Deciphering the morphology of turbiditic lobe bodies according to hierarchy and system size

Louison Mercier, Jean-Louis Grimaud, Fabien Ors

Turbiditic lobe bodies (LBs) are the ultimate deposits of source-to-sink systems. Their geometry and architecture vary with depositional environment (marine vs. lacustrine), hierarchy (lobe elements, lobes, lobe complexes), system size (large vs. small) and topographic confinement. Constraining these variations is useful for characterizing the dispersion of sediments, carbon, nutrients, and pollutants into lacustrine and deepwater environments. Although LBs are known to be dominantly ellipsoidal, robust statistics of scaling relationships describing their morphology are still lacking. Here, we compile data (n = 365) from seabed surface, subsurface, and outcrops of modern and ancient systems to investigate the morphometric scaling of LBs. We show that the shape of LBs is firstly controlled by the hierarchy of LBs and secondly by the system size. The LBs from large systems are one order of magnitude more voluminous than those from small systems. We demonstrate for the first time that each hierarchical level has its own elongation (i.e., length-to-width) ratio, but also its own 3D morphometric scaling where its length correlates with its width-to-thickness ratio. This is consistent with the construction of the highest hierarchy LBs dominated by the lateral stacking of lower hierarchy LBs, promoting sediment spreading in the abyssal plains and lacustrine bottoms, while aggradation is secondary.