The present study gives evidence for three major regional paleostress fields that affected the Oslo Region: A compressional stress field with a NW–SE-directed maximum compression (σ1) has been identified as a Caledonian imprint. The most prominent regional stress field, however, is tensional, characterised by a WNW–ESE directed minimum compression (σ3), and related to the Permo-Carboniferous rifting. Later, the area was affected by a wrench regime with a roughly N–S directed σ1 and a maximum age of Permian, whereas the absolute timing of this stress field is unclear due to the lack of exposed rocks younger than Permian.
For a large number of estimated stress states, none of the principal axes are sub-vertical. These “oblique” paleostresses cannot be integrated into a common regional stress field but rather correspond to local effects of intense magmatic activity during the Permo-Carboniferous phase of rifting.
The present study tends to show that the Oslo Region remained unaffected by major tectonic activity for much of the Mesozoic and Cenozoic – which is when the Central European Basin System to the south experienced several phases of intense deformation.