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Dinoflagellate Cysts in Early Late Miocene Sediments of ODP Hole 911A, Yermak Plateau

Kari Grøsfjeld1, Jochen Knies1, Karl Previous HitFabianTop1, Stijn de Schepper2, and Katrine Husum3
1Geological Survey of Norway, Trondheim, Norway.
2University of Bremen, Bremen, Germany.
3University of Tromso, Tromso, Norway.

The basal sediments of ODP Hole 911A (Leg 151), drilled on the Yermak Plateau, northwest of Svalbard have been re-sampled due to major uncertainties in terms of timing and paleoenvironmental conditions. We provide first evidence that the lowermost ~13 m (505 - 492 mbsf) span an age from 11.4 to 5.89 Ma. This is based on the co-occurrence of the dinocysts Amiculosphaera umbraculum and Cleistosphaeridium placacanthum in the lowermost investigated sample at 505.64 mbsf., indicating an age of 11.4 Ma, and the oldest paleomagnetically dated sample located at 492 mbsf. suggesting an age of 5.89 Ma. Barssidinium graminosum, B. pliocenicum, Lingulodinium machaerophorum and Operculodinium centrocarpum sensu Wall and Dale (1966), together with the absence of sea-ice indicator species, indicate that relatively warm, ice-free conditions prevailed during the early Late Miocene around 11,4 Ma (505,64 to 503,61 mbsf.). The latter species suggests that relatively warm waters may have reached the high latitudes of Site 911 via surface currents. After 11.4 Ma a marked change in the surface water conditions occurred. This might have been caused by the eustatic sea level drop at the time when the Antarctic ice sheet reached its maximum size. Sea ice formation around 6 Ma is indicated by a few specimens of Islandinium? minutum.


AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.