--> Abstract: Source Rock Variability in a Tropical Rift Lake: New Results from Scientific Drilling in Lake Malawi, East African Rift, by Christopher A. Scholz; #90078 (2008)

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Source Rock Variability in a Tropical Rift Lake: New Results from Scientific Drilling in Lake Malawi, East African Rift

Christopher A. Scholz
Department of Earth Sciences, Syracuse University, Syracuse, NY

Organic-rich lacustrine source rocks are directly responsible for charging many hydrocarbon systems around the globe, and are especially important in many areas of frontier exploration today. The modern tropical lake systems of Africa have been shown to be useful recent analogues for ancient lacustrine basins around the world, and significant oil discoveries in the Lake Albert Rift over the past two years have validated the prospectivity of the active extensional basins of East Africa. The spatial and temporal variability in organic matter richness in these highly productive lake systems is assessed using a combination of surface sediment, shallow core and deeper drill core sample material. New scientific drill cores acquired from Lake Malawi, in the southern part of the East African Rift, provide a continuous, high-resolution record of source rock facies variability extending back a million years or more. Modern Lake Malawi has a maximum water depth of 700 m, and the Lake Malawi Drilling Project’s deep core site was situated in a water depth of 600 m. Down-core lithologic and geochemical data, correlated to nested seismic reflection site survey data sets, suggest that marked variations in total organic carbon, d13C, C/N, and Rock-Eval data are linked to high amplitude, climatically-forced lake level shifts. TOC values vary from near zero to ~5%, with high values correlated to high lake-level conditions, and low TOC intervals to periods when the lake level was reduced 550 m or more (lake volume reductions of at least ~98%). The dramatic climate shifts included periods of megadrought, and were controlled by orbital precession during periods of high orbital eccentricity, prior to about 70 kyr BP. The resulting changes in lake hydrology and rift valley landscapes had a major impact on facies architecture in the basin.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas