Sedimentary Records of Shelf Edge Glaciation: A Young Trough-Mouth Fan on the Gulf of Alaska Yakutat Margin

Abstract:

The St. Elias Mountains in Southeastern Alaska are an active orogen that host temperate marine glaciers. Here, ice streams advancing across the continental shelf during glacial periods create wide shelf-crossing troughs and deliver large sediment volumes directly to the shelf edge, and from there to the continental slope and the deep sea Surveyor Fan. The continental slope exhibits steep morphology (~10°-30°), controlled by the Transition Fault, a transform boundary between the Yakutat micro-plate and the Pacific plate. Prior statistical analysis of continental slope morphology indicates that these steep initial slope conditions have been modified by proximal sedimentation during repeated glacial advances. Downslope of the Yakutat Sea Valley an incipient trough-mouth fan exists while between the troughs and downslope of the Alsek Sea Valley sediment slope-bypass dominates. Seismic analysis indicates that the Yakutat margin has seen significant slope sedimentation since the intensification of northern hemisphere glaciation ~2.6 Ma, but it is only recently that sufficient sediment supply has existed to overwhelm the steep margin topography and form the young trough-mouth fan. The mid-Pleistocene climate transition at ~1 Ma, and its associated shift from 41Kyr to 100Kyr glacial-interglacial climate cycles, could have potentially allowed sustained ice stream advances to the shelf edge and associated high proximal sedimentation on the continental slope. Integration of seismic data and newly obtained age constraints from recent IODP cores allows for investigation into the timing of Yakutat trough-mouth fan sedimentation and its relation to climate transitions.