Post-rift sedimentary evolution of the Gebra Debris Valley. A submarine slope failure system in the Central Bransfield Basin (Antarctica)

• An evolutive model for the Gebra Valley is proposed.
• The Gebra Valley is the result of repeated large-scale slope failures
• Different cut-and-fill features characterized the stratigraphic architecture
• The onset of the major mass-movement processes was at about 3.0 Ma

The combined analysis of paleomorphology, stratigraphy and seismic facies allows us to present new insights into the formation and evolution of the Gebra Valley, located on the lower continental slope of the Central Bransfield Basin (NE Antarctic Peninsula). Repeated large-scale slope failure events were responsible for the cut-and-fill features forming the Gebra Valley. This study revealed a mid-Pleistocene Gebra paleovalley that was progressively and completely infilled. During the last glacial cycle the infilled paleovalley was reoccupied, forming the present day Gebra Valley. Both valley incisions are genetically related to large-scale failures associated with high-energy gravity flows or mass flows. The infilling of the valley involved channelized mass flows of various dimensions and channelized and unchannelized turbidity currents. Alternating erosive periods, during which the valley evacuated sediment from the slope toward the basin, and depositional periods, during which it was fully infilled, allows it to be defined as the “Gebra Debris Valley”.Taking into account the presence of faults controlling the headwall locations and the stratigraphic correlation established with glacial periods, the genesis of the Gebra Debris Valley could have been controlled by the interplay of both the tectonic history of the Bransfield Basin and the glacial cycles that allowed grounding events to reach the upper continental slope.