Abstract
“XM” field, a clastic sedimentary domain within the Albertine Graben, southwestern Uganda, was studied using palynological data, complemented with wire-line well logs, to determine the stratigraphy, age, and depositional setting. Field wide correlation was attempted using additional geological and stratigraphical data from the larger Albertine Graben. The study involved the use of geological computing tools such as Petrel and Strata Bug softwares which allowed for the graphic plots of palynoflora, identification of marker species, species abundances, species first and last occurrences and the geological correlation of the two wells. The palynological marker species identified include; Podocarpus spp., Tournefortia spp., Praedapollis flexibilis, Peregrinipollis nigericus, Gramineae spp., Laevigatosporites spp. and Verrucatosporites usmensis. This association of species indicates Early Pliocene to Holocene age. These species were further used in delineating the Early Pliocene age of well T2 into TZ1a and TZ1b. The TZ1a subzone is marked by index species of Laevigatosporites spp., the quantitative top occurrence of Sapotaceae spp. and Verrucatosporites usmensis. TZ1b is marked by the presence of index species of Laevigatosporites spp. and top occurrence of Sapotaceae spp. Further, the study revealed five informal palynological biozonation of the well T3 into; TZI, TZII, TZIII, TZIV and TZV all ranging in age from Early Pliocene to Holocene and defined based on top occurrences, downhole increases and decreases of some of the stratigraphical important species recorded in the well as follows: TZI is marked by the top occurrence of index specie Gramineae spp. TZII by the presence of index specie of Peregrinipollis nigericus and top occurrence of Praedapollis flexibilis. TZIII is defined by top occurrence of Tournefortia spp. and the downhole decrease in Podocarpus spp. TZIV is defined by the top downhole increase in Podocarpus spp. and TZV by the base downhole decrease in Podocarpus spp. In arriving at these interpretations, data and publications from other basins such as the Niger Delta in West Africa and the Muglad and Burundi Basins in Central and East Africa were used as analogues. The age of the drilled wells ranged from Early Pliocene to Holocene while the paleo environment of deposition was determined to be mostly continental ranging from fluvial to lacustrine settings.
Highlights
Studies in the Semliki Basin of southwestern Uganda have not yielded definitive age control for the basin
In view of the critical role played by biostratigraphy in sequence analysis, this study intends to establish both the relative and the absolute ages of the succession traversed by wells in the basin
The top is defined by the top occurrence of Praedapollis flexibilis while the base is marked by the downhole decrease in Gramineae species
Summary
Studies in the Semliki Basin of southwestern Uganda have not yielded definitive age control for the basin. The best sequence stratigraphic models of the sedimentary fill of basins are built using a combination of seismic data, well logs and cores and outcrop information in conjunction with biostratigraphy data [1]. It is bordered to the east by Kenya, to the north by South Sudan, to the west by the Democratic Republic of the Congo, to the southwest by Rwanda, and to the south by Tanzania. It is in the heart of the Great Lakes region, and Received: January 22, 2019, Accepted: February 11, 2019, Published: February 18, 2019
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