Subsidence History of the Rukwa Rift in South West Tanzania Analysed from Ivuna Well.

Abstract

The variation in subsidence rate during rift basin development is a good indication for the Geodynamic history of a sedimentary basin. The sedimentary section of Ivuna Well is herein used to explain the structural evolution of Rukwa Basin within the Western Rift of the East African Rift System. The sedimentary record of Ivuna Well is extracted from published information. The effects of sedimentary load, corrected for compaction and variation in water depth, and lake-level have been removed to obtain the "tectonic subsidence." Curves show two phases of accelerated subsidence related to the fault controlled rifting phases: The Karoo rifting and the Late Cenozoic rifting. Though several phases of rifting are proposed within Karoo time in eastern and southern Africa, it is difficult, with the present information from Ivuna well, to infer them. But the change of gradient of the Geohistory plots within the Karoo section does suggest at least variations of sedimentation rates. The Karoo rifting phase is followed by a steady subsidence which resulted from thermal contraction of the lithosphere thinned during Karoo crustal and lithospheric stretching, while Late Cenozoic rifting is still young at its initial phase of rifting (t = 0).


Tanzania Journal of Science Volume 26 (2000), pp. 1-14