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ABSTRACT: Divergent/Passive Margin Basins

John D. Edwards

Divergent/Passive Margin Basins, 1989, (J. D. Edwards and P. A. Santogrossi, eds., AAPG Memoir 48), the first of five AAPG World Petroleum Basin Memoirs, contains detailed discussions and illustrations of the geological, geophysical, and hydrocarbon content of the Campos basin, Gabon basin, Niger delta, and basins of the Northwest Shelf of Australia. Contrasting stratigraphic sequences and structural styles related to hydrocarbon habitats are emphasized. Sediment thickness ranges from 10 to 15 km in these basins. The complete set of stratigraphic sequences that may be present in divergent margin basins are pre-rift, rift, transition-early drift, and late drift. Reservoir sandstones can be high quality due to their origin as first-cycle sediments derived from proximal quar z-rich cratonal basement. The importance of rich source rocks in the rift sequence is demonstrated, as well as the source potential of paralic facies, coastal swamps, and shallow-marine environments in deltaic sequences.

All phases in the development of divergent margin basins are dominated by gravity driven extensional tectonics. A variety of structural traps in each basin are illustrated. Stratigraphic trap potential was recently demonstrated by giant Tertiary turbidite discoveries in the Campos basin.

This basin type is capable of developing and preserving source rocks, reservoir rocks, and traps during continuous burial in one tectono-stratigraphic megacycle. The prospectiveness of divergent margin basins is enhanced by these processes and by traps formed contemporaneously with sedimentation in both the rift and drift phases.

AAPG Search and Discovery Article #91001©1989-1990 AAPG Distinguished Lecture Tours 1989-1990