Importance of Deep Structural Grain for Late Paleozoic and Mesozoic Evolution in the Fingerdjupet Subbasin to Bjarmeland Platform Region

Abstract

In this study, high resolution 3D seismic data, supplemented with regional 2D seismic lines covering the Fingerdjupet Subbasin to Bjarmeland Platform region have been interpreted. The scope of this study has been to constrain the presence, geometry and possible subsequent influence of offshore, intrabasement structures. Mapping of intrabasement reflection patterns has led to the distinction of five basement units. Seismic facies signature analysis, correlated with onshore outcrop studies on Bjørnøya and Svalbard has led the units to be interpreted to represent Precambrian basement, Caledonian extensional allochthons, a major shear zone and two units representing Devonian sedimentary deposits. A correlation to regional gravity and magnetic anomaly maps has also been performed. The Fingerdjupet Subbasin developed during Late Paleozoic on a heterogeneous crust comprising inherited structures and basins from the Caledonian orogeny and Devonian, post-orogenic extension. The Fingerdjupet Subbasin straddles a NNE-SSW striking detachment-fault, dipping ESE and recording minimum displacement of ~25 km. The detachment separates post-orogenic extension related metamorphic core complexes from a Devonian supradetachment basin holding syn-tectonic deposits. The Ringsel Ridge, bounding the Fingerdjupet Subbasin to the west, became a pronounced topographic high due to metamorphic core complex exhumation during orogenic extensional denudation. This caused a hiatus of Pennsylvanian age within the Fingerdjupet Subbasin, meanwhile carbonate and evaporite deposition occurred in, e.g., the Maud and Ottar basins on the Bjarmeland Platform. Underlying the Ringsel Ridge, a shear zone reflects post-Caledonian extensional collapse of the Caledonides. The shear zone was reactivated during Late Paleozoic and Mesozoic tectonic events; it governed structural styles, through exerting control on the western boundary of the Late Paleozoic Maud Basin and the establishment of the Randi Fault Set between the Fingerdjupet Subbasin and the Bjarmeland Platform. The findings of this study further challenge existing interpretations of magnetic anomalies on the Barents Shelf. Seismic analysis indicates various magnetic sources within basement contributing to the present magnetic anomaly response.