Jökull - 01.12.1985, Blaðsíða 42

jpj

Fig. 9. View to SE of N end of
Tröllkonustígur over Bessastaðaá.
The relatively unsorted Skridu-
klaustur deposit is exposed at the
left-hand side of the section. — 9.
mynd. Séð frá norðurenda
Tröllkonustígs yfir að Bessastaðaá.
of the Tröllkonustígur above Skriðuklaustur along the
lower slopes of the valley side up to about 100 m
altitude, northwards for about 5 km, (Fig. 1). At its
southern end the deposit forms thin, discontinuous,
lobes running downward from the lowest steps of the
Tröllkonustígur, and here no good exposure is avail-
able, samples varying considerably in analysis but not
showing much sign of sorting. The deposit is thicker
where it is cut by the Bessastaðaá ravine, (Fig. 9), but
the best exposure was found a little to the N in a stream
tributary valley, the sample giving an analysis shown as
80/3 in Fig. 6. fn appearance the material at first sight
seems to be an unsorted mass of fine material including
mainly rounded stones, but closer examination shows
some definite layering. The analysis suggests a till
deposit partly re-arranged and redeposited by water
action.
Apart from this material, however, samples from
deposits in the upper part of the valley and its tributar-
ies, above the recent alluvium, prove to be well sorted.
Most seem to occur at 40 m to 50 m around the valley
margins. Opposite the Múli farm, on the N side of
Norðurdalur, hard, layered and fine-grained deposits
are exposed in a road cutting at about 40 m, (No. 80/8 in
Fig. 6) and similar but much softer material is exposed
in a bank in the Ytri-Víðivellir farm in Suðurdalur, (No.
80/6 in Fig. 6). Both materials show a similar analysis
and the difference in hardness may only reflect the fact
that the Norðurdalur deposit is not weathered. Neither
appears to be a rhythmite, but both were probably
deposited in still water. A small section of apparently
similar material is exposed just N of thé Hvammur farm
site on the W side of the main valley at the edge of a
platform running down the valley side, on which the
main parts of the Valthjófsstaður farms are sited at just
over 40 m. A gravel terrace at Múli, in the middle of the
main valley, is shown in Hjartarson et al. (1981) as being
at 50 m altitude.
Two exposures of possibly deltaic material have been
found in the same area. In Norðurdalur, just to the S of
sample No. 80/8, a roadside quarry at 35 m to 40 m
altitude has exposed some 3 m of markedly rippled and
contorted, layered sands and small pebbles apparently
displaced by frost wedges, (Fig. 8). The mechanical
analysis, and the degree of disturbance and folding
could show an esker rather than a sub-aerial delta. It is
covered by a variable thickness of unsorted material,
(80/10 in Fig. 6).
Current-bedded material of coarser sands and gravels
is exposed in a roadside quarry just above Skriðuklaust-
ur at about 70 m. A sheepfold below is on a likely
extension of the platform at 40 m running from Hvamm-
ur, while above is the relatively unsorted material runn-
ing from Skriðuklaustur N across Bessastaðaá, No. 80/3
in Fig. 6. It is not possible to see any clear contacts with
these deposits above or below (Fig. 11). The current-
bedding in the bedded material appears to be arched,
suggesting an origin in an esker rather than a sub-aerial
delta.
Rather similar material is exposed in both sides of a
40 JÖKULL 35. ÁR