Late Cenozoic basin development of the eastern North Sea Basin

Abstract

The Cenozoic succession in the Danish part of the North Sea Basin includes two significant breaks in sedimentation; 1) at the Eocene-Oligocene boundary and 2) at mid Miocene time. The sediment transport direction was from the west during the Middle-Late Eocene and mainly from northeast and east in post Eocene times, and a change from a concordant seismic reflection pattern to a progradational pattern is seen. A clear change in Iithology occurs at the Eocene-Oligocene boundary, from a finegrained clay-dominated deposit below the boundary to a clay with silt and mica above. Near shore marine and fluvial sediments of Early Oligocene to mid Miocene age are known from the offshore and onshore areas, witnessing that the coastline migrated into the basin for the first time since the earliest Cretaceous. This change in sedimentation pattern was probably caused by the initial uplift of Scandinavia. At mid Miocene time a significant environmental change occurred in the North Sea. A change from dark coloured to light coloured deposits indicates introduction of a well-oxygenated environment. A marked increase in rate of sedimentation (and subsidence) is evidenced by the approx. 1500 m thick sedimentary package in the central part of the basin. Late Middle Miocene starved sedimentation seen in the central North Sea may indicate a significant increase in subsidence rates. The base of the Quaternary is a major erosional unconformity, mainly created by erosion caused by uplift of Scandinavia. 1000-1200 m of uplift is calculated for the eastern part of the North Sea Basin. With a post-Eocene subsidence of 2500 m in the central North Sea, the amplitude of the post-Eocene tectonic movements is approx. 3700 m.