Biogeography in the Sub-Arctic. Группа авторов

Figure 2 Relative age of Cenozoic (pre‐Holocene) volcanics and sedimentary rocks of the Brito‐Arctic Igneous (floral) Province (BIP). Stratigraphic occurrences of Paleogene floras of West Greenland, the Faroe Islands and the British Isles (Scotland) discussed in the text are indicated. 1 – Agatdalen flora; 2 – Upper Atanikerluk A flora; 3 – Upper Atanikerluk B flora; 4 – Hareø flora; 5 – Mykines flora; 6 – Prestfjall flora; 7 – Mull flora. Geological time scale based on ICS (2020).

      Neogene plant fossils from the sub‐arctic North Atlantic have recently been shown to be important for understanding modern biogeographic patterns in northern temperate plant groups and assessing the subsidence history of the Greenland‐Scotland Transverse Ridge (Tiffney and Manchester 2001; Grímsson and Denk 2007; Tiffney 2008; Denk et al. 2010a, 2011). Biogeographic inferences from plant fossils have also important implications for understanding molecular differentiation in plants and animals (e.g. Denk and Grimm 2010; Kornobis et al. 2011).

      In this chapter, we review previous work on the plant fossil record from Palaeocene to Pleistocene sedimentary formations of the sub‐arctic North Atlantic region. This includes Paleogene plant assemblages from Greenland, the Faroe Islands and Scotland, as well as Neogene floras from Iceland (Figures 1 and 2). In addition, we present revised macro‐fossil and new palynological data from Palaeocene to Eocene sediments of Greenland and the Faroe Islands, which considerably change our understanding of the biogeographic history of several northern temperate woody plant taxa that are among the most ecologically important tree species in the mid‐latitudes of North America, Europe and East Asia.

Paleogene Floras and Vegetation

      Greenland

      Palaeocene to Eocene plant‐bearing sedimentary rocks are exposed in the Disco–Nuussuaq–Svartenhuk Halvø area (at 69 to 72°N), West Greenland, and in the Kap Gustav Holm–Scoresby Sund–Shannon area (at 69 to 74°N), East Greenland (Figure 1). Extensive fossil plant collections exist from the Paleogene sediments of West Greenland (e.g. Heer 1868 et seq.; Seward and Conway 1935; Koch 1963), whereas material from East Greenland is sparse (e.g. Mathiesen 1932; Seward and Edwards 1941), rendering these floras less informative.

The Cretaceous–Cenozoic lithostratigraphy in the Disco–Nuussuaq–Svartenhuk Halvø area, West Greenland, including the plant‐bearing Paleogene sediments, has recently been revised by Dam et al. (2009). The strata of the Nuussuaq peninsula are divided into two major units, the Nuussuaq Group and the younger Western Greenland Basalt Group (WGBG). The Nuussuaq Group is composed of five Cretaceous formations (Kome, Slibestensfjeldet, Upernivik Næs, Atane, Itilli), one Cretaceous/Palaeocene formation (Kangilia), and four Palaeocene formations (Agatdal, Quikavsak, Eqalulik, Atanikerluk). Some formations extend over vast areas, whereas others are local and contemporaneous with formations in neighbouring regions (for details see Dam et al. 2009). The Agatdal Formation comprising the ‘Agatdalen flora’ of Koch (1963, 1972a, b) and the Quikavsak Formation (Nuuk Qiterleq Member) comprising the ‘Upper Atanikerluk A flora’ of Heer (1868, 1869, 1874, 1880, 1883) are believed to be partly contemporaneous and resulting from the same tectonic event prior to accumulation of the overlying so‐called Naajaat palaeo‐lake sedimentary rocks (e.g. Pedersen et al. 1998; Dam et al. 2009; Grímsson et al. 2016b). The Quikavsak Formation is followed by the Atanikerluk Formation (Naujât Member), which comprises the ‘Upper Atanikerluk B flora’ of Heer (1880, 1883). Radiometric ages of contemporaneous volcanic structures give an age between 62 and 60 Ma (Selandian age; Storey et al. 1998; Dam et al. 2009) for the Atanikerluk Formation (Upper Atanikerluk B flora; Figure 2). The older Agatdal Formation (Agatdalen flora) and Quikavsak Formation (Upper Atanikerluk A flora) are between 64 and 62 Ma (late Danian age; see Figure 7 in Grímsson et al. 2016b).

The Paleogene strata on the island of Hareø (west of Disco; Figure 1) are divided into the Maligât Formation and the younger Hareøen Formation, both of which are part of the WGBG. The Hareøen Formation is divided into two successive members, the Aamaruutissaa Member (clastic) and the Talerua Member (volcanic; Hald 1976, 1977; see Figure 2 in Grímsson et al. 2015). The Aamaruutissaa Member comprises the ‘Hareø flora’ of Heer (1883) and Nathorst (1885). Lavas of the overlying Talerua Member have been radiometrically dated at ca. 39 Ma (cf. Schmidt et al. 2005) and are of late Bartonian age (late Eocene). This suggests that the underlying sedimentary rocks comprising the Hareø flora are of late Lutetian to early Bartonian age, ca. 42–40 Ma old (Figure 2); this is also supported by palynological data (Grímsson et al. 2015).

      The first comprehensive treatment of fossil plants from the Cenozoic of Greenland was by Heer (1868, 1869, 1874, 1883), who studied plant fossils from 20 localities in Greenland. Heer described 143 plant species from Upper Atanikerluk A and 78 from the younger Upper Atanikerluk B horizon; from Hareø, 53 plant species were described (Heer 1883). Taxa recovered from nearly all localities were Metasequoia [as Sequoia langsdorfii, Taxodium] and Trochodendroides [as Populus arctica]. From the Upper Atanikerluk A flora, 12 species of Fagaceae were identified, among which nine were Quercus. In addition, four species of (evergreen) Laurus were recognized by Heer in this horizon. The latter were missing in the Upper Atanikerluk B flora (Heer 1883). From Upper Atanikerluk B, 10 species of Fagaceae were recorded and two species of Ilex (Aquifoliaceae) indicating the presence of evergreen angiosperms in the lower Palaeocene. From Hareø, the most characteristic elements reported by Heer were Ginkgo, Cupressaceae (incl. Taxodiaceae), Pinus, Acer, Fagaceae (three species of Fagus and Castanea, four species of Quercus) and Platanus (Heer 1883). Some of Heer's original taxa have later been revised and lumped, resulting in many less species for the individual floras (cf. Koch 1963; Kvaček et al. 1994). Other of Heer's taxa are in need of revision (Figure 3A as Paliurus pusillus and 3D as Cissites steenstrupi Heer).

      A few studies briefly summarized the Palaeocene floras of (West) Greenland (Pedersen 1976; Mai 1995; Kvaček 2010) but did not provide new data or comprehensive revisions of the Greenland floras. However, Mai (1995) pointed to the presence of the extinct Fagaceae Eotrigonobalanus in the early Palaeocene flora of Atanikerluk, along with several other extinct types of Fagaceae. This observation has recently been confirmed