Deepwater Systems Reloaded: Advances on our understanding on submarine lobe deposits

Submarine lobes are high aspect ratio sand-rich deposits that are fed by turbidity currents and debris flows via channels in deep-marine settings. As a major component of submarine fans, they represent 1) an important archive of palaeo-environmental change, 2) sinks for organic carbon and pollutants, and 3) are also of economic interest. Classic models describe lobes as purely depositional tabular sheets that thin and fine from an apex. Over the last decade, outcrop studies, numerical and stochastic modelling, and flume tank experiments have been undertaken to constrain the hierarchy, geometries and stacking patterns of submarine lobe deposits and test these simple models for lobe deposition.

With this talk I want to give an insight into the discoveries made and new understanding gained about lobe deposits, including: 1) The variety of lobe fringe deposits depending on the level of confinement experienced by the lobe: Distinguishing frontal and lateral lobe fringes enables more accurate reconstructions of the geometry, distribution, and orientation of deep-water lobes, whereas the recognition of aggradational lobe fringes enables the reconstruction of subtle intrabasinal relief. 2) Boundary conditions governing lobe dimensions: lobe dimensions, and their relation to their feeder channels, vary with basin-floor angle, and the concentration of sediment within the feeding gravity-current. Discharge rate is also important, controlling when deposition starts. Because these parameters change during evolution of natural deepwater systems, lobes formed at different times will have different geometries.