Oligocene deep-water agglutinated foraminifers at Site 985, Norwegian Basin, southern Norwegian Sea

Abstract

The stratigraphic distribution of deep-water agglutinated foraminifers was examined using 50 samples from Ocean Drilling Program (ODP) Hole 985A, drilled on the gentle slope of the Iceland Plateau in the Norwegian Basin. A total of 40 species and generic groupings was determined in this study. Three stratigraphically meaningful assemblages are recognized in Hole 985A: a basal assemblage with coarsely agglutinated forms (Cores 162-985A-62X through 50X), a Spirosigmoilinella compressa assemblage (Cores 162-985A-49X through 40X), and a sparse assemblage with pyritized radiolarians in the uppermost part of the studied interval (Cores 162-985A-39X through 32X). The whole succession from the base of Hole 985A to Core 162-985A-32X is here assigned to the Dorothia siegliei-Rotaliatina bulimoides Zone of Oligocene age. The stratigraphic ranges of several species extended into younger strata compared with biostratigraphic records from the Voring Slope (ODP Hole 643A) and from an exploration well on the Voring Plateau. Taxonomic differences between the foraminiferal records of the Norwegian Sea and the deep Labrador Sea provide evidence for faunal isolation of the deep Norwegian basin during the Oligocene. This isolation is attributed to limited marine connections across the Greenland-Scotland Ridge, resulting in Norwegian Sea deep water that was corrosive and poorly ventilated. Foraminiferal evidence suggests that Norwegian Sea deep water was poorly oxygenated during the Oligocene.