Abstract

Sirius Group tillite near the summit of Mount Feather, Transantarctic Mountains, is critically located for reconstructing past behavior of the East Antarctic Ice Sheet. New ice-direction indicators and tillite geometry show that the tillite accumulated beneath wet-based ice on a transverse paleovalley floor—a hanging remnant of a landscape largely removed by erosion. We conclude that the Mount Feather tillite formed primarily by lodgment as part of an ancient, wet-based, outlet glacier system when the Transantarctic Mountains were at least 1500 m lower than today. Till deposition took place before 20 Ma on the basis of estimated past uplift rates.

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