Late quaternary sedimentation and glacial history of the western Svalbard continental margin

Abstract

Glacigenic sediments recovered in shallow cores from the western Svalbard continental slope, are subdivided into five facies associations based on grain-size, sedimentary structure, mineralogy, petrography and geochemistry. Two diamicton facies are recognised, one of which is interpreted as hemipelagic mud with variable amounts of ice-rafted debris (IRD), and the other as a product of mass-movement. The diamictons are associated with melting of icebergs during glacial melt events and debris flow deposition on the submarine fans during peak glaciation, respectively. Laminated-to-layered mud and turbidites seem to be closely related to eustatic fall in sea level and erosion of banks located on the continental shelf, resulting in accumulation of fine-grained organic-rich deposits and thin silt- and sand layers on the continental slope. Middle Weichselian was characterised by several phases of extensive iceberg production and input of IRD. The first phase (60−55 ka) is correlated with a glacier advance on Svalbard, but the following phases (54≌44 ka) can not be correlated with glacier advances on land. This demonstrates that there may have been more glaciations than recorded on Svalbard, and that ice sheets at high northern latitudes fluctuated more frequently than previously assumed. The composition of the IRD deposited after 54 ka, suggests that the ice sheets during these advances were located in the eastern Svalbard-Barents Sea area. The Late Weichselian growth of the Svalbard-Barents Sea Ice Sheet occurred probably in two steps; Nucleation of a continental-based ice sheet between 27 and 22.5 ka, followed by a rapid advance to the shelf edge when the ice margin reached the soft, clay-rich sediments on the continental shelf. Eustatic lowering of the sea level during the initial phase led to bank exposure and erosion, bringing large quantities of fine-grained, organic-rich sediments to the deep-sea. During peak glaciation, glaciers provided a localised supply of sediments to the shelf troughs and the upper slope, which were redistributed by debris flows. The marine-based Svalbard-Barents Sea Ice Sheet started to retreat around 14.5 ka through massive iceberg discharge. The retreat was interrupted by a short-lived advance, accompanied by erosion of the shelf banks and redistribution of organic-rich sediments to the continental slope. The final ice recession started around 12 ka and ended close to 9 ka, when the fjords of Svalbard were essentially ice-free. Large amounts of meltwater released during the removal of the Svalbard-Barents Sea Ice Sheet, cooled down the surface waters of the Norwegian-Greenland Sea and formed a widespread sea-ice cover between 12 and 8 ka. Input of terrigenous material was greatly reduced during the early part of Holocene. The present interglacial is characterised by erosion of the shelf and upper slope by bottom currents, leaving a prominent lag deposit.