Glacial Sequence Stratigraphy and Channel Evolution in the Yakutat Margin, Southeastern Gulf of Alaska

The sedimentary records in the southeastern Gulf of Alaska provide clue to the past glacial dynamics and its complex climate-tectonics interaction. One way to understand the past glacial dynamics is through a systematic analysis of glacimarine sequences and their systems tracts. In this regard, a Glacial Sequence Stratigraphic Model was used to understand the evolution of the Yakutat margin. Using multi-resolution seismic reflection dataset, eight glacimarine sequences, labeled as YK-1 through YK-8, are interpreted as having formed during the major Milankovitch-driven glacial expansions. In a seismic section, an ideal sequence package is identified by a lower and upper glacial erosional or bounding surfaces and an internal upward succession of ice-retreat and ice-distal sediments. Our analysis shows that only the younger three sequences preserve retreat and ice-distal sediments while the older sequences only resolve retreat episodes. The younger sequences are carved by major glaciated troughs whereas sequences older than YK-3 lack cross-shelf troughs which indicates the dynamics shifted from older sheet like to younger ice-streaming behavior. Near the Yakutat Bay mouth, a multitude of buried valley features with variable size, morphology, and internal facies are present. Some channels are associated with the glacial bounding surfaces and are formed by subglacial erosional process whereas some channels in the older sequences are formed within ice-retreat packages suggesting proglacial erosion process as their origin. Systematic comparisons of the different formation mechanisms suggest that these channels are associated with sediment gravity flow and thus are interpreted as turbidity channels. The analysis of the shelf architecture reveals that the sequence geometry varies from aggradational to progradational temporally and spatially, and is controlled primarily by tectonics and secondarily by ice-dynamics. A tentative and visual correlation of the chronology of sequence packages was made with the global oxygen isotope curve which indicates that the major shelf-wide glaciations would have started during the Mid-Pleistocene period. The shift in ice-streaming behavior from the older to younger sequences does not seem to correlate directly with the Mid-Pleistocene Climate Transition.