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Abstract

During the 1987 United States Antarctic Program-Polar Duke Cruise, 3200 kilometers of seismic reflection profiles were collected on the northern Antarctic Peninsula shelf. These data, plus the results of land-based studies (from Polish and U.S. scientists) and ocean drilling (DSDP Leg 35) were used to reconstruct the tectonic and climatic development of the shelf and to assess possible hydrocarbon prospects of the region.

The study area consists of a foredeepened shelf, typical of the Antarctic continental shelf. The continental margin has evolved from an active margin to a tectonically passive one as the Aluk Ridge was gradually subducted at the Antarctic Plate Boundary. This transition was diachronous, as the timing of ridge subduction proceeded from south to north (oldest to youngest). Thus, the shelf is segmented both tectonically and sedimentologically as the extent of tectonic deformation and post-tectonic sedimentation varies correspondingly.

Besides the obvious tectonic controls, major changes in shelf sedimentation also took place due to climatic changes during the Ceno- zoic. Antarctica is unique in that as its climate cooled and ice sheets formed, the source of terrigenous organic carbon to the shelf was completely eliminated. Also, streams and rivers were gradually eliminated (by early Neogene) so that running water was no longer contributing to the transport of terrigenous sediments to the shelf. The shelf was later overdeepened by glacial erosion (middle Miocene?). By the late Miocene there was an intensification of oceanic circulation and an increase in the flux of organic-rich, siliceous biogenic sediments to the continental margin.

Seismic records show four sequences reflecting different episodes of shelf development. Sequence 4, the oldest sequence, consists of folded and faulted pretectonic and syntectonic (subduction) deposits, presumably volcaniclastic material deposited as subduction occurred. Sequence 3 is an accretionary sequence unconformably overlying S4 and reflecting efficient sediment transport across the shelf after subduction ceased. Sequence 2 rests unconformably on Sequence 3 and is interpreted as glacial deposits that are bounded by erosional surfaces. This sequence marks the onset of glaciation sufficient to overdeepen the shelf. Sequence 1 is believed to consist of glacial-marine deposits.

The hydrocarbon potential for that portion of the continental shelf situated north of the Tula Fracture Zone is low, but is slightly higher for that portion of the shelf situated south of the Tula Fracture Zone. This is because the age and thickness of sedimentary deposits increases to the south, and the time window for formation and burial of suitable source and reservoir rocks increases in that direction. Sequence 4 is believed to include carbonaceous marine shales deposited when the climate was temperate and is considered to be the most likely hydrocarbon source, at least south of the Anvers Fracture Zone. The siliciclastic deposits of Sequence 3 are the most probable reservoir rocks.

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