Abstract:
Present-day seafloor morphology and sediment distribution in the deep-water Surveyor Fan, Gulf of Alaska, is dominated by the >700-km-long Surveyor Channel, an anomaly in a system with no major fluvial input or shelf canyons. The sediment supply instead has been provided by glacial erosion in the still-active Chugach-St. Elias orogen, and glacial transport across the shelf. Glaciation has periodically increased in the St. Elias Range since the Miocene, but began dominating erosion and spurred enhanced exhumation since the mid-Pleistocene transition, at approximately 1 Ma. Ice associated with this glacial intensification carved cross-shelf sea valleys that connect the St. Elias Range to the Surveyor Fan. The direct deposition of newly increased terrigenous sediment flux into the fan triggered the formation of the Surveyor Channel and its growth across the Surveyor Fan. Through the formation of the Surveyor Channel, climate events created three major differentiable sequences across the Surveyor Fan that we mapped using seismic-reflection profiles. The change in morphology observed throughout the sequences allows us to characterize the influence that a glaciated orogen can have in shaping margin processes and the sediment pathway from source to sink. We show that the large variation in sediment flux between glacial-interglacial cycles together with sea valley formation leads to a glacial shelf transport process not typical of a fluvial system. This glacial shelf transport along with the channel terminus in the Aleutian Trench makes the Surveyor Fan and Channel morphologically one of the most unique systems in the world.