Early to middle Cenozoic paleoenvironment and erosion estimates of the southwestern Barents Sea: Insights from a regional mass-balance approach

摘要

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 Sorvestsnaget 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.