Ocean Drilling Program (ODP) Leg 162 Site 985 is located in the central part of the Norwegian Sea in 2788 m water depth, on a gentle, east-facing slope of the Iceland Plateau (Fig. 1, Fig. 2). Two holes were drilled, Holes 985A and 985B. This report discusses the lower part of the deeper hole, Hole 985A, which reached a total depth of 587.9 meters below seafloor (mbsf) and from which was obtained 553.42 m of core.
Drilling at Site 985 had two main objectives (Shipboard Scientific Party, 1996, pp. 254-256). The primary objective was to provide additional data for a paleoenvironmental transect across the Norwegian Sea, including previous sites drilled on Legs 104 and 152. The aim of this transect was to study late Cenozoic development of water-mass circulation between the Arctic and the Atlantic Oceans. The secondary objective was to obtain Paleogene carbonate-bearing sediments that would yield material suitable for paleotemperature and paleoceanographic studies. Paleogene sediments have been recovered from only a few previous Deep Sea Drilling Project (DSDP)/ODP sites in the Norwegian-Greenland Sea, and poor recovery and diagenetic overprinting have precluded stable isotope studies. Scarcity or absence of calcareous and siliceous microfossils has also hampered biostratigraphic control in the Paleogene sections (Goll, 1989).
Site 985 was located on Anomaly 22 crust (~50 Ma) with an assumed normal subsidence history, so it was considered promising for attainment of the secondary objective. Contrary to expectations, both calcareous and siliceous microfossils were scarce. The Shipboard Scientific Party (1996, pp. 268-269) considered the uppermost nine cores to be Pliocene on the basis of the nannofossils. The sparse siliceous microfossils suggested that Cores 162-985A-24X through 31X could be middle Miocene. Below Core 31X, agglutinated benthic foraminifers indicated a late Oligocene-early Miocene age for Cores 162-985A-33X through 40X and an undifferentiated Oligocene age for Cores 41X through 62X.
In contrast to other microfossil groups, dinoflagellate cysts (dinocysts) occur consistently in the Paleogene section of Hole 985A, as is true elsewhere in the Norwegian-Greenland Sea where they have proved useful for age control (Manum, 1976; Manum et al., 1989; Firth, 1996; Poulsen et al., 1996). As shown in this report, dinocysts provide improved age control for the Oligocene and lowermost Miocene cores from Site 985.
In order to elucidate the geological history in the bottom part of Hole 985A, where none of the other microfossil groups provided age control, we studied dinocysts from Core 162-985A-62X (579.09 mbsf) up to and including Core 32X (290.49 mbsf; Fig. 3; Table 1). The lowest sample for which there was independent control was Core 162-985A-31X, which was considered to be of definite Miocene age by the shipboard stratigraphers. A total of 98 5-cm3 samples were processed using standard palynological methods. Forty-eight samples (approximately every other sample) were processed in the palynology laboratory at the Geological Survey of Canada (Atlantic) in Dartmouth, Nova Scotia; the remainder, in the palynology laboratory in the Geology Department of the University of Oslo, Norway.
Lithostratigraphically, the studied section comprises Unit V and the lower part of Subunit IVC as defined by the Shipboard Scientific Party (1996, pp. 261-268). These units are composed of clay with varying minor occurrences of silt and are distinguished mainly on the basis of a sharp increase in magnetic susceptibility at their boundary in Section 162-985A-50X-2.
Site 985 was approximately conjugate to Site 643, with respect to the spreading axis, until Anomaly 7 time (Oligocene-early Miocene transition) when the axis shifted to west of the Iceland Plateau (Shipboard Scientific Party, 1996, p. 267). The evolution of the basin was presumably similar at both sites, which is confirmed by the correspondence in the succession of dinocyst events in the Oligocene and lower Miocene sections (Fig. 4).