Jökull - 01.12.1983, Page 42

the lignite beds have been mined in a small scale.
Geological observations of W-Iceland are summ-
arized by Kjartansson (1968, 1969) in the geological
maps.
The lignite and plant bearing sediments date to
Neogene (Middle to Late Miocene). The Middle
Miocene flora consisted of forests of warm loving
trees, vine and ficus included, reflecting a warm
temperate climate with annual temperature 9-10°C
above today’s (Askelsson 1954, Schwarzbach 1955,
PJlug 1959, Friedrich 1966, Friedrich et al. 1972, Fried-
rich and Símonarson 1975, 1976; Símonarson et al. 1975,
Jónsson 1978, Friöriksdóttir 1979). The warm loving
flora gradually changed during the Pfiocene as the
climate grew cooler (Buchard 1978). The present
climate was established about 3.5 m.y. ago
(Ahmétejéf 1978).
Interbasalt lignite and laterite are well known
within various parts of the North Atlantic Tertiary
Region (Sabine 1971, Sabine et al. 1972, Curry et al.
1978, Bain et al. 1980, Whalley 1978, pers. comm.)
and from the Iceland — Faeroe Ridge (Nilsen and
Kerr 1976, 1978, Nilsen 1978). In Europe a relatively
uniform tropical to sub-tropical climate prevailed
during the Lower and Middle Tertiary and kaolin-
ite weathering continued until Miocene time (Störr
et al. 1978, Wilson and Tait 1977, Dejou and Chesworth
1979).
Icelandic clays and zeolites
Previous investigations on Icelandic clays are
mainly related to geothermal areas (Sigvaldason
1963, Tómasson and Kristmannsdóttir 1972, Kristmanns-
dóttir and Tómasson 1976). Kristmannsdóttir (1975 a, b,
1977, 1979) established a series of zeolite and clay
mineral zones in geothermally altered rocks and
related the zones to borehole temperatures.
Few data exist on the Tertiary sediments.
Tryggvason (1940, 1960) investigated two clay
samples from Vestfirðir (Fig. 1, zone 1) which he
found mainly to consist of smectite (or metahalloy-
site), kaolinite, and iron hydroxides/oxides. Gibb-
site, pyroxene and magnetite were traced micros-
copically.
Thermal metamorphism — healing of lava pile
Based on intensity of magnetic remanence Kristj-
ánsson (1968) considered that the Tertiary lava pile
has been reheated to less than 120°C since its
formation. Across most of the lava pile, there is less
than 10 dikes/km, which means that if a 3 m thick
dike with magma temperature of 1000°C intrudes
the lava pile, the 100°C isotherm is reached less
than 10 m from the dike (Piper 1973). Lava tempera-
tures as measured on flow surfaces, may reach 900-
1000°C. As most of the heat escapes through the
surface, the top of the underlying sediments („The
baked red layer“) have been heated to at most
500°C (Piper 1973).
Weathering
Lateritic soils form under tropical to sub-tropical
conditions. The essential requirement for their
formation appear to be high rainfall, intense leach-
ing and a strongly oxidizing environment. Under
such conditions organic matter accumulation is in-
hibited. The leaching solutions tend to flush out all
potendally mobile constituents leaving high con-
centrations of alumina, dtania, and ferric oxide
(Keller 1957, Loughnan 1969). Smectite and illite
form in early stages of chemical weathering, while
gibbsite, boehmite, and quartz represent the
residual products (Chesworth 1973, 1977).
Kuzvart (1978) defines the conditions for exogen-
ous kaolinidzadon to be: annual temperatures 16 to
18°C and annual precipitadon about 1000 mm. In a
tectonically quiet environment the downward rate
of kaolinidzadon is about 0.1-1 m per 10,000 years.
The purpose of this investigation is to examine
the mineralogical and chemical composition of
selected interbasaltic sediments and relate the re-
sults to geologic age, depositional environment and
weathering conditions. In Iceland the weathered
soils are preserved between lavas and can be indi-
recdy dated from the age of the over-and underlying
lava. This gives an unique opportunity to bring
light on the weathering and climatic condidons of
North Europe in the Late Terdary.
TABLE 1. Selected profiles, locality and age.
TAFLA 1. Valin snið, staðsetning og aldur.
Locality Staður Sediments Set Age Aldur
Óshlíð—Gil Laterite, lignite 14-13 m.y.
Húsavíkurkleif Lignite, clay 10-9 m.y.
(tonstein, underclay)
Hreðavatn Lignite, lacustrine sediments 7-6.5 m.y.
Sámsstaðir Red and yellow sediments ~ 3.4 m.y.
40 JÖKULL 33. ÁR