The Upper Cretaceous and Palaeocene evolution of the northern North Sea Basin
Apparent anomalous subsidence events have been observed in the Palaeogene succession of the northern North Sea basin and the aim of this project was to verify and explain these observations. Data from the logs of 275 boreholes were collected. The stratigraphic sequences were decompacted using a computer programme (I.G.I. MATURE) and the results were used to produce maps showing the development in time and space of the post-rift sequences in the studied basin. Seismic sections were analysed and used to verify the interpretation in the maps. Sediment thickness distributions and sediment geometries were used to draw conclusions about the tectonic evolution of the area during Upper Cretaceous, Palaeocene and Eocene. The influence of the opening North Atlantic Ocean upon the northern North Sea basin was considered. The following conclusions were drawn from the work: 1. The Upper Cretaceous sediment distribution shows that the basin was slowly filled from the centre outwards. Due to this, the sediment thicknesses show considerable variations across the studied area with the thickest sequences aligned north-south over the centre of the Jurassic rift. 2. The Palaeocene sediment distribution does not follow the Upper Cretaceous pattern. Instead, the sediments are aligned NE-SW. The sediment thickness distribution indicates uplift of the East Shetland Platform and the Hebrides. This observation agrees with work published by other researchers. The uplift might have been caused by stresses related to the developing NE Atlantic Ocean to the west of the studied area. 3. Areas of increased thicknesses in the Palaeocene sequence coincide with clusters of boreholes where apparent anomalous subsidence can be observed. Similar events have also been found in the Oligocene and Miocene sequences. The results from the Eocene sequence are not conclusive. 4. Analysis of the Eocene sequence shows that the sediment distribution returns to the Upper Cretaceous pattern with the thickest sediments in the centre of the graben. This would indicate that the 'disturbance' causing the changing alignment of the Palaeocene sediments was only short-term, and further supports the idea of a relationship with the formation of the NE Atlantic.