Introduction to the Nature and Geology of Iceland

Abstract

Iceland is an island in the northern North Atlantic halfway between Europe and Greenland/North America and some of its northern
parts touch the Arctic Circle. Its position at the conjunction of warm southerly and cold northerly waters and air masses
contribute to a particular climate that is unusually mild considering the high latitude of the island. From a biogeographical
point of view, Iceland is an important place for both palaeontologists and recent botanists and zoologists. Geologically,
Iceland is unique as it is situated at the boundary of the North American and Eurasian plates and is one of the few places
on the Earth where sea-floor spreading can be witnessed on land. In this northern part of the Atlantic, the North American
continent began to move away from the Eurasian continent by rifting and sea-floor spreading in the early Palaeogene, ca 55
Ma. When sea-floor spreading initiated in this area, a rich flow of magma generated by a mantle plume caused thermal doming
of the crust and formed a connection or ‘land bridge’ between the continents known as the Greenland-Scotland Transverse Ridge.
Subsequently, the eastern and western limits of this bridge sank as a consequence of continuous rifting and crustal cooling.
Today, Iceland is still subaerial because of its position over this very same mantle plume. In the late Cainozoic, rift relocation
had an important effect on the geology of Iceland and caused massive erosion and deposition of sediments, some of which contain
the plant fossils described in this book. This chapter provides an introduction to the recent climate, weather systems and
ocean currents affecting Iceland, and presents the most important details of the island’s living fauna and flora. We also
outline the geological background necessary to place the fossiliferous formations in a context.

Full text

1
T. Denk et al., Late Cainozoic Floras of Iceland, Topics in Geobiology 35,
DOI 10.1007/978-94-007-0372-8_1, © Springer Science+Business Media B.V. 2011
Travelling in the interior of Iceland is very arduous work, for
the country lies high and consists for the most part of sand and
lava deserts, often absolutely without grass. The traveller has
consequently to take with him even fodder for the horses. The
summer, moreover, is short, and the route into the interior
occupies much time.
Dr. Thoroddsen’s explorations in Iceland, Anonymous 1893
Chapter 1
Introduction to the Nature
and Geology of Iceland
Abstract Iceland is an island in the northern North Atlantic halfway between
Europe and Greenland/North America and some of its northern parts touch the
Arctic Circle. Its position at the conjunction of warm southerly and cold northerly
waters and air masses contribute to a particular climate that is unusually mild
considering the high latitude of the island. From a biogeographical point of view,
Iceland is an important place for both palaeontologists and recent botanists and
zoologists. Geologically, Iceland is unique as it is situated at the boundary of the
North American and Eurasian plates and is one of the few places on the Earth where
sea-floor spreading can be witnessed on land. In this northern part of the Atlantic,
the North American continent began to move away from the Eurasian continent
by rifting and sea-floor spreading in the early Palaeogene, ca 55 Ma. When sea-
floor spreading initiated in this area, a rich flow of magma generated by a mantle
plume caused thermal doming of the crust and formed a connection or ‘land bridge’
between the continents known as the Greenland-Scotland Transverse Ridge.
Subsequently, the eastern and western limits of this bridge sank as a consequence
of continuous rifting and crustal cooling. Today, Iceland is still subaerial because of
its position over this very same mantle plume. In the late Cainozoic, rift relocation
had an important effect on the geology of Iceland and caused massive erosion and
deposition of sediments, some of which contain the plant fossils described in this
book. This chapter provides an introduction to the recent climate, weather systems
and ocean currents affecting Iceland, and presents the most important details of the
island’s living fauna and flora. We also outline the geological background neces-
sary to place the fossiliferous formations in a context.

2 1 Introduction to the Nature and Geology of Iceland
1.1 Geographic Position
Iceland is the second largest island in Europe, after Great Britain, with a total area
of 103,100 km2, the mainland comprising 102,950 km2 (Fig. 1.1). The island lies
between longitudes 13°29.6¢W and 24°32.1¢W and between latitudes 63°23.4¢N
Fig. 1.1 A MODIS satellite image of Iceland, taken on NASA’s Aqua satellite on August 11,
2004. Part of Greenland can bee seen NW and the Faeroe Islands SE (top right) of Iceland (Image
courtesy of MODIS Rapid Response project at NASA/GSFC, http://modis.gsfc.nasa.gov/)

31.2 Climate and Ocean Currents
and 66°32.3¢N, with the northernmost parts touching the Arctic Circle. Outside
these limits are the skerries of Kolbeinsey and Hvalbakur, and also some of the
Vestmannaeyjar (Westman Islands). The southernmost of the Vestmannaeyjar is the
newborn island of Surtsey, which rose from the sea during a submarine eruption in
1963. The shortest distance to Greenland is ca 280 km, to the Faeroe Islands ca
435 km, to Scotland ca 790 km, and to Norway ca 970 km. Thus, Iceland has a
unique and biogeographically important position in the northern North Atlantic,
midway between North America and Europe, and at the boundary between the
Arctic and Boreal regions.
1.2 Climate and Ocean Currents
1.2.1 Climate
The Icelandic climate is influenced by various air masses, some of which originate
in polar regions while others have a tropical origin (Einarsson 1976). The interac-
tion between warm southerly and cold northerly ocean currents and air masses
affects both the course and the frequency of the weather systems around Iceland
and is the cause of its typical instability. Einarsson (1984) described the main
weather systems relevant to Iceland. Depending on the track and position of low
and high pressure zones in and adjacent to Iceland (Greenland, British Isles, and
Scandinavia), weather systems such as “Southern with warm air masses” or
“Northern” bring humid or dry and cold or warm air masses from different direc-
tions. The “Southern with warm air masses”, for instance, is active when a low
pressure zone over southern Greenland and an anticyclone over Western Europe
cause tropical air masses to flow northwards, towards Iceland (Einarsson 1984).
Since Iceland is mountainous, precipitation and cloudiness increase windward of
the mountains and decrease leeward.
The climate is considerably warmer than might be expected, considering how far
north Iceland lies. During the years 1878–2002 the mean annual temperature in
Reykjavík, situated on the southwest coast, was 4.3°C, with −0.6°C as the mean
temperature in January, the coldest month, and 10.8°C in July, the warmest month
(Hanna et al. 2004). In northern Iceland, the mean annual temperature during these
years was 2.3°C on the island of Grímsey, with −1.3°C and 7.7°C, respectively for
the coldest and warmest months (Hanna et al. 2004). The lowest temperature mea-
sured in Iceland was −37.9°C at Grímsstaðir á Fjöllum in northeastern Iceland, in
January 1918, and the highest temperature was 30.6°C at Teigarhorn in eastern
Iceland, in June 1939 (Eythorsson and Sigtryggsson 1971).
In the years 1931–1960, the mean annual precipitation was 805 mm at Reykjavík
(90 mm in January, 48 mm in July), 474 mm at Akureyri (45 mm in January and
35 mm in July) and 2,256 mm at Vík in Mýrdalur on the south coast (182 mm in
January and 169 mm in July; Eythorsson and Sigtryggsson 1971). The true precipi-
tation may have been higher, because the amount of snowfall is difficult to quantify,
particularly when it occurs during stormy weather (Rögnvaldsson et al. 2004).

4 1 Introduction to the Nature and Geology of Iceland
The highest precipitation is in the southeast with estimated maximum annual
values of more than 4,000 mm on the ice caps Vatnajökull and Mýrdalsjökull,
whereas in the highlands north of Vatnajökull the mean value for the years 1931–1960
was less than 400 mm (Einarsson 1976). Snow cover as a percentage of total surface
area for every day in October to May in the years 1931–1960 was 17% in
Fagurhólsmýri, on the south coast, 32% in Reykjavík, 53% in Húsavík on the north
coast, and 70% on Suðureyri in northwestern Iceland (Einarsson 1976).
In general, the climate of Iceland can be categorized as cold-temperate oceanic. The
climate is temperate and humid, with cool and short summers (Cfc climate; Köppen and
Geiger 1928; Köppen 1936; Kottek et al. 2006) in the southern and western parts of the
country as well as the inner parts (fjords) of northern and eastern Iceland. Here, the
mean temperature of the warmest month is ca 10°C and of the coldest month >−3°C.
In contrast, the climate is arctic (ET, sensu Köppen 1936; Kottek et al. 2006) on penin-
sulas and promontories in northwestern, northern and eastern Iceland as well as in the
highlands, where the warmest month mean temperature is <10°C (Einarsson 1984).
During the last century, there has been a slight climatic amelioration (Hanna et al.
2004; Fig. 1.2a). The warming was non-uniform in time, with three distinct phases;
approximately from 1880 to 1900, from 1925 to 1940, and from 1983 onwards.
Warming was most rapid during the second phase, reaching the maximum value over
the entire record in 1939 and 1941 (Hanna et al. 2004). This gradual increase in tem-
perature was not accompanied by a shift in mean annual precipitation, which has
remained essentially constant between 1881 and 2001 (Hanna et al. 2004; Fig. 1.2b).
Glaciers in Iceland result from special climatic conditions (Fig. 1.3), of which
temperature and precipitation, mainly as snowfall, are the most important. During
the Pleistocene cold phases, glaciers affected environmental conditions in Iceland.
During the Last Glacial Maximum at ca 20 ka BP, glaciers extended towards the
shelf break around Iceland. Ice-free enclaves occurred in a few high coastal moun-
tains (Norðdahl et al. 2008). Although glaciers have greatly declined in size since
then, their fluctuations are a good indicator of subtle climatic changes. After the
1890s, a general recession of glaciers in Iceland started, and this became quite rapid
after 1930. However, cooler summers occurred after 1940 and glaciers retreated
more slowly after the 1960s, with steep glaciers starting to advance around 1970.
Since 1985, the climate has once more started to warm, and this has steadily led to
a more widespread glacial retreat (cf. Björnsson and Pálsson 2008; Fig. 1.2a).
1.2.2 Ocean Currents
The climate of Iceland is strongly affected by the conflux of two ocean currents
with very different characteristics: the cold, southwards flowing euhaline East
Greenland Current and the warm, saline northwards flowing North Atlantic
Current, a continuation of the Gulf Stream. This pattern of ocean currents is one of
the key climatic factors in the North Atlantic and adjacent land masses and a clear
relationship has been demonstrated between air and sea surface temperatures
around Iceland (Stefánsson 1991).

51.2 Climate and Ocean Currents
The main oceanic circulation pattern around Iceland was probably established
when the final closure of the Central American Seaway at 4.6–3.6 Ma led to a flow
of surface water from the Pacific Ocean into the Arctic Ocean, via the Bering Strait
(Backman 1979; Haug and Tiedemann 1998; Marincovich 2000; Símonarson and
Fig. 1.2 Recent development of mean annual temperature (a), and mean annual precipitation
(b), in Iceland (Modified after Hanna et al. 2004)

6 1 Introduction to the Nature and Geology of Iceland
Eiríksson 2008). Due to the presence of a submarine ridge (Iceland-Faeroe Ridge,
part of the Greenland-Scotland Transverse Ridge) lying between Iceland and the
Faeroe Islands, the North Atlantic Current is deflected westwards and forms the
Irminger Current that flows clockwise around the south and west coasts of Iceland
(Fig. 1.4). Another branch of the North Atlantic Current, the Norwegian Atlantic
Current, continues northwards to the Norwegian-Greenland Seas (Fig. 1.4), where
it ultimately sinks and forms the dense North Atlantic Deep Water that flows back
southwards, past the east side of Iceland, towards the equator.
The cold euhaline East Icelandic Current is a southeast flowing branch of the
East Greenland Current that meets warmer Atlantic waters off the northeast coast
of Iceland, at the polar front (PF; Fig. 1.4). The cold period of 1965–1971 (Fig. 1.2a)
was caused when the East Icelandic Current was mixed with the warmer Irminger
Current, north of Iceland (Stefánsson 1994). This weakened the influence of the
latter towards the east, along the north coast of Iceland, so that it almost completely
died out off the northeast and east coasts. As a result, temperatures in Iceland
dropped markedly. Another effect of the changing interplay of these two currents
was that a considerable amount of arctic drift-ice came to the northwestern, northern,
and eastern coasts of Iceland, a further cause of the decreased temperatures at that
time (Stefánsson 1994).
Fig. 1.3 The meltwater lake Jökulsárlón, southeastern Iceland, with floating icebergs in front of
a retreating glacier. Note the outlet glaciers visible behind the lake that are running from the large
Breiðamerkurjökull glacier (part of Vatnajökull icecap) in the background

71.3 Flora and Vegetation
1.3 Flora and Vegetation
The modern biota of Iceland is characterized by a remarkably low number of
endemic plants and animals (cf. Brochmann et al. 2003; Ægisdóttir and Þórhallsdóttir
2004). Apart from the apomictic genera Alchemilla, Taraxacum and Hieracium,
endemic plants in Iceland are restricted to taxa below the species rank.
At present, about 460 vascular plants have been found in Iceland (Table 1.1), the vast
majority of which are of European origin (Einarsson 1963). Of these species, ca 40 are
ferns and fern allies, but only one native conifer species exists (Juniperus communis L.).
Fig. 1.4 Map of the northern North Atlantic showing the main oceanic currents around Iceland
(Modified after Hurdle 1986; Eiríksson et al. 1992)

8 1 Introduction to the Nature and Geology of Iceland
Table 1.1 Plant families and number of genera found in the Icelandic flora. The number of
woody plants is indicated (List based on Löve 1945, 1977; Stefánsson 1948; Bjarnason 1983;
Kristinsson 1998)
aBoldface indicates a woody habit of at least some Icelandic members of this family
FamilyaGenera Species
Lycopdiales
Isoetaceae 1 2
Lycopodiaceae 3 5
Selaginellaceae 1 1
Equisetales
Equisetaceae 1 7
Polypodiales
Adiantaceae 1 1
Aspleniaceae 1 3
Blechnaceae 1 2
Dryopteridaceae 2 3
Hymenophyllaceae 1 1
Ophioglossaceae 2 6
Polypodiaceae 1 1
Thelypteridaceae 1 1
Woodsiaceae 4 6
Coniferales
Cupressaceae 1 1
Angiosperms,
Monocots
Alliaceae 1 1
Cyperaceae 5 53
Juncaceae 2 20
Juncaginaceae 1 2
Orchidaceae 6 7
Poaceae 27 47
Potamogetonaceae 2 8
Sparganiaceae 1 3
Tofieldiaceae 1 1
Trilliaceae 1 1
Zannichelliaceae 1 1
Zosteraceae 1 1
Angiosperms,
Eudicots
(Tricolpates)
Apiaceae 4 5
Araliaceae 1 1
Asteraceae 19 25
Betulaceae 1 2
Boraginaceae 2 5
Brassicaceae 10 21
FamilyaGenera Species
Callitrichaceae 1 5
Campanulaceae 1 2
Caryophyllaceae 10 27
Chenopodiaceae 2 4
Cornaceae 1 1
Crassulaceae 3 5
Diapensiaceae 1 1
Dipsacaceae 2 2
Droseraceae 1 1
Empetraceae 1 1
Ericaceae 9 11
Fabaceae 5 11
Gentianaceae 5 7
Geraniaceae 1 1
Haloragaceae 1 2
Hippuridaceae 1 2
Lamiaceae 3 3
Lentibulariaceae 2 2
Linaceae 1 1
Menyanthaceae 1 1
Onagraceae 2 9
Oxalidaceae 1 1
Papaveraceae 1 1
Plantaginaceae 2 4
Parnassiaceae 1 1
Plumbaginaceae 1 1
Polemoniaceae 1 1
Polygonaceae 5 10
Portulacaceae 1 1
Primulaceae 3 4
Pyrolaceae 2 3
Ranunculaceae 5 10
Rosaceae 13 26
Rubiaceae 1 6
Salicaceae 2 5
Saxifragaceae 1 15
Scrophulariaceae 7 20
Urticaceae 1 2
Valerianaceae 1 1
Violaceae 1 5
Total 211 460

91.3 Flora and Vegetation
A further ca 275 species are angiosperms, of which ca 145 species are monocotyledons
(Löve 1945, 1977; Stefánsson 1948; Bjarnason 1983; Kristinsson 1998). The most
species-rich families are the monocot families Cyperaceae and Poaceae (Table 1.1).
The Caryophyllaceae and Asteraceae are the most diverse families among the remain-
ing angiosperms.
The only tree that forms woodlands is Betula pubescens Ehr., which can grow
up to 10–12 m tall (Blöndal 1987; Fig. 1.5). Scattered within birch woods are soli-
tary trees of Sorbus aucuparia L., which can also grow up to 12 m high. A few
isolated stands of Populus tremula L. exist, mainly in the northeastern part of the
island. One species of Salix (S. phylicifolia L.) is a typical element of birch woods,
mostly as a shrub, but sometimes attaining tree stature (Blöndal 1987).
The bryophyte flora of Iceland includes ca 600 species (Jóhannsson 2003) and
ca 735 species of lichens are known (Kristinsson 2009). Fungi comprise ca 2,000
species (Kristinsson 2009). Furthermore, about 1,500 species of algae have been
reported in Icelandic waters (Kristinsson 2009).
About 97% of the vascular plants native to Iceland have also been recorded in
Norway and about 86% in the British Isles. In contrast, only 64% are also found in
Greenland (Einarsson 1963, 1975). The western elements in the Icelandic flora, i.e.
plants with their main distribution area in the west of Iceland, are very few in num-
ber; only ten species of vascular plants belong to this group (Einarsson 1975).
About 33% of the vascular plants in Iceland are arctic-alpine disjuncts while the
others are boreal (Einarsson 1975).
Fig. 1.5 A small tree of Betula pubescens standing out from the surrounding vegetation made up
of willow and heath in Þingvellir national park, southwestern Iceland

10 1 Introduction to the Nature and Geology of Iceland
1.3.1 Development of Modern Vegetation
The origin of biota located in formerly glaciated areas, such as Iceland, has been a
matter of considerable debate. Two main hypotheses have been put forward. The
‘nunatak hypothesis’(Blytt 1876; Sernander 1896) suggests that plants survived
during glaciations on mountain tops whilst the ‘tabula rasa hypothesis’ (Nathorst
1892) proposes total elimination of vascular plants in glaciated areas.
Rundgren and Ingólfsson (1999) used a pollen profile from northern Iceland span-
ning the period 11.3–9.0 ka to suggest that at least some plant taxa survived the
Younger Dryas glacial between 11.0 and 10.0 ka, in situ, in ice-free places of Iceland.
From this, they concluded that these taxa might also have survived the whole
Weichselian cold phase on the island. However, the larger part of the modern flora
appears to have reached Iceland from Europe and northern Eurasia, via long-distance
dispersal. A continuous long-distance influx of seeds and vegetative parts by ocean
currents (in sea water or on drift-ice) and by wind and birds, in both the Holocene
and earlier epochs, has been suggested as an explanation for the lack of endemics in
Iceland (for references see Rundgren and Ingólfsson 1999). Repeated long-distance
dispersal by wind and drifting sea-ice has also been suggested to have facilitated the
colonization of Arctic islands after the Pleistocene glaciations by a number of phy-
logeographic studies. For nine plant species, Alsos et al. (2007) showed that repeated
colonization of Svalbard has occurred, from all possible adjacent source areas.
Gabrielsen et al. (1997) and Abbott et al. (2000), based on a review of the fossil
record of the Arctic-Alpine disjunct species Saxifraga oppositifolia L. and molecular
data, found clear evidence for a post-glacial colonization of high latitude areas that
were covered by ice, by southern periglacial populations. These studies, and the
comprehensive review by Brochmann et al. (2003), provide good evidence for recent
(post-glacial) migration of many plant and animal taxa across the Atlantic.
When Iceland was first settled in the ninth century, no herbivorous mammals
were living on the island and most of the lowlands were covered by birch woods
and scrubs. Sigurðsson (1977) estimated that at least 25–30% of the island was
covered by birch woods, and 65% of the island was covered by vegetation. After
the settlement, woods were cut down for fuel and building purposes and were also
heavily grazed by sheep. Hence, wood- and scrublands were gradually destroyed
and soil erosion started (Thorarinsson 1944). As a consequence, the present-day
vegetation cover amounts only to ca 25% of the country’s area (Blöndal and
Thorsteinsson 1986).
1.4 Fauna on Land and in Adjacent Waters
Iceland has very few native terrestrial mammals. At the time of settlement, the
Arctic Fox (Alopex lagopus L.; Fig. 1.6) was the only living land mammal and it is
still common (Hersteinsson 2004). Polar bears (Ursus maritimus Phipps) occasion-
ally visit, drifting on ice to the shores of northern and northwestern Iceland from

111.4 Fauna on Land and in Adjacent Waters
Greenland, but such stragglers are usually killed soon after their arrival (Haraldsson
and Hersteinsson 2004; Skírnisson 2009; Sæmundsson et al. 2009). Four species of
rodents arrived with man; the Long-tailed Field Mouse (Apodemus sylvaticus L.), the
House Mouse (Mus musculus L.), the Brown Rat (Rattus norvegicus Berkenhout), and
the Black Rat (Rattus rattus L.). The Field Mouse is common throughout the country
and the House Mouse and the Brown Rat are common in towns and villages; the Black
Rat occurs sporadically in Reykjavík and other ports (Skírnisson 2004a, b, c, d).
Two further mammal species have been introduced by man in more recent times;
the Reindeer (Rangifer tarandus L.), now living in the wild in eastern Iceland
(Þórisson 2004), was introduced from Norway and Finland, and the Mink [Mustela
vison Schreber, syn. Neovison vison (Schreber) Abramov], a North American mus-
teline introduced for fur-farming that subsequently escaped from captivity and has
steadily multiplied and spread over large areas (Skírnisson et al. 2004).
A distinctive feature of the fauna of Iceland is the complete absence of reptiles
and amphibians.
In total, ca 349 species of birds have been reported from Iceland (Petersen
1998). Of these, 75 nest regularly, one species has become extinct worldwide (the
Great Auk, Pinguinus impennis L.) and two species have become extinct on the
island (the Water Rail, Rallus aquaticus L. and the Little Auk, Alle alle L.). Six
species are winter visitors, seven species are regular migrants, and the remaining ca
259 species are drifters or accidental. Of the drifters, ca 40 species visit the island
regularly every year (Petersen 1998). The best known Icelandic bird is the Icelandic
Gyrfalcon (Falco rusticolus L.; Fig. 1.7). The huge White-tailed Eagle (Haliaeetus
Fig. 1.6 The Arctic Fox, the only Icelandic land mammal that was living in Iceland before the
settlement (Courtesy Daníel Bergmann)

12 1 Introduction to the Nature and Geology of Iceland
albicilla L.) was fairly common in Iceland, but now comprises only a few nesting
pairs and is listed as a threatened species (Petersen 1998).
Very few species of fish have been reported in the fresh water lakes and rivers
on Iceland. The most common are the Salmon (Salmo salar L.), the Trout (Salmo
trutta L.) and several varieties of the Arctic Char (Salvelinus alpinus L.; Jónsson
and Pálsson 2006).
More than 90 species of spiders and 800 species of insects have been recorded on
Iceland. Among insects, the diptera (flies, gnats, and midges) represent the largest and
most important group. Beetles, bees, and butterflies are also fairly well represented,
but ants are entirely lacking (Guðmundsson 1975; Einarsson 1989). Fresh water
bivalves and gastropods and land snails are quite common (Mandahl-Barth 1938).
The marine mammalian fauna in Icelandic waters is composed of ca 23 species
of whales and dolphins, and about seven species of seals and walrus. Although most
of the whales migrate to Iceland in springtime and leave in the autumn, others
(ca nine species) are rarely seen (Hersteinsson 2004). Only two species of seals
breed along the islands shorelines; the Common Seal (Phoca vitulina L.; Hauksson
et al. 2004) and the Grey Seal (Halichoerus grypus Fabricius; Hauksson and
Ólafsdóttir 2004). Occasionally, the Walrus (Odobenus rosmarus L.) visits Iceland
as a single straggler or in pairs (Þórðarson and Hauksson 2004).
About 340 species of marine fish have been recorded from Icelandic waters
(Jónsson and Pálsson 2006). Approximately one third of these are known to breed
in the seas and shallows around Iceland. Others are regarded as rare migratory
visitors or accidental stragglers from more oceanic waters; these are mostly
Fig. 1.7 The Icelandic Gyrfalcon seen from below during flight (Courtesy Ólafur Karl Nielsen)

131.5 Opening of the Northern North Atlantic and the Birth of Iceland
bathypelagic species of southern origin (Hallgrímsson 1975; Jónsson 1983; Jónsson
and Pálsson 2006).
The marine invertebrate fauna is mainly composed of arctic-boreal and boreal spe-
cies. Most have also been found in western European waters and some American
species occur as well. In 1975, marine annelids belonging to the polychaete worms
constituted about 225 species, amphipod crustaceans about 185 species, non- parasitic
crustaceans about 170 species, bivalves about 95 species, gastropods about 130
species, and echinoderms about 90 species (Hallgrímsson 1975). Since then, these
numbers have increased, mainly due to the BIOICE-project (Guðmundsson et al.
1999), during which several new species have been reported in Icelandic waters.
After the Pliocene closure of the Central American Seaway at ca 3.6 Ma, the
flow of surface water from the Pacific through the Bering Strait and Arctic Ocean
brought a tide of Pacific marine invertebrates to Iceland and the North Atlantic,
including molluscs (gastropods and bivalves), brachiopods and echinoderms
(Durham and MacNeil 1967; Backman 1979; Símonarson and Eiríksson 2008; see
Chap. 10). This migration included several well-known species of common occur-
rence in the North Atlantic today, including the Blue Mussel (Mytilus edulis L.),
Northern Horsemussel (Modiolus modiolus L.), Greenland Smooth Cockle (Serripes
groenlandicus Mohr), Ciliatocardium ciliatum Fabricius, Arctic Hiatella (Hiatella
arctica L.), Atlantic Great or Oval Paddock (Zirfaea crispata L.), Common Whelk
(Buccinum undatum L.), and the Rejected Neptune (Neptunea despecta L.).
Additionally, several Pacific species reached Iceland during the Pleistocene;
amongst them is the well-known Blunt Gaper (Mya truncata L.).
1.5 Opening of the Northern North Atlantic
and the Birth of Iceland
Geological evidence shows that the East Greenland continental margin (part of the
North American Plate) began to move away from the Scandinavian and the British
Isles margin (part of the Eurasian Plate) by rifting and sea-floor spreading close to
anomaly 24, in the early Palaeogene (ca 55 Ma; Talwani and Eldholm 1977; Soper
et al. 1976; Larsen 1978; Eldholm et al. 1994). When the plates first started to drift
apart, the magma generated by a mantle plume hotspot in this area formed a con-
nection or ‘land bridge’ between North America/Greenland and Europe (Nilsen
1978). This ridge, nowadays mostly submarine, is known as the Greenland-Scotland
Transverse Ridge (GSTR). Iceland, which lies on the GSTR is the surface expres-
sion of the hotspot, which currently lies at the boundary of the North American and
Eurasian plates (Vink 1984).
The continental break-up and related volcanism caused the formation of exten-
sive basaltic lava successions in the northern North Atlantic area (Fig. 1.8), found
in Eastern Greenland, Iceland, the Faeroe Islands, Scotland (Ardnamurchan, Skye,
Rhum, Arran) and Northern Ireland (Giants Causeway; Dickin 1988; Pedersen
et al. 1997; Saunders et al. 1997). In the early Cainozoic, the Eurasian and North

14 1 Introduction to the Nature and Geology of Iceland
American plates were close enough for the plume magma to sustain a complete
subaerial connection (continuous land bridge) between Greenland and the European
mainland. However, during the Neogene, as the northern North Atlantic Ocean
widened and subsided, the marginal eastern and western parts of this transverse
ridge cooled and were gradually submerged. When, how and to what extent this
land bridge broke down is a matter of dispute (see Chap. 12), but it seems that parts
of the transverse ridge (other than oldest parts of present-day Iceland) were still
above sea level in the Middle Miocene (Nilsen 1978; Thiede and Eldholm 1983;
Eldholm et al. 1994; Poore 2008).
1.6 Tectonic and Mantle Plume History of Proto-Iceland
After the initial spreading, the East Greenland and the European continental mar-
gins became submarine (Fig. 1.9), but the mantle plume kept the GSTR (including
proto-Iceland and the Faeroe Islands) above sea level at 60–50 Ma. At this time, the
mantle plume is thought to have been located under East Greenland, west of the
Scoresby Sound (Vink 1984). Extrusive basalts in this region have been dated to
Fig. 1.8 Schematic map showing the geographical position of Iceland, with the Mid-Atlantic
Ridge crossing the island, the Reykjanes Ridge on the south-western side and the Kolbeinsey
Ridge on the northern side. Terrestrial Cainozoic basalt successions in Greenland, Iceland, the
Faeroe Islands, and the British Islands are indicated with dark grey colour. Anomalies of the ocean
floor (different shades of grey) as well as relative age (numbers in Ma) are shown. The general
outline of the Greenland-Scotland Transverse Ridge (GSTR) is indicated (Modified after Talwani
and Eldholm 1977; Larsen 1980; Steinþórsson 1981)

151.6 Tectonic and Mantle Plume History of Proto-Iceland
Fig. 1.9 Schematic reconstruction showing the opening of the northern North Atlantic, widening
of the ocean, rift history of the area, and the “birth” of Iceland. GSFZ Greenland Senja Fracture
Zone, EJMFZ East Jan Mayen Fracture Zone, JMFZ Jan Mayen Fracture Zone, JMR Jan Mayen
Ridge, GSTR Greenland-Scotland Transverse Ridge (Modified after Larsen 1978, 1980; Vink
1984)

16 1 Introduction to the Nature and Geology of Iceland
Fig. 1.9 (continued)
60–55 Ma (Beckinsale et al. 1970). Later, the mantle plume moved (in relative
terms) from underneath the Greenland continental shelf and at 36 Ma it lay under
oceanic crust, feeding the then active Reykjanes Ridge, south of proto-Iceland,
and the Aegir Ridge to the north. The oldest volcanic successions east and west
of Iceland, formed at 55–36 Ma (anomalies 25–16), originated from these
ridges (Fig. 1.9). When the spreading activity along the Aegir Ridge, north of
proto-Iceland, ceased at 27 Ma the Kolbeinsey Ridge took over (Vogt et al.
1980; Larsen 1980). Apparently the spreading centre of the now inactive Aegir
Ridge jumped westwards closer to the mantle plume, activating the Kolbeinsey
Ridge. Activity along the Kolbeinsey Ridge led to the separation of part of the
East Greenland continental margin (Fig. 1.9), now known as the Jan Mayen
Ridge (Talwani and Udintsev 1976; Talwani and Eldholm 1977). At around
20 Ma, all seafloor spreading north of Iceland took place along the Kolbeinsey
Ridge (Vink 1984).
1.7 Tectonic and Rift Relocation History of Iceland
Due to steady spreading along the Mid-Atlantic Ridge that separates the Eurasian
and the American plates and therefore divides Iceland into two parts, the island
widens approximately 20 km/Ma (Steinþórsson 1981) along the central inland rift
zone (known as the Western Rift and the Northern Rift Zones). In a simplified

171.8 Geological Outline of Iceland
overview, the geological successions become younger towards the centre of the
island. But, as the rift zones in Iceland continually become inactive and new rift
zones are formed closer to the mantle plume, older successions are broken up,
tilted, eroded, and separated by new younger geological constructions. The rift
zones show repeated eastward relocation of the spreading axis in response to west-
ward migration of the plate boundary relative to the plume centre, which seems to
be quite stable (Steinþórsson 1981). At 24–15 Ma, the main spreading activity on
land was located in the Northwest Iceland Rift Zone, now submarine off the
northwest coast, and around 15 Ma a new rift zone, the Snæfellsnes-Húnaflói Rift
Zone (see anticline axis on the Snæfellsnes peninsula in Fig. 1.10), evolved to the
east (Harðarson et al. 1997, 2008). At 7–6 Ma, the southern part of the
Snæfellsnes-Húnaflói Rift Zone became extinct and the presently active Western
Rift Zone developed (Fig. 1.10). Then, at about 3–2 Ma the northern part of the
Snæfellsnes-Húnaflói Rift Zone also became extinct and the presently active
Northern Rift Zone formed (Jóhannesson 1980). This continuous rift relocation has
had an important effect on the geology of Iceland, and, among others, caused
massive erosion and deposition, forming extensive sedimentary formations that
often contain plant and, in some rare cases, animal fossils.
1.8 Geological Outline of Iceland
Geologically, Iceland is a young volcanic island, built up during the later part of the
Cainozoic. It is located on top of a mantle plume and at the junction of two subma-
rine ridges, the Mid-Atlantic Ridge (active spreading boundary) and the GSTR
(topographic relief caused by the presence of the Icelandic mantle plume at the
plate boundaries). The mid-oceanic ridge bordering Iceland is represented by two
segments, the Reykjanes Ridge in the south and the Kolbeinsey Ridge in the north
(Fig. 1.8). These ridges are the submarine segments of the Mid-Atlantic Ridge that
are closest to Iceland. The inland part of the mid-ocean ridge is characterized by
rift zones or volcanic zones with active faulting and volcanism extending from the
southwest to the north (Fig. 1.10). Spreading and volcanism takes place on discrete
fissure swarms, 10–100 km long, known as volcanic systems. These systems are
characterized by extensional tectonic features, open fissures, tensional cracks, gra-
ben structures, dikes, normal faults, and volcanic fissures, crater rows, small or
large craters, cinder or spatter cones, and shield volcanoes. The most active part is
generally in the middle and is often the site of a central volcano, such as a caldera
or a stratovolcano (Saemundsson 1979; Steinthórsson and Thorarinsson 1997).
The rocks in Iceland are predominantly volcanic and are divided into four
stratigraphic units or groups, the boundaries of which are defined by changing rock
types (sedimentary and/or volcanic) and/or by their palaeomagnetism (Fig. 1.10).
These four groups are: the Miocene-Pliocene Succession 16–3.1 Ma; the
Pliocene-Pleistocene Succession 3.1–0.78 Ma; the Upper Pleistocene Succession
0.78 Ma to 11.5 ka; and the Holocene Succession 11.5 ka to Recent (Saemundsson
1979; Steinthórsson and Thorarinsson 1997).

18 1 Introduction to the Nature and Geology of Iceland
Fig. 1.10 Geological map of Iceland showing the basic bedrock geology, the presently active rift
and volcanic zones, anticline axis, syncline axis, transcurrent faults, and volcanic systems. WRZ
Western Rift Zone, NRZ Northern Rift Zone, TFZ Tjörnes Fracture Zone, SISZ South Iceland
Seismic Zone (Modified after Saemundsson 1974; 1979; Jóhannesson 1980; Jóhannesson and
Sæmundsson 1989)

191.8 Geological Outline of Iceland
The Miocene-Pliocene Succession, 16–3.1 Ma (Fig. 1.10), comprises the oldest
geological units on Iceland, built up during the Middle to Late Miocene and Pliocene.
The succession covers an area of over 50,000 km2 and includes the plateau basalt
series typical of northwestern, western, northern, and eastern Iceland (Fig. 1.11).
This succession is mostly composed of tholeiitic lava flows and generally associ-
ated intermediate and acidic rocks. Volcanic activity during the Miocene and Pliocene
was similar as today, confined to volcanic systems mainly along eruptive fissures and
shield volcanoes (basaltic) or central volcanoes (calderas, stratovolcanoes; basaltic,
intermediate and acidic). The most common intrusions are basaltic dikes which run
vertically through the lava series. The majority of the dikes are oriented northeast-
southwest as the central rift zone (Western Rift Zone-Northern Rift Zone). Central
volcanoes were fed by magma from chambers underneath the volcanoes and when
activity ceased the magma in the chamber solidified as plutonic rocks of gabbro or
granophyre. Many plutonic intrusions in the Miocene-Pliocene Succession origi-
nated in this way (Saemundsson 1979; Steinthórsson and Thorarinsson 1997). The
succession includes all the oldest and more than half of all the fossiliferous sedimen-
tary rock formations discussed in this book (see Chaps. 4–10).
The younger Pliocene-Pleistocene Succession, from 3.1 to 0.78 Ma (Fig. 1.10),
covers about 25,000 km2 of land and occupies mostly the area between the older
Miocene-Pliocene Succession and the younger Upper Pleistocene Succession.
Volcanic rocks from the Upper Pliocene and Pleistocene in Iceland differ from the
Miocene-Pliocene rocks, depending on whether they were erupted during intergla-
Fig. 1.11 Typical basaltic lava flow series from Mount Skor and Stálfjall on the Northwest
Peninsula, northwestern Iceland (Courtesy Oddur Sigurðsson)

20 1 Introduction to the Nature and Geology of Iceland
cials or subglacially during glacial periods. During interglacial times, the volcanic
activity was similar to that in the Middle to Late Miocene and Early to Middle
Pliocene, but during glacial periods of the Late Pliocene and Pleistocene magma
erupted underneath ice sheets of different thicknesses. Then the volcanic products
accumulated in meltwater supported by the ice walls. Initially, pillow lavas formed
but later on explosive activity started and the magma was quickly cooled by water
and disintegrated into tephra. The basaltic glass in the tephra was altered to brown
Fig. 1.12 Hyaloclastite ridges originating from volcanic fissure eruptions below thick icecaps.
Skaftá, southern Iceland (Courtesy Oddur Sigurðsson)

211.9 Fossiliferous Sedimentary Rocks
palagonite which was cemented together as hyaloclastite (móberg). Hyaloclastite
mountains (Fig. 1.12) mainly grew on fissures and formed ridges underneath the
large icecaps. If the magma reached the surface of the ice, table mountains were
formed when the hyaloclastites were capped by a lava shield and the melt water
from the ice could no longer reach the erupting magma (Saemundsson 1979;
Steinthórsson and Thorarinsson 1997). Sediments are sometimes much thicker in
the Pliocene-Pleistocene successions than in the older Miocene-Pliocene succes-
sion, since fluvial, glacial, and marine related erosion as well as sedimentation due
to isostatic changes were much more frequent. Plant bearing sediments were
mainly accumulated during interglacial periods (see Chap. 11).
The Upper Pleistocene Succession, 0.78 Ma to 11.5 ka, covers about 30,000 km2
of land and is essentially identical with the now active volcanic zones (Fig. 1.10).
The strata of this succession were formed during the Brunhes palaeomagnetic chron
(0.78 Ma to 11.5 ka; corresponding to Middle and Upper Pleistocene), continuing
up to the Holocene. The volcanic rocks of this period are mostly interglacial basaltic
lavas and subglacial pillow lavas and hyaloclastites (Saemundsson 1979;
Steinthórsson and Thorarinsson 1997). The youngest flora investigated for this
book (Svínafellsfjall Formation, see Chap. 11) is derived from the boundary
between the Pliocene-Pleistocene and Upper Pleistocene successions.
The Holocene Succession, 11.5 ka until Recent, is composed of recent lava
flows and pyroclastics, marine sediments, glacial sediments and soil formed after
the retreat of the icecaps. Holocene volcanism has been confined to the now active
volcanic/rift zones. Plant remains from this succession are not dealt with in this
book.
1.9 Fossiliferous Sedimentary Rocks
Miocene to Holocene sediments in Iceland are mostly of volcanic origin, ranging
from thin ash layers (very fine tuff; Fig. 1.13) to thick pyroclastic formations and
ignimbrites. The grain size ranges from finest ash and lapilli tephra to large blocks
and bombs (fine tuff, lapilli tuff, and volcanic breccias). The thickness of the sedi-
mentary units can easily change over short distances, and the difference in grain
size from one outcrop to the other is often substantial. All the Miocene, Pliocene,
and Pleistocene ash layers, tephra, scoria beds, plinian pumice deposits, various
pyroclastic units, and phreatoplinian deposits, as well as clastic- and organic sedi-
ments have been subjected to burial diagenesis and low-grade metamorphism (to
Zeolite facies) due to loading and burial (Walker 1960; Roaldset 1983).
Additionally, the uppermost parts of sedimentary units have often been subjected
to thermal metamorphism by overlying lava (Roaldset 1983). Because of this, no
loose sediments are found from the Miocene, Pliocene, and Pleistocene; all parti-
cles have been compacted, cemented and lithified, forming hard and often glassy
sedimentary rock. Loose sediments are only known from the Holocene of
Iceland.

22 1 Introduction to the Nature and Geology of Iceland
Fig. 1.13 Fine blackish and whitish ash layers in a Holocene soil section (Photo taken by
Sigurður Þórarinsson)
Clastic sedimentary rocks from the Miocene to Pleistocene are also quite variable
with different types of clays, siltstones, sandstones, and conglomerates, as well as
tillites. These rocks reflect a diverse origin, having accumulated in lagoons, lakes,
river channels, and alluvial fans, in deltas, on flood plains, in marshlands and swamps,
around glaciers, or in other landforms (Thorarinsson 1963; Grímsson 2002, 2007a, b;
Grímsson et al. 2007). Relatively thin palaeosoils and aeolian silt- and sandstones of
reddish colour are also prominent in the Miocene and Pliocene strata; they frequently
separate lava flows (Fig. 1.14). Lacustrine sedimentary rocks from the Miocene to
Pleistocene are often present and usually have a rather limited distribution, except
when formed in connection with rift relocation, but may be of considerable thickness.
The lacustrine rocks typically consist of thin-bedded shales, mudstones and siltstones
interfingered with turbidites and overlain by coarser deltaic deposits of sandstone and
conglomerate (Grímsson 2007a, b). In the Pleistocene, drop-stones become promi-
nent in glacial related environments. Fluvial sediments from the Miocene to
Pleistocene, reflecting river channels and flood plains, occur as large lenses of sand-
stone and conglomerate with surrounding thin-bedded shales that reappear and inter-
finger with coarser sedimentary rocks. Delta marshlands and swamp deposits from
the Miocene to Pleistocene are often found as various types of fine- to coarse-grained,
organic rich and dark coloured sedimentary rock (Grímsson 2007a, b). These units
are rich in plant remains (detritus) and are accompanied by numerous lignites or coal

231.9 Fossiliferous Sedimentary Rocks
Fig. 1.14 Red coloured sedimentary rocks between basaltic lava flows at Þuríðará river in
Vopnafjörður, eastern Iceland
beds (Fig. 1.15), especially in the Miocene-Pliocene Succession. Other types of
organic sedimentary rocks are not as common except for yellow to whitish diatomite
that accumulated in freshwater environments (Friedrich 1968; Grímsson 2007a, b),
and have been found mostly in Miocene strata.
Depending on the sediment origin, accumulation rate, type of sediment and dif-
ferent taphonomic processes, the sedimentary rocks contain no or abundant plant
fossils. To date, numerous plant fossils of angiosperms, gymnosperms, mosses,
club mosses, ferns, and horsetails have been recorded. Plant parts that have been
recovered include roots, rhizomes, stems, branches, shoots, leaves, fronds, isolated
pinnae, cuticles, catkins, seeds, fruits (capsules, cones, and samaras), cone scales,
pollen, and spores.
The oldest Miocene plant fossils are approximately 15 Ma old and are found
in sedimentary rocks in northwestern Iceland (Table 1.2; see Chap. 4, Fig. 4.1).
Slightly younger fossiliferous sedimentary rocks, 12–8 Ma old, are also found on
the Northwest Peninsula (Table 1.2; see Chaps. 5–7, Fig. 5.1, Fig. 6.1, Fig. 7.1).
Fossils from the latest Miocene are found around Lake Hreðavatn in western
Iceland (Table 1.2; see Chap. 8, Fig. 8.1) and in Fnjóskadalur in the north (Table 1.2;
see Chap. 9, Fig. 9.1). Plant remains from the Pliocene and Pleistocene are known

24 1 Introduction to the Nature and Geology of Iceland
Fig. 1.15 Lignite mine in Mount Stálfjall at Stálvík, northwestern Iceland. Upper photo showing
entrance to the mine, and the lower one a close up of the mined lignite surface (Courtesy Ólafur
Sigurðsson). Small photo showing typical weathered lignite from the Húsavíkurkleif outcrop in
Steingrímsfjörður, northwestern Iceland

25References
from the Tjörnes peninsula, northern Iceland (Table 1.2; see Chap. 10, Fig. 10.1),
the Snæfellsnes peninsula and Víðidalur in western Iceland, and Svínafell in Öræfi
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