Timanian fold-and-thrust system and Caledonian overprint in the Loppa High, Norwegian Barents Sea

Abstract

The western Norwegian Barents Sea is located between northern Norway in the south and the Svalbard Archipelago in the north, and consists of a series of late Paleozoic–Cenozoic basins and highs formed on top of Precambrian–lower Paleozoic basement rocks. Among these, the Loppa High is an elongated, N–S-trending structural element partly bounded by post-Caledonian brittle faults. The Loppa High is cored by basement rocks forming a N–S-trending ridge. The late Paleozoic–Cenozoic tectonic history of the Loppa High is relatively well studied and is recorded by thick, overlying and adjacent sedimentary successions deposited during various episodes of post-Caledonian subsidence and tectonic extension. The earlier history of the high is much less understood, mostly because seismic data resolution does not allow accurate mapping of intra-basement reflections and because of the scarcity of exploration wells penetrating basement rocks. A new 3D seismic attribute analysis and spectral decomposition have proven to be an excellent tool for basement characterization, helping to identify and delineate intra-basement geometries. The study reveals the presence of a 40–50 km wide system of E–W folds and thrusts, including a major, 4–5 km thick, top-southwest shear zone. These structures are reworked (folded) by a system of less developed N–S folds and thrusts with top-west vergence, which parallel inferred Caledonian trends in the Barents Sea and adjacent onshore area like Bjørnøya. Since the E–W-trending system of folds and thrusts is orthogonal to and is reworked by Caledonian structures, we propose that it formed earlier, most likely in the latest Neoproterozoic during the Timanian Orogeny. In addition, post-Caledonian brittle faults appear to localize along and merge with inherited Timanian structures at depth, thus suggesting repeated partial reactivation/overprint of Timanian structures in the Phanerozoic and a strong influence of these on subsequent faults and basins. Other major implications of this work include (1) the accretion of the Loppa High and the western Barents Sea to northern Baltica (at least) in the latest Neoproterozoic, (2) the location of the Caledonian suture west of the Loppa High, (3) the location of the Timanian suture south of or on the southern edge of the Loppa High.