Late Cenozoic evolution of high-gradient trough mouth fans and canyons on the glaciated continental margin offshore Troms, northern Norway—Paleoclimatic implications and sediment yield

Abstract

Trough mouth fans contain information about the evolution of high-latitude continental margins, including rates of glacial sedimentation and hinterland erosion. Here, the late Cenozoic evolution of high-gradient trough mouth fans and canyons on the Troms margin, northern Norway, is reconstructed. Paleocanyons were active prior to the Quaternary glaciations. Glaciomarine and glaciofluvial conditions prevailed between ca. 2.7 Ma and ca. 1.5 Ma, and ice sheets possibly reached the paleo–shelf break at least once. The minimum average sedimentation rate of this period was 0.22 m/k.y. From ca. 1.5 Ma to ca. 0.7 Ma, the glaciations intensified, and fast-flowing ice streams reaching the shelf break were established in the cross-shelf troughs. Subglacial deformation till was deposited at the outer shelf and later reworked by debris flows and turbidity currents. The Fennoscandian Ice Sheet started to route much of its ice mass to the north and south of the study area, and so the Troms margin possibly was a low-ice-flow sector from this time, with a minimum average sedimentation rate of 0.15 m/k.y. During the last ca. 0.7 m.y., ice streams continued to traverse the troughs, while sluggish-flowing ice prevailed on the banks. A minimum average sedimentation rate of 0.14 m/k.y. is estimated for this period. The minimum total erosion and erosion rate for the Quaternary are 50–140 m and 0.02–0.05 m/k.y., respectively. Compared with previous studies from other areas, this implies up to one order of magnitude variation in average glacial erosion rates along the western sector of the Fennoscandian–Barents Sea ice sheets. This is interpreted to be due to the size and bedrock composition of the catchment areas and the timing of ice growth and ice-sheet dynamics. In addition, the steep preglacial continental slope promoted high sediment flow velocity for the glacigenic sediments, causing much of the debris flows to transform into turbidity currents, which efficiently transported sediments across the slope and thereby maintained its steep gradient.