The evolution of the northwestern Barents Sea continental margin, part of a NW-SE trending mega shear zone, has been reconstructed in order to quantify the sedimentation and erosion affecting this area during and after its formation in the Paleogene-Neogene. This development was closely related to the sea-floor opening of the Norwegian-Greenland Sea. Our study incorporated 2D seismic data, well data, and information from shallow cores.During the Paleocene-Eocene, the northwesternmost Barents Sea margin was subjected to compression-transpression that led to the development of the West Spitsbergen Fold-Thrust Belt (WSFTB) and largely affected the northern part of the study area. To the south, the Vestbakken volcanic province developed in a pull-apart setting. A transition zone separates these two areas marked by a basin morphology becoming more pronounced to the south suggesting increasing subsidence and extension. Subsequently, during the Oligocene, extension and sea-floor spreading was initiated along the whole margin, resulting in the opening of the Fram Strait between Spitsbergen and NE Greenland in the Miocene.During the Paleocene, the Stappen High and a part of the NE Greenland shelf sourced sediments into the newly developing basins. The southwestern part of the WSFTB, the Stappen High, and part of the northeastern Greenland margin is interpreted as the main sediment source areas in the Eocene. During the Oligocene and Neogene, a larger part of the northwestern Barents Sea shelf is interpreted to have acted as source area including the Edgeøya platform. As a result of this development, the wider Barents Sea shelf itself is inferred to have been a lowland prior to the northern hemisphere glaciations.We found that the average sedimentation rate for the Paleogene-Neogene at the northwestern Barents Sea margin is about 0.034 m/k.y. This number is in agreement with the sedimentation 2 rate reported from present-day fluvial systems and modern rates coastal erosion. By using a mass-balance approach, we have also estimated the average net erosion and erosion rate for the Paleogene-Neogene period to be ~2440 m and 0.038 m/k.y, respectively. This erosion rate is two times higher compared to the southwestern Barents Sea margin, probably reflecting erosion of a more tectonically active northwestern margin. Thus, for the western Barents Sea margin, a general increasing trend of pre-glacial erosion northwards can be inferred. This study also suggests that more than half of the Cenozoic erosion affecting the studied part of the northwestern Barents Sea was of pre-glacial origin.
The Cenozoic pre-glacial development of the southwestern Barents Sea is discussed, with focus on the early to middle Cenozoic net erosion that was poorly constrained. From 2D and 3D seismic mapping, the western Barents Sea continental margin development shows a complex history of structural configuration of highs and basins related to the Greenland and Eurasian plate movement and subsequent seafloor spreading in the Norwegian-Greenland Sea. Our subdivision of the Sørvestsnaget Basin allows for a closer focus on the tectonostratigraphic development in an overall transtensional setting. To the west, the lower to middle Cenozoic sediments are observed to be systematically overlying the oceanic crust in the Lofoten Basin in accordance to the progressive seafloor's opening. Based on interpretation of five seismic units including sediment progradation (clinoforms) as well as lithology information from exploration wells, the paleoenvironments for the Paleocene, Eocene, Oligocene and Neogene periods were reconstructed. The mass-balance approach has then been used to quantify the corresponding erosion of the southwestern Barents Sea source area. The Stappen High, the Loppa High, and part of mainland Northern Norway are proposed as the key drainage areas covering a combined area of 191,500 to 334,000 km 2 , depending on the location of its eastern limit. Our result shows that an average net erosion of 858-1362 m and an average erosion rate of 0.014-0.021 m/k.y have characterized the Cenozoic pre-glacial period. The calculated sediment discharge is 8.7 x 10 6 t/y and the sediment yield is 26.2-45.7 t/km 2 /y. Comparison with present-day fluvial systems shows a similar rate of sediment discharge suggesting that our estimates are reasonable. The pre-glacial sedimentation rate is estimated to be 0.026-0.071 m/k.y, which is on average one order of magnitude lower than for the preceding glacial period characterizing this area.
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