Summary

The Antarctic continental margin holds a thick Cenozoic sedimentary section that is characterized by both long-period and short-period lithostratigraphic transitions, which are seen locally in drill cores and regionally in seismic-reflection data. Age resolution is inadequate to link individual stratigraphic events, but is sufficient to make general statements about glacial history. The transitions point to the last 40 m.y. being a period of increasing glaciation and sediment distribution by glacial processes via short-period fluctuations (e.g. Milankovitch frequencies) of grounded ice sheets across the continental shelf and accompanying sea-level changes. The proximal history is generally similar to that of distal proxy records from isotopic studies in adjacent ocean basins (e.g. Zachos et al., 2001) and from stratigraphic studies on low-latitude continental margins (e.g. Miller et al., 2005, 2000). Key inferences from the Antarctic margin for the Cenozoic, based on published data and inferences from extensive seismic-reflection and limited drilling records, are:

• Although tectonic histories differ around the Antarctic margin, similar geomorphic features (e.g. overdeepened and foredeepened seafloor; broad erosional troughs, sediment fans and drift mounds) are seen everywhere on the margin, as a result of ubiquitous fluctuating glaciers eroding and distributing sediments.

• East and West Antarctic margin segments may have similar glacial histories, based on similar geomorphologies and known ages offshore for glacial strata. Current differences result partly from lack of sufficient drilling into likely Paleogene offshore sections beneath the margin.

• Seismic geometries and facies from all segments of the continental margin show evidence for up-section increases in the dynamic movement of sediment across the margin (e.g. shelf troughs, slope sediment fans, channel-levee systems) and along the margin (e.g. rise-drift deposits), reflecting increased glacial and ocean current activity from the Oligocene to the present.

• Stratal geometries of the continental shelf and slope were controlled principally by eustatic changes (with ice fluctuations) from the Paleogene to about the middle Miocene, and thereafter principally by fluctuating grounded glaciers (in tandem with sea-level changes) on the shelf, leading to the overdeepening and foredeepening of the shelf.

• Extensive prograding and aggrading of the continental shelf from the early Miocene to the latest Neogene is the principal result of sediment dispersal by ice sheets during glacial and interglacial periods at near-Milankovitch periodicities, as documented from drilling of drift deposits on the continental rise in East Antarctica (PB) and West Antarctica (AP), and from near-coastal sequences (RS).

• The principal locus of sediment deposition on the margin has shifted from the outer rise (and beyond) during the Paleogene, to the inner rise and slope in the early Miocene to early Pliocene, and to the mid slope thereafter. The depocentre shift reflects the increases in glacial activity (and increases in ocean currents) and decrease in sediment being supplied due to erosion of onshore and shelf areas.

• Specific circum-Antarctic glacial events in the evolution of the margin include: first glaciers at the coast and initiation of channel-levee systems on the rise and the Crary Fan (early Oligocene); fluctuating glaciers, initial rapid progradation of the continental shelf, and initial growth of drift mounds and large levees on the rise (early Miocene); onshore ice buildup and initial overdeepening of the continental shelves (middle Miocene); dynamic ice movements and initial widespread development of cross-shelf troughs and upper-slope fans (early Pliocene); widespread deposition of biogenic interglacial sediment in deep inner-shelf troughs (Holocene).

Additional advances in our understanding of Antarctica's glacial history and the varied effects of ice sheets on the paleoceanographic and lithostratigraphic processes of the Antarctic continental margin can only be achieved through additional offshore deep stratigraphic drilling studies, such as the current IODP, ANDRILL and SHALDRIL projects.

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