the sequence as glaciomarine sedimenta-
tion gives way to sublittoral sand with burrows, finally
(stage I) to be truncated by an emergence facies associ-
ation (the Melagil gravels and sands), of beach gravels
and sands, found above a regionally extensive, time- and
space transgressive gravel lag.
The glacial stratigraphy and chronology of the Mela-
bakkar-Ásbakkar cliffs presented here differ substan-
tially from previous interpretations of the lower Bor-
garfjördur strata (lngólfsson 1984). According to the
deglaciation synthesis of Einarsson (1961,1968,1971) the
Borgarfjördur main valley/fjord was not glaciated after
ca. 13.000 BP. It has also been maintained that glaciers
did not reach the coastal areas of W-Iceland after the
Álftanes Stadial, correlated with the Older Dryas of
Scandinavia, and that the region was not seriously af-
fected by glaciation during the Budi Stadial, correlated
with the Younger Dryas of Scandinavia (c/. Einarsson
1968,1979, Andersen 1981). The evidence from the Me-
labakkar-Ásbakkar cliffs suggests that glaciers ad-
vanced down the Borgarfjördur valley both around
12.000 BP and after 11.400 BP, indicating a more exten-
sive glaciation than hitherto assumed for W-Iceland dur-
ing the last stages of the Late Weichselian.
For explaining the development of the depositional
basin with regard to lithofacies distribution and stra-
tigraphic associations, I have applied recent models for
sedimentation in a subarctic glaciated fjord environ-
ment, as outlined by e.g. Powell (1981, 1984), Molnia
(1983), Mode et al. (1983), Domack (1983) and Eyles et
al. (1985). These models primarily relate to glacial reces-
sion sequences, but the Melabakkar-Ásbakkar example
indicates that they can also be applied to ice-transgres-
sive sequences.
The development of glaciotectonic deformations in
the Melabakkar-Ásbakkar strata is probably best ex-
plained by a combined effect of frontal push, differential
ice loading and hydrodynamic mechanisms on pro- and
subglacial unfrozen sediments.
ACKNOWLEDGEMENTS
Thorleifur Einarsson, of the University of Iceland, pro-
posed this investigation, and placed his resources at my
disposal during the first stages of the work. Christian
Hjort supervised the investigation on behalf of the Uni-
versity of Lund, and has given valuable comments and
advise during all stages ofthe work. I have also benefitted
from discussions with Erik Lagerlund and Per Möller at
the University of Lund and Hreggvidur Norddahl at the
University of Iceland. Lena Adrielsson and two anony-
mous reviewers gave valuable comments on the manu-
script. My good-humouredfield assistant during twofield
seasons, Ingólfur Gíslason, is warmly thanked. The
Radiocarbon datings were carried out by Sören Hákans-
son at the Radiocarbon Dating Laboratory in Lund.
Lena Barnekow and Gun Hansson did the laboratory
work on my sedimentsamples. My English was improved
by Ingela Bergenrud. Financial assistance for the in-
vestigation was received from the Swedish Society for
Anthropology and Geography, the Royal Swedish Aca-
demy ofSciences and the Arctic Institute ofNorth Amer-
ica, which is gratefully acnowledged. Since 1983 the study
has been supported by a research scholarship at the Uni-
versity of Lund.
REFERENCES
Aber, J.S., 1982: Model for Glaciotectonism. Bulletin of the
Geological Society of Denmark, 30:79-90.
— 1985: The character of glaciotectonism. Geologie en Mijn-
bouw 64: 389-395.
Andersen, B.G. 1981: Late Weichselian Ice Sheets in Eurasia
and Greenland. In: G.H. Denton and T.J. Hughes (eds.).
The Last Great Ice Sheets. John Wiley and Sons, Inc., New
York: 1-65.
Ashwell, I. Y. 1975: Glacial and Late Glacial processes in West-
ern Iceland. Geografiska Annaler 57: 225-245
Banham, P.H. 1975: Glacitectonic structures: a general dis-
cussion with particular reference to the contorted drift of
Norfolk. In: A.E. Wright and F. Moseley (eds.). Ice Ages:
Ancient and Modern. Geological Journal, Special Issue No.
6. Steel House Press, Liverpool, pp. 69-94.
Bárðarson, G.G. 1923: Fornar sjávarminjar vid Borgarfjörð og
Hvalfjörð. Vísindafélag íslendinga, Rit 1: 116 pp.
Berthelsen, A. 1978: The methodology of kinetostratigraphy as
applied to glacial-geology. Bulletin of the Geological Society
of Denmark 27: 25-38.
— 1979: Recumbent folds and boudinage structures formed by
subglacial shear: an example of gravity tectonics. Geologie
En Mijnbouw 58: 253-260.
Blatt, H., G. Middleton and R. Murray 1972: Origin of Sedi-
mentary Rocks. Prentice Hall Inc., Englewood Cliffs. 634 p.
Boothroyd, J.C. and G.M. Ashley 1975: Process, Bar Morphol-
ogy, and Sedimentary Structures on Braided River Outwash
Fans, Northeastern Gulf of Alaska. In: A.V. Jopling and
B.C. McDonald (eds). Glaciofluvial and Glaciolacustrine
Sedimentation. Society of Economic Paleontologists and
Mineralogists, Special Publication No. 23. Tulsa, pp. 193-
222.
Boulton, G.S. 1968: Flow tills and related deposits on some
Vestspitsbergen glaciers. Journal of Glaciology 7: 391—412.
— 1976: A genetic classification of tills and criteria for dis-
tinguishing tills of different origin. In: W. Stankowski (ed.).
Till, its genesis and diagenesis. Univ. Mickiewicza W. Poz-
naniu. Ser. Geografia 12: 65-80.
78