Douglas A. Paton¹, John R. Underhill²

(1) University of Edinburgh, Edinburgh, Scotland
(2) University of Edinburgh

ABSTRACT: Controls on Conjugate Passive Margin Evolution : Insights from Seismic Stratigraphic Studies in the North Falklands Basin and South African Basins

It is generally accepted that the North Falklands Basin (NFB) was adjacent to eastern South Africa prior to Cretaceous South Atlantic opening and recent exploration in the frontier region of the NFB has for the first time enabled a detailed tectono-stratigraphic comparison between the two areas. This comparison has proved to be crucial in furthering the understanding of the evolution, and hence the hydrocarbon systems, of the southern South Atlantic. Through the identification and correlation of mega-sequences in South Africa and the NFB, the principle basin architectural styles have been determined and have revealed that there are very close similarities in the rifted geometries of the two margins. In particular both regions have basin bounding faults with overall displacements of at least 12 kms, resulting in abnormally thick sedimentary basins for their aerial extent (60 x 40 km).

Subsequent to the opening of the South Atlantic and the evolution of the conjugate passive margins, both regions underwent multiple phases of compression leading to fault reactivation (structural inversion). The tectonic styles, geometries, temporal and spatial extent, and genesis of the inversion structures are all consistent with regional tectonic events resulting from the inception, and migration of the sea-floor spreading axis in the South Atlantic. Although these inversion structures have a posititive influence on the hydrocarbon potential of the basins because they result in major trap formation, source rock maturation is arrested. However, subsequent subsidence may enable rejuvenation of source rock maturation and hydrocarbon migration in to the traps. The results from this study suggest that sea-floor spreading may play a significant role in the development of similar trap formation along passive margins basins not just in the South Atlantic margins, but in any ocean marginal setting.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado