Sedimentary Response to Coupled Climatic Change and Active Rifting in the On-Shore Lake Edward Basin, Albertine Rift, Uganda
Wilson M. Tumushabe¹ and Christopher J. Nicholas²
¹Petroleum E&P Department, Ugandan Ministry of Energy and Mineral Development, Entebbe, Uganda
²Trinity College, Dublin, Ireland, UK
The study area is the onshore Ugandan Lake Edward basin, Albertine rift, Uganda that is located in the northernmost part of the western arm of East African Rift System (EARS). Dominion Petroleum Ltd has been carrying out intensive petroleum exploration in the Lake Edward basin i.e., field geological mapping, seismic data acquisition and interpretation etc. This resulted in the drilling of the Ngaji-1 well, the only deep well in the entire area. The major aspects of this research project however were; (1) to evaluate the sedimentology and stratigraphy of different lithologies in this area using 'lithofacies' or 'lithofacies associations' (2) re-visit the lithostratigraphic framework of this area and (3) determine how climate and tectonism have influenced sedimentation style, with the major emphasis on further unravelling the petroleum potential of the area. XRF and clay mineralogy (XRD) studies have been confirmed to be of less significance in the paleoclimatic interpretations of sediments within the study area, Lake Edward basin, only ICP-MS/OES data has been used in this project.
From field geology and geochemical data (ICP-MS/OES), it was confirmed that climate and tectonism played a significant role during sedimentation in this basin. It has been found that all scenarios that had been raised in the predictive coupled climatic-tectonic model are present within Lake Edward basin. Results from this research however have also shown that rift-fill sediments in the south and eastern Lake Edward basin (close to the rift shoulders) are majorly dominated by fluvial and alluvial distributary fan complexes and within these fan complexes, could be recognised during the detailed stratigraphic logging to describe the different Lacustrine packages were encountered within the basin fill sediments close to the present day Lake Edward.
Sediments within the study area were identified and classified into four members: (1) Kabagwe, (2) Rushaya and (3) Kiruruma and (4) Kisenyi members. However, like in previous research work within the area, the main challenge was to locate the definite chronostratigraphic markers for these members. It has been further confirmed that sediments in the Lake Edward basin represent a petroleum play for hydrocarbon generation, accumulations, in which the necessary elements of a valid petroleum system were identified i.e., there are excellent or good potential for reservoirs and top seals as well as circumstantial evidence of regionally source rocks, possible seals, traps and hydrocarbon-migration pathways.
AAPG Search and Discovery Article #90206 © AAPG Hedberg Conference, Interpretation Visualization in the Petroleum Industry, Houston, Texas, June 1-4, 2014