Jökull - 01.01.2013, Side 33

Reviewed research article
Stratigraphy, 40Ar–39Ar dating and erosional history of
Svínafell, SE-Iceland
Jóhann Helgason1 and Robert A. Duncan2,3
1National Land Survey of Iceland, Stillholti 14–16, 300 Akranes, Iceland
2College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
3Department of Geology and Geophysics, King Saud University, Riyadh, Saudi Arabia
jhelgason@internet.is, rduncan@coas.oregonstate.edu
Abstract — The interplay of volcanism and erosion in the Svínafell massif, on the western slope of the Öræfa-
jökull volcanic center, SE-Iceland, is traced with geological mapping, magnetostratigraphy and 40Ar–39Ar
age determinations. The volcanic strata are mainly of Quaternary age, i.e., geomagnetic chrons of lower
Matuyama to upper Brunhes. The 1832 m thick sequence in Svínafell is composed of 37 discrete lithologic
formations, assigned to seven volcano-stratigraphic groups beginning with the onset of volcanism in the Öræfa-
jökull stratovolcano during lower Brunhes magnetic chron (C1n < 781 ka). A regional basin formed shortly
before the initiation of volcanism, generating a depocenter for the plant-fossil bearing Svínafell sediments
between 0.70 and 1.78 Ma. The Svínafell volcanic strata accumulated during a minimum of eight glacial and
inter-glacial stages. We document the Svínafell erosion history and landscape evolution, including 12 erosion
surfaces. Erosion has led to extended stratigraphic hiatuses and removal of thick volcanic sequences.
INTRODUCTION
Volcanoes and glaciers in the Öræfi district have ac-
tively shaped the landscape for millions of years. Re-
lief increased and glaciers began to form and persist
during inter-glacial intervals. Although glacial ero-
sion occurred during inter-glacials it reached maxi-
mum extents during glacial intervals. Key erosion
factors include ice thickness, duration of glaciation,
lithology, as well as the mass balance between ac-
cumulation of new volcanic material versus eroded
material and mass wasting. Much of the build up of
erupted material during glacial periods occurred sub-
glacially as hyaloclastite deposits, or móberg (Helga-
son and Duncan, 2001). The interplay, magnitude
and timing of the above factors are poorly known.
We present data that contribute to an understanding
of the erosion history of the Öræfi district, an area
that experienced active volcanism and erosion from
before the onset of major northern hemisphere glacia-
tions (∼2.7 Ma) to the present (Helgason and Duncan,
2001; Eiríksson, 2008).
Active glaciers in the Öræfi district, SE-Iceland,
have dissected strata into isolated mountain ranges.
One of these is Svínafell, bounded by Svínafellsjökull
on the north side and Virkisjökull to the east. The
Svínafell massif is located at the western margin of
the Öræfajökull volcano. The purpose of this study
is threefold, i.e., to 1) provide a basic geological
bedrock map of Öræfajökull’s volcanic history, 2) de-
termine the stratigraphic age range for the Svínafell
lacustrine sediments, and 3) trace Svínafell’s erosion
history and evolving landscape.
Geological setting
The Svínafell massif, located 8 km southwest of
the Öræfajökull stratovolcano’s caldera rim, consists
mainly of volcanic rocks. The distance to Hrúts-
fjöll, an extinct Brunhes age (<781 ka) volcano far-
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