Unconformities, cosets, and folds within the east antarctic ice sheet: 3.2 MHz profiles from a megadunes region of East Antarctica

We discuss two 50-70 km profiles of unconformities, bedding sequences, and englacial folding recorded to the icebed with 3.2 MHz radar in East Antarctica. The unconformities result from localized accumulation on windward slopes that produce cosets of bedding sequences up to 150 m thick. The folding occurs across ice streams, extends more than 2600 m and nearly to the ice bed, and is both parallel and non-parallel. Parallel folding implies that slip occurred under uniform strain, and the depth of the folding shows that it occurred near or at the ice bed. Basal slip implies that the surface topography beneath which these cosets formed is spatially and long-term stabilized over large icebed depressions. Consequently, the coset depths, and the ice flow direction and estimated speed, show that they formed 100-300 km from our transect, and beneath still active accumulation zones identified within a RADARSAT image.