Sediment Dynamics of Megaslides along the Svalbard continental Margin and the Relation to paleoenvironmental Changes and Climate History

Abstract

With increasing interest in slope stability issues on continental shelves the causes and trigger mechanism of submarine slides get more and more into the scientific focus. Within the ESF EUROMARGINS project 'Slope Stabilities on Europe's passive continental Margin' (SPACOMA) sediment dynamics of megaslides along the passive continental margin north of Svalbard have been investigated. The study concentrated on identification and sedimentological characterisation of megafailure events, their dating and interpretation in relation to paleoceanography and climate history of the Svalbard archipelago.Integrated interpretation of multibeam bathymetric, sediment-penetrating acoustic (PARASOUND) and seismic data shows a multiple slope failure on the northern European continental margin, north of Spitsbergen. One huge submarine slide has been identified which was first described by Cherkis et al. (1999) - the Yermak Slide (later named Hinlopen/Yermak Megaslide).The extent of the Hinlopen/Yermak Megaslide has been revised based on new acoustic and detailed bathymetric data. Details from the side's internal structure give evidence for one main slide event followed by repeated minor events. The first slide event occurred during MIS 3 around 30 cal. kyr. BP and was characterised by highly dynamic and rapid evacuation of ca. 1.250 kmà ³ of sediment from the lower to the upper part of the shelf slope. During this megaslide event, headwalls up to 1600 m have been created and ca. 1150 kmà ³ material from hemipelagic sediments and from the lower preexisting trough mouth fan has been entrained and transported into the semi-enclosed Sophia Basin. This megaslide was followed by a secondary evacuation of debris material to the Nansen Basin accomplished by funnelling of the debris through the Littke Channel between Polarstern Seamount and the adjacent continental slope. The main slide debris is overlain by a set of fining-upwards sequences as evidence for the associated suspension cloud and following minor failure events. Subsequent adjustment of the eastern headwalls led to failure of rather soft sediments and creation of smaller debris flows that followed the main slide superficial topography. Discharge of the Hinlopen ice stream during the Last Glacial Maximum and the following deglaciation draped the central headwalls and created a new trough mouth fan (TMF) deposit of glacigenic debris flows south of the remnants of the original (now abandoned) TMF.The true geometry, with an affected area of at least 10,000 km2 and more than 2400 km3 involved sedimentary material, puts the Hinlopen/Yermak Megaslide among the largest exposed submarine slides worldwide, comparable to the Storegga Slide off central Norway. The side's geometry and internal physical appearance point to a tectonically induced partial shelf collapse.The timing of the Hinlopen/Yermak Megaslide around 30 cal. kyr. BP coincides with the transition of the Kapp Ekholm Interstadial into Glaciation G of Svalbard (Mangerud et al., 1998) and the buildup phase of the Svalbard-Barents Sea Ice Sheet. Thus, the slide occurred during a period of falling sea level, increasing ice volume and, presumably, increasing glaciotectonic activity. Following a detailed assessment of the paleoenvironmental conditions as well as possible trigger mechanisms of the Hinlopen/Yermak Megaslide, including paleo-sealevel, paleoceanographic circulation, glacial processes, tectonics and earthquakes, it is concluded that the Hinlopen/Yermak Megaslide has been the consequence of the rapid onset of Late Weichselian glaciation resulting in a drastic sealevel drop, asymmetrical ice loading and a fore bulge development. As the final trigger we assume a strong earthquake positionedbelow or close to the SE-Sophia Basin.