Models for Evolution of Weddell Basin

John L. Labrecque

The evolution of the Weddell basin constitutes the keystone for Gondwana reconstructions. During the last decade major exploration efforts including marine and aerogeophysical surveys and OPD drilling have been directed toward the evolution of the Weddell sector. As a result of these efforts, we can now show that the Weddell basin formed as the result of the relative motion between East and West Antarctica, South America, and Africa.

Both paleomagnetic and marine geophysical data support a reconstruction in which West Antarctica has undergone nearly 90° of clockwise rotation. Magnetic anomalies reveal both sea-floor spreading and fracture zone lineations which can be used to constrain this motion since Gondwana breakup in the Jurassic.

The basement of the Weddell was formed at the southern flank of the America-Antarctica spreading system since the Jurassic. The northern flank of the spreading system was subducted beneath the Scotia Sea and the southern Andes since the Late Cretaceous. The eastern and western boundaries of the basin were developed as transcurrent faults, while the southern margin appears to have been an extensional margin.

The Weddell basin is heavily sedimented with well over 3 km of sediment along the southern margin. While little to no seismic data have been gathered for the southern and western portions of the basin, profiles along the eastern margins show extensive erosion. Sedimentation within the basin appears to have been dominated by turbiditic deposition since formation.

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