Jökull - 01.01.2012, Page 178

Í. Ö. Benediktsson
Figure 6. Section 2b. A) Drawing of the section. B) Photograph of the proximal and central core. C) Axes of an
anticline and a syncline exposed on the surface in the distal part. D) The central core with frequent faults and
shears. E) Structural data. – A) Teikning af sniði 2b. B) Ljósmynd af sniðinu. Á myndina vantar þó ysta hlutann.
C) Mynd sem sýnir ása samhverfu og andhverfu í ytri hluta garðsins. D) Miðhluti sniðsins sem samanstendur
af sandi og silti og er alsettur smáum misgengjum. E) Gröf sem sýna þrívíða legu fellingaása og misgengja í
sniðinu, sjá skýringar við 3. mynd. Þrýstingur jökuls frá vinstri til hægri.
prominent thrust faults dipping 27–35◦ W were ob-
served at 6-9 m. Fault-propagation folds occur along
these thrusts, indicating flexural bending of the layers
in advance of the actual rupture and development of
the fault planes. At 9–11 m, small-scale overturned
folds (ductile thrusts) can be observed in the upper
part. Small-scale backthrusts, particularly in the white
Öræfajökull AD 1362 tephra marker, are associated
with the overturned folds and probably indicate an ob-
struction in front that interrupted the folding (Figure
6). Structural data show preferred dip of fault planes
to the north, indicating that most of the faults observed
in this part of the section are normal faults and back-
thrusts.
Section 2b, the central part, 11–16 m.
The central part consists of a fault zone in in-
terbedded sand and silt (Figure 6). The sand and silt
beds outline an inclined, east-verging anticline be-
tween 14 and 15 m. The upper and lower limbs of
this anticline have been cross-cut by several small-
scale thrust faults, most of which are low-angle thrust
faults dipping towards the south-west to south-east.
Steeply dipping backthrusts also occur, particularly at
12–13 m in the lower part and around 15 m in the up-
per part, cross-cutting folded layers of the interbedded
sand and silt. Measurements of the faults in this part
of the section show southward dip of the faults and
strongly indicate pressure from the south.
176 JÖKULL No. 62, 2012