A Challenging Regional Model for the Pre-Permian Basins Architecture of the Western Barents Sea

Laurent Gernigon, Marco Brönner, and Odleiv Olesen
Continental shelf geophysics, Geological Survey of Norway (NGU), Trondheim, Norway.

The post-Caledonides tectonic history of the Western Barents Sea is mostly dominated by extensional tectonics. Evidence for early rift episodes has been documented in the Late Paleozoic and renewed rifting episodes in the mid-Carboniferous were associated with a change to a more arid climate. During this period and until Early Permian, most of the grabens of the Western Barents Sea area were sites of extensive salt deposition. Mobilisation of Paleozoic salt began in the Early Triassic and since then the diapirs have undergone several phases of development.

The architecture of the Mesozoic grabens and associated platform in the Western Barents Sea is presently relatively well constrained. However, the geometry and regional architecture of the deep pre-Permian basins still remain unclear. North of the Finnmark Platform, thick Paleozoic basins such as the Ottar and Maud basins have earlier been identified on seismics. The presence of deeply buried salt pillows also suggests that the pre-Permian saliferous basins may also extend towards the north underneath the thick Triassic-Jurassic Platform recognised on the Bjarmeland Platform.
Long-believed interpretations suggest that these deep Paleozoic basins are almost sub-parallel to the Mesozoic grabens system and may extend over most of the Western Barents Sea and follow a dominant NE-SW to NNE-SSW regional trend. In light of two new aeromagnetic surveys (BAS-06 and BASAR-08) combined with gravity and seismics, we challenge this interpretation and propose a different tectonic model for the pre-Permian basin development. The new surveys confirm most of the previous structural elements but new features appear and illustrate the complexity of the basement architecture. We propose a tectonic scenario in which the Caledonian nappes initially swung from a NE-SW trend close to Varanger Peninsula to NW-SE across the Nordkapp Basin and the Bjarmeland Platform. The magnetics correlate perfectly with the onshore structures and easily explain the formation of the transfer zones that segment the Nordkapp Basin offshore. On the Bjarmeland Platform, the dominant magnetic grain is clearly NNW-SSE. We show that this pattern reflects a regional pre-Permian system involving several Caledonian thrust sheets that collapsed and controlled the Post-Caledonian Paleozoic rift development of the West Barents Sea during Paleozoic time. Contrary to the previous models, we believe that the pre-Permian basins have dominantly a NNW-SSE orientation in most of the Bjarmeland Platform and we do not see magnetic evidences that could support the long-established NE-SW or NNE-SSW regional trends previously proposed for the Paleozoic rift system. The data acquisition was financed by Det norske oljeselskap, Eni Norge, the Geological Survey of Norway, the Petroleum Directorate and Statoil.

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