The Quaternary evolution of the mid-Norwegian continental margin

• Main Author: Montelli, Aleksandr
• Format: Thesis
• Language: English
• Published: Apollo - University of Cambridge Repository 2019
• Subjects: Marine geophysics; Paleoceanography; Quaternary; Marine Geology; Quaternary Geology; Sedimentary Geology; Palaeoclimatology; Palaeoglaciology; Ice-sheets; Fennoscandian Ice Sheet; Glacial landforms; Geomorphology; Norwegian Sea; Vøring Plateau; Fennoscandian; Ice Sheet; north atlantic current; North Atlantic
• Online Access: https://dx.doi.org/10.17863/cam.44971; https://www.repository.cam.ac.uk/handle/1810/297917

In this thesis, high-resolution two- and three-dimensional seismic reflection datasets are used to examine the Quaternary Naust Formation on the mid-Norwegian continental shelf and slope, both at a high level of detail and over a huge areal extent of over 150,000 km2. First, the analysis of broad-scale margin architecture demonstrates the gradual development and increase in number of cross-shelf troughs produced by past ice streams that periodically drained the growing and decaying Fennoscandian Ice Sheet since approximately 1.5 M.y. ago. The development and intensification of focused ice flow from about 0.8 M.y. ago resulted in enhanced erosion on the shelf and increased sediment flux to the adjacent continental slope, with rapid shelf edge progradation and associated changes in margin architecture. The structural high of the Vøring Plateau, characterised by initially low (1-2º) slope gradients and reduced accommodation space, exerted a strong control over the long-term architectural evolution of the margin. Slope sediment fluxes were higher in the Vøring Plateau area, having increased up to 32 km3 k.y.−1 over the Quaternary compared to the maximum of 7 km3 k.y.−1 in the neighbouring sectors of the slope, which were characterised by steeper gradients (3-5º), more available accommodation space and smaller or no palaeo-ice streams on the adjacent shelves. Second, submarine glacial landforms found on the 500-km long mid-Norwegian continental shelf allow the reconstruction of the ice-sheet configuration over several Quaternary glacial–interglacial cycles. Evidence of iceberg ploughmarks found within the earliest Quaternary Naust surfaces documents a marine-terminating, calving Fennoscandian Ice Sheet margin extending periodically onto the mid-Norwegian shelf since the earliest Quaternary. Buried subglacially-produced mega-scale glacial lineations and ice-marginal grounding-zone landforms show the changing locations of fast-flowing ice streams as well as areas of slow-flowing ice, indicating dynamic ice-sheet behaviour and drainage variability on millennial timescales. The identification of the first buried glacitectonic hill-hole pair, as well as a few small channels formed both subglacially and at the margin of an ice-sheet, demonstrate complex, highly spatially and temporally variable ice-sheet subglacial thermal structure. Third, Quaternary sedimentary processes both down and along the continental slope are examined. Identification of more than 300 buried slope landforms provides a process- based palaeo-environmental reconstruction. The early Quaternary slope record (2.7-0.8 M.y. ago) is dominated by channels, indicating glacimarine sedimentation influenced by dense bottom-water flow and turbidity currents. The middle-late Quaternary (0.8-0 M.y. ago) slope succession shows a transition to dominance of glacigenic debris-flows delivered by progressively more erosive ice streams. This broad-scale palaeo-environmental shift coincides with the intensification of Northern Hemispheric glaciations, highlighting first- order climate control on the sedimentary processes on high-latitude continental slopes. In addition, individual sediment drifts found within different parts of the slope throughout the Naust Formation stratigraphy show the persistent influence of the North Atlantic Current over the Quaternary. Rapid formation of a large sediment drift (i.e., 720 km3 of accumulated sediment over the last 240 k.y.) located on the slope off Suladjupet cross-shelf trough emphasises how a combination of abundant glacially-derived sediment and its consequent delivery by alongslope processes may exert considerable influence on continental margin morphology over geologically short timescales. Finally, the Quaternary development of the North Atlantic Current is examined from evidence of past iceberg drift. Over 7,500 buried linear and curvilinear depressions interpreted as iceberg ploughmarks were identified and analysed within the Quaternary Naust Formation. The wide geographical distribution of ploughmarks suggests unrestricted iceberg drift and an open Norwegian Sea during the periods of iceberg calving since the early Quaternary. Ploughmark trajectory analysis demonstrates that the ocean current circulation, now dominated by the northeasterly flowing North Atlantic Current, has largely persisted throughout the Quaternary, with potential short-lived current reductions possibly related to major phases of iceberg discharge and/or meltwater pulses from the Fennoscandian Ice Sheet during the middle and late Quaternary. : Gates Cambridge Trust