Jökull - 01.12.1982, Page 58

Fig. 5. The southern bank of
the upper part of the Tijávid-
arlækur channel. The arrow
points to the location of profile
I (Fig. 4). Note the tillite in the
inner part of the channel
bottom.
Mynd 5. Suðurbakkinn ofarlega
við Trjáviðarliek. Örin bendir á
snið I (Mynd 4). Glöggt má sjá
jókulbergið innst í farveginum.
Table 1. Tijáviðarlækur. C14 datings 1980, carried
out by Ingrid Olsson at Uppsala University.
Tafla 1. Geislakolsgreiningar.
Sample no. Stratigraphic loca- C14 age B. P.
tion, see profile III, Fig. 4 Ti/2=5570 years
Syni Staðsetning Aldur
U-4359 Immediately above H5 6130±90
U-4358 Immediately below H5 6070± 120
U-4360 About 1.5 m below H5 8960 ±100
U-4361 About 1.5 m below H5 8940± 110
overlain by a thick reworked layer (4 m thick in
profile II). The reworked part is stratified with
alternating bands of dark and light tephra. Thin
sand lenses are common. The dark tephra is more
common, and the overall color is dark grey (Fig. 9).
The H3 tephra both primary and reworked. The re-
worked H4 tephra is overlain by the acid tephra
layer from Hekla, designated H;s, which is about
2,800 years old (Thorarinsson 1958, Larsen and Thor-
arinsson 1977). The primary part is about 2 m thick,
and sometimes it has been eroded away as can be
seen in Figs. 5 and 9. The pumice is often pinkish
white in color, and the coarsest fragments here are
at least 10 cm in diameter. The thickness of the
reworked part is irregular. The H ( pumice breaks
down very easily to form oval platy grains, yellowish
in color. Sometimes scattered rests of roots and
branches are seen in the reworked part, but no trace
of organic soil. Sand lenses are less common than in
the reworked H4.
Loessial soil with tephra layers. As shown in profile I
in Fig. 4 and also in Fig. 10, a loessial soil has
accumulated on the top of the reworked H3 layer.
Fig. 5 shows how it follows the H3 topography. The
loessial soil is sandy, and in profile I at least three
tephra layers were found, two ofwhich were ident-
ified. Fhe lower one is the so called Settlement
layer, approximately 900 AD (Einarsson 1962), and
the upperoneis Katla 1000 AD (Thorarinsson 1967).
The Hj tephra, both primary and reworked. On the
loessial soil rests an acid tephra layer from Hekla,
H[, which was erupted in 1104 AD and led to
wasting of Pjórsárdalur valley (Thorarinsson 1944,
1967). In profile I (Fig. 4), H^ is about 1 m thick in
the primary condition. It is similar to Hs both in
color and composition, but the two layers are dis-
tinguishable through their position in the soil pro-
files. As can be seen in Figs. 5 and 10, the Hj follows
the H3 topography. The reworked part, which can
be seen in Fig. 5, is similar to the reworked part of
H3, and oval platy grains from it are common in
loessial soil in the area.
54 JÖKULL 32. ÁR