Jökull - 01.01.2013, Page 39

Stratigraphy, 40Ar–39Ar dating and erosional history of Svínafell, SE–Iceland
Figure 5. Sedimentary horizon in the Hrútagil gully. Erosion surface SR1 has an angular unconformity on a
breccia/tillite? that dips 14◦/75◦. The horizon is intercalated between lavas H10 (formation SV3) and H11
(formation SV5). – Rofflötur SR1 í Hrútagili er á breksíu/jökulbergi. Um hann er mislægi sem hallar 14◦/75◦.
Figure 6. Stratigraphic group division on the western side of the Svínafell massif, view toward east. – Skipan
jarðlaga í vestanverðu Svínafelli, horft til austurs.
a handheld magnetometer, and therefore assumed to
be of Brunhes age, less than about 0.781 Ma. Hyalo-
clastite deposits form the strata on top of the Svína-
fell sediments (SV11). They are 53 m thick, formed
through subglacial volcanic processes and appear to
have accumulated within the Svínafell sediment de-
pression, probably as a result of jökulhlaup based
on its homogeneity. SV12 is a thick tillite overlain
by subglacial volcanic rocks. Volcanism within the
Öræfajökull volcano appears at this stratigraphic level
(Figure 10). Formations SV13–SV23 consist either of
lava flows, subglacial volcanics or sedimentary rocks
(Figure 4) and are all assumed to be part of the Öræfa-
jökull volcano.
Volcanism led to accumulation of strata under
both sub-glacial and inter-glacial conditions. Ab-
sent from the early Brunhes age section are acidic
tephras and lavas, indicating that during the initial
stage of Öræfajökull volcanism, eruptions were only
of basaltic composition. This suggests that the Öræfa-
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