Late Cenozoic geological evolution of the northern North Sea: development of a Miocene unconformity reshaped by large-scale Pleistocene sand intrusion

Abstract

Despite hundreds of wells and extensive 3D seismic coverage, the late Cenozoic geological evolution is still not completely understood in the prolific northern North Sea hydrocarbon province. This is mainly due to post-depositional modification of sediment body geometries by injections of large volumes of sand. Using high-quality 3D seismic and well data above the Snorre and Visund Fields we propose a new late Cenozoic geological model that describes pre-injection geomorphological forms and sand injection events. The northern North Sea was exposed during mid- and late Miocene times (10 myr), simultaneously with the regional Miocene compression phase. Subaerial and coastal cliff erosion formed escarpments, up to 100 m high. Around the Miocene–Pliocene boundary the northern North Sea subsided below sea level and a layer of glauconitic sand was deposited. During the early Pleistocene glacial period, high fluid pressures fractured the regional Hordaland Group seal. Fluidized sand either vented to the sea floor or was deposited in irregular sand bodies up to 150 m thick. Above them, the injected sand lifted the overburden and formed irregular mounds that reshaped the top Hordaland Group unconformity regionally. During the glacial period the area was tilted regionally by 0.3° towards the NNE.