Eocene and Oligocene radiolarians were recovered from two sites on Ocean
Drilling Program (ODP) Leg 151. Early Oligocene to early late Oligocene radiolarians have been
extracted from material cored at Site 908 on the Hovgård Ridge (Fram Strait). Although
rare and only moderately preserved, these assemblages represent the northernmost occurrence of
radiolarians recovered by either the Deep Sea Drilling Project or ODP thus far. Site 913 on the
East Greenland margin has yielded a sequence of moderately diverse middle Eocene to earliest
Oligocene radiolarians. In total, ~75 species have been documented herein from both sites.
Previous radiolarian biostratigraphics developed for the Norwegian-Greenland Sea
were used as an initial basis for Leg 151 age dating. However, complications introduced by Leg
38 spot-coring techniques and radiolarian endemism are highlighted by Site 913 material that does
not fit easily into either of the previous biostratigraphic zonations proposed for this region.
Consequently, age determinations are based in part on comparison of Site 913 with Leg 38 sites
as well as calibration of radiolarian events with other microfossil groups (diatoms,
silicoflagellates, and dinoflagellates) present in Hole 913B. The combined stratigraphics suggest
the presence of the Eocene/Oligocene boundary in the uppermost part of the biosiliceous
sequence at Site 913. The uppermost part of this interval is characterized by the dominance of
robust radiolarian groups, broken radiolarian tests, rare diatoms and increased reworking of
radiolarians and dinoflagellates. These changes are interpreted as evidence for increased
bottomwater circulation associated with radiolarian blooms at or just above the Eocene/Oligocene
boundary. These findings concur with previous studies indicating increased bottomwater
circulation in the North Atlantic during this same period of geologic time.
Date of initial receipt: 30 June 1995
Date of acceptance: 6 December 1995
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