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The study is concentrated in the Central Tertiary Basin of Spitsbergen, which contains a c. 2300 m thick Paleogene sedimentary succession. In addition, data from the Forlandsundet Graben are also included. The Spitsbergen basins were marginal to the Paleo Arctic Ocean, and it is assumed that overall environmental conditions of the ocean are reflected in the sediment infill of these basins, but modified by local facies changes. In the Central Basin, these facies changes range from delta plain, lagoonal, through prodelta to marine shelf. The facies analyses are based on foraminiferal assemblage parameters combined with sedimentary data derived from mudstones and siltstones of the following formations: Firkanten, Basilika, Frysjaodden and Battfjellet.
The foraminiferal succession of the Central Basin consists of agglutinated taxa except for a few samples containing calcareous benthics in very low amounts. The species diversities are low in the studied intervals, with an average alpha value of 2.3 (range 1.2 to 3.0). The assemblages are of endemic nature as shown by dominance of Reticulophragmium, Convalina, Trochammina and Thurammina. In these deposits, the total organic carbon content is on average 1.1% (range 0.5 to 2.6%), while the calcium carbonate content averages 0.4% (range 0.0 to 4.2%).
The low diversity agglutinated nature of the foraminiferal assemblages indicates restricted environmental conditions. The main restricting factor was apparently low salinity, which is in accordance with the extremely low carbonate content. Low salinity can originate from local deltaic influx in lagoonal and prodelta settings (e. g. the Firkanten and Battfjellet formations). Reduced salinity in marine shelf settings (e. g. the Basilika and part of the Frysjaodden formation) requires, however, much more extensive developments of regional scale.
Low diversity agglutinated assemblages of endemic nature, closely similar to those of the Central Tertiary Basin, are recorded from the Beaufort-Mackenzie Basin and Western Siberia, suggesting that reduced surface salinity prevailed in the Arctic Ocean in Paleocene-Eocene times. These foraminiferal facies developments accord with the Azolla (freshwater fern) boom recorded from the Lomonosov Ridge, and explained by episodic presence of fresh surface waters in the Eocene Arctic Ocean.
In Paleocene-Eocene times, low salinity carbonate-starved conditions developed in the Arctic Ocean owing to the absence of a deep water connection between the Polar Basin and the world ocean. At the Eocene-Oligocene transition, deep water connection with the North Atlantic was established by seafloor spreading between Spitsbergen and Greenland leading to development of normal marine salinity conditions in Arctic Ocean waters. This turnover is signaled by occurrence of calcareous foraniniferal assemblages of Western European affinity in the Oligocene of the Forlandsundet Graban.
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