The glacier-influenced Scoresby Sund Fan, East Greenland continental margin: evidence from GLORIA and 3.5 kHz records

Abstract

A major submarine fan (gradient about 2 °) offshore of the Scoresby Sund fjord system is indicated by the crescentic shape of the shelf break. GLORIA long-range side-scan sonar imagery was obtained over about 20,000 km 2 of the fan along with 1000 km of 3.5 kHz records. Three acoustic facies were defined from GLORIA backscatter signatures and sea-floor morphology and sediment acoustic character on 3.5 kHz records. Facies 1 includes a series of acoustically transparent features (0.5–2 km in width), elongate downslope, with irregular surface topography, which are interpreted as debris flows. This makes up the bulk of relatively recent sedimentation on the upper fan. Diamictic sediments in a core support a debris-flow origin. Facies 2 is featureless on GLORIA images. 3.5 kHz profiles reveal irregular former sea-floor morphology, above which is a draping unit (< 15 m thick). This northern region of the fan is a less active area where hemipelagic sediments and limited ice-rafted debris overlie older material formed by past debris-flow activity. The more distal area of the adjacent ocean basin has a flat floor with parallel sub-bottom reflectors of Facies 3. This facies is probably an area of low-energy hemipelagic sedimentation, punctuated by occasional ice rafting and turbidity current activity. The debris flows interpreted from GLORIA and 3.5 kHz data are basic building blocks in the long-term development of the Scoresby Sund Fan. Glacier-influenced fan volume is about 15,000 ± 5000 km 3, based on seismic reflection studies. During full glacials in East Greenland, the inland ice sheet advances to fill the Scoresby Sund fjord system and extends across the shelf to reach the shelf break in some glacial cycles. Debris flows form in areas of most rapid sediment flux. The Scoresby Sund Fan is relatively similar to the Storfjorden Fan on the eastern Polar North Atlantic margin, but differs from the larger Bear Island Fan in having a steeper fan gradient, much smaller debris flows and no large-scale slides.