A synthesis of Cenozoic sedimentation in the North Sea

摘要

The North Sea Basin contains an almost complete record of Cenozoic sedimentation, separated by clear regional unconformities. The changes in sediment characteristics, rate and source, and expression of the unconformities reflect the tectonic, eustatic and climatic changes that the North Sea and its margins have undergone. While the North Sea has been mapped locally, we present the first regional mapping of the Cenozoic sedimentary strata. Our study provides a new regional sub-division of the main seismic units in the North Sea together with maps of depocentres, influx direction and source areas. Our study provides a regional synthesis of sedimentation based on a comprehensive interpretation of a regionally covering reflection seismic data set. We relate observations of sediment characteristics and unconformities to the geological evolution. The timing, regional expression and stratigraphic characteristics of many unconformities indicate that they were generated by eustatic sea-level fall, often in conjunction with other processes. Early Cenozoic unconformities, however, relate to tectonism associated with the opening of the North Atlantic. From observation on a regional scale, we infer that the sediment influx into the North Sea during the Cenozoic is more complex than previously suggested clockwise rotation from early northwestern to late southern sources. The Shetland Platform supplied sediment continuously, although at varying rates, until the latest Cenozoic. Sedimentation around Norway changed from early Cenozoic influx from the southwestern margin, to almost exclusively from the southern margin in the Oligocene and from all of southern Norway in the latest Cenozoic. Thick Eocene deposits in the Central Graben are sourced mainly from a western and a likely southern source, indicating that prominent influx from the south did not only occur from the mid-Miocene onwards. We infer a new age for the increased progradational sediment influx in the Pleistocene of 2.5 Ma, coeval with Fennoscandian glaciation.