Biogeography in the Sub-Arctic. Группа авторов

Biogeography in the Sub-Arctic - Группа авторов


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alt="Photos depict (a) conglomerate from a 2–3 m thick stratum separating Cretaceous shales from the base of the overlying plateau lavas on Wollaston Forland, East Greenland (75° N). Cobbles are of quartzite and muscovite granite. (b) Aerial photograph of the same stratum on Kap Broer Ruys, East Greenland (73°30′N)."/>

      Source: B.G.J. Upton.

      Early in the Eocene mantle temperatures in the head of the plume may have fallen rapidly (Smallwood and White 2002) and the plume is inferred to have assumed a narrower sub‐cylindrical form with a ‘central core’ about a 100 km across. Magmatism due to this ‘plume tail’ marked out the shallow submarine welt of the Greenland–Iceland–Faeroes ridge as the Greenland/American tectonic plate migrated westwards. This ridge is characterized by an abnormal thickness (30–40 km) of oceanic crust and rises to shallow depths. The plume tail itself (the Iceland plume) is now considered to underlie eastern Iceland.

      Before the arrival of the postulated mantle plume, the landscapes of Greenland, Norway and Britain largely consisted of relatively high ground composed of early Palaeozoic and Precambrian metamorphic rocks transected by low‐lying faulted basins. The latter, developed during Mesozoic extensional tectonics, were subject to occasional marine inundation. The faulting had structurally preconditioned a tract of the Laurasian continent to a state ripe for exploitation by later rifting and magmatism in the Palaeocene. The embryonic ocean first appeared at approximately 56 Ma around the Palaeocene–Eocene boundary (currently defined at 55.8 ± 0.2 Ma). For the previous 10 Ma we may visualize rifted landscapes roughly comparable to those of Kenya and Ethiopia at present and which appears to have been well vegetated with an equable climate (Walker 1979).

Schematic illustration of fault pattern in the North Atlantic region on a map restored to continental dispositions prior to ocean opening.

      Source: Jolley and Bell (2002).

An illustration of a map depicting the orogenic belts on either side of the North Atlantic. Note that between Greenland and Norway the North Atlantic is approximately bilaterally symmetrical through the Caledonian Orogenic belt.

      Source: Gee et al. 2008.

Photo depicts a coastal section on Cape Searle Island, Baffin Island, Canada, showing a succession similar to that of parts of the East Greenland coast. Palaeocene non-marine sediments form the basal third, with white sandstones and dark coals and organic-rich shales. The central part is of sub-aqueous volcanic rocks. The upper third consists of subaerially erupted picritic lavas.

      Source: B.G.J.Upton


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