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Abstract

During the Jurassic and Early Cretaceous, Arctic seas were linked with the Atlantic and Pacific Oceans. Warm oceanic currents penetrated from the Atlantic Ocean, and a greater abundance and diffusion of the marine fauna in the Atlantic part of the Arctic resulted; this penetration was especially pronounced during the Late Jurassic. The north pole, on the basis of paleomagnetic and paleobiogeographic data, was situated north of the Bering Strait during the whole Jurassic and Neocomian.

The marine fauna was only slightly differentiated during the Hettangian, Sinemurian, and early Pliens-bachian. The Tethyan and Boreal faunal provinces developed; the latter, situated around the north pole, was characterized by sparser cephalopod associations and by the appearance of endemic forms (up to families) in the benthos. During the late Pliensbachian, faunal differentiation reached the province level. The Boreal region was differentiated into the West European and Arctic provinces, which continued during the Toarcian and early Aalenian. During the Middle Jurassic (from late Aalenian), faunal variability in the Boreal region greatly increased, and the Arctic and North American provinces became differentiated within this region. The West European province appears to have extended beyond the limits of the Boreal region. During the Callovian, Oxfordian, and Kimeridgian, the Boreal region tended again to fall info two subregions: the Arctic region—which included the North Siberian, Chukchi-Canadian, and North American provinces— and the Boreal-Atlantic region—which included the West European and Greenland-Uralian provinces.

During the Volgian and early Berriasian, the Boreal fauna was still somewhat isolated from the Tethyan fauna and constituted a Boreal realm with Arctic and Boreal-Atlantic regions. The Arctic region included the North Siberian, Chukchi-Canadian (around the pole), and Boreal-Pacific provinces, and the Boreal-Atlantic region consisted of the West European, East European, and Greenland-Uralian provinces. During the late Berriasian, Valanginian, and early Hauterivian, the Arctic region extended westward and included the Trans-Uralian region.

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