Glaciomarine sedimentation in a modern fjord environment, Spitsbergen

Abstract

By means of high resolution acoustic profiling and correlation of echo character and sediment lithology, fjords in western and northern Spitsbergen are shown to be blanketed by a 5-20 m layer of acoustically transparent sediments consisting mainly of soft homogeneous mud with ice rafted clasts. Acoustically semi-transparent material is found on slopes and sills reflecting their coarser composition. The areal average depositional rate in the outer fjord is in the range of from 0.1 to l.Omm/year, increasing towards the glaciers. In Kongsfjorden, 5&100mm/year of muddy sediments is deposited at a distance of lOkm from the calving Kongsvegen glacier. Close to the ice front (4. 5 km) coarser grained, interbedded (sanqmud) sediments are deposited. The main sediment sources are from settlement out of the turbid surface sediment plume, combined with various types of gravity flow (sediment creep, minor slides, and slumping). Material deposited from turbidity current is probably of minor importance. On shallow sills the sediments are remobilized by icebergs. The sediment adjacent to the ice front is reworked and compacted during surges, a common form of glacial advance for Spitsbergen glaciers. During the surge considerable amounts of coarse-grained sediment are deposited by meltwater in front of the ice margin.

Submarine landform assemblages and sedimentary processes related to glacier surging in Kongsfjorden, Svalbard

“…This is in accordance with similar findings from Elverhøi et al [17,18]. Ice rafting probably occurred mainly from icebergs, but some contribution by sea ice is likely.…”

“…6), and numerous glacier advances occurred, it is likely that the sediments are either bedrock or glacigenic sediments (cf. [32]), the latter possibly representing glacitectonite (sensu [27]) or subglacial till (see also [18]). From its onlapping character, its wedge-like shape and its close association with distal moraine slopes we infer that Facies 3 represents the debris lobes described in section ''Large transverse ridges and lobe-shaped deposits: terminal moraines and debris lobes''.…”

“…The variable thickness of Facies 1 is probably related to the distance from the ice margin: in ice-proximal areas sedimentation rates are usually high, whereas they decrease exponentially with increasing distance from the glacier margin (e.g. [18]). We infer the bottom reflector of Facies 1 to represent the surge surface of 1948, and the bottom reflector of Facies 2 to represent the surge surface from 1869, when Kronebreen surged (cf.…”

“…We infer the bottom reflector of Facies 1 to represent the surge surface of 1948, and the bottom reflector of Facies 2 to represent the surge surface from 1869, when Kronebreen surged (cf. [18,35]). The increased thicknesses of Facies 1 and 2 in bathymetric depressions might indicate elevated sediment input from the surrounding slopes.…”

“…As exceptionally high discharge of turbid meltwater is common during and immediately after glacier surges (e.g. [6,18,34]), a former SAR of about 30 cm a À1 at the core site seems reasonable. Such high accumulation rates are also in accordance with the low number of IRD in lithological Unit 3, which was linked to high input of fine-grained material from meltwater plumes, masking the contribution of IRD (see section ''Sedimentology'').…”