Biostratigraphy and Palynofacies of Four Exploration Wells from the Albertine Graben, Uganda

Joshua M. Lukaye
Petroleum Exploration and Production Department, Ministry of Energy and Mineral Development, Entebbe, Uganda

The Albertine graben forms the northernmost part of the western arm of the great EARS. It runs from Rwanda in the south to the Uganda/Sudan border in the North. Within this graben, the ages of the sediments especially in the subsurface, and their palaeoecological and palaeoclimatological implications have been unknown despite the extensive exploration for oil.

Biostratigraphic studies recently carried out on four wells from the Semliki and Kaiso-Tonya basins located within the graben resulted in recognition of over 80 types of palynomorphs with their respective frequency distributions. This in turn resulted in a palynostratigraphic zonation of the basins. Four distinctive zones ranging from Lower Miocene to Pleistocene were established in the Semliki Basin. Two of these zones are also evident in the Kaiso-Tonya Basin. Comparisons made with the stratigraphic occurrence of similar microfloras recorded by numerous authors within tropical areas permitted calibration of the palynozones. The formations in which they were identified have thus been dated.

The source of palynomorphs was probably in the hinterland and other adjacent low-laying land such as swamps, transported to the depositional site by streams as observed from the palynoflora spectrum. Sediment accumulation involved deposition in deep freshwater environment, followed by deposition in a shallow fresh-brackish water deltaic environment, and finally, by fluvial or fan delta deposition in lake margin facies. Burial of sediments was not deep enough for their organic contents to be rendered thermally mature. Variations in depositional conditions and source areas are in the character of the assemblages and in the density of palynomorph population, interpreted to be predominantly due to climatic fluctuations. The climate that prevailed was probably warm and humid.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery