--> Abstract: Stratigraphy, Paleogeography, and Source Potential of Lower Cretaceous Strata in Central African Rift Basins: Comparison to the South Atlantic, by R. Cunningham, M. G. Watson, and J. E. Neal; #90933 (1998).
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Abstract: Stratigraphy, Paleogeography, and Source Potential of Lower Cretaceous Strata in Central African Rift Basins: Comparison to the South Atlantic

Cunningham, R. and Watson, M. G. - Exxon Exploration Company; Previous HitNealTop, J. E. - Exxon Production Research Company

Lacustrine source beds within thick, non-marine, syn-rift fill have charged prolific hydrocarbon systems in the basins of the Central African (CAS) and South Atlantic (SAS) rift systems. Both rifts are attributed to the breakup of Gondwana. But, whereas SAS progressed to seafloor spreading, thereby adding thick Late Cretaceous and Tertiary drift deposits and additional hydrocarbon systems, CAS aborted in the aulocogenic stage.

The richest source beds within CAS basins of southern Chad (Doba, Doseo, Bongor, and Salamat) occur in the rift-sag transition phase of Aptian to Lower Albian age. Lacustrine shales enriched with mixtures of Type I/II kerogen occur in each basin. The content of Type III kerogen is related to proximity to deltas and fluvial systems located where the rift framework created axial and lateral drainage networks. Basin architecture, single graben in Doseo versus multiple half-graben geometry in the other CAS basins, sets the Doseo basin apart in terms of paleo-lake physiography and hydrology. Greater gross shale and individual shale bed thicknesses plus sedimentary features suggestive of perennial stratification and anoxic conditions indicate the Doseo basin contained a large, deep, long-lived lake. Generally, ephemeral lakes with more oxygenated waters occurred elsewhere in CAS.

The rich lacustrine source beds in CAS are younger than their pre-Aptian counterparts in SAS, the Bucomazi-equivalent off West Africa and the Lagoa Feia-equivalent off Brazil. However, in both settings the main period of lacustrine source bed deposition generally occurred during the transition from rift to sag phase, in response to expansion and deepening of lake systems.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil