Jökull - 01.12.1983, Page 50

TABLE 4. Major elemental composition (weight %) of Sámsstaðir profile (youngest ~ 3.4 m.y.).
TAFLA 4. Niðurstöður efnagreininga á sýnum frá Sámsstöðum.
Upper basalt (259) Hraun Interbasalt soil red and brown layers I( Millilag Lower basalt (258) Hraun Hyaloclastic sediment Móberg
Si02 48.3 45.5 47.6 51.0
tío2 3.67 3.67 3.44 2.67
ai2o3 12.8 16.0 13.8 13.6
Fe203 (tot.) 16.5 18.3 16.0 17.1
MnO 0.24 0.27 0.25 0.29
MgO 4.69 2.53 4.59 3.34
CaO 9.33 3.16 9.52 7.64
Na20 3.04 0.43 2.73 2.18
k2o 0.53 0.51 0.46 0.46
LOI 11 0.28 9.2 1.29 2.73
Total 99.38 99.57 99.68 100.83
h2o_2> 23.0
Density 31 2.36
SÍO2/AI2O3 3.8 2.9 3.5 3.8
2Mg0+Ca0+Na20 17.1 6.1 16.8 13.0
%
1) Average of 6 samples.
2) Average of 5 samples.
3) Average of 6 samples.
values than the lavas (Table 2). The lower lava has
higher water content and lower density than the
upper, thus indicating a higher degree of weather-
ing. For the Húsavíkurkleifand Hreðavatn samples
the great range in ignition loss and carbon values
reflect the alternating layers of lignite and clay.
Major elemental composition
The chemical composition of selected profiles
and samples are given in Tables 3, 4, and 5. Due to
the composite character of the sediments, regular
changes in composition from top to base of the
interlava sections have not been recorded.
I'he main residual elements in the interlava sedi-
ments show the following variation ranges (weight
percentages):
SiO, : 30—62%
Al,Oj : trace — 31,5%
Fe,03 : trace — 25,0%
In comparison, economic bauxites have Al2Os
contents in the range 45-50%, Fe203 contents
below 20%, and only 3-5% combined silica.
The lateritic red beds from Óshlíð are relatively
enriched in A1203, Fe203 and H,0. The maximum
A1203 content (31.5%) is however, found for the
white beds (argillized rhyolite). The mobile bases
have been leached during weathering and amount
to only 2-3% in the sediment, while 15-16% in the
unweathered basalt (Table 3).
The youngest red beds from Sámsstaðir (Table 5)
reflect a slight enrichment ofAl203 from 12 to 16%,
a nearly constant Fc2Os content, and a certain
leaching of bases relative to the over and underlying
basalts and hyaloclastites. The weathering has
reached a considerable less advanced stage than for
the Óshlíð profile and the retained bases amount to
6-7%.
The different degree of weathering for the oldest
and youngest soil profile, is also expressed in the
average Si02/Al,03 ratios, being 1.5 for the Óshlíð
and 2.9 for the Samsstaðir profile, and in the
amount of citrate extractable components, which
for the former amounts to 36-54% and for the latter
to 16-27%.
The Húsavíkurkleif samples (Table 5) are in gene-
ral low in MgO and alkalies, but rather high in SiO,
48 JÖKULL 33. ÁR