Abstract

Stratigraphic and sedimentological data are presented from a region likely to directly record the evolution of the East Antarctic ice sheet. Along the western margin of the Lambert graben, which now drains ∼1 × 106 km2 or one-eighth of the total area of the East Antarctic ice sheet, extensive remnants of Cenozoic glaciomarine fjordal sediment, known as the Pagodroma Group, are preserved as far as several hundred kilometers inland from the open coast. The sediments resemble those produced by tidewater glaciers in the Arctic, rather than those of modern Antarctica. Four separate formations of the Pagodroma Group, spanning the interval from early Miocene (or older) to Pliocene or early Pleistocene are preserved; the oldest and highest crop out at nearly 1500 m above sea level. Each formation was deposited in close proximity to an ice margin grounded on the fjord bottom during major recessional phases of the Lambert Glacier. Underlying each formation is a glacially cut erosion surface. Each surface records a separate stage of fjord excavation when ice expanded onto the continental shelf in Prydz Bay. Evidence from offshore drilling in Prydz Bay and these data indicate fluctuations of the Lambert Glacier terminus in excess of 500 km in Neogene time, thereby reflecting large changes in the volume of the ice sheet. Depositional episodes were succeeded by phases of uplift totalling more than 1500 m.

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