The Gebra Slide: A Late Quaternary large-scale sliding event along the Trinity Peninsula Margin, Antarctic Peninsula

• Main Authors: Imbo, Y., De Batist, M., Baraza, J., Canals, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2001
• Subjects: Antarctic; Antarctic Peninsula; Barents Sea; Canada; Greenland; Norwegian Sea; Svalbard; The Antarctic; Trinity Peninsula; Antarc*; Ice cap; Ice Sheet
• Online Access: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=210159

Numerous studies illustrate that high-latitude, ice-sheetdominated, continental margins are more prone to largescale mass-movements than lower-latitude margins. Major slope instabilities are well-documented along the northern hemisphere, glacial margins of the Norwegian Sea (e.g.Storegga Slide) and the Svalbard-Barents Sea and of Greenland and eastern Canada. However, similar slopeinstabilities along the Antarctic Margins seem to be much more scarce. Here, we present the first detailed analysis of a Late Quaternary slide along an Antarctic margin.The Gebra Slide is situated along the Trinity Peninsula margin in the Central Bransfield Basin, Antarctic Peninsula. The slide scarp, clearly revealed by multibeam bathymetric data, extends over a length of about 30 km, from 1500 to 2000 m of water depth on the lower slope, well below the slope break which is here at about 750 m. The head of the slide is formed by an amphitheatre-shaped set of scarps with an elevation of 100 m. Further upslope, but still detached from the slope break, a second less-developed set of scarps suggests a multi-stage retrogressive mass-wasting process. The slide scarp area covers about 230 km 2 .Seismic reflection (airgun) profiles show that the associated deposit covers about 315 km 2 of the western King George basin. Its typical acoustically transparent to chaotic seismic facies suggests it is essentially a debris flow deposit. The deposit is draped by the recentmost hemipelagic sedimentary unit. According to seismic-stratigraphic correlations, we put the age of the main sliding event at about 13.500 a B.P., around the last deglaciation in this part of the Antarctic (Banfield et al., 1995). The volume of this debris flow (21 km 3 ) agrees very well with the disappeared volume higher on the slope.Although the Gebra Slide is positioned in front of a glacial trough with a higher sedimentary input, the sedimentation rates during both the present interglacial and the last glacial maximum - estimated as 0.24 cm/yr and 3.4 cm/yr, respectively, based on sediment cores and seismic stratigraphy - are too low for significant build-ups of excess pore pressure to develop in the sedimentary column. The position of the main scarp on water depths of 1500 m is far below the maximum grounding depth of the Antarctic Peninsula ice sheet (about 1000 m), excluding a possible triggering by loading/unloading of an advancing/retreating ice cap as a possible cause. No deep faulting in the underlying basement is observed on the seismic profiles, which also rules out a purely tectonic control. On the other hand, triggering by an earthquake in the volcanically and seismically active Bransfield Basin should not be excluded. Therefore, we propose that only an interaction between all above processes - in space and time - could have lead to the triggering of the Gebra Slide.