Iceland is geologically quite young, and mostly formed from volcanic processes, so fossils there are rare. The oldest fossils found in Iceland are from the Miocene, about 15 mya, and are plant remains. In addition to plant remains, fossilized remains of insects from the Miocene and Pliocene have been found. Miocene and Pliocene fossil sites are found mainly in the West of Iceland and the Westfjords. Remains of invertebrates have been found In Ice age strata, especially in fresh water and marine sediments. It is rare to find fossil remains of land animals in Iceland, although remains of deer bones have been found.
Fossiliferous strata Between the layers of the basaltic plateau lavas in Iceland, there is an abundance of clay rich reddish silt- and sandstone layers. These layers are formed from ancient soil wherein are preserved the fossilized remains of plants. It is estimated that about five to ten thousand years passed on average between the formation of two adjacent layers that make up the basaltic plateau. Volcanic eruptions with frequency of one in every few years facilitated soil formation and thus enabled plants to gain a foothold. In the sediments between the basalt layers there are in places marks left by stems and leaves along with carbonated plant material. These sediments, however, are not the only ones that carry plant remains, among the thickest sediments among the basaltic formations there are finely grained silt and clay sediments formed in basins that once were filled by ancient lakes (lacustrine deposits). These sediments also include plant fossils. Some invertebrate remnants have been found in Ice age sediments, especially in fresh water and marine sediments. Remains of marine invertebrates can abundantly be found in the sediments at Tjörnes peninsula.
Plant fossils Remains of plants from the Cenozoic have been found in sediments, giving information on climate, vegetation and wildlife at that time. Plant fossils are most commonly found in sedimentary rocks of the West of Iceland and the Westfjords.
Plant fossils found in basalt layers Fossilized plant material from the late Cenozoic have been found in basalt layers. These are most commonly holes and traces from branches and tree trunks while Pseudomorphs (in this case basaltic casts of tree trunks) have also been found.
Lignite Lignite is abundant in sediments between the basalt layers. Lignite from the Westfjords and Tjörnes contains mainly the remnants of conifers such as pine, giant sequoia, Glyptostrobus and larch but also deciduous trees. A variety of plant remnants have been found in adjacent sediments. These remnants are mainly preserved in silty or sandy fresh water sediments, e.g. in Surtarbrandsgil in Brjánslækur.
Cenozoic flora Fossilized Icelandic vegetation older than 10 million years old shows similarities to vegetation that grew in the deciduous forests of North America and bears witness to a milder climate than is currently prevalent on the island. It is therefore likely that, at this time or earlier, there was a land bridge between proto-Iceland and North America. The average temperature must have been around 8-12 °C in this period.
Warm temperate climate The vegetation remains in the Þórishlíðarfjall mountain in Selárdalur are around 15 million years old and contain the remnants of warm temperate forest of deciduous and coniferous trees. The most abundant are beech, chestnut, elm, linden, magnolia, Cercidiphyllum, Glyptostrobus, giant sequoia and Sequoia abietina.
Temperate climate Vegetation remains in Dufansdalur in Fossafjörður (in Arnarfjörður) contain 13.5 million years old remains of a forest, which grew in temperate climates. Most abundant are beech, birch, hornbeam and elm are most common, but angiosperms are more pronounced than gymnosperms. The remains in Surtarbrandsgili at Brjánslækur and at Seljá in Vaðalsdalur are estimated to be about 12 million years old. Most notable are fir, spruce, giant sequoia, bay laurel, magnolia, maple, alder, birch, willow, tulip trees, elm and hazel. At this time, deciduous trees were beginning to give way to conifers and beech was no longer the main tree. Plant remains from sediments at Tröllatunga and at Húsavíkurkleif in Steingrímsfjörður and in Hólmatindur at Reyðarfjörður are 10-9 million years old. Ferns, willow, maple, magnolia, birch, walnut and hickory appear to have been dominant in lowland vegetation at this time. In Hrútagil in Mókollsdalur in Strandasýsla there are 9-8 million years old vegetation remnants, where beech seems to have been common again, but also found is maple, birch, alder, elm, Pterocarya (wingnuts) and hazel.
Cold temperate climate Fossilized plant remains in the vicinity of lake Hreðavatn are estimated to be 7-6 million years old, where birch, willow and conifers have prevailed rather than warmer climate species. The climate was cooling on the upper part of the Miocene, as the remains of Hreðavatn show. Remains in Sleggjulækur in Borgarfjörður, which indicate further cooling, are probably about 3.5 million years old. Birch, willow and grass became more and more prominent at the same time as the forest cover was diminishing.
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