Sedimentary architecture of submarine channel-lobe systems under different seafloor topography: Insights from the Rovuma Basin offshore East Africa

Abstract

Seafloor topography plays an important role in the evolution of submarine lobes. However, it is still not so clear how the shape of slope affects the three-dimensional (3-D) architecture of submarine lobes. In this study, we analyze the effect of topography factors on different hierarchical lobe architectures that formed during Pliocene to Quaternary in the Rovuma Basin offshore East Africa. We characterize the shape, size and growth pattern of different hierarchical lobe architectures using 3-D seismic data. We find that the relief of the topographic slope determines the location of preferential deposition of lobe complexes and single lobes. When the topography is irregular and presents topographic lows, lobe complexes first infill these depressions. Single lobes are deposited preferentially at positions with higher longitudinal (i.e. across-slope) slope gradients. As the longitudinal slope becomes higher, the aspect ratio of the single lobes increases. Lateral (i.e. along-slope) topography does not seem to have a strong influence on the shape of single lobe, but it seems to affect the overlap of single lobes. When the lateral slope gradient is relatively high, the single lobes tend to have a larger overlap surface. Furthermore, as the average of lateral slope and longitudinal slope gets greater, the width/thickness ratio of the single lobe is smaller, i.e. sediments tend to accumulate vertically. The results demonstrate that the shape of slopes more comprehensively influences the 3-D architecture of lobes in natural deep-sea systems than previously other lobe deposits and analogue experiments, which helps us better understand the development and evolution of the distal parts of turbidite systems.