Natural Constraints on Exploring Antarctica's Continental Margin, Existing Geophysical and Geological Data Basis, and Proposed Drilling Program

John B. Anderson

In recent years there have been a number of multichannel seismic reflection and seismic refraction surveys of the Antarctic continental shelf. While glacial erosion has left acoustic basement exposed on portions of the inner shelf, thick sedimentary sequences occur on the passive margin of east Antarctica. The thickness and age of these strata vary due to different breakup histories of the margin. Several sedimentary basins have been identified. Most are rift basins formed during the early stages of Antarctica's separation from other Gondwana continents and plateaus.

The west Antarctic continental shelf is extensive, being approximately twice the size of the Gulf of Mexico shelf. It has been poorly surveyed to date, owing mainly to its perennial sea ice cover. Gradual subduction of the spreading center from south to north along the margin resulted in old active margin sequences being buried beneath passive margin sequences. The latter should increase in thickness from north to south along the margin although no data bear this out. Hydrocarbon potential on the northern portion of the west Antarctic margin is considered low due to a probable lack of reservoir rocks.

Establishment of ice sheets (by late Oligocene) on Antarctica caused destruction of land vegetation and greatly restricted siliciclastic sand-producing environments. So only sedimentary basins which contain pre-early Miocene deposits have good hydrocarbon prospectivity.

The Antarctic continental shelf is the deepest in the world, averaging 500 m and in places being more than a kilometer deep. The shelf has been left rugged by glacial erosion and is therefore prone to sediment mass movement. Widespread sediment gravity flow deposits attest to this. The shelf is covered with sea ice most of the year and in a few areas throughout the year. Icebergs, some tens and even hundreds of square kilometers in area, drift freely in the deep waters of the shelf; drift speeds of 1 to 2.5 km/year are not uncommon. To add to these hazards, the seas surrounding Antarctica are among the roughest and most unpredictable in the world.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.