Are all lobes made equal? Comparing the sedimentological processes and depositional architecture of submarine lobes in different palaeogeographic and sequence stratigraphic positions

Submarine lobes are high aspect ratio sand-rich deposits fed by sediment gravity flows via channels. They are a major component of submarine fans, the largest depositional bodies on the planet, and therefore represent an important archive of palaeo-environmental change. Basin-floor, or terminal, lobes, are well-studied. Here, lobes in other geographical positions and the influence of confinement (especially when subtle and dynamic) and stratigraphic position on submarine lobe geometry, stacking patterns, and sedimentary facies are investigated.
Extensive outcrop exposures and near-outcrop research boreholes from Permian fine-grained basin-floor and intraslope lobes in the Karoo Basin (South Africa) allow spatial and stratigraphic variability in sedimentary facies and architecture to be constrained. One hundred and seventy outcrop logs (~6.9 km total length) and 11 core logs (~1 km) from Units A and E, Laingsburg depocentre and Fan 4, Tanqua depocentre, were integrated to enable the analysis of different lobe types within a physical hierarchy and enabled detailed facies distribution trends, stacking patterns and depositional models to be established.
The main outcomes of the study are: 1) recognition criteria for three distinctive lobe fringe settings: frontal, lateral and aggradational lobe fringes; observed differences between frontal and lateral lobe fringe deposits are controlled by flow processes, while aggradational lobe fringes form in response to subtle confinement by intrabasinal slopes; 2) the documentation of lobe stacking patterns within lobe complexes and complex sets. Karoo lobes show a range of stacking patterns that are controlled by seabed topography and sediment supply; 3) the evaluation of hybrid bed distribution that indicates strong geographic but weak stratigraphic trends at different hierarchical scales. Lobe stacking patterns are shown to be a major control in these trends; and 4) the comparison of depositional models established from basin-floor and rare examples of exhumed intraslope lobe complexes that show distinct differences.