Sedimentary evolution and source rock potential of Lower Jurassic successions in the Mandawa Basin, SE Tanzania

Lower Jurassic successions that form syn-rift sedimentary packages in the Mandawa Basin preserve a complete stratigraphy that records tectonic processes related to the break-up of Gondwana as well as evidence of an extension of the Neothethys Sea (a.k.a. the Somali Ocean) into the East African Margin prior to the opening of the Indian ocean, and thus is considered to be important in Tanzania’s geological history. Previous exploration activities have indicated the presence of a working petroleum system in the subsurface, with key elements such as source rocks, reservoirs, and seals present in both syn-rift and post-rift sedimentary packages. Syn-rift sedimentary packages have received little attention compared with post-rift sequences that are outcropping and have good biostratigraphic control. An understanding of the sedimentary facies evolution, depositional conditions of syn-rift sedimentary packages is important in assessing the petroleum potential of Lower Jurassic successions in the Mandawa Basin. 

In this thesis, an integrated geochemical approach, which includes bulk organic matter analysis (CNS, TOC), stable isotope analysis of organic matter (δ13Corg), and programmed pyrolysis analysis, was employed to determine the variation in organic matter types and quality with respect to lithofacies evolution in the Mandawa Basin during Early Jurassic times. In addition to geochemical data, Spectral Gamma Ray logs (Th, U, K) and sediment lithotype data (carbonates, salts, and clastics) were integrated in the study to improve an interpretation and for reconstructing the basin-fill of the Lower Jurassic successions in the Mandawa Basin.


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