Sedimentary process of channel-feeding fan delta in the south of Albert Rift, Uganda: Insight from sensitivity analysis of forward stratigraphic modeling

Abstract

Channel-feeding fan deltas without any conglomerates have recently been discovered on the steep slope in the Albert basin at the northern end of the west branch of the East African Rift. However, the new deposition system's mechanics and patterns are unknown. To reveal the sedimentary process of the distinctive fan delta, we integrate forward stratigraphic modeling (FSM) technology with interpretations of the core, well logs, and 3D seismic data. Firstly, a reference FSM model is constructed to describe the evolution of the fan delta, taking into account initial bathymetry, source supply, lake level, and fluvial discharge as independent variables. Then, the Orthogonal Experimental Design (OED) is employed based on the uncertainty analysis of each independent factor to generate FSM multi-realizations for formation thickness and Net-to-Gross. Sensitivity analysis of Multi-FSM realizations reveal that source supply is the most influential variable affecting formation thickness and texture. Combined with the tectonic evolution of Albert Basin, the formation dip during the deposition period is much smaller than present. Multiple incised channels were formed in the provenance area, which became the primary source system of the fan delta, facilitating the sediments' transportation over a certain distance to produce well-developed cross-bedding sandstone. The channel-feeding fan delta has a narrower plain and wider front, and the principal sand body is high-quality distributary channel. The discovery of the channel-feeding fan delta without any gravel formed on the steep slope of the rift basin enriches the theory of deposition in rift basins. In addition, the application of FSM technology helps to improve the quantification of sedimentary processes.