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ABSTRACT: Sedimentary Sequences of the Pacific-Indian Ocean Sector of the Antarctic Continental Margin

Alan Cooper, Steve Eittreim, John Anderson, Howard Stagg

Seismic-reflection data across the Pacific-Indian Ocean sector of the Antarctic continental margin commonly reveal preglacial and glacial sedimentary sections up to 14 km thick. In this sector, diverse tectonic regimes have controlled the locations of preglacial riftdeposits as well as glacial-till deltas. These regimes include major rift embayments (Prydz Bay and Ross Sea), passive margins (Prydz Bay to Marie Byrd Land), formerly active and presently active margins (Marie Byrd Land to Antarctic Peninsula), and active rifts (Western Ross Sea and Bransfield Straits).

The sedimentary sections are principally of Mesozoic and Cenozoic age, although Paleozoic strata may exist at great depth. The upper parts of these sections commonly comprise prograding and aggrading sigmoidal sequences that are separated by unconformities and are up

to 6 km thick. Where drilled in Prydz Bay and the Ross Sea, these upper sequences are solely glacial marine rocks of early Oligocene and younger age. The lower portions of the sections are commonly well-layered sequences (up to 8 km thick) that infill structural basins. The lower sequences have not been sampled by drilling but are likely syn-rift and post-rift sedimentary and volcanic rocks mostly of Paleogene and older age.

The evolution of these sedimentary sequences is strongly controlled by extensional tectonic processes. Depocenters are located primarily within rift structures that formed initially during Gondwana breakup and later during magmatic-arc development (Marie Byrd Land to Antarctic Peninsula). Rift-related deposits (mostly preglacial) fill the basement grabens and are unconformably covered by glacial-till deltas. The till deltas apparently have been deposited beneath and at the front of former grounded ice sheets that selectively moved through rift embayments (Prydz Bay, Ross Sea) and over thermally subsiding margins (Wilkes Land, Antarctic Peninsula). Since initial Cenozoic glaciation, these thick till deltas have prograded the continental shelf edge up to 70 km seaward to its present loc tion.

The sedimentary sequences underlying the Antarctic margin hold a record of Antarctic (Gondwana) rifting and glaciation--a record that would, if drilled, greatly improve our understanding of global climate and sea-level changes.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990