Micropalaeontological Evidences of the North Atlantic and the Arctic Biotic Connection in the Jurassic

Boris Nikitenko

Biogeographic analysis of microfossil distribution allows the reconstruction of biotic connection between different basins for short time intervals. In the Early and partially Middle Jurassic, stable connections between the biota of the Arctic and Pacific occurred, while the connection with the North Atlantic occurred only periodically and intensified during the major transgressions. Jurassic microbiotas of Arctic Seas were dominated by panboreal (cosmopolitan) taxa. Nevertheless, some migrant taxa from southern areas reached the Arctic. On the other hand, some typically Arctic forms occurred in the Boreal-Atlantic basin. They migrated through the Viking corridor which probably opened in the beginning of the Late Pliensbachian. In the Arctic, the first migrant taxa from NW European Seas appeared at the early Late Pliensbachian. European taxa almost always occur in Arctic microbenthic communities in the middle of the Late Pliensbachian, in the earliest Toarcian, in the latest Toarcian and Early Aalenian, latest Bajocian and earliest Bathonian. In the Arctic basin and European Seas, several simultaneous biotic and abiotic events have been recognized during the Late Pliensbachian – Early Toarcian. One of the most striking biotic events is the Early Toarcian biotic crisis. In the Late Pliensbachian, the transgression and climatic warming caused the invasion of a number of thermophilic migrant taxa in the microbenthic communities of the Arctic Seas. The regressive stage of the Arctic basin began at the latest Pliensbachian and a rather sharp cooling has been observed. These events apparently resulted in biotic connections with NW European Seas being partially broken. During the earliest Toarcian, there were reliable links between the microbenthic communities of the Arctic and NW European Seas caused by transgression and climatic warming. In the Arctic basin, this stage is characterized by periodic invasions of migrant taxa of both foraminifers and ostracods, which were widespread in the Toarcian Seas of NW Europe. At the same time, some specific Arctic forms migrated into European seas giving rise to new taxa there. At the beginning of the Middle Jurassic, a number of geographic barriers were formed in the region of the North Sea. These separated the Arctic and North Atlantic basins making reciprocal migrations of the benthos difficult. This isolation occurred from the Late Aalenian to Bathonian. South invasions of North Atlantic foraminifers in Arctic basins took place only in the latest Bajocian and the earliest Bathonian. In the Callovian and the Late Jurassic, the biotic connections and migrations between the Arctic and Boreal-Atlantic basins renewed in both through the Viking corridor and opened Russian Sea. The successions of the first appearances (FADs) of migrant taxa in the Arctic and North Atlantic calibrated against the Ammonite Zonation is the reliable instrument for interregional correlations of Mesozoic sections.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013