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ABSTRACT: Cenozoic Evolution of the Antarctic Peninsula Continental Margin

John B. Anderson

Cenozoic evolution of the Antarctic Peninsula continental margin has involved a series of ridge (Aluk Ridge)-trench collisions between the Pacific and Antarctic plates. Subduction occurred episodically between segments of the Pacific plate that are bounded by major fracture zones. The age of ridge-trench collisions decreases from south to north along the margin. The very northern part of the margin, between the Hero and Shackleton fracture zones, has the last surviving Aluk-Antarctic spreading ridge segments and the only remaining trench topography.

The sedimentary cover on the northern margin is relatively thin, generally less than 1.5 km, thus providing a unique setting in which to examine margin evolution using high resolution seismic methods. Over 5000 km of high resolution (water gun) seismic profiles were acquired from the Antarctic Peninsula margin during four cruises to the region.

The margin is divided into discrete fracture-zone-bounded segments; each segment displays different styles of development. Highly tectonized active margin sequences have been buried beneath a seaward-thickening sediment wedge that represents the passive stage of margin development. Ice caps, which have existed in the Antarctic Peninsula region since at least the late Oligocene, have advanced onto the continental shelf on numerous occasions, eroding hundreds of meters into the shelf and depositing a thick sequence of deposits characterized by till tongues and glacial troughs. Glacial erosion has been the main factor responsible for overdeepening of the shelf; isostasy is of secondary importance.

As the shelf was lowered by glacial erosion, it was able to accommodate thicker and more unstable marine ice sheets. The shelf also became a vast reservoir for cold, saline shelf water, one of the key ingredients of Antarctic bottom water. These changes were probably reflected in the global eustatic (high-frequency low-magnitude fluctuations) and paleo-oceanographic record. The margin is presently being draped by pelagic and hemipelagic sediments and has taken on a more passive role in terms of bottom-water production and marine ice sheet grounding.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990