--> Abstract: Breakup of Gondwana: The Evolution of Sedimentary Basins of Madagascar, by C. W. Harris and I. O. Norton; #91012 (1992).

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ABSTRACT: Breakup of Gondwana: The Evolution of Sedimentary Basins of Madagascar

HARRIS, CHARLES W., and IAN O. NORTON, Exxon Production Research Company, Houston, TX

Madagascar is a small continental block bounded by steep and wide passive margins. Rift-related basins of western Madagascar contain remnants of Karoo age (Permian to Early Jurassic) deposits with significant reserves of heavy oil and asphalt. In addition, post-Karoo passive-margin siliciclastic rocks contain gas. Protracted slow rifting between East Africa and Madagascar plus India, from the Early Permian to Middle Jurassic, created extensional horsts and grabens in western Madagascar. Permian facies are glaciogenic in the south and alluvial to shallow marine in the north. They are unconformably overlain by Permian-Triassic sandstones and interbedded shales that are a potential source. Another unconformity separates these rocks from Early Jurassic alluvial to shallow marine sandstone that mark the final phase of rifting. Initiation of sea-floor spreading in the Middle to Late Jurassic resulted in southward movement of Madagascar relative to Africa along the Davie Transform fault. Phases of transpression during transcurrent motion in southwestern Madagascar resulted in local uplift, erosion, and degradation of the Karoo hydrocarbon system. Continued thermal subsidence and passive margin development is recorded by Middle Jurassic marine carbonates overlain by interbedded Cretaceous sandstones (reservoirs) and shales (source and seal). Late Cretaceous volcanism and rifting of Madagascar, Seychelles, and India interrupted sedimentation. In eastern Madagascar, a steep, narrow margin was created. It contains isolated small grabens that are filled with Upper Cretaceous, Pa eogene, and Neogene age sedimentary rocks. No hydrocarbons have been found in these basins. From the Paleogene to the present, Madagascar has been fixed to the African plate and has accumulated marine carbonate and minor siliciclastic rocks.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)