North sea Basin depositional history of the Oligocene based on dinoflagellate studies

Category Paleontology and Stratigraphy
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Sliwinska, Katarzyna۱; Heilmann-Clausen, Claus۱; Dybkjaer, Karen۲
Holding Date 08 October 2008

A major shift in the depositional pattern of the North Sea Basin took place at the Eocene/Oligocene transition, synchronous with the change from greenhouse to icehouse climate. From the beginning of the Oligocene locally distributed, thick sediment bodies prograded into the basin from the North. These progradations have been interpreted to indicate an uplift of the Norwegian land area as a source of the sediments. This view is, however, disputed by others, who assume that the changed pattern of sedimentation was caused by the installation of a cooler climate.
The Oligocene succession of the Danish land area is known to be less complete than that of the central North Sea. A Ph.D. study financed by Aarhus University and Fur Museum aims at elucidating the dynamics of the Oligocene sedimentation pattern primarily based on dinoflagellate cysts. In particular the role of the climate is in focus: are the onshore hiati coinciding with colder part of the Oligocene?
The Horn-1 borehole in eastern Jutland is being studied as a main section for the mapping of sedimentation near the eastern limit of the Oligocene deposits. It will be compared with boreholes and outcrops in central Jutland and stratigraphically more complete wells from the central and eastern North Sea, including the wells Sten-1 and Nini-1.
The preliminary results of the project are presented, including a first zonation of the Oligocene in the Danish North Sea Basin. The Oligocene-Miocene boundary is marked by a strong decrease of Deflandrea phosphoritica and a simultaneous increase of Homotryblium spp. in the examined samples.
The Uppermost Oligocene can be easily correlated with studies of Dybkjær (2007) in the Frida-1 North Sea well and stratigraphical sequences A and B of Rasmussen (2004). The lowermost Oligocene can be correlated with studies of Heilmann-Clausen & Van Simaeys (2005) in the onshore Kysing Research Borehole.