Major Neogene fluctuations of the East Antarctic ice sheet: Stratigraphic evidence from the Lambert Glacier region

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 similar to 1 x 10(6 ) km(2) or one-eighth of the total area of the East Antarctic ice sheet, ex tensive remnants of Cenozoic glaciomarine fjordal sediment, known as the Pa godroma Group, are preserved as far as several hundred kilometers inland fr om the open coast. The sediments resemble those produced by tidewater glaci ers in the Arctic, rather than those of modern Antarctica. Four separate fo rmations of the Pagodroma Group, spanning the interval from early Miocene ( or older) to Pliocene or early Pleistocene are preserved; the oldest and hi ghest crop out at nearly 1500 m above sea level. Each formation was deposit ed 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 o f fjord excavation when ice expanded onto the continental shelf in Prydz Ba y. Evidence from offshore drilling in Prydz Bag and these data indicate flu ctuations of the Lambert Glacier terminus in excess of 500 km in Neogene ti me, thereby reflecting large changes in the volume of the ice sheet. Deposi tional episodes were succeeded by phases of uplift totalling more than 1500 m.