Biogeography in the Sub-Arctic. Группа авторов

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Figure 7 Eocene fossil leaves from Hareø, West Greenland. (A) Fagus sp., S110238. (B) Aponogeton sp., S110339. (C) Aponogeton sp., S110337.

      Plant macrofossils have been known from the Faroe Islands since 1901 (see Hartz 1903). Until now the only detailed description is of Metasequoia vegetative long and short shoots (Rasmussen and Koch 1963; Figure 3E). Remains of other Cupressaceae have also been recorded and believed to represent Sequoia, Taxodium and Juniperus. The few fragmentary angiosperm leaf fossils recovered have been considered unidentifiable (Hartz 1903; Rasmussen 1925; Rasmussen and Koch 1963). Despite the current lack of macrofossils from the Faroe Island, two previous light microscopic palynological studies by Laufeld (1965) and Lund (1989) suggest that a rather diverse palaeovegetation existed during the accumulation of the early Eocene coal‐bearing Prestfjall Formation.

      The early Eocene palynological assemblage was characterized by swamp forests and riparian elements comprising several ferns, taxodiaceous Cupressaceae (intermittently amounting to over 30% of the palynological assemblage), Juglandaceae and Betulaceae. On more mesic sites Fagaceae, Juglandaceae and other eudicots may have thrived along with Pinus, Sciadopitys and possibly Sequoia.

      Island of Mull

      The Palaeocene flora of Mull, Scotland, originally described by Gardner (1887) is the only Paleogene BIP flora that has been revised in more recent years (Boulter and Manum 1989; Figures 1 and 2). The age of the intrabasaltic plant‐bearing sediments of Mull has been radiometrically dated at 60–58 Ma (Chambers and Pringle 2001).

      Among riparian and wetland elements, the ferns Dennstaedtia, Onoclea and Osmunda were widespread in Paleogene Arctic plant assemblages, commonly co‐occurring with Metasequoia. Among the diverse gymnosperms, Ginkgo gardneri Florin represents a lineage more closely related to Mesozoic ginkgoes than to the Cenozoic Ginkgo adiantoides (Ung.) Heer from Europe and Svalbard (Denk and Velitzelos 2002). Further, Amentotaxus, cf. Cephalotaxus, Glyptostrobus, Elatocladus (with affinities to modern Taxodium and Sequoia), Metasequoia and Pinus and cf. Tsuga are recorded (Boulter and Kvaček 1989; Kvaček 2010). Platanites hebridicus Forbes is an extinct Platanaceae distinct from the coeval Platanus schimperi (Heer) Saporta and Marion of Gelinden (Belgium; Mai 1995) and Platanus aff. leucophylla (Unger) Knobloch from western Greenland. The genus Platanites has also been recorded from the Paleogene of Saskatchewan (Canada; McIver and Basinger 1993) and possibly from the Eocene of north‐western Wyoming (Crane et al. 1988). In addition, few pentafoliate leaves and leaflets belong to the extinct Platanus subgenus Glandulosa Kvaček, Manchester and Guo. These were assigned to Platanus fraxinifolia (Johnson and Gilmore) Walther by Boulter and Kvaček (1989) in contrast to the trifoliate leaves of P. bella from Greenland.

Common elements of Mull, mostly shared with the floras of Greenland, are Trochodendroides (and rare Ziziphoides), betulaceous leaves of Corylites [shared with Svalbard], Fagopsiphyllum groenlandicum (Heer) Manchester [as Fagopsis groenlandica (Heer) Wolfe; shared with the floras of Greenland and Svalbard], Ushia olafsenii (Heer) Boulter and Kvaček, Juglandiphyllites spp., foliage with affinity to Fagaceae (Castanopsis, Lithocarpus, Quercus sect. Cyclobalanopsis [as Camptodromites spp.] and Macclintockia. A number of taxa not found in other BIP floras are the distinct foliage of Davidoidea (similar to Platanaceae, Hamamelidaceae and Euptelea) and of Vitiphyllum with affinities to Vitis along with a flower of unclear taxonomic relationships (Calycites).

      Similar floras are known from Isle of Skye, Scotland (Poulter et al. 2008, 2010) and Ballypalady (County Antrim, Ireland; Mai 1995). In the latter flora, cones of Pinus plutonis Baily are abundant and biogeographically interesting. According to Mai (1995), P. plutonis belongs to section Sylvestres subsection Resinosae and provides another potential link between Europe and North America.

Neogene Floras and Vegetation

      Iceland

      Iceland is a volcanic island with several intrabasaltic plant‐bearing sedimentary rock formations. The oldest sedimentary rocks are found in Northwest Iceland (ca. 15 Ma) and East Iceland (ca. 14 Ma) and are of Miocene age (Figures 1 and 2). In a simplified version the strata become progressively younger towards the volcanic zones crossing the centre of the island from southwest to northeast (for a recent review of the geology of Iceland see contributions in Sigmundsson et al. 2008). Sedimentary rock formations occur in Miocene to Pleistocene strata and often contain plant fossils. The palaeo‐floras of Iceland have been comprehensively studied in recent years (e.g. Denk et al. 2011; see also Denk et al. 2005; Grímsson et al. 2005, 2008; Grímsson and Símonarson 2006, 2008a, 2008b).

      The middle Miocene plant assemblages of Iceland (15–12 Ma) record vegetation thriving under a warm and moist climate. Wetlands and riparian vegetation of the lowlands was characterized by warmth‐loving taxa, such as taxodiaceous Cupressaceae, Magnoliaceae (Magnolia, Liriodendron), Lauraceae (Sassafras), Platanaceae (Figure 4E and F) and others, whereas the well‐drained vegetation of the hinterland comprised forests dominated by Fagus with evergreen trees and shrubs in the understorey (Rhododendron, Ilex). The endemic linden tree, Tilia selardalense Grímsson, Denk and Símonarson (Figure 4B) was confined to these forests (Grímsson and Denk 2005; Grímsson et al. 2007a, 2007b; Denk et al. 2011). The oldest floras of Iceland share a few taxa with the Paleogene floras of Greenland and/or Svalbard: Glyptostrobus, Platanus, Fagus, and Tilia.

A major change is seen in the early Tortonian (10 Ma) floras of Iceland, both in the palynological and the macrofossil record. Whereas herbaceous taxa did not play a significant role in the older floras, they amount to 30% of all recorded plant taxa in the 10 Ma floras. This increase in herbaceous plants is accompanied by the first occurrence of small‐leaved Ericaceae typical of the modern tundra vegetation in Iceland (Vaccinium, Arctostaphylos) and boreal conifers such as Larix. Nevertheless, several warmth‐loving elements persisted and new elements are recorded (Ginkgo; Denk et al. 2005, 2011). Floras preserved in strata between 10 and 3.6 Ma reflect stepwise cooling; Fagus persisted until 7–6 Ma and Quercus until 5.5 Ma, whereas the evergreen, large‐leaved Rhododendron aff. ponticum L. ranges from the oldest to the 3.8–3.6 Ma floras. At 4.4–3.6 Ma, small‐leaved Salicaceae occur for the first time. The second major reorganization of the vegetation is recorded in floras from the Pliocene–Pleistocene transition. Temperate woody elements are not found in any of the Pleistocene floras, which are essentially similar to the modern flora of Iceland (Denk et al. 2011).

Biogeographic Implications

      Paleogene СКАЧАТЬ