Biogeography in the Sub-Arctic. Группа авторов

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СКАЧАТЬ 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 by both pollen and leaf fossils from Agatdalen (Grímsson et al. 2016a, 2016b).

Koch (1963) collected and described plant fossils from the late Palaeocene Agatdalen Formation, Nuussuaq Peninsula. Most common macrofossil elements of the Agatdalen flora are Metasequoia (locally), Trochodendroides [as Cercidiphyllum], Macclintockia, and Platanus bella (Heer) Kvaček, Manchester and Guo [as Dicotylophyllum bellum (Heer) Seward and Conway]. Koch (1963) recognized the extant genus Liriodendron (Figure 3B) but placed leaf imprints similar to modern Sassafras (Figure 3C) within the extinct genus Lauraceaephyllum based on subtle differences in venation between the fossil and the modern genus. Revision of the Agatdalen macroflora by Grímsson et al. (2016a) reduces the ca. 38 taxa by Koch (1963) down to ca. 32. Still, the newly studied palynoflora from the same formation is relatively rich, comprising at least 145 angiosperms, 25 gymnosperms and around 30 different spore types (Grímsson et al. 2016a, 2016b). Overall, the palaeovegetation of the Agatdalen area appears to have been dominated by riparian elements (ferns, Taxodioideae, Trochodendroides, Platanus, Figure 4C and D), and Fagaceae, Betulaceae, Hamamelidaceae and Vitis (Figure 4A) as elements of the well‐drained hinterland. The enigmatic plant Macclintockia also played a significant role in the palaeofloral assemblages.

Figure 3 Palaeocene fossil leaves from West Greenland (Agatdalen, Atanikerluk) and the Faroe Islands (Mykines). (A) Small acrodromous leaf from Upper Atanikerluk B, MGUH 6443 [as Paliurus pusillus Heer in Heer (1883; Pl. LXXXI, figs 9 and 10)]. (B) Liriodendron sp., from Agatdalen, MGUH 10393 [as cfr. Liriodendron sp. in Koch (1963; Pl. 16, fig. 1)]. (C) Sassafras sp., from Agatdalen, MGUH 10420 [as Lauraceaephyllum stenolobatus Koch in Koch (1963; Pl. 30, fig. 2)]. (D) Large actinodromous leaf from Upper Atanikerluk B, MGUH 6435 [as Cissites steenstrupi Heer in Heer (1883; Pl. LXXXI, fig. 1)]. (E) Metasequoia occidentalis (Newb.) Chaney, from Mykines (Beinisvørð Formation), S134471. (See colour plate section for colour representation of this figure.)

Figure 4 Palaeocene leaves and Eocene pollen from West Greenland (Agatdalen, Hareø) and the Miocene of Iceland (Selárdalur, Botn). (A) Vitis sp., from Agatdalen, MGUH 10421 [as cfr. Vitis olriki Heer in Koch (1963; Pl. 30, fig. 3)]. (B) Tilia selardalense Grímsson, Denk & Símonarson, from Selárdalur. (C) Platanus sp., from Agatdalen, MGUH 10412 [as Platanus sp. cfr. aceroides Goepp. in Koch (1963; Pl. 26, fig. 1)]. (D) Platanus sp., from Hareø. (E) Platanus sp., from Botn. (F) Platanus leucophylla (Unger) Knobloch, from Selárdalur, IMNH 302.

Figure 5 Palaeocene fossil leaves from Atanikerluk, West Greenland. (A) Fagopsiphyllum groenlandicum (Heer) Manchester, СКАЧАТЬ