A Middle to Late Miocene compression phase along the Norwegian passive margin

Abstract

A Middle to Late Miocene compression phase has been documented along the Norwegian margin from 62°N to 68°N. Reverse faults and inversion domes are numerous on the 300 to 450km wide central mid-Norwegian margin, but are only locally observed on the Møre and Lofoten margins. A major regression forced the coastline of the syn-tectonic Kai Formation 50–150km west of the present coastline and a genetic link between the regression and the smaller-scale contraction structures is observed. Long wavelength (200–300 km) lithospheric bulging is suggested to explain the coastline regression at the onset of the compression phase. The position of the regressed coastline suggests that the continent–shelf transition guides the lithospheric buckling such that the thicker crust segment is uplifted. Long wavelength folding may account for additional crustal shortening along the sharp crustal transitions on the Lofoten and Møre margins. It is suggested that the Norwegian onshore domes were formed during at least two independent stages – a Middle to late Miocene compression related uplift and later regional glacial isostatic uplift. The syn-tectonic Kai Formation fills in the depressions around the contraction-related structures and is dated as late Middle to Late Miocene. It is suggested that both the Utsira Formation and the assumed northern equivalent, the Molo Formation, were deposited after the compression event and, thus, are mainly early Pliocene in age. The Middle to Late Miocene compression phase is observed throughout the North Atlantic and the sea-level fall at the initiation and rise at the termination corresponds with significant shifts in climate.

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

“…2). Regionally, the Kai Formation of the Nordland Group (Dalland et al 1988), syntectonic to the North Atlantic Miocene compression phase, wedges out southwards north of 62°N (Løseth & Henriksen 2005). The Cenozoic Seismic Sequence (CSS)-6, located stratigraphically below the Utsira Formation (CSS-7), wedges out northwards around 58°N (Jordt et al 1995).…”

“…This suggests rapid flooding with little marine erosion during the associated transgression. Løseth & Henriksen (2005) interpreted a 400 m sea-level rise at the termination of the regional Miocene compression phase in mid-Norway and assigned it to a regional stress release. The same process could give a similar magnitude of subsidence in the northern North Sea, resulting in rapid transgression.…”

“…The initial uplift of the northern North Sea occurred simultaneously with the onset of mid-to late Miocene compression in the Norwegian Sea and west of Shetland (Ritchie et al 2003;Løseth & Henriksen 2005;Stoker et al 2005;Doré et al 2008). MiocenePliocene flooding of the North Sea is time equivalent to the end of the compression phase in the Norwegian Sea (Løseth & Henriksen 2005), the end of the Messinian salinity crisis in the Mediterranean Sea (Krijgsman et al 1999) and a global sea-level rise (Haq et al 1988).…”

“…MiocenePliocene flooding of the North Sea is time equivalent to the end of the compression phase in the Norwegian Sea (Løseth & Henriksen 2005), the end of the Messinian salinity crisis in the Mediterranean Sea (Krijgsman et al 1999) and a global sea-level rise (Haq et al 1988). However, there is surprisingly little evidence of Miocene compression in the northern North Sea compared with the tens of kilometres wide, hundreds of kilometres long and kilometres high domes west of Shetland and in the Norwegian Sea (Stoker et al 2005;Doré et al 2008).…”

“…In contrast, surprisingly little evidence has been reported of Miocene compression in the northern North Sea. A few reverse faults have been described along its northern limit in the eastern Møre Basin (Blystad et al 1995;Løseth & Henriksen 2005). Rundberg & Eidvin (2005) described a long-wavelength dome in the northern North Sea and related it to the compression phase.…”