THE GLACIER-INFLUENCED SCORESBY SUND FAN, EAST GREENLAND CONTINENTAL-MARGIN - EVIDENCE FROM GLORIA AND 3.5 KHZ RECORDS

A major submarine fan (gradient about 2 degrees) offshore of the Score sby Sund fjord system is indicated by the crescentic shape of the shel f break. GLORIA long-range side-scan sonar imagery was obtained over a bout 20,000 km(2) of the fan along with 1000 km of 3.5 kHz records. Th ree acoustic facies were defined from GLORIA backscatter signatures an d sea-floor morphology and sediment acoustic character on 3.5 kHz reco rds. Facies 1 includes a series of acoustically transparent features ( 0.5-2 km in width), elongate downslope, with irregular surface topogra phy, 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 GLO RIA images. 3.5 kHz profiles reveal irregular former sea-floor morphol ogy, above which is a draping unit (<15 m thick). This northern region of the fan is a less active area where hemipelagic sediments and limi ted ice-rafted debris overlie older material formed by past debris-flo w activity. The more distal area of the adjacent ocean basin has a fla t floor with parallel sub-bottom reflectors of Facies 3. This facies i s 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 bloc ks in the long-term development of the Scoresby Sund Fan. Glacier-infl uenced fan volume is about 15,000+/-5000 km(3), based on seismic refle ction studies. During full glacials in East Greenland, the inland ice sheet advances to fill the Scoresby Sund fjord system and extends acro ss the shelf to reach the shelf break in some glacial cycles. Debris f lows form in areas of most rapid sediment flux. The Scoresby Sund Fan is relatively similar to the Storfjorden Fan on the eastern Polar Nort h Atlantic margin, but differs from the larger Bear Island Fan in havi ng a steeper fan gradient, much smaller debris flows and no large-scal e slides. (C) 1997 Elsevier Science B.V.