The source rock of the Nyasa Rift Basin and oil shows of Tanzania

Abstract

Several organic geochemical analyses have been carried out in the Nyasa Rift Basin. The main objective was to assess the hydrocarbon potential of this southern part of the East African Rift Valley. Much interest has been shown in the carbonaceous shales and the coals of the Karroo Formation of Carboniferous/ Permian age, locally known as K 2. They are characterized by coal measures alternating with bituminous/ carbonaceous shales, mudstones and occasional sandstone. The cores and outcrop samples from the Ilima Colliery, Mwalesi and Ivogo Ridge were studied. The screening analysis showed the samples of both the coal and carbonaceous shales to be fair to good source rocks. the visual kerogen compositions, together with HI values, suggest kerogen type III or mixed up type III/II. The thermal maturity data as shown by T max, vitrinite reflectance, spore color fluorescence, and thermal alternation index, indicate an early mature to mature oil source rock. The oil shows, as observed in the Tundaua (Pemba) and Msimbati seeps and the bituminous sands of the Wingayongo and Msimbati areas, indicate the presence of oil-generating source rocks.