Jökull - 01.12.1988, Page 7

Fig. 3. The Búðaberg section. 1) Pillow lava. 2) Till. 3) Búðaberg diamicton. 4) Sand. 5) Gravel. 6) Soil.
7) The Þjórsá lava. 8) Dated sample. 9) Shells.
Mynd3. Snið um Búðaberg. 1) Bólstraberg. 2) Jökulurð. 3) Leirsteinsvöluberg (Búðabergsset). 4) Sandur.
5) Möl. 6) Jarðvegur. 7) Þjórsárhraun. 8) Aldursgreint sýni. 9) Skel.
Fig. 4. Outline of the Þrándarholt section. 1) Diamicton (Búðaberg diamicton). 2) Till. 3) Laminated silt.
4) Aeolian sand. 5) Gravel. 6) Soil. 7) Dated sample. 8) Shell.
Mynd 4. Snið um Búðaröðina við Þjórsá milli Þrándarholts og Kálfár. 1) Leirsteinsvöluberg (Búðabergsset).
2) Jökulurð. 3) Lagskipt silt. 4) Foksandur. 5) Möl. 6) Jarðvegur. 7) Aldursgreint sýni. 8) Skel.
its thickness above the watertable of Þjórsá river is
about 1 m. The outcrop in the westemmost part of
the section has a maximum thickness of about 4 m,
and lateral extent of some 500 m. The diamicton is
disturbed and fractured, probably due to a glacial
push. We interpret this diamicton to be a till deposit.
Its age is not known.
The till is unconformably overlain by about 4 m
thick laminated silt unit (unit B), exposed at 650 to
850 m in Fig. 4. The lamination is due to thin bands
of sand. Rippled surfaces were observed, as well as
small-scale deformation stmctures. In this unit,
which we interpret as a glaciomarine deposit, we
observed scattered shell fragments.
In its upper part there is a layer of 0.4 - 4 m thick
silty sand grading up into gravel, with lateral extent
of about 100 m. Shells (Table IV) are found through-
out this unit which we interpret as a glaciomarine
near-shore sediment. A radiocarbon dating of shells
from this strata gave the value of 9.995+90 BP
(Table II: Lu-2403).
Unit B is unconformably overlain by a silty diam-
icton (unit C). It is very similar to the Búðaberg
diamicton, both in lithology and stmcture. They are
probably of same age and origin. The thickness of
unit C in the section varies between 10 and 20 m. It
is very rich in clasts of all sizes between 100 and
500 m in Fig. 4. Scattered Balanus fragments were
found in the unit, but they were not sampled for
radiocarbon dating. The Þrándarholt section is
covered by a thick soil layer (unit D).
Askelsson (1934) was the first to describe this sec-
tion and report shell findings. Kjartansson (1943)
also mentions this locality but neither of them men-
tions that the shell-bearing strata (unit B) is below
the diamicton.
JÖKULL, No. 38, 1988 5