Читать книгу Biogeography in the Sub-Arctic - Группа авторов - Страница 56

At the type locality the lower part of the Île de France Formation in North‐East Greenland is heterogeneous, consisting of diamicton, fine‐grained sand, homogenous silt and rhythmically layered silt and sand. This part contains no macro‐fossils and was presumably laid down in a glaciomarine environment. The upper part of the sequence is more homogenous and consists of bioturbated silt and fine sand with scattered shell fragments of marine molluscs. At a few sites on northern Île de France sand with organic detritus is found (Bennike et al. 2002a).

Twenty‐four species of marine molluscs have been found and the fauna includes Trichotropis bicarinata, which formerly as a fossil in Greenland has only been reported from the Kap København Formation (Bennike 1989), and Astarte alaskensis, which is not known from other sites in Greenland. Diatoms are represented by 99 species, of which the vast majority are marine species, but the diatom flora also includes some freshwater taxa. The latter as well as colonies of the fresh water algae Pediastrum sp. and Botryococcus sp. indicate some outflow of freshwater. The diatom flora comprises Fossula arctica, which is associated with sea ice and is only known from the Arctic.

The marine fauna show that the sediments were deposited at sub‐littoral water depths on the inner shelf. The molluscs comprise warmth demanding species such as A. islandica, which shows that the water temperature was considerably higher than at present. The dinoflagellate cysts indicate polar to sub‐polar environments.

In addition to remains of marine organisms and microscopic freshwater algae scattered fragments of wood and bark are found, as well as rare seeds and fruits. This material comprises Picea, probably P. mariana, Thuja sp. and M. trifoliata. These sparse remains may imply that the adjoining land areas were covered by coniferous forest or forest tundra.

The Île de France Formation may have been deposited during the Olduvai normal polarity subchron at 1.95–1.78 Ma, based on palaeomagnetic studies and data from benthic foraminifera (Bennike et al. 2010). This means that it is slightly younger than member B of the Kap København Formation.