Reconstructing Eocene to Oligocene oceanographic events in the Norwegian-Greenland Sea using integrated micropalaeontological, geochemical and magnetic analysis

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Reconstructing Eocene to Oligocene oceanographic events in the Norwegian-Greenland Sea using integrated micropalaeontological, geochemical and magnetic analyses

The presence of abundant age-diagnostic dinocysts at Site 913B (ODP Leg 151), Site 338 (DSDP Leg 38) and Site 643A (ODP Leg 104) has enabled the development of a high-resolution biostratigraphy for the Eocene-Oligocene interval in the Norwegian-Greenland Sea. This a particularly important as the calcareous microfossils usually used for biostratigraphy in this interval are generally absent in these high latitude Eocene-Oligocene sediments due to dissolution. In parallel with this biostratigraphic analysis, a new magnetic reversal stratigraphy has been defined for the Norwegian-Greenland Sea. This has allowed independent age determination and enabled the dinocyst biostratigraphy to be firmly tied into the global geomagnetic timescale for this period. Hole 913B, has proven to be the most complete and best-preserved record of the Eocene to Oligocene interval in the high latitudes of the Northern Hemisphere, thus have the potential to provide detailed palaeoenvironmental reconstructions of this critical period in early history. Integrated micropalaeontological, geochemical and environmental magnetic analyses of sediments from Site 913B have indicated that throughout the Eocene this site was located in a relatively offshore depositional environmental. Dinocyst and palynofacies assemblages from Site 338 indicate a transition from a marginal marine to a relatively deep-water offshore environment during the mid Eocene, reflecting the gradual subsidence of the Outer Voring Plateau and Voring Plateau escarpment. The final subsidence of these features occurs at ~46 Ma and is reflected by the cessation of predominantly terrestrially derived clastic sedimentation at Site 338. Coeval dinocyst assemblages indicate that a surface-water marine connection existed between the Norwegian-Greenland Sea and the North Sea, the Arctic Ocean and to a lesser extent the North Atlantic Ocean throughout the Eocene to Oligocene period. The Norwegian-Greenland Sea was characterised by relatively warm conditions in the early Eocene, which were replaced by significantly cooler conditions by the Eocene-Oligocene transition. Several distinct cooling episodes are identified throughout the Eocene in the Norwegian-Greenland Sea and Adjacent regions, culminating in a permanent drop in high-latitude surface water temperatures at the Eocene-Oligocene boundary.</p

Palynology analyses of Eocene to Oligocene sediments of DSDP Hole 38-338

Against the background of the profound global climatic shift from greenhouse to icehouse conditions during the Eocene–Oligocene transition, major geographic and oceanographic changes were taking place in the Norwegian–Greenland Sea region. The Vøring Plateau was a prominent structural feature which influenced the evolution of water mass circulation in the Nordic seas, and we present detailed palaeoenvironmental reconstructions of this structure. New palynological results suggest that shallow water inner-neritic environments were developed across parts of the Vøring Plateau during early Eocene times, with terrestrial and brackish water palynomorphs indicating that both basement highs to the north, and the crestal part of the Vøring Escarpment, may have been emergent. A transition from marginal-marine to open marine conditions occurred around 44 Ma ago, with the complete subsidence of the Vøring Plateau below sea level, facilitating inter-basinal surface water circulation and promoted a significant increase in photic zone fertility. Carbon sequestration associated with such enhanced productivity in the late Eocene Nordic seas may have contributed to declining Cenozoic atmospheric carbon dioxide levels, thence to declining global temperatures and the development of limited Northern Hemisphere continental ice on Greenland in the latest Eocene