Stefán Arnórsson, Gudni Axelsson, and Kristján Saemundsson

Water-Rock Interaction 205–208, Balkema, Rotter-dam.

Tómasson, J. and H. Franzson 1992. Alteration and tem-perature distribution within the margin of the volcaniczone on the Reykjanes peninsula, SW-Iceland. Water-Rock Interaction (eds. Y. K. Kharaka and A. S. Maest),1467–1469. Balkema, Rotterdam.

Walker, G. P. L. 1960. Zeolite zones and dike distributionin relation to the structure of basalts of eastern Iceland.J. Geol. 68, 515–528.

Walker, G. P. L. 1963. The Breiddalur central volcano,eastern Iceland. Q. J. Geol. Soc. London 119, 29–63.

Walker, G. P. L. 1974a. Eruptive mechanisms in Iceland.In: Kristjánsson, L. ed. Geodynamics of Iceland andthe North Atlantic Area. NATO ASI Series, 189–201(ISBN 90 277 0505 4).

Walker, G. P. L. 1974b. The structure of eastern Iceland.

In: Kristjánsson, L. ed. Geodynamics of Iceland andthe North Atlantic Area. NATO ASI Series, 177–188(ISBN 90 277 0505 4).

Weisenberger, T. 2005. Zeolite facies mineralization in theHvalfjördur area, Iceland. Unpubl. Diploma thesis,Albert Ludwigs University, Freiburg, 142 pp.

White, D. E., L. J. P. Mufer and A. H. Truesdell 1971.Vapour-dominated hydrothermal systems comparedwith hot-water systems. Econ. Geol. 66, 75–97.

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World Geothermal Congress, proceedings 2000. Kyushu-Tohoku, Japan, 4111 pp.

World Geothermal Congress, proceedings 2005. Antalya,Turkey.

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Reviewed research article

Upper Tertiary non-marine environments and climatic changesin Iceland

Friðgeir Grímsson1,2 and Leifur A. Símonarson1

1Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, 101 Reykjavík2 Icelandic Institute of Natural History, Hlemmur 3, 105 Reykjavík

fossil@hi.is; leifuras@raunvis.hi.is

Abstract — Palaeontological research on the Miocene and Pliocene oras and faunas of Iceland date backto the 1770’s. At that time, plant fossils from Iceland were considered belonging to a single ora, and inthe early 20th century scientist considered this ora of Eocene age. During the past few decades systematicpalaeontology, palaeoclimatology, stratigraphy, and palaeogeography have been linked to results from isotopic(K/Ar and Ar/Ar) absolute age determinations and palaeomagneticmeasurements of Cainozoic lavas in Iceland.As a result, numerous fossil oras and a few faunas identied from terrestrial sediments in Iceland are nowknown to give a contiguous record dating back 15 Ma. The oldest oras are therefore Middle Miocene in age.Younger oras are quite different from the older ones and their composition changed as the Miocene came toan end. Gradual cooling that occurred on Iceland since 12 Ma, when the climate was mild with no dry seasonand warm summers, and continuous isolation of Iceland, in the northern North Atlantic, had its affect on theIcelandic ora. Thermophilous plants soon became extinct and more cold tolerant species became prominent.

INTRODUCTION

The fossil record of Iceland extends back as far as itsoldest rocks, which have been radiometrically datedto about 15 Ma (McDougall et al., 1984; Hardarsonet al., 1997). The Icelandic lava pile formed almostexclusively above sea level and as a result the fos-sil bearing strata are primarily of terrestrial origin. Anumber of sedimentary formations containing identi-able plant remains occur interstratied with the lavas(Figure 1). Studies of their fossil oras were initiatedmore than a hundred years ago and a Miocene age wascorrectly assigned to the oldest of them (Heer 1868).This was later rejected in favour of an Eocene age andthat view persisted into the 1960’s (see Kristjánsson,1993). Radiometric dating of the lavas, which startedin the mid-1960’s, veried that the oras could be noolder than Miocene, as originally proposed by Heer

(1868). The global cooling that has occurred on Earthsince the Middle Miocene is well documented in therecord of fossil oras in Iceland, owing to the reg-ular spacing of plantbearing sedimentary formationswithin the lava pile (Figure 2). Unfortunately, wellpreserved remains of terrestrial faunal assemblagesare rarely found in these formations.

Iceland is the only landmass in the northern NorthAtlantic that has a fairly continuous fossil recordfrom the early Middle Miocene to the present. Thegeographical position of Iceland, between Greenlandand continental Northwest Europe, and its rich fossilrecord makes it an interesting place to study possi-ble transcontinental migration of plants and animalsbetween North America/Greenland and Europe/Asiaduring the Late Cainozoic and to interpret and re-construct palaeoclimate and palaeoenvironment in thenorthern North Atlantic based on terrestrial proxies.

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PALAEOENVIRONMENTSThe geology of Iceland is fairly well known

(see Saemundsson, 1979; Steinthórsson and Thorar-insson, 1997; Thordarson and Höskuldsson, 2002).At present, extensional forces that are driven byup-owing magma along the Mid-Atlantic Ridgecause many of the geological features of the island(Steinþórsson, 1981). The volcanic and tectonic envi-ronments of present-day Iceland have been the samefor millions of years, or since the mantle plume be-came positioned under proto-Iceland, between Green-land and Scandinavia (Vink, 1984).

During the Miocene and Pliocene Iceland was, asit is now, characterized by volcanic systems with largecentral volcanoes and surrounding ssure swarms andcrater rows (Walker, 1959, 1964; Hald et al., 1971).Eruptions were frequent (Saemundsson, 1979; Mc-Dougall et al., 1984, 1987) and of various types asevident by various sorts of igneous rocks in the geo-logical formations of the island (Walker, 1959).

Even though modern day Iceland is characterizedby U-shaped fjord landscape this was not so duringthe Miocene and Pliocene. The fjord landscape ofnorth-western and eastern Iceland (Figure 3A), wasformed by the glaciers only during the last ice age, andthe hyaloclastite (palagonite) mountains and ridgesalong the active rift zone crossing the island were alsoformed only during the last ice age (Pjetursson, 1901)and date back no further than 3 Ma (Geirsdóttir andEiríksson, 1994).

Sedimentary rocks in the Tertiary formations ofIceland give critical information on various environ-ments during the Miocene and Pliocene. Sedimentsof volcanic origin, lake, river and lagoon sediments,as well as various other types suggest diverse en-vironments and changing landscape (Walker, 1959;Friedrich, 1966; Saemundsson, 1979; Roaldset, 1983;Grímsson, 2002; Grímsson, 2007a; Grímsson, et al.,2007).

As evident from the geological record and basedon volcanic products and sedimentary rocks one canvisualize the Icelandic Miocene and Pliocene envi-ronments as following. Were ocean and land metthere were long and sandy beaches and steep cliffs,and bay-mouth bars fronting bays forming lagoons.

From the shoreline, vast lowlands with meander-ing rivers and streams, oxbow lakes, marshlands,oodplains and terraces, stretched towards the high-lands. Volcanoes with an altitudinal range up to2000m (stratovolcanoes)marked the landscapes, withsmaller shield volcanoes, spatter ring craters, scoriacones, cinder craters, explosion craters (maars), tuffrings, tuff cones, and calderas. Rivers and streamseroded canyons and valleys. V-shaped valleys, gorges,ravines, gullies, and steep canyons cut into the high-land and high-lying valleys that were surrounded byvolcanic mountains. Lakes were numerous and of var-ious types, and formed, as some of the present Ice-landic lakes, by volcanic activity or extensional riftforces. Large lakes could have been present in riftvalleys, calderas, and following the closure of a lavaow at the mouth of a valley. Other lakes could havebeen present in small explosive craters reaching belowgroundwater level.

These environments were full of life as evidentfrom the fossil record. Vegetation thrived fromthe lowland to highlands (Grímsson et al., 2007)and freshwater animals (Friedrich, 1966; Friedrichet al., 1972; Sigurðsson, 1975) occupied lakes andstreams. Insects were common in various environ-ments (Friedrich et al., 1972; Heie and Friedrich,1971) and small terrestrial mammals, herbivores,were grazing in the undergrowth (Símonarson, 1990).

THE MIOCENE–PLIOCENESEDIMENTARY ROCKS

Upper Tertiary sedimentary rocks in Iceland are quitevariable. The most prominent are of volcanic origin,ranging from thin ash layers (very ne tuff) to thickpyroclastic formations and ignimbrites. The grainsize ranges from nest ash and lapilli tephra to largeblocks and bombs (ne tuff, lapilli tuff, and volcanicbreccias). The thickness of these sedimentary rockscan easily change over short distances, and the dif-ference in grain size from one outcrop to the other isoften quite substantial. Most of the ash layers, tephra,scoria beds, plinian pumice deposits, various pyro-clastic units, and phreatoplinian deposits have under-gone different stages of geothermal alteration due to

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Figure 1. Geological map of Iceland with localities mentioned in the text (modied from Jóhannesson andSæmundsson, 1989). – Jarðfræðikort af Íslandi með fundarstöðum steingervinga sem nefndir eru í texta (byggtá korti Hauks Jóhannessonar og Kristjáns Sæmundssonar, 1989).

loading and burial (Roaldset, 1983). The uppermostparts of sedimentary units have often been subjectedto thermal metamorphism by overlying lava. All Ter-tiary sedimentary units have subsequently been sub-jected to burial diagenesis and low-grade metamor-phism to zeolite facies (Roaldset, 1983). Loose par-ticles have therefore become compact, cemented andlithied, forming hard glassy sedimentary rock.

Clastic sedimentary rocks in the Miocene–Pliocene strata are also quite variable with differenttypes of clays, siltstones, sandstones and conglom-erates. These sedimentary rocks show a diverse ori-gin, having accumulated in lagoons, lakes, river chan-nels, alluvial fans, deltas, on ood plains, in marsh-lands and swamps or other landforms (Grímsson,2002, 2007a; Grímsson et al., 2007). Relatively thinpalaeosoils and aeolian silt- and sandstones of reddishcolour are also prominent; they are frequently found

separating two successive lava ows (Figure 3B). Thered colour of some sedimentary units is partly be-lieved to be the result of surface weathering in a warmand moist Miocene climate (Kristjánsson, 1973). La-custrine sedimentary rocks are often present, usu-ally having rather limited distribution but consider-able thickness. The lacustrine rocks typically con-sist of thin-bedded shales, mudstones and siltstonesinterngered with turbidites (Figure 3D) and over-lain by coarser deltaic deposits of sandstone and con-glomerate (Grímsson, 2007a). Fluvial sediments re-ecting river channels and ood plains occur as largelenses of sandstone and conglomerate with surround-ing thin-bedded shales that reappear and interngerwith coarser sediments. Delta marshland and swampdeposits are often found as various types of ne- tocoarsely-grained, organic rich and dark coloured sed-imentary rock (Grímsson, 2007a). These units are rich

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PALAEOENVIRONMENTSThe geology of Iceland is fairly well known

(see Saemundsson, 1979; Steinthórsson and Thorar-insson, 1997; Thordarson and Höskuldsson, 2002).At present, extensional forces that are driven byup-owing magma along the Mid-Atlantic Ridgecause many of the geological features of the island(Steinþórsson, 1981). The volcanic and tectonic envi-ronments of present-day Iceland have been the samefor millions of years, or since the mantle plume be-came positioned under proto-Iceland, between Green-land and Scandinavia (Vink, 1984).

During the Miocene and Pliocene Iceland was, asit is now, characterized by volcanic systems with largecentral volcanoes and surrounding ssure swarms andcrater rows (Walker, 1959, 1964; Hald et al., 1971).Eruptions were frequent (Saemundsson, 1979; Mc-Dougall et al., 1984, 1987) and of various types asevident by various sorts of igneous rocks in the geo-logical formations of the island (Walker, 1959).

Even though modern day Iceland is characterizedby U-shaped fjord landscape this was not so duringthe Miocene and Pliocene. The fjord landscape ofnorth-western and eastern Iceland (Figure 3A), wasformed by the glaciers only during the last ice age, andthe hyaloclastite (palagonite) mountains and ridgesalong the active rift zone crossing the island were alsoformed only during the last ice age (Pjetursson, 1901)and date back no further than 3 Ma (Geirsdóttir andEiríksson, 1994).

Sedimentary rocks in the Tertiary formations ofIceland give critical information on various environ-ments during the Miocene and Pliocene. Sedimentsof volcanic origin, lake, river and lagoon sediments,as well as various other types suggest diverse en-vironments and changing landscape (Walker, 1959;Friedrich, 1966; Saemundsson, 1979; Roaldset, 1983;Grímsson, 2002; Grímsson, 2007a; Grímsson, et al.,2007).

As evident from the geological record and basedon volcanic products and sedimentary rocks one canvisualize the Icelandic Miocene and Pliocene envi-ronments as following. Were ocean and land metthere were long and sandy beaches and steep cliffs,and bay-mouth bars fronting bays forming lagoons.

From the shoreline, vast lowlands with meander-ing rivers and streams, oxbow lakes, marshlands,oodplains and terraces, stretched towards the high-lands. Volcanoes with an altitudinal range up to2000m (stratovolcanoes)marked the landscapes, withsmaller shield volcanoes, spatter ring craters, scoriacones, cinder craters, explosion craters (maars), tuffrings, tuff cones, and calderas. Rivers and streamseroded canyons and valleys. V-shaped valleys, gorges,ravines, gullies, and steep canyons cut into the high-land and high-lying valleys that were surrounded byvolcanic mountains. Lakes were numerous and of var-ious types, and formed, as some of the present Ice-landic lakes, by volcanic activity or extensional riftforces. Large lakes could have been present in riftvalleys, calderas, and following the closure of a lavaow at the mouth of a valley. Other lakes could havebeen present in small explosive craters reaching belowgroundwater level.

These environments were full of life as evidentfrom the fossil record. Vegetation thrived fromthe lowland to highlands (Grímsson et al., 2007)and freshwater animals (Friedrich, 1966; Friedrichet al., 1972; Sigurðsson, 1975) occupied lakes andstreams. Insects were common in various environ-ments (Friedrich et al., 1972; Heie and Friedrich,1971) and small terrestrial mammals, herbivores,were grazing in the undergrowth (Símonarson, 1990).

THE MIOCENE–PLIOCENESEDIMENTARY ROCKS

Upper Tertiary sedimentary rocks in Iceland are quitevariable. The most prominent are of volcanic origin,ranging from thin ash layers (very ne tuff) to thickpyroclastic formations and ignimbrites. The grainsize ranges from nest ash and lapilli tephra to largeblocks and bombs (ne tuff, lapilli tuff, and volcanicbreccias). The thickness of these sedimentary rockscan easily change over short distances, and the dif-ference in grain size from one outcrop to the other isoften quite substantial. Most of the ash layers, tephra,scoria beds, plinian pumice deposits, various pyro-clastic units, and phreatoplinian deposits have under-gone different stages of geothermal alteration due to

304 JÖKULL No. 58, 2008

Upper Tertiary non-marine environments in Iceland

Figure 1. Geological map of Iceland with localities mentioned in the text (modied from Jóhannesson andSæmundsson, 1989). – Jarðfræðikort af Íslandi með fundarstöðum steingervinga sem nefndir eru í texta (byggtá korti Hauks Jóhannessonar og Kristjáns Sæmundssonar, 1989).

loading and burial (Roaldset, 1983). The uppermostparts of sedimentary units have often been subjectedto thermal metamorphism by overlying lava. All Ter-tiary sedimentary units have subsequently been sub-jected to burial diagenesis and low-grade metamor-phism to zeolite facies (Roaldset, 1983). Loose par-ticles have therefore become compact, cemented andlithied, forming hard glassy sedimentary rock.

Clastic sedimentary rocks in the Miocene–Pliocene strata are also quite variable with differenttypes of clays, siltstones, sandstones and conglom-erates. These sedimentary rocks show a diverse ori-gin, having accumulated in lagoons, lakes, river chan-nels, alluvial fans, deltas, on ood plains, in marsh-lands and swamps or other landforms (Grímsson,2002, 2007a; Grímsson et al., 2007). Relatively thinpalaeosoils and aeolian silt- and sandstones of reddishcolour are also prominent; they are frequently found

separating two successive lava ows (Figure 3B). Thered colour of some sedimentary units is partly be-lieved to be the result of surface weathering in a warmand moist Miocene climate (Kristjánsson, 1973). La-custrine sedimentary rocks are often present, usu-ally having rather limited distribution but consider-able thickness. The lacustrine rocks typically con-sist of thin-bedded shales, mudstones and siltstonesinterngered with turbidites (Figure 3D) and over-lain by coarser deltaic deposits of sandstone and con-glomerate (Grímsson, 2007a). Fluvial sediments re-ecting river channels and ood plains occur as largelenses of sandstone and conglomerate with surround-ing thin-bedded shales that reappear and interngerwith coarser sediments. Delta marshland and swampdeposits are often found as various types of ne- tocoarsely-grained, organic rich and dark coloured sed-imentary rock (Grímsson, 2007a). These units are rich

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in plant remains (detritus) and are accompanied by nu-merous lignites or coal beds (Icelandic: surtarbran-dur) (see Figure 3C), especially in the Miocene strata(Bárðarson, 1918). Other types of organic sedimen-tary rocks are not as common, with the notable excep-tion of diatomite, made up of diatom silica shells thataccumulated in a freshwater environment (Friedrich,1968). The resulting sedimentary layer is yellow towhitish in colour and of low density (Figure 3D).

The present appearance and composition of thesedimentary rock types have resulted from a singleor several secondary processes such as palagoniti-zation and devitrication, weathering, thermal meta-morphism (metasomatism), diagenesis, and regionalburial metamorphism (Roaldset, 1983).

FOSSIL BIOTARemains of organisms from the Miocene and Pliocenein Iceland are found both in sedimentary and ig-neous rocks (Friedrich, 1968). To date, numer-ous plant fossils of angiosperms (Figure 3E), gym-nosperms, mosses, club mosses, ferns and horsetailshave been recorded. Plant parts that have been foundinclude, among others: stems, branches, shoots, roots,leaves (Figure 3E), needles, fruits, capsules, catkins,cones, scales, samaras, seeds, rhizomes, fronds, pin-nae, pollen, spores, and cuticles.

Fossils of terrestrial or freshwater animals fromthe Miocene and Pliocene of Iceland are rare. Insectremains (beetles) have been recorded from Brjáns-lækur (12 Ma) and in sedimentary rocks at Trölla-

Figure 2. Map of Northwest Ice-land showing the age of sedimen-tary formations, fossil localities, andextinct central volcanoes (modiedfrom Jóhannesson and Sæmundsson,1989; 1998). – Kort af Vestfjörðumer sýnir aldur setlagamyndana, fund-arstaði steingervinga og útkulnað-ar megineldstöðvar (byggt á kortumHauks Jóhannessonar og KristjánsSæmundssonar, 1989 og 1998).

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Figure 3. A) Typical fjord landscape in Northwest Iceland. B) Red intrabasaltic sediments with white tephra layers inNorthwest Iceland, 15 Ma. C) Lignite (surtarbrandur) in Húsavíkurkleif, 10 Ma. D) Diatom-rich lake sediments in Surtar-brandsgil, Brjánslækur, 12 Ma. E) Fagus friedrichii Grímsson & Denk, from Selárdalur, 15 Ma. Scale bar 3 cm. F) Bonesfrom a small deer, Þuríðará in Vopnafjörður, 3.5–3.0 Ma. Scale bar 2 cm. G) Trace fossils, repichnia, Þórisdalur, 6–5 Ma.Scale bar 2 cm. (Photos A and C-G from Friðgeir Grímsson, 2007; B: from Þorleifur Einarsson, 1974). – A) Landslag áVestfjörðum. B) Rautt setlag með ljósum gjóskulögum á milli hraunlaga á Vestfjörðum, 15 millj. ára. C) Surtarbrandur íHúsavíkurkleif, 10 millj. ára. D) Kísilríkt stöðuvatnaset í Surtarbrandsgili hjá Brjánslæk. E) Arnarbeyki frá Selárdal, 15millj. ára. Mælikvarði er 3 cm. F) Bein úr litlu dýri af hjartarætt frá Þuríðará í Vopnarði, 3,5–3,0 millj. ára. Mælikvarðier 2 cm. G) Skriðför í siltsteini frá Þórisdal í Lóni, 6–5 millj. ára. Mælikvarði er 2 cm. (Myndir A og C-G tók FriðgeirGrímsson, 2007, en mynd B tók Þorleifur Einarsson, 1974).

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in plant remains (detritus) and are accompanied by nu-merous lignites or coal beds (Icelandic: surtarbran-dur) (see Figure 3C), especially in the Miocene strata(Bárðarson, 1918). Other types of organic sedimen-tary rocks are not as common, with the notable excep-tion of diatomite, made up of diatom silica shells thataccumulated in a freshwater environment (Friedrich,1968). The resulting sedimentary layer is yellow towhitish in colour and of low density (Figure 3D).

The present appearance and composition of thesedimentary rock types have resulted from a singleor several secondary processes such as palagoniti-zation and devitrication, weathering, thermal meta-morphism (metasomatism), diagenesis, and regionalburial metamorphism (Roaldset, 1983).

FOSSIL BIOTARemains of organisms from the Miocene and Pliocenein Iceland are found both in sedimentary and ig-neous rocks (Friedrich, 1968). To date, numer-ous plant fossils of angiosperms (Figure 3E), gym-nosperms, mosses, club mosses, ferns and horsetailshave been recorded. Plant parts that have been foundinclude, among others: stems, branches, shoots, roots,leaves (Figure 3E), needles, fruits, capsules, catkins,cones, scales, samaras, seeds, rhizomes, fronds, pin-nae, pollen, spores, and cuticles.

Fossils of terrestrial or freshwater animals fromthe Miocene and Pliocene of Iceland are rare. Insectremains (beetles) have been recorded from Brjáns-lækur (12 Ma) and in sedimentary rocks at Trölla-

Figure 2. Map of Northwest Ice-land showing the age of sedimen-tary formations, fossil localities, andextinct central volcanoes (modiedfrom Jóhannesson and Sæmundsson,1989; 1998). – Kort af Vestfjörðumer sýnir aldur setlagamyndana, fund-arstaði steingervinga og útkulnað-ar megineldstöðvar (byggt á kortumHauks Jóhannessonar og KristjánsSæmundssonar, 1989 og 1998).

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Figure 3. A) Typical fjord landscape in Northwest Iceland. B) Red intrabasaltic sediments with white tephra layers inNorthwest Iceland, 15 Ma. C) Lignite (surtarbrandur) in Húsavíkurkleif, 10 Ma. D) Diatom-rich lake sediments in Surtar-brandsgil, Brjánslækur, 12 Ma. E) Fagus friedrichii Grímsson & Denk, from Selárdalur, 15 Ma. Scale bar 3 cm. F) Bonesfrom a small deer, Þuríðará in Vopnafjörður, 3.5–3.0 Ma. Scale bar 2 cm. G) Trace fossils, repichnia, Þórisdalur, 6–5 Ma.Scale bar 2 cm. (Photos A and C-G from Friðgeir Grímsson, 2007; B: from Þorleifur Einarsson, 1974). – A) Landslag áVestfjörðum. B) Rautt setlag með ljósum gjóskulögum á milli hraunlaga á Vestfjörðum, 15 millj. ára. C) Surtarbrandur íHúsavíkurkleif, 10 millj. ára. D) Kísilríkt stöðuvatnaset í Surtarbrandsgili hjá Brjánslæk. E) Arnarbeyki frá Selárdal, 15millj. ára. Mælikvarði er 3 cm. F) Bein úr litlu dýri af hjartarætt frá Þuríðará í Vopnarði, 3,5–3,0 millj. ára. Mælikvarðier 2 cm. G) Skriðför í siltsteini frá Þórisdal í Lóni, 6–5 millj. ára. Mælikvarði er 2 cm. (Myndir A og C-G tók FriðgeirGrímsson, 2007, en mynd B tók Þorleifur Einarsson, 1974).

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tunga in Steingrímsfjörður deposited at 10 Ma (Fig-ure 4). The best preserved insect remains were foundat Hrútagil in Mókollsdalur, Northwest Iceland (Fig-ures 1 and 2), in sedimentary rocks dated to 9–8 Ma(Heie and Friedrich, 1971; Friedrich et al., 1972,Akhmetiev et al., 1978). The occurrence of the aphidLongistigma caryae Harris (giant bark aphid) is inter-esting as this species is presently conned to NorthAmerica. The North American-Icelandic aphid ismost closely related to L. liquidambaraTakahasi fromTaiwan (Heie and Friedrich, 1971). This relation sug-gest a much wider circumpolar distribution of largeaphids during the Miocene than at present. Sev-eral remains of ies, belonging especially to Bibion-idae (marsh ies), have been found in the sedimen-tary rocks in Mókollsdalur. Insect remains have alsobeen found in Langavatnsdalur and aroundHreðavatn,West Iceland (Figures 1 and 2), in sedimentary rocksdated to 7–6 Ma (Figure 4).

Spicules of fresh water sponges (Spongilla cf.fragilis) have been recorded from Surtarbrandsgilat Brjánslækur in sedimentary rocks dated to about12 Ma (Friedrich, 1966). Remains of water eas(Daphnia sp., belonging to Cladocera) have beenfound at Hrútagil in Mókollsdalur. Freshwater pul-monate gastropods have been collected from MountSúlur close to Akureyri (Figure 1) in sedimentaryrocks slightly younger than 8 Ma (Margrét Hallsdót-tir pers. comm., 2007), as well as a few schizodontbivalves most likely belonging to Unionidae in about5.5 Ma old sedimentary rocks in Selárgil in Fnjóska-dalur (Figures 1 and 4), North Iceland (Sigurðsson,1975).

Trace fossils, mainly foodichnia, domichnia,repichnia, and pascichnia, reecting the activity ofinvertebrates, are quite frequently found in IcelandicMiocene and Pliocene freshwater sedimentary rocks,such as those around Hreðavatn and at Þórisdalur (6–5 Ma) in Southeast Iceland (Figure 3G). They are of-ten found even when there are no body fossils (Vil-hjálmsson and Símonarson, 1987; Grímsson, 2002).Trace fossils such as leaf mines, galls, pierce holes,and various traces left by a range of insects are alsofound in fossil plants remains (F. Grímsson, unpub.material).

Terrestrial vertebrate fossils are extremely rare inIceland (Figure 3F). So far only fragmentary shoul-der bones, scapula and other bone parts belonging toa small deer have been found (Símonarson, 1990).The bones were found in the Burstarfell Formationat Þuríðará in Vopnafjörður (Figures 1 and 4) in redinterbasaltic sandstone of Pliocene age, 3.5–3 Ma.The animal was probably a descendant of the ter-restrial vertebrate fauna that found itself isolated onproto-Iceland when it became an island in the LateOligocene or Early to Middle Miocene.

MIOCENE–PLIOCENE VEGETATIONThe oldest oras known from Iceland are in sedi-mentary rocks approximately dated to 15 Ma. Atthis time in the island’s vegetational history, indi-vidual oras were already quite distinct as macro-fossils from different localities suggest various veg-etation units. For instance, in Selárdalur (Figures2 and 4) the most prominent fossil type is Fagusfriedrichii (Figure 3E). Leaves of this type make upover 90% of the fossils encountered in this outcrop(Grímsson and Denk, 2005; Grímsson and Símonar-son, 2006). Other types belong to Aesculus, Cercidi-phyllum, Lonicera, Magnolia, Platanus leucophylla,Rhododendron, Tilia selardalense, Ulmus, and Picea(Áskelsson, 1946a, 1957; Akhmetiev et al., 1978;Grímsson et al., 2007). The Selárdalur ora is thoughtto represent broadleaved deciduous and partly ever-green beech forests. The sedimentary rocks sug-gest that this was a highland ora found mainly onwell drained slopes. Components of the Selárdalurora are typical representatives of hardwood forestspresently found in a humid warm temperate climate.Interestingly enough, in another outcrop, the Botn lo-cality (Figure 2) of similar age, the strata is composedof ne grained lowland sedimentary rocks, mostlylignite, and the plant fossils found there are mainlyconifers. Most prominent taxa encountered are Se-quoia abietina and Glyptostrobus europaeus (Gríms-son et al., 2007). It is believed that Glyptostrobuswas present on oodplains and that Sequoia occupieddryer regions (mostly on hummocks). This lowlandora is likely to have merged with a hardwood forestsimilar to the Selárdalur ora at higher elevation.

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Figure 4. Chronology of the Upper Tertiary sedimentary formations and biozones mentioned in the text. Theyare both west and east of the volcanic zone. - Aldursröð jarðmyndana með steingervingum frá efri hlutatertíertímabils sem greint er frá í texta. Þær eru sitt hvoru megin gosbeltisins.

Only a few oras have been recorded from sed-imentary rocks deposited at 13.5 Ma, but they arerather badly preserved. Macrofossils from the Taaoutcrop at Ketilseyri (Figures 2 and 4) are mostly ofthe same taxon as those found in the older Selárdalurora (Símonarson et al., 2000, 2002; Grímssonand Símonarson, 2006), with Fagus friedrichii be-ing the most prominent. Some of the taxa knownfrom Selárdalur have not been recorded from Taa,namely Cercidiphyllum and Aesculus. Judging fromthe macrofossils and pollen (Akhmetiev et al., 1978)there does not seem to have been any major changein either the vegetation or the climate between 15 and13.5 Ma (Grímsson et al., 2007).

Plant fossils from Brjánslækur and Seljá, dated to12 Ma (Figure 4), represent the richest ora knownfrom Iceland (Friedrich, 1966; Denk et al., 2005;Grímsson, 2007b). Modern living analogues of thefossil taxa suggest that the vegetation thrived in amoist, warm-temperate to temperate climate. Thewoody vegetation at this time was dominated bybroadleaved deciduous trees, mixed with conifers andsome evergreen taxa. The most common fossils fromBrjánslækur (Figure 2) are Alnus cecropiifolia, Betulaislandica, and Acer crenatifolium subsp. islandicum.Other macrofossils include Acer askelssonii, Alnusgaudinii, Carpinus, Comptonia hesperia, Corylus,Fraxinus, Juglans, Laurophyllum, Lonicera, Magno-

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tunga in Steingrímsfjörður deposited at 10 Ma (Fig-ure 4). The best preserved insect remains were foundat Hrútagil in Mókollsdalur, Northwest Iceland (Fig-ures 1 and 2), in sedimentary rocks dated to 9–8 Ma(Heie and Friedrich, 1971; Friedrich et al., 1972,Akhmetiev et al., 1978). The occurrence of the aphidLongistigma caryae Harris (giant bark aphid) is inter-esting as this species is presently conned to NorthAmerica. The North American-Icelandic aphid ismost closely related to L. liquidambaraTakahasi fromTaiwan (Heie and Friedrich, 1971). This relation sug-gest a much wider circumpolar distribution of largeaphids during the Miocene than at present. Sev-eral remains of ies, belonging especially to Bibion-idae (marsh ies), have been found in the sedimen-tary rocks in Mókollsdalur. Insect remains have alsobeen found in Langavatnsdalur and aroundHreðavatn,West Iceland (Figures 1 and 2), in sedimentary rocksdated to 7–6 Ma (Figure 4).

Spicules of fresh water sponges (Spongilla cf.fragilis) have been recorded from Surtarbrandsgilat Brjánslækur in sedimentary rocks dated to about12 Ma (Friedrich, 1966). Remains of water eas(Daphnia sp., belonging to Cladocera) have beenfound at Hrútagil in Mókollsdalur. Freshwater pul-monate gastropods have been collected from MountSúlur close to Akureyri (Figure 1) in sedimentaryrocks slightly younger than 8 Ma (Margrét Hallsdót-tir pers. comm., 2007), as well as a few schizodontbivalves most likely belonging to Unionidae in about5.5 Ma old sedimentary rocks in Selárgil in Fnjóska-dalur (Figures 1 and 4), North Iceland (Sigurðsson,1975).

Trace fossils, mainly foodichnia, domichnia,repichnia, and pascichnia, reecting the activity ofinvertebrates, are quite frequently found in IcelandicMiocene and Pliocene freshwater sedimentary rocks,such as those around Hreðavatn and at Þórisdalur (6–5 Ma) in Southeast Iceland (Figure 3G). They are of-ten found even when there are no body fossils (Vil-hjálmsson and Símonarson, 1987; Grímsson, 2002).Trace fossils such as leaf mines, galls, pierce holes,and various traces left by a range of insects are alsofound in fossil plants remains (F. Grímsson, unpub.material).

Terrestrial vertebrate fossils are extremely rare inIceland (Figure 3F). So far only fragmentary shoul-der bones, scapula and other bone parts belonging toa small deer have been found (Símonarson, 1990).The bones were found in the Burstarfell Formationat Þuríðará in Vopnafjörður (Figures 1 and 4) in redinterbasaltic sandstone of Pliocene age, 3.5–3 Ma.The animal was probably a descendant of the ter-restrial vertebrate fauna that found itself isolated onproto-Iceland when it became an island in the LateOligocene or Early to Middle Miocene.

MIOCENE–PLIOCENE VEGETATIONThe oldest oras known from Iceland are in sedi-mentary rocks approximately dated to 15 Ma. Atthis time in the island’s vegetational history, indi-vidual oras were already quite distinct as macro-fossils from different localities suggest various veg-etation units. For instance, in Selárdalur (Figures2 and 4) the most prominent fossil type is Fagusfriedrichii (Figure 3E). Leaves of this type make upover 90% of the fossils encountered in this outcrop(Grímsson and Denk, 2005; Grímsson and Símonar-son, 2006). Other types belong to Aesculus, Cercidi-phyllum, Lonicera, Magnolia, Platanus leucophylla,Rhododendron, Tilia selardalense, Ulmus, and Picea(Áskelsson, 1946a, 1957; Akhmetiev et al., 1978;Grímsson et al., 2007). The Selárdalur ora is thoughtto represent broadleaved deciduous and partly ever-green beech forests. The sedimentary rocks sug-gest that this was a highland ora found mainly onwell drained slopes. Components of the Selárdalurora are typical representatives of hardwood forestspresently found in a humid warm temperate climate.Interestingly enough, in another outcrop, the Botn lo-cality (Figure 2) of similar age, the strata is composedof ne grained lowland sedimentary rocks, mostlylignite, and the plant fossils found there are mainlyconifers. Most prominent taxa encountered are Se-quoia abietina and Glyptostrobus europaeus (Gríms-son et al., 2007). It is believed that Glyptostrobuswas present on oodplains and that Sequoia occupieddryer regions (mostly on hummocks). This lowlandora is likely to have merged with a hardwood forestsimilar to the Selárdalur ora at higher elevation.

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Figure 4. Chronology of the Upper Tertiary sedimentary formations and biozones mentioned in the text. Theyare both west and east of the volcanic zone. - Aldursröð jarðmyndana með steingervingum frá efri hlutatertíertímabils sem greint er frá í texta. Þær eru sitt hvoru megin gosbeltisins.

Only a few oras have been recorded from sed-imentary rocks deposited at 13.5 Ma, but they arerather badly preserved. Macrofossils from the Taaoutcrop at Ketilseyri (Figures 2 and 4) are mostly ofthe same taxon as those found in the older Selárdalurora (Símonarson et al., 2000, 2002; Grímssonand Símonarson, 2006), with Fagus friedrichii be-ing the most prominent. Some of the taxa knownfrom Selárdalur have not been recorded from Taa,namely Cercidiphyllum and Aesculus. Judging fromthe macrofossils and pollen (Akhmetiev et al., 1978)there does not seem to have been any major changein either the vegetation or the climate between 15 and13.5 Ma (Grímsson et al., 2007).

Plant fossils from Brjánslækur and Seljá, dated to12 Ma (Figure 4), represent the richest ora knownfrom Iceland (Friedrich, 1966; Denk et al., 2005;Grímsson, 2007b). Modern living analogues of thefossil taxa suggest that the vegetation thrived in amoist, warm-temperate to temperate climate. Thewoody vegetation at this time was dominated bybroadleaved deciduous trees, mixed with conifers andsome evergreen taxa. The most common fossils fromBrjánslækur (Figure 2) are Alnus cecropiifolia, Betulaislandica, and Acer crenatifolium subsp. islandicum.Other macrofossils include Acer askelssonii, Alnusgaudinii, Carpinus, Comptonia hesperia, Corylus,Fraxinus, Juglans, Laurophyllum, Lonicera, Magno-

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lia, Rosaceae, Salix gruberi, Sassafras ferrettianum,Smilax, Ulmus cf. pyramidalis, Phragmites, Abiessteenstrupiana, Cathaya, Cryptomeria anglica, Piceasect. Picea, Equisetum, Dryopteris, and Osmundaparschlugiana (Heer, 1868; Áskelsson, 1946b, 1954,1956; Friedrich, 1966; Akhmetiev et al., 1978; Denket al., 2005; Grímsson, 2007b).

In the Seljá ora (Figure 2) most abundant fos-sil types are Salix gruberi, Alnus cecropiifolia, andPopulus. Over 90% of the broadleaved-type fossilscollected from Seljá belong to one of these three taxa(Grímsson, 2007b). Other fossils frequently found be-long to Phragmites and Equisetum. Additional fos-sils have been identied as Alnus cf. kefersteinii,Betula islandica, Carpinus, Pterocarya, Magnolia,Rosaceae, and Acer crenatifolium subsp. islandicum.

Sedimentary rocks at Seljá and Brjánslækur sug-gest that the surrounding region consisted of lowlandand highland environment with an extensive river sys-tem, oodplains, oxbow lakes, several small lakes andponds, as well as swamps. The lowlands were sur-rounded by highland hillsides with valleys and vol-canic mountains. At Seljá the macrofossils indicatean azonal riparian ora, with Alnus, Salix, and Popu-lus growing along rivers and streams (wetland veg-etation). In areas with stagnant water Phragmitesand Equisetum became more prominent. Close by onslightly more elevated areas the vegetation includedAcer, Betula, Carpinus, Corylus, Pterocarya, Mag-nolia, and Rosaceae (riverbank woodland) (Gríms-son, 2007b). At Brjánslækur the macrofossils in-dicate a shallow lake environment with azonal andzonal vegetation. The shores of the lakes wereoccupied by herbaceous aquatic and semi-aquaticplants: Equisetum, Phragmites, Osmunda, and Dry-opteris (wetland vegetation). Close to the shore-line, woody plants adapted to wet ground becameprominent: Salix, Alnus, Betula, and Acer (lakeshorewoodland). The vegetation cover became denserand additional broadleaved and conifer species be-came prominent. The zonal forest around the lakewas a mixed broadleaved coniferous forest with occa-sional evergreen trees (Grímsson, 2007b). Additionaltaxa included Magnolia, Sassafras, Comptonia, Smi-lax, Laurophyllum, Liriodendron, Rosaceae, Corylus,

Fraxinus, Juglans, Lonicera, Carpinus, Ulmus, Abies,Cathaya, Picea, and Tsuga (mixed forests).

The plant bearing formation in Gerpir, EastIceland (Figures 1 and 4), that contains pollen,spores, and rare macrofossils is of similar age as theBrjánslækur-Seljá Formation, which is dated to about12 Ma (McDougall et al., 1984; Akhmetiev et al.,1978).

The Icelandic vegetation at 10 Ma is representedin many fossil-rich outcrops. In spite of the numer-ous localities, these oras are much less diverse thanthe Brjánslækur and Seljá oras (12 Ma). At Trölla-tunga (Figures 2 and 4) some of the best-preservedplant fossils in Iceland have been found. The sedi-mentary rocks at Tröllatunga are rich in warm tem-perate to temperate taxa; the most common types be-long to Acer crenatifolium subsp. islandicum andRhododendron aff. ponticum. For the rst time, smallleaved Vaccinium and Arctostaphylos are present andquite common (Denk et al., 2005). Other woodytaxa belong to Juglandaceae (Símonarson, 1991), Be-tulaceae, and Rosaceae. Sedimentary rocks at thenearby Húsavíkurkleif locality (Figure 2), are mostlycomposed of fossils from ferns and fern allies and thefew woody taxa belong to Salix gruberi, Pterocaryaand Alnus cecropiifolia (Grímsson and Denk, 2007).The fossil oras from Tröllatunga and Húsavíkurkleifgive information on both zonal and azonal vegetation,indicating mixed coniferous and broadleaved warmtemperate to temperate forests. Fossil occurrence andsedimentary rocks suggest that Salix, Alnus, and Pte-rocarya grew on banks along rivers. Other hardwoodtaxa were dominant on drier ground, with other jug-landaceous types, Rhododendron, Acer, and conifer-ous taxa (Denk et al., 2005; Grímsson, 2007b; Gríms-son and Denk, 2007).

The Hólmatindur Formation in East Iceland (Fig-ures 1 and 4), which contains pollen, spores, and fewmacro remains, is of the same age, 10 Ma (Meyer andPirrit, 1957; Akhmetiev et al., 1978).

Hrútagil in Mókollsdalur (Figures 2 and 4) is thebest know macrofossil locality from the 9–8 Ma for-mation. The Hrútagil ora is composed of Acer cre-natifolium subsp. islandicum, Acer askelssonii, Alnuscecropiifolia, Alnus cf. kefersteinii, Betula cristata,

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Betula subnivalis, Carpinus, Corylus, Fagus gussonii,Juglandaceae, Lonicera, Populus, Pterocarya, Salixgruberi, Ulmus pyramidalis, Phragmites, Bryophyta,Picea sect. Picea, and Pseudotsuga (Friedrich et al.,1972; Akhmetiev et al., 1978; Denk et al., 2005;Grímsson and Denk, 2007). It is noteworthy that Fa-gus gussonii is recorded for the rst time in these 9–8 Ma sediments. This beech species was previouslyonly known from Late Miocene sediments in south-ern Europe. Its presence in Iceland might suggestmigration from continental Europe after accumulationof the 10 Ma sediments (Grímsson and Denk, 2005),but it cannot be excluded that it is a new species thatevolved in Iceland parallel to Fagus gussonii in Eura-sia (Grímsson and Símonarson, 2006). Fossiliferousoutcrops from this time reect different vegetationunits of both zonal and azonal origin. Most fossils be-long to deciduous broadleaved taxa but some outcropsare richer in conifer remains. The fossil ora from thistime suggests mixed conifer and broadleaved decidu-ous forests of temperate afnity.

Icelandic oras from the Late Miocene (7–6 Ma)are quite different from the 15 and the 12 Ma oras.All the warm-temperate taxa are missing and morecold adapted taxa dominate (Heer, 1868; Akhmetievet al., 1978; Grímsson, 2002). Floras from thistime are quite numerous and no other time period inthe Miocene of Iceland is represented by so manyfossiliferous outcrops. In sedimentary rocks aroundLake Hreðavatn (Figures 2 and 4) Betula cristata(Lindquist, 1947) is by far the most common fos-sil found. Other prominent woody plants are Alnus,Salix, Acer (Símonarson and Friedrich, 1983), andAbies. The ora and sedimentary rocks from thistime suggest lacustrine vegetation, and Betula, Al-nus, Salix, and Populus growing close to the shore-line (Grímsson, 2002). The high amount of dispersedconiferous remains of Abies, Picea, Pinus, Pseu-dotsuga, and Larix suggests that conifer-dominatedwoodland forested the highlands surrounding thebasins. The vegetation at this time was a temperateto cool-temperate mixed boreal forest.

Fossiliferous localities from the latest Miocene arerather scarce and Selárgil in Fnjóskadalur, North Ice-land (Figures 1 and 4) is one of few. The Fnjóska-

dalur ora (5.5 Ma) is relatively poor in species (Sig-urðsson, 1975). The most common fossils are Salixleaves and for the rst time small-leaved Salix arerecorded. Other taxa rarely found are Alnus, Betulaand Abies, whereas Equisetum and Phragmites arecommon. This ora suggests a cool-temperate, mixedboreal forest.

The Hengifoss Formation in East Iceland (Fig-ures 1 and 4), which contains pollen, spores, and fewmacro remains, is of similar age or slightly older asit has been dated to 5.7 Ma (McDougall et al., 1976;Akhmetiev et al., 1978).

From 6–3 Ma Betula and Salix shrubs and grassesbecame more and more common whereas the forestdeclined, as indicated by the Sleggjulækur ora inWest Iceland (Figures 1, 2, and 4) and the PlioceneTjörnes ora in North Iceland (Akhmetiev et al.,1978).

CLIMATIC CHANGESFossil plants from the Miocene–Pliocene of Icelandindicate that a humid warm temperate climate withno dry season and warm summers (Cfa climate ofKöppen, 1936) prevailed in Iceland between 15 and10 Ma. The disappearance of important taxa between12 and 10 Ma, between 10 and 9–8 Ma, and againbetween 8 and 7–6 Ma, was most likely the resultof gradual cooling and indicates the change from awarmer to a cooler summer (change from Cfa to Cfbclimate of Köppen, 1936; Denk et al., 2005).

The 15 Ma oras with typical taxa like Sequoia,Fagus, Cercidiphyllum, and Tilia, grew under a mildand moist climate. The presence of warmth lovingtaxa such as Cryptomeria, Sassafras, Liriodendron,and Magnolia in the 12 Ma oras strongly indicatesan increase in mean annual temperature as comparedto the 15 Ma oras. The climate became consider-ably warmer at 12 Ma and the mean annual tempera-ture was 12–15◦C during this time. In the 10 Ma o-ras cooler types began to coexist with warm temper-ate taxa, signaling decreasing temperatures beween 12and 10 Ma (Denk et al., 2005). The younger, LateMiocene oras at 8–5 Ma that are increasingly domi-nated by Betulaceae, Salicaceae, and conifers suggestfurther climate cooling (change towards Cfb and Cfc

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lia, Rosaceae, Salix gruberi, Sassafras ferrettianum,Smilax, Ulmus cf. pyramidalis, Phragmites, Abiessteenstrupiana, Cathaya, Cryptomeria anglica, Piceasect. Picea, Equisetum, Dryopteris, and Osmundaparschlugiana (Heer, 1868; Áskelsson, 1946b, 1954,1956; Friedrich, 1966; Akhmetiev et al., 1978; Denket al., 2005; Grímsson, 2007b).

In the Seljá ora (Figure 2) most abundant fos-sil types are Salix gruberi, Alnus cecropiifolia, andPopulus. Over 90% of the broadleaved-type fossilscollected from Seljá belong to one of these three taxa(Grímsson, 2007b). Other fossils frequently found be-long to Phragmites and Equisetum. Additional fos-sils have been identied as Alnus cf. kefersteinii,Betula islandica, Carpinus, Pterocarya, Magnolia,Rosaceae, and Acer crenatifolium subsp. islandicum.

Sedimentary rocks at Seljá and Brjánslækur sug-gest that the surrounding region consisted of lowlandand highland environment with an extensive river sys-tem, oodplains, oxbow lakes, several small lakes andponds, as well as swamps. The lowlands were sur-rounded by highland hillsides with valleys and vol-canic mountains. At Seljá the macrofossils indicatean azonal riparian ora, with Alnus, Salix, and Popu-lus growing along rivers and streams (wetland veg-etation). In areas with stagnant water Phragmitesand Equisetum became more prominent. Close by onslightly more elevated areas the vegetation includedAcer, Betula, Carpinus, Corylus, Pterocarya, Mag-nolia, and Rosaceae (riverbank woodland) (Gríms-son, 2007b). At Brjánslækur the macrofossils in-dicate a shallow lake environment with azonal andzonal vegetation. The shores of the lakes wereoccupied by herbaceous aquatic and semi-aquaticplants: Equisetum, Phragmites, Osmunda, and Dry-opteris (wetland vegetation). Close to the shore-line, woody plants adapted to wet ground becameprominent: Salix, Alnus, Betula, and Acer (lakeshorewoodland). The vegetation cover became denserand additional broadleaved and conifer species be-came prominent. The zonal forest around the lakewas a mixed broadleaved coniferous forest with occa-sional evergreen trees (Grímsson, 2007b). Additionaltaxa included Magnolia, Sassafras, Comptonia, Smi-lax, Laurophyllum, Liriodendron, Rosaceae, Corylus,

Fraxinus, Juglans, Lonicera, Carpinus, Ulmus, Abies,Cathaya, Picea, and Tsuga (mixed forests).

The plant bearing formation in Gerpir, EastIceland (Figures 1 and 4), that contains pollen,spores, and rare macrofossils is of similar age as theBrjánslækur-Seljá Formation, which is dated to about12 Ma (McDougall et al., 1984; Akhmetiev et al.,1978).

The Icelandic vegetation at 10 Ma is representedin many fossil-rich outcrops. In spite of the numer-ous localities, these oras are much less diverse thanthe Brjánslækur and Seljá oras (12 Ma). At Trölla-tunga (Figures 2 and 4) some of the best-preservedplant fossils in Iceland have been found. The sedi-mentary rocks at Tröllatunga are rich in warm tem-perate to temperate taxa; the most common types be-long to Acer crenatifolium subsp. islandicum andRhododendron aff. ponticum. For the rst time, smallleaved Vaccinium and Arctostaphylos are present andquite common (Denk et al., 2005). Other woodytaxa belong to Juglandaceae (Símonarson, 1991), Be-tulaceae, and Rosaceae. Sedimentary rocks at thenearby Húsavíkurkleif locality (Figure 2), are mostlycomposed of fossils from ferns and fern allies and thefew woody taxa belong to Salix gruberi, Pterocaryaand Alnus cecropiifolia (Grímsson and Denk, 2007).The fossil oras from Tröllatunga and Húsavíkurkleifgive information on both zonal and azonal vegetation,indicating mixed coniferous and broadleaved warmtemperate to temperate forests. Fossil occurrence andsedimentary rocks suggest that Salix, Alnus, and Pte-rocarya grew on banks along rivers. Other hardwoodtaxa were dominant on drier ground, with other jug-landaceous types, Rhododendron, Acer, and conifer-ous taxa (Denk et al., 2005; Grímsson, 2007b; Gríms-son and Denk, 2007).

The Hólmatindur Formation in East Iceland (Fig-ures 1 and 4), which contains pollen, spores, and fewmacro remains, is of the same age, 10 Ma (Meyer andPirrit, 1957; Akhmetiev et al., 1978).

Hrútagil in Mókollsdalur (Figures 2 and 4) is thebest know macrofossil locality from the 9–8 Ma for-mation. The Hrútagil ora is composed of Acer cre-natifolium subsp. islandicum, Acer askelssonii, Alnuscecropiifolia, Alnus cf. kefersteinii, Betula cristata,

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Betula subnivalis, Carpinus, Corylus, Fagus gussonii,Juglandaceae, Lonicera, Populus, Pterocarya, Salixgruberi, Ulmus pyramidalis, Phragmites, Bryophyta,Picea sect. Picea, and Pseudotsuga (Friedrich et al.,1972; Akhmetiev et al., 1978; Denk et al., 2005;Grímsson and Denk, 2007). It is noteworthy that Fa-gus gussonii is recorded for the rst time in these 9–8 Ma sediments. This beech species was previouslyonly known from Late Miocene sediments in south-ern Europe. Its presence in Iceland might suggestmigration from continental Europe after accumulationof the 10 Ma sediments (Grímsson and Denk, 2005),but it cannot be excluded that it is a new species thatevolved in Iceland parallel to Fagus gussonii in Eura-sia (Grímsson and Símonarson, 2006). Fossiliferousoutcrops from this time reect different vegetationunits of both zonal and azonal origin. Most fossils be-long to deciduous broadleaved taxa but some outcropsare richer in conifer remains. The fossil ora from thistime suggests mixed conifer and broadleaved decidu-ous forests of temperate afnity.

Icelandic oras from the Late Miocene (7–6 Ma)are quite different from the 15 and the 12 Ma oras.All the warm-temperate taxa are missing and morecold adapted taxa dominate (Heer, 1868; Akhmetievet al., 1978; Grímsson, 2002). Floras from thistime are quite numerous and no other time period inthe Miocene of Iceland is represented by so manyfossiliferous outcrops. In sedimentary rocks aroundLake Hreðavatn (Figures 2 and 4) Betula cristata(Lindquist, 1947) is by far the most common fos-sil found. Other prominent woody plants are Alnus,Salix, Acer (Símonarson and Friedrich, 1983), andAbies. The ora and sedimentary rocks from thistime suggest lacustrine vegetation, and Betula, Al-nus, Salix, and Populus growing close to the shore-line (Grímsson, 2002). The high amount of dispersedconiferous remains of Abies, Picea, Pinus, Pseu-dotsuga, and Larix suggests that conifer-dominatedwoodland forested the highlands surrounding thebasins. The vegetation at this time was a temperateto cool-temperate mixed boreal forest.

Fossiliferous localities from the latest Miocene arerather scarce and Selárgil in Fnjóskadalur, North Ice-land (Figures 1 and 4) is one of few. The Fnjóska-

dalur ora (5.5 Ma) is relatively poor in species (Sig-urðsson, 1975). The most common fossils are Salixleaves and for the rst time small-leaved Salix arerecorded. Other taxa rarely found are Alnus, Betulaand Abies, whereas Equisetum and Phragmites arecommon. This ora suggests a cool-temperate, mixedboreal forest.

The Hengifoss Formation in East Iceland (Fig-ures 1 and 4), which contains pollen, spores, and fewmacro remains, is of similar age or slightly older asit has been dated to 5.7 Ma (McDougall et al., 1976;Akhmetiev et al., 1978).

From 6–3 Ma Betula and Salix shrubs and grassesbecame more and more common whereas the forestdeclined, as indicated by the Sleggjulækur ora inWest Iceland (Figures 1, 2, and 4) and the PlioceneTjörnes ora in North Iceland (Akhmetiev et al.,1978).

CLIMATIC CHANGESFossil plants from the Miocene–Pliocene of Icelandindicate that a humid warm temperate climate withno dry season and warm summers (Cfa climate ofKöppen, 1936) prevailed in Iceland between 15 and10 Ma. The disappearance of important taxa between12 and 10 Ma, between 10 and 9–8 Ma, and againbetween 8 and 7–6 Ma, was most likely the resultof gradual cooling and indicates the change from awarmer to a cooler summer (change from Cfa to Cfbclimate of Köppen, 1936; Denk et al., 2005).

The 15 Ma oras with typical taxa like Sequoia,Fagus, Cercidiphyllum, and Tilia, grew under a mildand moist climate. The presence of warmth lovingtaxa such as Cryptomeria, Sassafras, Liriodendron,and Magnolia in the 12 Ma oras strongly indicatesan increase in mean annual temperature as comparedto the 15 Ma oras. The climate became consider-ably warmer at 12 Ma and the mean annual tempera-ture was 12–15◦C during this time. In the 10 Ma o-ras cooler types began to coexist with warm temper-ate taxa, signaling decreasing temperatures beween 12and 10 Ma (Denk et al., 2005). The younger, LateMiocene oras at 8–5 Ma that are increasingly domi-nated by Betulaceae, Salicaceae, and conifers suggestfurther climate cooling (change towards Cfb and Cfc

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climates of Köppen, 1936).Still younger 6–3 Ma oras indicate further cool-

ing that nally resulted in an arctic climate with notrue summer (ET climate of Köppen, 1936) and thebeginning of perennial ice formation, marking the on-set of the last ice age.

SUMMARYIcelandic non-marine sediments contain both fos-silized plants, and remains of invertebrates and ver-tebrates. The oldest fossils are from the MiddleMiocene, approximately 15 million years old, and canbe found at outermost parts of the Northwest Penin-sula. Younger fossils are known from sedimentaryformations between lava ows on either side of theactive volcanic zone and decrease in age towards themiddle of the island.

The Tertiary sediments are rather rich in plant fos-sils and a considerable number of oras and vegeta-tion types are known from the Miocene and Plioceneof Iceland. Animal fossil are not as common. Somefreshwater animals like sponges, crustaceans, gas-tropods, and bivalves as well as insects have been col-lected, but only a few fragmentary bones of terrestrialvertebrates.

Plant fossils reect part of the vegetation that grewin Iceland millions of years ago, and based on themit was possible to conclude about the palaeo-climate.Furthermore, the composition of woody taxa showsthat island was covered with various broadleaved andconiferous forests. Modern living analogous of thefossil taxa presently thrive at southern latitudes in awarm-temperate climate. It has been assumed thatwhen the Iceland climate was at its maximum themean annual temperature was approximately 10◦Chigher than it is now. Apparently the precipitationwasmore or less constant throughout the year.

It is not known exactly when plants colonized Ice-land, as the oldest sedimentary rocks are only about15 million years old, but it is likely that plants livedon proto-Iceland from the beginning, shortly after theopening of the northern North Atlantic. It is assumedthat older fossiliferous sediments and fossils can befound below sea level on the Icelandic shelf and fur-

ther in the west (towards Greenland) and the east (to-wards the Faeroe Island).

The oldest Icelandic oras are distinguishablefrom other coeval oras of nearby continents. Herea number of endemic species occur and the compo-sition of the oras changes considerably as they getyounger. The change in species composition seemsin direct correlation with gradual cooling of climatein the late Cainozoic. The number of thermophilousspecies decreased when the Miocene came to an end.The cooling climate as well as continuous isolation ofIceland in the North Atlantic is believed to have hadstrong affects on the evolution of the islands palaeo-biota.

AcknowledgementsWe would like to thank Dr. Margrét Hallsdóttir, Ice-landic Institute of Natural History, Dr. Ole Bennike,GEUS, and Dr. Leó Kristjánsson, Institute of EarthSciences, University of Iceland, for valuable com-ments on the manuscript. The University of IcelandResearch Fund and Rannís are thanked for nancialsupport.

ÁGRIPÍ íslenskum setlögum hafa fundist plöntuleifar ásamtleifum hryggleysingja og hryggdýra. Elstu steingerv-ingar landsins eru um 15 milljón ára (frá því um mið-bik míósentíma) og hafa fundist á ystu nesjum Vest-fjarða. Yngri lífveruleifar hafa síðan fundist í set-lagasyrpum milli hraunlaga sitt hvoru megin gosbelt-isins og yngjast er nær dregur miðju landsins.

Íslensk tertíerlög eru frekar auðug af plöntustein-gervingum og töluverðum fjölda gróðurfélaga hefurnú þegar verið lýst úr íslenskum setlögum. Töluvertminna hefur fundist af dýraleifum. Einkum hafa fund-ist leifar ferskvatnsdýra eins og svampa, krabbadýra,snigla og samlokna svo og skordýra, en einungis örfábrot úr beinum landhryggdýra.

Plöntuleifarnar endurspegla hluta af þeim gróðrisem óx hér fyrir milljónum ára og af þeim má sjáhvers konar loftslag ríkti hér á landi á míósen- ogplíósentíma. Tegundafjöldi viðarplantna, sem fundisthafa, sýna að hér uxu bæði laufskógar og barrskóg-ar. Núlifandi tegundir, sem eru skyldastar íslensku

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tertíerplöntunum, þrífast nú mun sunnar og vaxa þarog dafna í heittempruðu loftslagi. Gera má ráð fyrirað ársmeðalhiti ha verið um 10◦C hærri en nú þegarloftslag var hlýjast á míósentíma fyrir um 12 milljón-um ára og úrkoma verið jafndreifð á árið.

Ekki er nákvæmlega ljóst hvenær plöntur námuland á Íslandi þar sem elstu setlög landsins eru varteldri en 15 milljóna ára. Hins vegar verður að telja lík-legt að plöntur ha þrist á frum-Íslandi alveg frá upp-ha, stuttu eftir að norðurhluti Norður-Atlantshafs tókað myndast. Ætla má að eldri setlög með steingerv-ingum nnist neðansjávar í setlögum á landgrunni Ís-lands og áfram til vesturs (til Grænlands) og austurs(til Færeyja).

Elstu gróðurfélög landsins sýna ákveðin sérkennief þau eru borin saman við gróðurfélög úr jafngöml-um setlögum á meginlöndunum. Hér hafa myndastnokkrar einlendar (séríslenskar) tegundir og töluverð-ur munur er á misgömlum félögum plantna. Breyting-ar á þeim virðast vera í nánu sambandi við hægfarakólnun loftslags á síðari hluta nýlífsaldar. Kulvísumtegundum fór fækkandi þegar líða tók á jarðsögunaog breytingar á loftslagi og síaukin einangrun Íslandsí Norður-Atlantshaf setja sterkan svip á þróun gróðursog dýralífs.

REFERENCESAkhmetiev, M. A., G. M. Bratseva, R. E. Giterman, L.

V. Golubeva and A. I. Moiseyeva 1978. Late Ceno-zoic Stratigraphy and Flora of Iceland. Trudy Geol-ogischeskogo Instituta Academia Nauk SSSR 316, 1–188 (in Russian).

Áskelsson, J. 1946a. Um gróðurmenjar í Þórishlíðarfjallivið Selárdal. Andvari 71, 80–86 (in Icelandic).

Áskelsson, J. 1946b. Er hin smásæja óra surtarbrandslag-anna vænleg til könnunar? Skýrsla Menntaskólans íReykjavík 1945–1946, 45–57 (in Icelandic).

Áskelsson, J. 1954. Myndir úr jarðfræði Íslands II. Fáeinarplöntur úr surtarbrandslögunum hjá Brjánslæk. Nátt-úrufræðingurinn 24, 92–96 (in Icelandic).

Áskelsson, J. 1956. Myndir úr jarðfræði Íslands IV.Fáeinar plöntur úr surtarbrandslögunum. Náttúrufræð-ingurinn 26, 42–48 (in Icelandic).

Áskelsson, J. 1957. Myndir úr jarðfræði Íslands VI. Þrjárnýjar plöntur úr surtarbrandslögunum í Þórishlíðar-fjalli. Náttúrufræðingurinn 27, 22–29 (in Icelandic).

Bárðarson, G. G. 1918. Um surtarbrand. Andvari 43, 1–71(in Icelandic).

Denk, T., F. Grímsson, and Z. Kvacek 2005. The Mioceneoras of Iceland and their signicance for Late Cain-ozoic North Atlantic biogeography. Botanical Journalof the Linnean Society 149, 369–417.

Friedrich, W. L. 1966. Zur Geologie von Brjánslækur(Nordwest-Island) unter besonderer Berücksichtigungder fossilen Flora. Sonderveröffentlichungen des Ge-ologischen Institute der Universität Köln 10, 108 pp.

Friedrich, W. L. 1968. Tertiäre Panzen im Basalt von Is-land. Meddelelser fra Dansk Geologisk Forening 18,265–276.

Friedrich, W. L., L. A. Símonarson and O. E. Heie 1972.Steingervingar í millilögum í Mókollsdal. Náttúru-fræðingurinn 42, 4–17 (in Icelandic).

Geirsdóttir, Á. and J. Eiríksson 1994. Growth of an inter-mittent ice sheet in Iceland during the Late Plioceneand Early Pleistocene. Quaternary Research 42, 115–130.

Grímsson, F. 2002. The Hreðavatn Member of theHreðavatn-Stafholt Formation and its fossil ora.Cand. scient. thesis, University of Copenhagen, 229pp.

Grímsson, F. 2007a. Síðmíósen setlög við Hreðavatn. Nátt-úrufræðingurinn 75, 21–33 (in Icelandic).

Grímsson, F. 2007b. The Miocene oras of Iceland. Ori-gin and evolution of fossil oras from north-west andwestern Iceland, 15 to 6 Ma. Ph. D. thesis, Universityof Iceland, 1–33.

Grímsson, F. and T. Denk 2005. Fagus from the Mioceneof Iceland: systematics and biogeographical consider-ations. Review of Palaeobotany and Palynology 134,27–54.

Grímsson, F. and T. Denk 2007. Floristic turnover in Ice-land from 15 to 6 Ma – extracting biogeographicalsignals from fossil oral assemblages. Journal of Bio-geography 34, 1490–1504.

Grímsson, F. and L. A. Símonarson 2006. Beyki úr íslensk-um setlögum. Náttúrufræðingurinn 74, 81–102 (inIcelandic).

Grímsson, F. , T. Denk and L. A. Símonarson 2007. Mid-dle Miocene oras of Iceland – the early colonizationof an island? Review of Palaeobotany and Palynology144, 181–219.

Hald, N. , A. Noe-Nygaard and A. K. Pedersen 1971. TheKróksfjördur central volcano in North-West Iceland.Acta Naturalia Islandica 2 (10), 29 pp.

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climates of Köppen, 1936).Still younger 6–3 Ma oras indicate further cool-

ing that nally resulted in an arctic climate with notrue summer (ET climate of Köppen, 1936) and thebeginning of perennial ice formation, marking the on-set of the last ice age.

SUMMARYIcelandic non-marine sediments contain both fos-silized plants, and remains of invertebrates and ver-tebrates. The oldest fossils are from the MiddleMiocene, approximately 15 million years old, and canbe found at outermost parts of the Northwest Penin-sula. Younger fossils are known from sedimentaryformations between lava ows on either side of theactive volcanic zone and decrease in age towards themiddle of the island.

The Tertiary sediments are rather rich in plant fos-sils and a considerable number of oras and vegeta-tion types are known from the Miocene and Plioceneof Iceland. Animal fossil are not as common. Somefreshwater animals like sponges, crustaceans, gas-tropods, and bivalves as well as insects have been col-lected, but only a few fragmentary bones of terrestrialvertebrates.

Plant fossils reect part of the vegetation that grewin Iceland millions of years ago, and based on themit was possible to conclude about the palaeo-climate.Furthermore, the composition of woody taxa showsthat island was covered with various broadleaved andconiferous forests. Modern living analogous of thefossil taxa presently thrive at southern latitudes in awarm-temperate climate. It has been assumed thatwhen the Iceland climate was at its maximum themean annual temperature was approximately 10◦Chigher than it is now. Apparently the precipitationwasmore or less constant throughout the year.

It is not known exactly when plants colonized Ice-land, as the oldest sedimentary rocks are only about15 million years old, but it is likely that plants livedon proto-Iceland from the beginning, shortly after theopening of the northern North Atlantic. It is assumedthat older fossiliferous sediments and fossils can befound below sea level on the Icelandic shelf and fur-

ther in the west (towards Greenland) and the east (to-wards the Faeroe Island).

The oldest Icelandic oras are distinguishablefrom other coeval oras of nearby continents. Herea number of endemic species occur and the compo-sition of the oras changes considerably as they getyounger. The change in species composition seemsin direct correlation with gradual cooling of climatein the late Cainozoic. The number of thermophilousspecies decreased when the Miocene came to an end.The cooling climate as well as continuous isolation ofIceland in the North Atlantic is believed to have hadstrong affects on the evolution of the islands palaeo-biota.

AcknowledgementsWe would like to thank Dr. Margrét Hallsdóttir, Ice-landic Institute of Natural History, Dr. Ole Bennike,GEUS, and Dr. Leó Kristjánsson, Institute of EarthSciences, University of Iceland, for valuable com-ments on the manuscript. The University of IcelandResearch Fund and Rannís are thanked for nancialsupport.

ÁGRIPÍ íslenskum setlögum hafa fundist plöntuleifar ásamtleifum hryggleysingja og hryggdýra. Elstu steingerv-ingar landsins eru um 15 milljón ára (frá því um mið-bik míósentíma) og hafa fundist á ystu nesjum Vest-fjarða. Yngri lífveruleifar hafa síðan fundist í set-lagasyrpum milli hraunlaga sitt hvoru megin gosbelt-isins og yngjast er nær dregur miðju landsins.

Íslensk tertíerlög eru frekar auðug af plöntustein-gervingum og töluverðum fjölda gróðurfélaga hefurnú þegar verið lýst úr íslenskum setlögum. Töluvertminna hefur fundist af dýraleifum. Einkum hafa fund-ist leifar ferskvatnsdýra eins og svampa, krabbadýra,snigla og samlokna svo og skordýra, en einungis örfábrot úr beinum landhryggdýra.

Plöntuleifarnar endurspegla hluta af þeim gróðrisem óx hér fyrir milljónum ára og af þeim má sjáhvers konar loftslag ríkti hér á landi á míósen- ogplíósentíma. Tegundafjöldi viðarplantna, sem fundisthafa, sýna að hér uxu bæði laufskógar og barrskóg-ar. Núlifandi tegundir, sem eru skyldastar íslensku

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tertíerplöntunum, þrífast nú mun sunnar og vaxa þarog dafna í heittempruðu loftslagi. Gera má ráð fyrirað ársmeðalhiti ha verið um 10◦C hærri en nú þegarloftslag var hlýjast á míósentíma fyrir um 12 milljón-um ára og úrkoma verið jafndreifð á árið.

Ekki er nákvæmlega ljóst hvenær plöntur námuland á Íslandi þar sem elstu setlög landsins eru varteldri en 15 milljóna ára. Hins vegar verður að telja lík-legt að plöntur ha þrist á frum-Íslandi alveg frá upp-ha, stuttu eftir að norðurhluti Norður-Atlantshafs tókað myndast. Ætla má að eldri setlög með steingerv-ingum nnist neðansjávar í setlögum á landgrunni Ís-lands og áfram til vesturs (til Grænlands) og austurs(til Færeyja).

Elstu gróðurfélög landsins sýna ákveðin sérkennief þau eru borin saman við gróðurfélög úr jafngöml-um setlögum á meginlöndunum. Hér hafa myndastnokkrar einlendar (séríslenskar) tegundir og töluverð-ur munur er á misgömlum félögum plantna. Breyting-ar á þeim virðast vera í nánu sambandi við hægfarakólnun loftslags á síðari hluta nýlífsaldar. Kulvísumtegundum fór fækkandi þegar líða tók á jarðsögunaog breytingar á loftslagi og síaukin einangrun Íslandsí Norður-Atlantshaf setja sterkan svip á þróun gróðursog dýralífs.

REFERENCESAkhmetiev, M. A., G. M. Bratseva, R. E. Giterman, L.

V. Golubeva and A. I. Moiseyeva 1978. Late Ceno-zoic Stratigraphy and Flora of Iceland. Trudy Geol-ogischeskogo Instituta Academia Nauk SSSR 316, 1–188 (in Russian).

Áskelsson, J. 1946a. Um gróðurmenjar í Þórishlíðarfjallivið Selárdal. Andvari 71, 80–86 (in Icelandic).

Áskelsson, J. 1946b. Er hin smásæja óra surtarbrandslag-anna vænleg til könnunar? Skýrsla Menntaskólans íReykjavík 1945–1946, 45–57 (in Icelandic).

Áskelsson, J. 1954. Myndir úr jarðfræði Íslands II. Fáeinarplöntur úr surtarbrandslögunum hjá Brjánslæk. Nátt-úrufræðingurinn 24, 92–96 (in Icelandic).

Áskelsson, J. 1956. Myndir úr jarðfræði Íslands IV.Fáeinar plöntur úr surtarbrandslögunum. Náttúrufræð-ingurinn 26, 42–48 (in Icelandic).

Áskelsson, J. 1957. Myndir úr jarðfræði Íslands VI. Þrjárnýjar plöntur úr surtarbrandslögunum í Þórishlíðar-fjalli. Náttúrufræðingurinn 27, 22–29 (in Icelandic).

Bárðarson, G. G. 1918. Um surtarbrand. Andvari 43, 1–71(in Icelandic).

Denk, T., F. Grímsson, and Z. Kvacek 2005. The Mioceneoras of Iceland and their signicance for Late Cain-ozoic North Atlantic biogeography. Botanical Journalof the Linnean Society 149, 369–417.

Friedrich, W. L. 1966. Zur Geologie von Brjánslækur(Nordwest-Island) unter besonderer Berücksichtigungder fossilen Flora. Sonderveröffentlichungen des Ge-ologischen Institute der Universität Köln 10, 108 pp.

Friedrich, W. L. 1968. Tertiäre Panzen im Basalt von Is-land. Meddelelser fra Dansk Geologisk Forening 18,265–276.

Friedrich, W. L., L. A. Símonarson and O. E. Heie 1972.Steingervingar í millilögum í Mókollsdal. Náttúru-fræðingurinn 42, 4–17 (in Icelandic).

Geirsdóttir, Á. and J. Eiríksson 1994. Growth of an inter-mittent ice sheet in Iceland during the Late Plioceneand Early Pleistocene. Quaternary Research 42, 115–130.

Grímsson, F. 2002. The Hreðavatn Member of theHreðavatn-Stafholt Formation and its fossil ora.Cand. scient. thesis, University of Copenhagen, 229pp.

Grímsson, F. 2007a. Síðmíósen setlög við Hreðavatn. Nátt-úrufræðingurinn 75, 21–33 (in Icelandic).

Grímsson, F. 2007b. The Miocene oras of Iceland. Ori-gin and evolution of fossil oras from north-west andwestern Iceland, 15 to 6 Ma. Ph. D. thesis, Universityof Iceland, 1–33.

Grímsson, F. and T. Denk 2005. Fagus from the Mioceneof Iceland: systematics and biogeographical consider-ations. Review of Palaeobotany and Palynology 134,27–54.

Grímsson, F. and T. Denk 2007. Floristic turnover in Ice-land from 15 to 6 Ma – extracting biogeographicalsignals from fossil oral assemblages. Journal of Bio-geography 34, 1490–1504.

Grímsson, F. and L. A. Símonarson 2006. Beyki úr íslensk-um setlögum. Náttúrufræðingurinn 74, 81–102 (inIcelandic).

Grímsson, F. , T. Denk and L. A. Símonarson 2007. Mid-dle Miocene oras of Iceland – the early colonizationof an island? Review of Palaeobotany and Palynology144, 181–219.

Hald, N. , A. Noe-Nygaard and A. K. Pedersen 1971. TheKróksfjördur central volcano in North-West Iceland.Acta Naturalia Islandica 2 (10), 29 pp.

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Hardarson, B. S., J. G. Fitton, R. M. Ellam and M.S. Pringle 1997. Rift relocation - a geochemicaland geochronological investigation of a palaeo-rift innorthwest Iceland. Earth and Planetary Science Let-ters 153, 181–196.

Heer, O. 1868. Flora Fossilis Arctica 1. Die fossile Florader Polarländer enthaltend die in Nordgrönland, aufder Melville-Insel, im Banksland, am Mackenzie, inIsland und in Spitzbergen endeckten fossilen Panzen.Friedrich Schulthess, Zürich, 192 pp.

Heie, O. E. and W. L. Friedrich 1971. A fossil specimenof the North American Hickory Aphid (Longistigmacaryae Harris) found in Tertiary deposits in Iceland.Entomologica Scandinavica 2, 74–80.

Jóhannesson, H. and K. Sæmundsson 1989. Geologicalmap of Iceland. 1:500 000. Bedrock geology. IcelandicMuseum of Natural History and Iceland Geodetic Sur-vey, Reykjavík.

Jóhannesson, H. and K. Sæmundsson 1998. Geologicalmap of Iceland. 1:500 000. Tectonics. Icelandic Insti-tute of Natural History, Reykjavík.

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Kristjánsson, L. 1993. Saga hugmynda um aldur Íslands.Jökull 42, 45–64 (in Icelandic).

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Lindquist, B. 1947. Two species of Betula from the IcelandMiocene. Svensk Botanisk Tidskrift 41, 339–353.

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Reviewed research article

Glaciation events in the Pliocene – Pleistocene volcanicsuccession of Iceland

Jón EiríkssonInstitute of Earth Sciences, University of Iceland, Sturlugata 7, 101 Reykjavik

jeir@hi.is

Abstract — The primarily volcanic succession of rocks in Iceland was accumulated during the Miocene toHolocene Epochs at the divergent plate boundary between North America and Eurasia. The present paper re-views the evidence for distinct changes in sedimentary and volcanic facies during the Middle and Late Plioceneand the Pleistocene related to recurrent expansions of glaciers. The preservation of an exceptionally long andwell preserved record of Northern Hemisphere terrestrial glaciations in Iceland is related to the climaticallysensitive geographical location and to frequently extruded lava ows which hamper the erosion of underlyingsediments. Explosive volcanism contributes to high sedimentation rates and produces extensive time markers.Recent advances in the interpretation of diamictites and volcaniclastic deposits intercalated between primaryvolcanic products and between a variety of sediments have contributed to the establishment of a coherent re-gional overview of the glaciation history of Iceland. Palaeomagnetic studies of the volcanic sequence enablecorrelation between sections at reversal levels, and absolute radiometric dating efforts during the last fewdecades have added to the reliability of the chronology. The oldest regional glaciation of Iceland occurredat close to 2.5 Ma, but the glaciers began to expand periodically from local mountainous massifs at 3.8 Ma.Miocene glaciation as early as 7 Ma was apparently conned to high mountains in the southeastern part ofIceland. Instances of early Pleistocene and Pliocene interglacial sediments on Tjörnes and Snaefellsnes, bothmarine and terrestrial, give insight into the climatic signicance of the glaciation events in Iceland.

INTRODUCTION

The present paper focuses on geological evidenceabout glaciation events in Iceland during the past 4Ma. There are several sequences in Iceland contain-ing Pliocene and Pleistocene interglacial deposits withfossil evidence about climate and ecology, but theseare beyond the scope of this overview study.

The recognition of glacial ice as a process capa-ble of forming widespread surface deposits discor-dantly covering older bedrock in Europe and NorthAmerica led to the Ice Age concept amongst geolo-gists by the mid-nineteenth century. The chronostrati-graphic term Quaternary (as well as the term Pleis-

tocene) has been used widely as a synonym for theIce Age (Gibbard and Kolfschoten, 2004). Tradition-ally, the Quaternary is considered to encompass theinterval of glacial-interglacial cycles which was ini-tiated at about 2.6 Ma in the Northern hemisphere,including the Pleistocene and the current interglacial,the Holocene. This usage is preferred in the presentpaper. However, the formal chronostratigraphic rankof the Quaternary remains unresolved (Gibbard et al.2005), and the formally accepted boundary betweenthe Pliocene and the Pleistocene is currently placed atabout 1.8 Ma, within but near the top of the Olduvaimagnetic subchron (Gradstein et al., 2004).

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