UPPER PALEOZOIC AND PESOZOIC SEDIMENTATION IN THE RUKWA-TUKUYU REGION, TANZANIA

The tectonic and sedimentary evolution of the Rukwa-Tukuyu region has through Paleozoic, Mesozoic and Tertiary time, generally followed the same patterns with only minor lateral changes. Faulting and half graben formation, combined with a general regional isostatic rebound and climatic improvements, controlled sedimentation in the region and can explain the various facies distributions found in beds from the Karoo sequence and the Red Sandstone Group. After deep pre-Karoo glacial erosion and related fault movements, the Karoo depositional basins were formed and later filled with glacial, glaciofluvial, lacustrine and fluvial to fluivodeltaic sediments which correspond to Karoo units K1, K2, K3 and K5. Tectonic movements were a major factor in controlling the alternations of coal, clastic units and partly calcareous, lacustrine sediments found in the Karoo. The Red Sandstone Group (Jurassic/Cretaceous) was deposited after a period of pronounced tectonic activity. This unit represents mainly fluvial (meandering and braided stream) facies, which is associated with alluvial fan deposits. Proximal and distal fan-deposits are also present. These prograded north to northeastward into lakes where carbonates precipitated. The Red Sandstone Group shows the best reservoir potential, while the K2 coals have a good potential for generating gas and light hydrocarbons.