Oligocene Deep-Water Gravity Flow Architecture in the Tanzania Basin: Regional Documentation and Source-to-Sink Interpretation

Significant natural gas discoveries in the Tanzania Basin, East Africa, underscore its hydrocarbon potential, yet the sedimentary architecture and controlling factors of its deep-water depositional systems remain poorly constrained. This study aims to characterize the Oligocene deep-water gravity flow architecture of the basin and to identify the factors that controlled its development and distribution. Three objectives are pursued: (1) to define the architectural elements and channel types present; (2) to document their spatial distribution and temporal evolution; and (3) to evaluate the tectonic, source, and topographic controls within a source-to-sink framework. This study integrates 2D seismic data (c. 3500 line-km), six exploration wells, and well-log correlations to investigate Oligocene deep-water gravity flow deposits. We identify three principal architectural elements—channels, levees, and lobes—and propose a refined channel classification comprising complex, lateral migrational, vertical aggradational, and single-channel types, based on seismic geometry, internal architecture, and depositional style. Spatial analysis reveals a systematic south-to-north variability: the southern basin is characterized by small-scale, SW–NE-oriented single channels and lobes, whereas the central and northern segments host larger, NW–SE-oriented channel–lobe systems, with depocenter areas ranging from 562 km2 (south) to 23,838 km2 (central). Source-to-sink analysis, in which modern drainage parameters are used as a modern analogue for relative source-area capacity, indicates that three interacting factors may have governed the development and distribution of these gravity flow systems: (i) a hinterland sediment source, whose magnitude and timing are not independently constrained; (ii) inherited Mesozoic seafloor topography, which is consistent with the orientation of the mapped Oligocene dispersal pathways; and (iii) the geometry of the outer shelf–upper slope interval, which is associated with the observed depositional style. Alternative explanations, including relative sea level change, climate, sediment storage and release, preservation, and autogenic behavior, cannot be excluded when analyzing the available data. The integrated model provides a testable framework for reservoir distribution in frontier deep-water passive-margin settings. The link between source-area capacity and depositional scale is presented as a hypothesis, because the Oligocene drainage configuration is not independently constrained.