Paleoceanography and Biostratigraphy of Paleogene Radiolarians from the Norwegian-Greenland Sea

Abstract

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 Hovgàrd 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 biostratigraphies 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 stratigraphies 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.

The onset of modern‐like Atlantic meridional overturning circulation at the Eocene‐Oligocene transition: Evidence, causes, and possible implications for global cooling

“…In addition, various indications for enhanced overturn of the water column in the Nordic seas are seen in drilling sites that sampled the EOT section. An abrupt intensification in bottom flow currents is seen in ODP Leg 151 (Site 913 is in depth > 3300 m) (Figure ) as “organic‐rich laminated diatom oozes and muds, deposited under sluggish bottom flow and presumably low oxygen conditions, abruptly became winnowed by bottom current activity, perhaps in the early early Oligocene” [ Scherer and Koç , ], and by reworking of radiolarians and dinoflagellates [ Hull , ]. A shift to oxygenated water column is indicated from deep drilling in the northernmost part of the Faroe‐Shetland channel by the shift from agglutinated foraminifera to diatoms and other calcareous benthic foraminifera [ Davies et al ., ].…”

“…The bathymetry of the basin is taken from Vogt et al []. The paleolocation of sites 908 and 913 is from Hull []. We estimated the paleolocation of Sites 336 and 985 by the location of the Aegir Ridge and the paleowater depth of 336 around the EOT (Figure f).…”

“…The spillout of this water to the North Atlantic was at the Faroe‐Shetland channel [ Davies et al ., ]. This E‐W asymmetrical route (Figure ) is based on (1) an absence of indicators for deepwater circulation in Site 985 (which is not located at the western part of the basin, Figure ) during the Oligocene [ Kaminski and Austin , ] and its presence in Sites 908 and 913 since the EOT, (2) this asymmetry was seen during the Neogene when periodic influxes of warmer water from the North Atlantic to the eastern part of the basin generated different faunas than the western part of the basin [ Goll and Bjorklund , ; Hull , ], and (3) such asymmetry is seen in the present Nordic seas circulation.…”

New species of Neogene radiolarians from the Southern Ocean – part III

“…B Hull, 1996 (pl. 1, figs 3-4, 9, 12) seems to have the same medullary shell as J. pseudodictyocha and their cortical shell are also very similar; however, the specimen in Hull, (1996) has a lower shell ratio and longer, more numerous spines.…”

“…The specimen illustrated as Botryopera? pseu doantarctissa Petrushevskaya & Kozlova, 1979in Hull (1996, figs 3-4) seems similar to B. piperata but lacks a sieve plate and robust horns (which can be due to preservation or ontogeny) and has larger, polygonal pores. B. pseudoantarctissa as described and illustrated in Petrushevskaya & Kozlova (1979) is distinguishable from this new species primarily in having a straight, cylindrical thorax and lacking horns.…”