Recent to Late Neogene Seafloor Instabilities on the Deep Pacific Margin of the Antarctic Peninsula

Valentina Volpi¹, Michele Rebesco¹, David Amblas², and Angelo Camerlenghi^2
1 OGS, Trieste, Italy
² University of Barcelona, Barcelona, Spain

The steep (13°) modern continental slope of the Pacific margin of the Antarctic Peninsula is relatively stable, not incised by canyons, showing widespread erosional gullies produced by the downward transit of the sediments delivered by ice grounded on the shelf. Conversely, a number of different kinds of instabilities affects the asymmetric sediment drifts on the continental rise. Sub-parallel gullies incising the steep SW are inferred to results from mass-wasting consequent to the progressive steepening produced by the contrast between continuous deposition on the SE side and erosion/non deposition on the SW. Larger step-like slide scars with sediment blocks inside occurring in the most proximal part of the gentle side are inferred to result from the relatively high local accumulation rate associated to base-cutting operated by the turbidity currents. Dramatic evidences of conjugate steep scarps tens of kilometres long occurs on gentle (< 1°) stratal surface in the distal parts of the sediment drifts. Conjugate sets of high angle listric faults sole out along a 600-m-deep silica diagenetic boundary with excess fluid pressure and lead to consequent downslope creeping of the above mostly under-consolidated sedimentary succession and shortening by gentle folding. In lower continental rise a late Pliocene mega debris flow deposit over 150 km long and up to 175 m thick, unique in the depositional history of the margin, is thought to have been originated by a catastrophic continental slope collapse following a major climatic change.