Middle Miocene floras of Iceland — the early colonization of an island? Friðgeir Grímsson a, ⁎ , Thomas Denk b , Leifur A. Símonarson a a University of Iceland, Earth Science Institute, Askja, Sturlugata 7, IS-101 Reykjavík, Iceland b Swedish Museum of Natural History, Department of Palaeobotany, 104 05 Stockholm, Sweden Received 23 February 2006; received in revised form 1 July 2006; accepted 4 July 2006 Available online 1 September 2006 Abstract Two macrofloras, 15 and 13.5 Ma old, are described from the oldest exposed plant bearing sediments on Iceland. Many of the taxa are mentioned for the first time and a lime tree, Tilia selardalense, is described as a new species. In case of the older flora, differences in the environment are reflected in plants derived from volcanic sediments from high elevations (Selárdalur, 15 Ma) and from lowland alluvial plains (Botn, 15 Ma). The former are characterized by zonal elements and dominated by Fagus. The latter is dominated by conifers inhabiting swamps and hummocks. The younger Ketilseyri flora (13.5 Ma) is poorer and more similar to the Selárdalur flora. Both floras suggest a humid warm temperate climate (mostly Cfa climate sensu Köppen) with a number of exotic elements (Glyptostrobus, Sequoia, Magnolia, Cercidiphyllum). Evaluating the dispersal mechanisms of all the taxa shows that at least some (Aesculus, Fagus) could not have possibly colonized Iceland crossing large ocean barriers. Furthermore, most anemochorous taxa recorded have a very limited dispersal radius. This suggests that when “proto-Iceland” was colonized, it was connected to the mainland or accessible via a chain of islands. This land could have been part of the Greenland–Scotland Transverse Ridge that is believed to have persisted from the early Cenozoic to Late Oligocene and partly into the Middle Miocene. © 2006 Elsevier B.V. All rights reserved. Keywords: Iceland; Middle Miocene; volcanic floras; biogeography; colonization 1. Introduction Iceland is mostly built up of basaltic plateau lavas ranging in age from 16 Ma to the present. Due to high volcanic activity, frequent lava flows have sealed off and preserved several sedimentary formations between them. At present, six distinct sedimentary formations are known from the Northwest peninsula and western part of Iceland (Fig. 1); the Selárdalur–Botn Formation 15 Ma, the Dufansdalur–Ketilseyri Formaton 13.5 Ma, the Brjánslækur–Seljá Formation 12 Ma, the Trölla- tunga–Gautshamar Formation 10 Ma, the Skarðsströnd– Mókollsdalur Formation 9–8 Ma, and the Hreðavatn– Stafholt Formation 7–6 Ma. Sediments composing these formations are mostly reddish aeolian palaeosoils, darkly coloured lignites, and different types of alluvial and lacustrine deposits. These sediments contain pollen, and some of them reveal quite nicely preserved plant macro- fossils. Fossils from the younger Miocene formations (12 to 6 Ma) have been studied to some extent by Heer (1868), Friedrich (1966), Akhmetiev et al. (1978), Grímsson (2002), and Denk et al. (2005). Review of Palaeobotany and Palynology 144 (2007) 181 – 219 www.elsevier.com/locate/revpalbo ⁎ Corresponding author. E-mail address: fossil@hi.is (F. Grímsson). 0034-6667/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.revpalbo.2006.07.003