Jökull - 01.12.1987, Page 79

Fig. 18. A thrust fault in the Asbakkar diamicton at 4975
m. The arrow points at a body of sand which has been
overturned by fault drag. The man pointing at the fault is
1.85 m high.
18. mynd. Þrýsti-misgengi við 4975 m.
glacigenic subaquatic debris flows, to form proglacial
shoals or banks. The relative sea level was probably
80-90 m above the present level. Beyond the ice-mar-
ginal zone, glaciomarine sedimentation continued with
strong influxes of meltwater underflows and subaquatic
debris flows. Continued advance of the glacier (stage C)
caused large-scale glaciotectonic deformations. The gla-
cier successively overran the whole basin (stage D).
Around 11.700 BP the glacier retreated to a position
somewhere north of the Melabakkar-Asbakkar section
(stage E), in the course of retreat depositing the esker
fan facies of the Látrar beds. The sea level was high, and
the rhythmic glaciomarine facies of the Látrar beds,
supporting a limited mollusc population, accumulated
from suspended fines, underflows and ice rafting.
Some time after 11.400 BP the basin was re-invaded by
a glacier advancing out of the Borgarfjördur main valley
(stage F). In connection with this readvance, lodgement
till (the Melar diamicton) and ice-proximal delta sedi-
ments (the Landhólmi sands) were deposited. The rela-
tive sea level was above 30 m above the present during
the delta deposition. There is evidence in the cliffs of the
glacier advancing about halfway across the section to-
wards south, but it may have advanced further. A trans-
verse ridge of subaquatic outwash (the Asgil gravels)
marks the position of the ice margin during some stage in
its retreat (stage G).
During stage H, some time prior to 10.000 BP, the
glacier retreated from the coastal areas and the sea
transgressed the isostatically depressed lowlands. Re-
Fig. 19. Stages in the development of the Melabakkar-
Ásbakkarcoastalcliffs. Legend: (UF) underflows, (TC)
tidal currents, (MS) meltwater streams, (DF) subaquat-
icglacigenicdebris flows, (1) bedrock, (2) Ásbakkar dia-
micton, (3) Ás beds, (4) Látrareskerfanfacies, (5) Látr-
ar glaciomarine silts and sands, (6) Melar diamicton, (7)
Landhólmi sands, (8) Ásgil gravels, (9) Melabakkar silts
and sands, (10) Melagil gravels and sands. See text for
further discussion.
19. mynd. Skeið í þróun Mela- og Ásbakka. Nánari
útskýringar í ágripi.
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