Age and palaeoenvironment of the utsira formation in the northern north sea based on marine palynology

Abstract

The Utsira Formation is a major player in the carbon capture and storage on the Norwegian Shelf. Although this northern North Sea unit has been subjected to several geological and monitoring studies, its lateral distribution and stratigraphic position are still not fully understood. This unit was considered to be late Neogene and deposited in neritic environments on the Norwegian Shelf, in an area from the Viking Graben to the Tampen Spur. Here, we present marine palynomorph (dinoflagellate cysts, acritarchs) data extracted mainly from cutting samples of eight industry wells that cover the entire distribution area of the Utsira Formation to provide an age and palaeoenvironmental reconstruction for this unit. We conclude that deposits classified as Utsira Formation are Late Miocene/Early Pliocene to Early Pleistocene in age. Early Pliocene sediments are found mainly in the Viking Graben area, whereas sediments with an Early Pleistocene age occur over the entire distribution area of the Utsira Formation. All sediments were deposited in neritic environments that gradually became shallower from the Early Pliocene to the Pleistocene. At the same time, the dinoflagellate cysts also indicate a cooling that corresponds well with late Neogene global cooling. Precise dating of the Utsira Formation is difficult, but this can be improved by (1) using samples from cored section (in contrast to using cuttings), (2) a clear and unquestionable lithological definition of the Utsira Formation and (3) a continuous, calibrated reference section in the Neogene North Sea for comparison of the bioevents.