Surficial sediments in the Norwegian sector of the North Sea between 60°30′ and 62°N

Abstract

Based on grain-size distribution and sea floor photographs, the sea bed sediments between Bergen and Måløy have been divided into four groups: (A) sand with coarse material on the northern part of the North Sea Plateau and the Måløy Plateau; (B) very well sorted sand on the southern part of the North Sea Plateau and the upper part of the western slope of the Norwegian Trench; (C) silty, clayey sand in lower part of the slopes; (D) silty, sandy clay in the central part of the Norwegian Trench. Large local variations are found in the group A sediments, on the Måløy Plateau partly caused by relict iceberg plough marks. The net deposition after the transition to boreal conditions with Atlantic water about 10,000 yrs ago is mostly between 0 and 30 cm on the northern part of the North Sea Plateau and exceeds 200 cm in the deepest parts of the Norwegian Trench. The total thickness of sediments above assumed overconsolidated material has been mapped based on sparker records. On the northern part of the North Sea Plateau the sediment cover above a supposed wavecut platform is less than 1 m over large areas, while a Late Weichselian coastal unit fringing the plateau consists of up to 40 m of sand and gravel. On the southern part of the plateau and the upper part of the western slope of the Norwegian Trench up to 10–30 m of sediments are found, probably dominated by sand formed by wave and tidal current action during a period of low sea level. In the central part of the trench a total thickness of up to 40 m of clay deposited during varying environments is found. Most of the investigated area is believed to be underlain by a till deposited by a north-northwestward moving ice sheet.