Interpretation of refelction seismic data from the Usangu Basin, East African Rift System

Reflection seismic data collected by AMOCO Tanzania Oil Company in the 80s, are herin used to correlate the main Usangu Basin parameters to those estimated from outcrop, gravity and aeromagnetic data. The seismic data are further used to constrain the geometry of crustal extension in this south-western sector of the East African Rift System (EARS) in Tanzania. Three distinct sedimentary packages on top of the basement reflector are interpreted and correlated to the Permo-Carboniferous Karoo rocks, the Jurassic/Cretaceous and Miocene Red Sandstone Group and Miocene to recent Lake Beds in the adjacent Rukwa basin, where the ages of the sedimentary sequences have been established on the basis of drill hole data. The Karoo beds, deposited on an undulating weathered basement surface are relatively thin (~ 200m). The Red Sandstone Group reach a maximum thickness of up to 420 m while the Lake Beds are up to 289 m thick. Beneath the Karoo, seismic reflections show interval velocities of 3.22 km/s, which are less than typical crystalline basement velocities of 4.2 km/s in the adjacent Rukwa Rift. These “sub-basement” velocities are attributed to the slightly metamorphosed sediments of Upper Proterozoic, Buanji Group that crop out extensively on top of the Chimala scarp. Previous estimate of the thicknesses of Buanji sediments from outcrop data has been up to 1.086 km. The present study, however, suggests a thickness of more than 2 km for the Buanji sediments beneath the Mesozoic to recent sediments in the Usangu Basin. Age wise the Usangu Basin, which has always been considered to be much younger than its south-western continuation, the Luangwa valley, is here suggested to be an old structure in which sedimentation has been going on since Karoo time. Recent faulting mechanism inferred from recent earthquake data and the present interpretation of seismic sections suggest that deformation in the Usangu Basin has been predominantly strike slip. Thus, the Usangu Basin is best interpreted as a transfer fault, accommodating the relative movement between the southern-most sub-basin of the Rukwa Rift and the northernmost sub-basin of the Malawi Rift. Tanzanian Journal of Science Vol. 28(1) 2002: 83-9

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

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. 1-1

Tectonic setting and uplift analysis of the Pangani rift basin in northern Tanzania using apatite fission track thermochronology.

Thirty four new Apatite Fission Track (AFT) ages and 32 track length distributions from samples of basement rocks flanking the Pangani rift, East African Rift System (EARS) are presented, in an attempt to elucidate the uplift and erosion of the rift flanks. The ages fall in the range of 207±15 to 48±4 Ma, spanning from Early Jurassic to Early Tertiary. These ages are much younger than the last termal event in the Mozambique belt that form the basement complex and are interpreted to represent the most recent tectonic events. Track length (TL) distributions suggest that uplift and erosion of the rift flanks are related to three different tectonic events, which are also recorded by the sedimentary units within the adjacent coastal basins. These include the Triassic/Early Jurassic, Late Cretaceous and Early Tertiary tectonic events. Erosion and isostatic rebound have modified the tectonically induced topographic patterns and the highly elevated plateaus flanking the Pangani rift represent an erosional surface referred to as the “Gondwana surface” of eastern and central Africa. The present AFT data suggest that initial exhumation of the “Gondwana surface” from the temperatures above 110º to temperatures less than 60ºC, in this area, took place during Early Jurassic times, but the final sub-aerial exposure of the surface did not take place until Early Tertiary. Tanzania Journal of Science Volume 27A (Special Issue) 2001, pp. 23-3

Overview of the Neoproterozoic sedimentary series exposed along margins of the Congo Basin

The Congo Shield is a central African large landmass with several Archean nuclei welded during the Eburnean orogeny approx. 2.1-1.8 Ga and subsequently stabilized as a coherent unit throughout late Paleoproterozoic to Meso-Neoproterozoic times. The early Neoproterozoic was marked by rifting along the margins of the Congo Shield related to the break-up of Rodinia at about 1.0 Ga, and opening of the Adamastor Ocean, followed by passive margin-type sedimentation and, finally, foreland basin deposition during the amalgamation of Gondwanaland initiated at approximately 600 Ma. We summarize the present knowledge of the lithostratigraphy of the Neoproterozoic basins exposed along margins of the Congo Basin in an attempt to establish chronostratigraphic correlations between these isolated basins in the Democratic Republic of Congo and neighboring countries.SCOPUS: ch.binfo:eu-repo/semantics/publishe