Archaeologia Islandica - 01.01.1998, Page 130

I. A. Simpson, K.B. Milek & Garðar Guðmundsson
Thin section micromorphology
Thin section micromorphology, in-
troduced to pedology by Kubiena
(1938), represents an extension of sedi-
ment profile observations made in the
field. Undisturbed blocks of sediment
are removed from an exposed section
profile, and in the laboratory water is
removed from the sample by acetone
exchange to prevent structural modifi-
cation of the sample during the drying
process. Samples are then impregnated
under vacuum with crystic polyester
resin and hardened through the
addition of a catalyst and an accel-
erator. Once cured, blocks are sliced,
bonded to glass and precision lapped
to 30 (im, with coverslipping complet-
ing the preparation of the thin section.
Thin sections are described using a
petrological microscope and by fol-
lowing the internationally accepted
procedures outlined in the Handbook
for Soil Thin Section Description
(Bullock et al. 1985). This allows sys-
tematic description of microstructure,
basic mineral components, organic and
anthropogenic inclusions and features
resulting from soil formation processes
(pedofeatures). A range of magni-
fications (from x2-x400) and light
sources (plane polarized, cross polar-
ized, circular polarized, reflected and
UV light) can be used to obtain
detailed, semi-quantitative descrip-
tions. Further quantification of key
features will be obtained through the
analysis of digitized images captured
by a video camera attached to the
microscope. Interpretation of features
in thin section rests upon the
accumulated evidence of a number of
workers, notably Courty et al. (1989)
and FitzPatrick (1993), on research
undertaken by one of the authors in
the North Atlantic context (Simpson
and Barrett 1996; Dockrill and Simp-
son 1994) and on the comparison of
sedimentary properties observed in
different areas of the Hofstaðir site. It
will also be aided by reference to
micromorphology samples taken from
known contexts in Þverá, a recently
abandoned turf house that is only
I4.25km away from Hofstaðir in the
same river valley (Laxádalur).
1996 Observations: emerging hypotheses
Two stratigraphic sections were ex-
amined during the 1996 season. Sec-
tion 1 was on the west face of the
structure designated as D-1 and Sec-
tion 2 was located in area G. Context
4, which was thought to be potentially
useful as a horizon marker, was also
examined at various locations on the
site.
Section 1 (Area D)
Sediments from Section 1 can be
considered in four stratigraphic units.
The lowest unit is comprised of
sequences of windblown silt (7.5YR
3/3 and 7.5YR 3/4) interspersed with
prehistoric tephra layers, including
Hekla-3 (2,900 BP), Hverfjall (2,800
BP), unidentified tephra (5YR 2.5/1),
and the Landnám tephra (AD 871 ±2)
(Magnús Sigurgeirsson, this volume).
There is also evidence of standstill
phases during which there was limited
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