Plate Tectonics and Tectonic Inversion in the Barents Sea

Roy H. Gabrielsen¹, Jan Inge Faleide¹, Christophe Pascal², and Trond H. Torsvik^3
1Department of Geosciences, University of Oslo, Olso, Norway.
²PGP, University of Oslo, Oslo, Norway.
³Geological Survey of Norway, Trondheim, Norway.

The Barents Sea constitutes an epicontinental platform that includes a number of separate basins of contrasting structural configuration, structural trends and structural histories. The basins are separated by deep-seated faults, structural highs and subplatforms. The most significant events that have affected the Barents Sea area since the Neoproterozoic are the Timanian (ca. 550 Ma), Caledonian (Silurian), Uralian (Late Carboniferous-Permian) and Byrrangian/Taimyrian (Late Triassic-Early Jurassic) orogenies. The structural grain generated through these orogenies is superimposed by the effect of the Atlantic rifting/strike-slip faulting and spreading in the west, and opening of the Arctic Ocean to the north. All these events have contributed to the activation or reactivation of the deep-seated (basement-involved) zones of weakness to different degrees. Thus, although the Barents Sea in many ways has been remarkably stable since the Palaeozoic, it has been delineated by tectonically active zones throughout its geological history. This is reflected in multiple stages of basin subsidence, reactivation, occasional tectonic inversion of fault systems and mild contraction (folding) of regional significance. As seen in this perspective, although subordinate episodes of tectonic inversion are documented, the western Barents Sea was dominated by E-W-oriented extension from the late Permian to the early Cenozoic, which must be accounted for in palaeogeographic reconstructions.

The late Cretaceous - Palaeocene rifting followed by Eocene seafloor spreading in the North Atlantic was connected through the de Geer mega-shear along the western Barents Sea margin. In this process, dextral shear dominated in the earliest stage, changing to spreading and a passive margin configuration in the Oligocene - Miocene. The shear margin was characterized by an irregular, right-stepping geometry where a system of pull-apart basins developed. In the northern continuation of this system the West Spitsbergen fold-and-thrust belt was generated by strain partitioning inside the dextral shear zone. This configuration also opened for an inhomogeneous, diachronous development with shifting principal stress situations characterizing the different segments at any time. The diachroneity became further exaggerated by the movement that was initiated in the SSE and spreading northwards through time. This also implies that rotated fault blocks generated in the pre-rift stages became affected by inversion, particularly focused in the master faults delineating larger fault blocks. Simultaneously, varying geometry and orientation of fault systems situated inboard of the plate margin caused contrasting response and hence, varying conditions of reactivation. A scaled numerical model is generated to investigate these contrasts.

After break-up, the spreading direction was NNW-SSE, switching to WNW-ESE at chron A13 time (33 Ma). During the spreading stage relief associated with the system of rotated fault blocks and exhumed inverted faults became passively filled by sediments and subsequently overstepped by glacial sediments derived from the Scandinavian mainland and dumped in the deep Atlantic and Arctic oceans. The present stress situation recorded offshore northernmost Norway is very homogeneous NW-SE-oriented compressive, and believed to be a ridge-push related stress system.

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.