--> Abstract: Offshore Benin, a Classic Passive Margin, by J. M. P. Mathalone; #91004 (1991)

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Offshore Benin, a Classic Passive Margin

MATHALONE, JEREMY M. P., International Petroleum Ltd, Dubai, United Arab Emirates

Offshore Benin comprises a narrow east-west continental shelf, some 30 km wide. A sharp shelf break running parallel to the coast borders the shelf, whereupon water depths rapidly increase to over 7000 ft.

The area lies within the Dahomey Embayment, one of a series of Cretaceous and younger basins lining the coast of Africa that owe their inception to the Late Mesozoic break-up of the Gondwanaland Continent. The basin extends some 100 km inland, but sedimentary section is thin onshore compared to a maximum of 20,000 ft of sediment offshore.

Initial sedimentation in this basin was of Neocomian alluvial and lacustrine clastics. These were deposited in east-west-trending narrow half-grabens associated with the initial break up of the South American and African continents. They are covered unconformably by more extensive Albian and Cenomanian transgressive clastics and shallow marine Turonian sandstones which are the main reservoir at Seme, Benin's only oilfield.

The Senonian section offshore comprises passive margin deep sea clastic sediments prograding southwards. Very large proximal deep sea channels up to 2500 ft thick are developed in this interval.

These channels are associated with excellent petroleum source rocks, averaging 4-5% oil-prone organic carbon, and form the main exploration target in the area when configured in a trap morphology.

Seismic data quality is excellent in the region allowing detailed examination of the relationships between the rifted section and later units. In addition, these data illustrate clearly both internal and external morphology of the Senonian proximal deep sea channels.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)